Japanese Deploy Solar Sail

Chuck1318 writes "The Japanese ISAS (Institute of Space and Astronautical Science) announced the launch and deployment of the first ever large-scale solar sail. In the news release they state "Because it carries no fuel and keeps accelerating over almost unlimited distances, it is the only technology now in existence that can one day take us to the stars.""

Comments

Stellar Pong?

[infonick]

"...it is the only technology now in existence that can one day take us to the stars." Well, unless the Japanese can automate retraction of the sails, it wont reach any stars. While it's powered by solar wind, it will slow down and reverse as it gets farther from the original star and closer to the destination star.

Re:Stellar Pong?

[mrchaotica]

What if it's only reflective on one side?

Re:Stellar Pong?

[Anonymous Coward]

I call baloney. Doesn't a solar sail work because of it's high reflectivity? Isn't that high reflectivity only on one side of the sail?

And what's so difficult about retracting the sail? The force on the sail at any given time is so miniscule it's trivial to retract them (as opposed to, say, when you have intense winds blowing on your sailboat's sail).

Re:Stellar Pong?

[Anonymous Coward]

Well, unless the Japanese can automate retraction of the sails, it wont reach any stars

Why retract? Just release. It's not like it's going to be used again.

Re:Stellar Pong?

[Anonymous Coward]

Actually you want to slow down when you reach the other star. Or else you miss your stop. Once there, you jettison the sale, or use it to fly around the star system.

Read "Flight of the Dragonfy"/"Rocheworld" (they are the same book) by Doctor Robert L. Forward for an informative and entertaining novel using (laser pumped) solar sails.

Re:Stellar Pong?

[Marsala]

That's why one crew member will be trained extensively in the use of tin snips in zero-gee environments.

Although that'd be a great way to freak out an alien race... Kind of like pulling a Rama on 'em.

Re:Stellar Pong?

[pclminion]

What if it's only reflective on one side?

A perfectly non-reflective surface (i.e. a black surface) would experience half the force that a perfectly reflective surface would. In other words, a black sail will work, but only half as well as a mirrored sail would work.

This is due to conservation of momentum. If a photon is reflected, its momentum p is reversed to be -p. Thus the sail must acquire a momentum 2p to conserve momentum. Whereas if the photon is absorbed, its momentum changes from p to 0, thus the momentum of the sail must increase by p, again to preserve momentum.

The difference in kinetic energy is converted into heat. A black sail heats up. An ideal, perfectly reflective mirrored sail does not heat up at all.

Re:Stellar Pong?

[eric76]

An interstellar yoyo?

Re:Stellar Pong?

[Igmuth]

And alot sooner than you would think... Once you cross the heliopause, the solar wind is basically moot.

Re:Stellar Pong?

[mark-t]

No. Once you have reached whatever your desired cruising velocity is, you discard the sail completely (or somehow retract it, if that is possible). The gravitational pull of the star at your destination will give you even more accelleration later on.

You use on board rockets to help steer as you draw close to your destination.

Re:Stellar Pong?

[halowolf]

Also the The Mote in God's Eye is a good read that has a solar sail powered craft, however a huge assortment of lasers were used to propel it up to speed, far beyond what solar energy would of provided. And its also not the focus of the book. But hey read it and find out!

There is also a sequel but I will leave that up to you as a project to find out what it is.

Re:Stellar Pong?

[BerntB]

Read "Flight of the Dragonfy"/"Rocheworld" (they are the same book) by Doctor Robert L. Forward for an informative and entertaining novel using (laser pumped) solar sails.

That was new!

Now, I'll agree with informative -- but entertaining??

I usually describe Forward as the absolutely worst author whose books I buy in hardcover.

You must be a nerd and talking about the physics and engineering as "entertaining" -- and not any literary qualities!

(-: Reminds me of when I recommended a Farmer book to an ex girl friend. I said "this is a classic that changed the sf/f genre, well worth reading!" She thought I meant it was good and is still angry, 8-10 years later...:-)

Re:Stellar Pong?

[JVert]

WHAT?
no.
try sailing upwind in a circular boat.

Regardless of how late it is, you should have caught this one before you hit 'post'... or am I about to Have A Nice Day?

Re:Stellar Pong?

[Anonymous Coward]

"I thought photos have no mass, and thus no momentum."

Photons have no rest mass, but they gain mass, like everything else, when approaching the speed of light.

Re:Stellar Pong?

[Anonymous Coward]

Unless I am misunderstanding your post, your physics is incorrect here. A modern sailboat, with the triangular sail, angles the sail somewhat into the wind, creating a pressure difference that pulls the sail in the direction of lower pressure. However, most of that pull is not linearly forward, but instead rotationally sideways - the only reason the ship does not immediately flip over is because of the keel, that being the strip of material that runs along the boat's centerline, on the bottom. The keel sticks out beyond the smooth hull, and as the sail tries to make the boat rotate, the keel pushes against the water, and the rotational motion is (partially) converted into fowards linear motion. This system does not work without three elements: sail, keel, and a fluid to flow in, that the keel pushes against. Older, square-rigged ships, like the workhorses from the 1800s back, simply work by having the wind push against the sails from behind, propelling the ship forward. This is how a solar sail works, except with light rather than wind. Check it out here:

http://en.wikipedia.org/wiki/Sailing#How_sailing_w orks

Cheers!

Re:Stellar Pong?

[NichG]

Photons have zero rest mass (which really doesn't apply to photons anyhow since they can't be at rest), but non-zero mass-energy. The momentum of a photon is proportional to its energy (with a direction degree of freedom).

Re:Stellar Pong?

[Famatra]

"Once there, you jettison the sale, or use it to fly around the star system."

Perhaps you'd like to explain how jettisoning a solar sail has enough force to slow down the craft.

That sail would have to be pretty massive, like the mass of a planet, in order to counteract years of acceleration so you could push it away from yourself to slow down ;).

That is the problem with getting somewhere in space. To get there the fastest you have to accelerate continually there till the 1/2 way point, turn the ship around around and use an equal force / fuel to decelerate. Reminds me of a scene in Battle Star Galatica Crew Member: "Sir we've ran out of fuel", Admiral "Come to a complete stop", The right reply: "But Sir, I said we ran out of fuel".

Re:Stellar Pong?

[FireFury03]

Same principles apply as in Earth-based ocean sailing - if you angle the sail, you can deflect the particles, thus allowing you to use the solar wind of another star even though you are approaching it rather than leaving it.

I'm not so sure that's the case - when we sail in water, we can either be on a run (the wind directly behind us, as you would expect a solar sail to work) or on a reach (the wind to one side).

On a reach the sail acts more or less like an aeroplane wing because of it's curved surfaces and as well as generating a forward force it generates a lot of lateral force too. The closer to the wind you sail, the greater the proportion of lateral force.

The only reason that's not a big problem for us is that your craft has a centreboard which greatly reduces it's ability to slide sideways, especially at speed - when I'm windsurfing in a reasonable wind, I will be doing about 30-35 knots and can easilly sail upwind with about 300cm^2 of fin area, but I won't be able to go upwind if the wind drops off because my speed will have greatly dropped. In space there is no way to have a centreboard to prevent the lateral forces pushing you sideways since there is nothing for it to react against.

I'm also not sure about the "aerodynamics" of a solar sail - as I described above, a modern sail works very much like an aeroplane wing when reaching and relies on the air have a laminar flow over both sides of the sail. I very much doubt photons are going to have a laminar flow over your sail so the sail isn't going to be anywhere near as efficient for reaching as boat or windsurfing sail. In windsurfing the most efficient point of sailing is on a slightly broad reach - i.e. the wind is coming from one side and slightly behind you, I would expect the most efficient use of a solar sail would be on a run.

Re:Stellar Pong?

[Phanatic1a]

Using onboard rockets to steer doesn't help you slow down. As you point out, the gravitational pull of the destination star will cause you to accelerate even more. You'll end up heading towards your destination at greater than the escape velocity for that system.

This doesn't help you stop. To do that, you flip yourself around so that the sail is pointing towards the destination, and you use the radiation pressure from that star to kill your velocity. Can't do this if you're already jettisoned it.

And, no, chemical rockets won't work to shed that much velocity. If you get get that much delta-v from chemical rockets, you'd just use chemical rockets to get on your way as well. But that's precisely why you're using a solar sail instead: chemical rockets suck in terms of specific impulse.

Re:Stellar Pong?

[cujo_1111]

While it's powered by solar wind, it will slow down and reverse as it gets farther from the original star and closer to the destination star.

But you want to slow down when you get to the other star. Problems occur when the destination star is much larger or has a higher energy output than Sol, thats when you will start to reverse. If you were going from one star to another, both of equal energy output, then in the virtually frictionless environment of space you would accelerate from your departure point and then when you get to your destination, it would slow you down to a nice gentle stop.

All you would need to do though is retract the sail when you get up to the required speed.

Re:Stellar Pong?

[Anonymous Coward]

far beyond what solar energy would of provided

It's would have, you blithering idiot.

Re:Stellar Pong?

[nacturation]

Same principles apply as in Earth-based ocean sailing - if you angle the sail, you can deflect the particles, thus allowing you to use the solar wind of another star even though you are approaching it rather than leaving it.

Regardless of space or the ocean, basic principles of physics apply. Action and reaction.

Uh, that's a resounding negative, Houston. In the ocean, we have this thing called *water* in which one sails. Action: wind pushes against sails from somewhere near the front. Reaction: sail pushes back agains wind and pushes into the water; water pushes back, and ship tends to go forward. In space, there is no dense medium through which one sails. Action: photons from a star push against sails from somewhere near the front. Reaction: ship pushes back and moves further away from the star. You can't "tack" in a vacuum.

Re:Stellar Pong?

[xsupergr0verx]

Wrong! This was developed in Japan, so all the astronaut needs to do is use the Starwaker baton and conduct a tune to change directions.

The Americans have to wait about 6 months to get this technology, unless they install a modchip on their spaceships.

Re:Stellar Pong?

[Mister Liberty]

As a matter of fact you do not actually want to 'reach' a star, rather some solar system of a
distant star.

Re:Stellar Pong?

[Biogenesis]

What about the charged particles that are shot out by the Sun? In both cases they would hit the sail and transfer an amount of energy to it but would this be more dominant than the momentum from the photons? Say the sail accelerates out of out solar system and eventually enteres another, assuming no breaking force at the remote solar system from particles it will travel some distance closer to the remote star if one side was black. However it could get unlucky and get right in the path of a solar erruption.

I'm just blabbing my thoughts without regard to speeling, move along now.

Re:Stellar Pong?

[Scarblac]

The right reply: "But Sir, I said we ran out of fuel"

"and besides, complete stop related to what, Sir?"

Re:Stellar Pong?

[Chris Hodges]

What about the perfectly reflexive sail? Having two such sails poiting against each other, the ping pong of the light particles would cause acceleration for both sides.. but who, to the hell, will pay for it?

(Assuming identical sails) of course the net momentum gain of the (closed) system is 0. The photons will become increasingly redshifted as the sails gain velocity away from each other (and the centre of mass). It is left as an exercise to the reader (I can't be bothered) to work out whether the energy lost by the photons can account for the energy gained by the sails.

Chris

Re:Stellar Pong?

[JWSmythe]

Actually, I was reading up on this a while back.. They'd use the gravity of the star to tack. Well, kinda.

It seems like a good idea, if they want to send something away from Sol for a long duration in one direction. Not too much navigation necessary (or possible).

The one thing I don't see really mentioned is debris in space. You know, micrometeors, and the like. It should make for a nice shreaded solar sail by the time it gets to the edge of the solar system. Hopefully it didn't encounter enough debris hitting it to knock it off course, or stop it all together.

But hey, if they're just looking to find out how fast a solar sail will accelerate away from SOL at Earth's distance, cool. It'd probably make for a faster way to get from Earth to our neighboring (outward) planets, if they can point it in the right direction. 1 degree makes a big difference over a few million miles. :)

Re:Stellar Pong?

[Anonymous Coward]

"Perhaps you'd like to explain how jettisoning a solar sail has enough force to slow down the craft."

It was not my intention to suggest that jettsoning the sail would slow the craft. You use the light from the star you're approaching to slow down. Actually in the case of Forward's design, you detach an outer ring of the sail. This outer ring accelerates faster than the ship and inner circle of sail because it doesn't have the mass of the ship to pull. Once ahead of the ship actuators on the ring bend it slightly to focus on the circle still attached to the ship. Now the laser in sol's orbit can be used to slow the craft much faster than using the light of the destination star, making for a faster overall trip.

I though Forward's book was entertaining. I love his aliens.

If I knew I'd get a +5 informative I'd have tried to dredge up my old slashdot profile and password!

Re:Stellar Pong?

[wisdom_brewing]

how about a one way mirror then? i know it currently depends upon light differentials and the like but im sure that by the time stars become near reachable (what? few hundred years?) someone will come up with a light diode of sorts... mirrored from one side, transparent from t'other

Re:Stellar Pong?

[Lord Kano]

Why retract? Just release. It's not like it's going to be used again.

Why not? Return trip? On to next destination?

LK

Re:Stellar Pong?

[PsiPsiStar]

Keep in mind that space isn't a perfect vacuume. At fractions of the speed of light, it can even become abrasive.

Re:Stellar Pong?

[essreenim]

I think he/she was trying to imply that the acceleration would not be infinite if its gathering solar wind from only one star...

Re:Stellar Pong?

[Anonymous Coward]

Correction: a square-rigged ship is just as capable of sailing against the wind as a ship with triangular sails. I spent a couple of weeks this summer sailing around with about a dozen other squarerigger enthusiasts in an Åfjordsbåd, an old Norwegian type used for fishing. It can comfortably sail about 60 degrees to the wind, which isn't impressive by modern standards, but keep in mind that this type was developed in the 14. century, as a continuation of the technology of the Viking-ships.
"Workhorses" of the 1800s were in fact usually gaff rigged, like clippers, while the war ships were square rigged. Square rigged ships require rather more crew, but are more maneuvrable, so for navies they were preferable until steam-ships became an option.

Re:Stellar Pong?

[famebait]

How do you plan to implement the keel? Have you ever tried to tack without one?

Re:Stellar Pong?

[CanadianCrackPot]

Retractable sails and momentum/inertia would take care of this. In space once you're up to speed there's no slowing you down unless you want to slow down.

Re:Stellar Pong?

[zogger]

I was wondering that. Interstellar dust and helium, etc, might tend to tear the sail up at very high velocities.

Re:Stellar Pong?

[Rick.C]

The difference in kinetic energy is converted into heat. A black sail heats up. An ideal, perfectly reflective mirrored sail does not heat up at all.

If you could somehow cause the energy absorbed by the leading black surface of the sail to be emitted out the rear surface as photons, then you would have something practical.

The parent's point was that as the sail gets farther away from Sol, the energy from other, nearer stars (the destination) would "push" on the leading surface and this force would eventually be greater than the force on the rear surface, causing the sail to be blown back towards home.

Think of two kids and a little sail boat in a small tub of water. Each kid is trying to blow the boat to the opposite side. As the boat nears one side, the "defender" has a clear advantage. The boat will ping-pong back and forth, never reaching either side.

Re:Stellar Pong?

[klaasvakie]

Action: photons from a star push against sails from somewhere near the front. Reaction: ship pushes back and moves further away from the star. You can't "tack" in a vacuum.

Actually the force generated on the solar sail is in the direction opposite the reflected photon. If you rotate your sail, the photons will be generated in a different direction than the one the light is coming from, and thus your force vector will not coincide with the direction of the light. You can "tack" using solar sails.

Re:Stellar Pong?

[anorlunda]

Not true that the sail would have to be massive. Some years back I read a proposal for a aluminum sail as big as the earth but weighing only 100 grams. It would only be 2 atoms thick.

Re:Stellar Pong?

[IdahoEv]

"Perhaps you'd like to explain how jettisoning a solar sail has enough force to slow down the craft."

Read the parent more carefully. He's not claiming the jettisoning of the sail slows you down.

The solar wind of the star you're approaching slows you back down. You use Sol to accelerate to interstellar speeds, and target star to slow you back down. You arrive in the destination system with reasonable interplanetary speed. You jettison the sail because you don't need it anymore. (Or, as he said, you use it to cruise around inside the new solar system, assuming your sail is built for that).

Re:Stellar Pong?

[the_consumer]

I recommended a Farmer book to an ex

Say no more.

Re:Stellar Pong?

[SEWilco]

Let's just change that to "that can one day take us between the stars."

Re:Stellar Pong?

[MidnightBrewer]

Keels are there to counter-balance the mast in a gravity environment. I don't think there's much chance of that in space.

Re:Stellar Pong?

[nmk]

Would it, perhaps, be possible to use two sets of sails aligned to two different stars to generate the forces necessary for movement in a certain direction. One set of sails could generate the same sort of force, in the opposite direction, that water would create in a sailboat. That way you would be able to the same "reach" sort of effect that you described in a sailboat.

Re:Stellar Pong?

[walueg]

Think of two kids and a little sail boat in a small tub of water. Each kid is trying to blow the boat to the opposite side. As the boat nears one side, the "defender" has a clear advantage. The boat will ping-pong back and forth, never reaching either side. It's not ping pong. You'd accelerate away from the solar system and you would slow down to a stop (or close to it) at your destination. You would need to do a mid course reverse though, but that's ideal for moving from here to nearby stars of similar radiant energy. The problem is if you want to go intragalactic distances with many stars in between your origin and destination. You'd be speeding up and slowing down a lot.

Re:Stellar Pong?

[mark-t]

No problem there... when you really need to slow down, you deploy another solar sail.

Re:Stellar Pong?

[swv3752]

It is Sci-Fi, they could have Quantum Foam/Flux or Superstring or Dark Matter anchors.

They do have FTL drives so some sort of anchor that latches onto Quantum Foam or Superstings could be considered plausible.

Re:Stellar Pong?

[swv3752]

Actually one would use a sail to help conserve fuel. But the rockets would be more used for steering and setup some gravity well slingshots. The slingshot manuever could shed momentum as well as gain momentum.

Re:Stellar Pong?

[skarmor]

I think they were going for would've. I'm not sure that contraction is allowed though.

Re:Stellar Pong?

[Anonymous Coward]

. The keel sticks out beyond the smooth hull, and as the sail tries to make the boat rotate, the keel pushes against the water, and the rotational motion is (partially) converted into fowards linear motion.

Actually, no. The keel board or center board is there to resist sideways skidding. In order to go downwind, you let the wind push your sail and you ride along. To the extent you want to go, say, right of that heading, you have to push left against something. Boats have to either have a deep enough hull to push against the water, or a keel board or centerboard to deepen the hull and provide that resistance. Without it a flat-bottom boat will just skid. Rotation is countered by gravity -- by keeping the center of flotation higher than the center of mass. As the boat heels over the moment arm between these forces grows, creating a rotational moment tending to right the boat. That's why racing hulls with huge keels still lean way over when they're running full out. That's also why the wide end of the triangle sail is at the bottom, to reduce the capsizing moment of the thrust from the sail.

Square and triangle sails work the same in this regard. The major difference is that triangular sails can be rigged to bend into an airfoil shape, providing more efficient wind spill thrust, when running cross wind, and they put the thrust vector lower on the mast than a square sail with the same surface area. Square sails are typically secured top-and-bottom and are less efficient at steep angles to the wind, but they carry a greater surface area for the same mast height so they work better for running down wind.

Re:Stellar Pong?

[pclminion]

The only way the incoming particle's p can be exactly reversed is in the limiting case of infinite mass of the resting mass.

I was trying to leave out the complications. The photon is redshifted after reflection. The frequency it redshifts to is the one which is consistent with conservation of both momentum and energy.

Re:Stellar Pong?

[pclminion]

I was thinking about how a radiometer works to measure thermal energy. Is this the same property that pushes the sails?

You are asking a textbook question :-)

No, the radiometer works in a different way. Notice in the radiometer that the rotation is clockwise when the black "sail" is exposed on the LEFT. If this were due to light pressure, the pressure would be greater on the RIGHT (reflective) sail and the radiometer would be spinning in the opposite direction.

What happens in the radiometer is the black sail heats up because it absorbs radiant energy. The gas around the sail (the glass bulb is very low pressure but not a perfect vacuum) conducts heat away from the sail, heating and expanding in the process. The expanding gas reacts against the sail, pushing it away.

If the radiometer bulb was evacuated to a perfect vacuum, the radiometer would actually spin the opposite direction because the light pressure effect would dominate.

Re:Stellar Pong?

[Rakishi]

I'm sure they all want the solar sail to fly right past the other star and never slow down to make observations... yeah that sounds like a great plan.

However, yes they would probably need to either retract the sail or disconnect it from it's cargo.

Re:Stellar Pong?

[grmoc]

However, you can never sail upwind.

I.e. you can go at angles asymptotically approaching 90 degrees to the light vector, but never can you accelerate towards the sun with a solar sail.

The reason a sail-boat can sail upwind is because of the keel shoving against the water, and the water shoving back, which works to counteract the 'away' push of the wind.

Re:Stellar Pong?

[jxe]

It is. It's?

Re:Stellar Pong?

[pclminion]

What about the perfectly reflexive sail? Having two such sails poiting against each other, the ping pong of the light particles would cause acceleration for both sides.. but who, to the hell, will pay for it?

The bouncing photons would progressively redshift, their frequency approaching zero until their wavelengths became large enough to escape from between the mirrors. At that point, all the lost photon energy would have been converted to kinetic energy in the sails (and some heat, if the sails are not perfect reflectors).

Re:Stellar Pong?

[Dr_Makarov]

There are light diodes already commercially avaialable, they're called Faraday isolators. They are used to protect high powered lasers from damage due to back reflection of the beam. Light from the laser goes through a polarizer, then through a rod of suitable material in a strong magnetic field. The field and optical rod rotate the polarization 45 degrees, then the beam goes out, hits something, gets reflected comes back through the rod, gets rotated 45 degrees more and is now blocked by the first polarizer. How to A) polarize both suns and B) build one of these big enough to act as a sail is left as an exercise to the student.

Re:Stellar Pong?

[2short]

You are incorrect. Sailboats sail in directions other than directly downwind by exploiting the difference in velocities between air and water.

In the solar sail scenario, there is no second medium, no aether if you will, to constrain your direction of movement as a keel in the water constrains the direction of a sailboats movement.

To those who think they can maneuver using only a solar sail:
Describe to me your design for an unpowered blimp that does anything but move directly downwind.

Re:Stellar Pong?

[dedalus2000]

is there no posibility of inter stellar tacking?

Re:Stellar Pong?

[nacturation]

You can "tack" using solar sails.

Absent of any other forces, you can never tack towards a star using the force applied from that star and a solar sail. You know, conservation of momentum and all that. That'd be like trying to hit the eight ball with the cue ball and (without rebounds off the cushion or using gravity to jump over) having the eight ball move towards the cue ball -- no matter how fine an angle you cut it on the side, it'll never happen.

Re:Stellar Pong?

[yakovlev]

You can't maneauver using only a solar sail, but you also can't maneauver using only a boat. It requires energy to maneauver, and in the case of a small sailboat, YOU provide that energy. As for propulsion, a combination of gravity and solar wind/photons provides that, either towards a star (gravity,) away from it (photons,) or somewhere in between(a calculated combination of the two, just like sailing.)

Re:Stellar Pong?

[2short]

"They'd use the gravity of the star to tack."

I don't see how the stars gravity helps. Gravity provides a force toward the star; the solar wind provides force away from it. Still no way to go sideways. Not even kinda.

Re:Stellar Pong?

[smithmc]

Well, unless the Japanese can automate retraction of the sails, it wont reach any stars. While it's powered by solar wind, it will slow down and reverse as it gets farther from the original star and closer to the destination star.

Does that mean what I think it means? Would this thing ultimately be pushed in a direction directly away from the site of the Big Bang, i.e. toward the edge of the (expanding[?]) universe? That could be kinda cool in and of itself for exploration purposes...

Re:Stellar Pong?

[2short]

In a sailboat, I can go sideways relative to the wind. I can even tie off the sheet and keep going sideways using only the winds energy.

With a solar sail, you can accelerate away from the star at some speed (sail fully unfurled); you can let gravity accelerate you toward the star (sail furled), or somewhere in between (sail partially furled; accelerating toward or away from the star at any speed between the two limits). But you cannot go sideways.

It is NOT like sailing. It is like flying a blimp with no engines. Attach all the sails and kites you want to said blimp; use your muscle energy to arange them how you want; you won't go sideways relative to the wind. You will just go downwind. If you like, you can spin around in circles while going downwind, but your center of mass will just go straight.

My muscle energy is not what makes a sailboat go sideways.

Re:Stellar Pong?

[bjverzal]

Well, why not mimic the behaviour of a modern day jet...leave the sail extended for the journey, then extend 'flaps' as you draw nearer (of course - after you've turned around) and allow the greater surface area to act upon the light, thereby eliminating the need to turn around 1/2 way there. BV

Re:Stellar Pong?

[astar]

I like the idea of shooting a lot of lasers at it when it gets far away. This would keep it going. And even accelerating.

Re:Stellar Pong?

[stevelinton]

There are so many misconceptions among the various responses to this post that it's a little hard to know where to start.

1. A solar sail powered by sunlight (not by the solar wind) is only useful within the (inner) solar system, maybe as far out as Jupiter or so. Within that area, it is pretty useful if you're not in too much of a hurry. You can use the Sun's gravity, and angle the sail to move around the inner system fairly freely, if slowly. I've seen plans for a solar sailing mission to Mercury that looked very promising. Lots of light there, and getting there any other way is hard work. Also the sail makes a dandy sunshade.

2. For interstellar missions you need a light beam to sustain the acceleration long enough. You then (unless you just want to do a fly-through, need to find a way of stopping. Science Fiction offers three options, none ideal:
a) dump all excess mass and dive close to the target star. Hope to stop before you burn -- "The Mote in God's Eye" approach.
b) split off part of the sail as a reflector which flies on ahead, bouncing the beam back onto the main part of the sail, which brakes the ship -- "The Flight of the Dragonfly" approach. Stability is a problem, even with active controls.
c) charge the ship to a high voltage, let the galactic magnetic field spin you round and enter the target system from behind. Use your original beam to
decellerate -- galactic magnetic fields are pretty fickle and this could add a lot of time to the mission. (also mentioned in "The Mote in God's Eye"

3. There are other kinds of sail. A magnet (presumably in the form of a large loop of (super-)conductor will deflect charged particles, stealing momentum from them. This "magsail" really does sail on the solar wind. The attraction is need be little more than a wire loop, so it can be really big. A beam-riding version would need a beam of charged particles. This is probably sent as a beam of neutral particles (anything from hydrogen atoms to missiles) and then blasted to ions by a laser cannon on the ship at the last moment -- charged beams spread.

Re:Stellar Pong?

[wetdogjp]

That is the problem with getting somewhere in space. To get there the fastest you have to accelerate continually there till the 1/2 way point, turn the ship around around and use an equal force / fuel to decelerate."

This topic was a key point in the SciFi book "Chasm City" by Alastair Reynolds. The fix? Get rid of mass. Lots of it.

In the book, one of a number of ships jettisoned chambers containing people intened to populate a new planet. This allowed the ship to decelerate faster than it accelerated. Of course, we can't exactly drop pieces of the ship into space; why bring them along to begin with if you don't need them?

Except fuel. Once you burn half your fuel, your mass has already decreased by a large percentage, depending on the type of fuel you're using. You could also drop the tank and the thrusters, as long as you have a seperate system for slowing down facing the other direction (as opposed to turning the ship around).

Re:Stellar Pong?

[JWSmythe]

Here is one of the pages I had read before on the matter.

Re:Stellar Pong?

[HuguesT]

Isn't that what you want, to slow down at your destination?

Re:Stellar Pong?

[HuguesT]

I think maybe you are talking about "the flight of the dragonfly" by R.L. Forward, not "The Mote in God's Eye". In the latter they have FTL travel, unless I'm not recalling correctly. The Forward book is all about a laser-powered solar sail craft.

Re:Stellar Pong?

[HuguesT]

As others have pointed out you can angle your solar sail and generate a sideway force.

Re:Stellar Pong?

[klaasvakie]

I agree

Re:Stellar Pong?

[halowolf]

SPOILER WARNING

Oh yes the human race did have the faster-than-light Alderson Drive which they used to get around the galaxy with, it did have limitations in that there was very limited points in space (called Alderson points [I think]) where the drive could be used to move from one solar system to the next.

The Moties probe was the solar sail craft as they were not able to get out of their system because their Alderson point jump destination (out of their solar system) was the outer layer of a red giant star, and since they didn't have the humans shield technology their Alderson drive crafts got vaporized when they tried to leave and hence the moties thought that the Alderson [Crazy-Eddie] drive didn't actually work. So they sent a probe out instead that traversed the distance between stars instead.

Re:Stellar Pong?

[famebait]

No, that is not the primary purpouse. Many types of small sailboats have small and light keels that providde no significant counterweight. They do still provide direction by "braking" sideways movement and thus "extracting" the forward component of the incoming force, and translating some of the sideways force into forward force. Without one you would more or less blow uselessly in the direction of the wind no matter what you did with the sail.

But as has been pointed out, solar sails have some different tricks up their sleeve: unlike air sails, the direction that the incoming "wind" is reflected will affect the direction of the resulting force. And once within the significant gravity of a star, you can navigate in and out by altering your speed only.

Re:Stellar Pong?

[MidnightBrewer]

The keel itself doesn't have to be that impressive; it all depends on how much lead you put in it. ;) Seriously, that's what you do.

I agree that the purpose of a keel or daggerboard is more than just vertical stability (as you pointed out, it obviously isn't counter-balancing the mast too much, or retractable ones wouldn't work.) My bad. It's been a while since I lived on a sailboat. :)

Re:Stellar Pong?

[wisdom_brewing]

as you said... getting it a few nanometres thick could be a tiny bit tricky :) ive heard of faradays, just had no idea how they worked... thanks

Re:Stellar Pong?

[pclminion]

True, the black sail will heat up from the absorbed proton. However the heat escaping from the sail will add to it's inital velocity.

First, it isn't absorbing protons. It is absorbing light. If it was absorbing protons, the sail would be charging up to an enormous voltage.

And if by "heat escaping from the sail" you mean infrared radiation, yes, that would exert a pressure on the sail, but there is no way to make the radiation go in a single direction. Both sides of the sail would radiate, and the pressures would cancel to no net effect.

Re:Stellar Pong?

[yakovlev]

It IS like sailing. With sailing, there are two (important) forces, that provided by the wind on the sails, and the normal force of the centerboard against the water. The sum of these two forces can be in any direction besides directly into the wind. Control of how these two forces sum is provided by muscle power that controls the rudder and sail position.

For Solar sailing, you are propelled in the direction that is the sum of the gravitational force from the sun and the force from the sails. Rockets, bending the sails, or some other secondary propulsion method are used to position the sails relative to the star. If the sails are at an angle relative to the star, then the sail will apply a sideways force, and thus sideways motion is possible.

NOTE: To get sideways force I believe a reflective sail surface is required, as it is the direction of the photons leaving the sail that provides the sideways propulsion.

Here's a simple diagram:

. O
sails closed, fall into the sun

| O
sails open, push away from the sun

\ O
sails open, move sideways relative to sun

And the path of the photons and resulting force on the sail.

\..^
.\.|
..\|
../\----Photons
|/..\
--...\ Sail
Force

Whatever happened to Big1

[Hido]

Does this mean that plans for taking the flying steam-powered train to the stars is cancelled?

Ironically

[chancycat]

Ironically, this technology can take us to 'the stars' but not toward our own. Better not change your mind and want to turn around less than half-way to Alpha Proxima...

Re:Ironically

[StarHeart]

There is probably some engineering trick to work around this. It might be possible to use mirrors to shine on the opposite side of the sail. Almost surely wouldn't be as fast, but seems like it would be doable.

Re:Ironically

[cliffy2000]

And why don't we just use a fan to move a sailboat?
(Hint: think conservation of energy.)

Re:Ironically

[andreMA]

Why would you want to go to the sun. You'll just die.

That, of course, is why you go at night!

Re:Ironically

[Anonymous Coward]

And why don't we just use a fan to move a sailboat? (Hint: think conservation of energy.)

You might be joking, but my dad used to do this all the time when he'd take us sailing if the wind would die down and we were all still out on the lake. He had a big gasoline generator and a 36-inch fan. Worked fine; moved us right along. (True, by "gasoline generator" I mean "all of us kids" and by "36-inch fan" I mean "enough oars for all of us," but, still, it worked just fine.)

Re:Ironically

[Beryllium Sphere(tm)]

Turn the mirror sideways so that thrust is lateral instead of radial.

Use the lateral thrust to kill your orbital velocity.

Furl the sail.

This would work great for a trip to Mercury, actually. If you want to reverse course in between stars you need to use one of the ideas the late Bob Forward played with, e.g. a disposable mirror in front of you reflecting a launch laser to force you backwards.

Re:Ironically

[gibodean]

I'm surprised that no-one else has mentioned this.

The truth is that a solar sail doesn't get you away from the sun by just having the sail aimed straight at the sun. It does it much more trickily than that :).

What happens is that you orientate the sail at 45% (or something like that) to the sun. That way, a large amount of the force from the sun actually goes to changing your orbital speed, and not just pushing you away from the sun. By orienting the sail so that it increases your orbital speed, you end up making greater size orbits around the sun, until you are far enough away from the sun and you can do some other tricky stuff to leave the solar system.

But, it works the opposite way too. Orient your sail so that you are decreasing your orbital speed. You go slower, and therefore your orbit size decreases, and you start approaching the sun.

Of course another poster queried why you would want to travel to the sun. Good question. But how about Mercury or Venus ?

Re:Ironically

[BerntB]

late Bob Forward

Helvete. Google confirmed. The world is a poorer place.

So that was why he stopped writing. :-(

You miss important stuff when you're too busy.

Re:Ironically

[mcrbids]

Ironically, this technology can take us to 'the stars' but not toward our own.

And, why not?

Sailing ships have sailed "upwind" for many centuries.

In outer space, you are either in orbit, or falling directly towards the nearest large body. A solar sail can be used to slow down or accellerate lateral speed simply by rotating it 45 degrees.

A simple google search turned up this in case you are curious.

Although they are right, in that solar sails do accelerate the entire trip and carry no fuel, I don't think that sails are "the way to go" unless we're talking about a ten thousand year multi-generational ship.

I consider the Bussard RamJet the "only way to fly". It carries no fuel, but is powered by carving a planet-sized swath out of the ambient hydrogen atoms out of interstellar space and fusing them.

With interstellar distances, the real issue is: how quickly can you get to relativistic speeds? Because, at .5 C, it'd take thousands to millions of years to get anywhere. But, at relativistic speeds, it'd still take thousands of years, but to the crew on board, it'd be like mere hundreds or even tens of years.

You need power to get you there in less than hundreds of years - thus the RamJet.

Re:Ironically

[MrBlue VT]

Homer: All that counts is that we're alive and rubbing elbows with the greats. [gasps] Ooh, there's Ross Perot, Dr. Laura, Spike Lee.

Bart: Wait a minute, they're not so great.

Homer: Okay but there's Dan Quayle, Courtney Love, [increasing panic], Tonya Harding, Al Sharpton, Ah! Tom Arnold! What the hell's going on?

Bart: [looking out porthole] Wait! Only that ship's going to Mars. Ours is headed for the sun.

Arnold: Yeah, ain't that a kick in the teeth? I mean, my shows weren't great but I never tied people up and forced them to watch. And I could've, because I'm a big guy and I'm good with knots.

Homer: So we're all going to die?

Arnold: 'Fraid so, but, hey, the grub's pretty good, huh? [chuckles, and then pours a can of peaches in his mouth]

Homer: The sun? That's the hottest place on Earth.

Shore: Gonna work on my tannage, buddy.

Arnold: Pauly Shore? Wow! Hey, we should do a show together, man. That's a sure cure for the blues!

Re:Ironically

[stevelinton]

Unfortunately, it turns out that the interstellar medium is much thinner, in most places and in particular around the Sun, than Bussard thought. Even if you could somehow persuade protons to fuse in the few nanoseconds while they are passing through your ship at nearly the speed of light (and on average it takes about 15 billion years for any given proton to fuse in the core of the Sun), there just aren't many of them around here.

A beamrider of some kind (leave the engines at home and ship momentum up to the spacecraft in some convenient form) or an antimatter rocket are looking like the best ideas at present.

Steve

Re:Ironically

[FireFury03]

There is probably some engineering trick to work around this. It might be possible to use mirrors to shine on the opposite side of the sail. Almost surely wouldn't be as fast, but seems like it would be doable.

Interesting idea... you wouldn't be able to carry the mirror with you once you turned around (since the mirror would be producing exactly the opposite force of your solar sail), but you could probably drop it in space pointing in the right direction - the mirror would accellerate backwards because of the light pressure but it would still reflect the light forwards which I guess you could use.

Re:Ironically

[atcurtis]

You're forgetting the biggest drawback of the Bussard Ramjet... That is the gas collection.

The gas collection mechanism will create such resistance at high velocities that it would jam up and slow the device down a lot.

I believe that there has been some research done which suggest that it would never be able to obtain velocities exceeding 0.1c let alone 'relativistic velocities'.

I think we are more or less stuck on this island Earth, until we can think of something better than Newtonian physics to traverse the gap between the stars... Some revolution akin to Gene Roddenberry's Warp drive or Iain Banks's Exotic Matter drive - something which doesn't require a reaction mass.

OT: Early STTOS was fun - somehow the warp drive sound effects always sound like the London Underground trains...

Re:Ironically

[antimatt]

Sailing ships have sailed "upwind" for many centuries.

Ships can sail upwind because they have rudders to push against the water beneath them. They can redirect the force of the wind, which is going in the wrong direction, using the rudder to push against the water to go in the right direction.

In space, there is nothing else to push against (except the ether, and I hear even that's come under some discussion). As far as the light/solar wind is concerned, the force diagram is in one direction: out.

Fortunately, nature foresaw this problem and made gravity. So fear not! We CAN fall into the sun.

Re:Ironically

[Deliveranc3]

A sailboat has a keel which forces into almost linear motion thanks to the pressure of the water resisting the wind. In space no water so if you turned the sail 45 degrees to the wind you would still move the same direction but with a speed reduced by the decrease in surface area.... You cannot use momentum to turn in space...

Re:Ironically

[Idarubicin]

There is probably some engineering trick to work around this. It might be possible to use mirrors to shine on the opposite side of the sail. Almost surely wouldn't be as fast, but seems like it would be doable.

Who modded this funny? Essentially this exact idea has been proposed already. I don't have time to come up with a link, but here is the essence of the technique.

Picture a circular solar sail in two attached pieces: an inner circle and an outer ring. The whole assembly can be accelerated away from the Sun. When you want to stop, separate the two rings. Bow the outer ring inward just slightly, so that it reflects light on to the outward-facing surface of the inner circle.

Presto! The outer ring will continue to accelerate outwards--it's a one shot brake--but the inner ring slows down.

Re:Ironically

[Rakishi]

At .5C we can reach nearby starts in a few decades, there are a lot of starts and not all of them are far away. Hell, at .5C you can reach any place in our galaxy in less than a 200,000 years. Althrough you would probably need to go decently faster for reltivistic time to make much difference. asfaik there isn't even a proposal for a working Bussard RamJet. It's a nice idea but for now it's a fantasy, solar sails are not.

Re:Ironically

[iamlucky13]

That's actually normal. If you want to turn around with chemical rockets, you can only do it at certain points. During the Apollo 13 mission, the engine on the command module actually had enough power and fuel to do a "direct abort," where they turn it around and fire in the opposite direction. The Cassini probe, however, could only make enough adjustment to park itself in orbit around Saturn. It wouldn't have come close even stopping it's radial velocity. The bottom line is, you're not losing any safety, expcept perhaps on short-distance missions where chemical propulsion will probably continue being the norm anyways, simply for speed.

Re: the last hundred something posts: In Soviet Russia, pong pings you! (had to)

Re:Ironically

[evil_morg]

This beamrider idea may have some potential. So what if you made, lets say, a ship with a solar sail. Could you not beam energy to the sail via a big laser pointed at the sail? There would be less power sent the further away the ship was but it would far more powerful the light from a star. The little extra push could be what a ship like that needs to get from one solar system to the next.

Re:Ironically

[chancycat]

Awesome - thanks for the insight. I hadn't thought of this.

Re: Stellar Tron

[weston]

While it's powered by solar wind, it will slow down and reverse as it gets farther from the original star and closer to the destination star.

No, see, that's where Jeff Bridges comes in.

Solar sail

[Uplore]

What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.

Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exerting equal force on the sails. With no fuel it is doomed to slow down and be 'blown' around in space.

Re:Solar sail

[Anonymous Coward]

please read this. The work because of the reflectivity. It's not really a 'sail' in the Earthly sense, it's a giant mirror that's only reflective on one side.

Re:Solar sail

[Anonymous Coward]

Ever seen a radiometer? or hear about the radiation pressure equation?

Well it's like this, a dark color like black will help one absorb "at least visible" light, which is converted into random motion of atoms, otherwise a kind of kinetic energy known as hear. But a reflective "color" is different. It doesn't just absorb the momentum. It acctually absorbes twice the momentum of the incoming light, but not the heat energy. The same amount of energy that came in on the light gets reflected out in the opposite direction.

Re:Solar sail

[Sparr0]

who cares if it gets knocked full of holes? as long as the dust doesnt hit whatever the sail is pulling, i dont see it mattering as long as the damage isnt total and is roughly uniform in distribution.

Re:Solar sail

[erice]

What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.

Maybe you don't. Just make the sail big enough that to generate adequate "thrust" with a few holes in it. Solar sails are very big and very thin. Any debries that hits is just going to create hole and keep on going.

Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exerting equal force on the sails

For interstelar travel, you can't rely on the sun. You need big honking lasers in your home system. The light from the lasers will be much stronger than the light from the target star, at least until the probe gets rather close.

Re:Solar sail

[Jetson]

What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.

They don't have to. The force imparted by the solar radiation is probably not strong enough to cause any holes to expand on their own. They could further prevent tearing using a cross-hatch "rip-stop" pattern of slightly greater thickness.

Re:Solar sail

[evilviper]

what happens when the craft is between 2 or more stars which are all exerting equal force on the sails.

It is directional. It can only be pushed by solar wind from one direction, so unless they turn-around, the star they are approaching will not affect the solar sail much at all.

Re:Solar sail

[whopis]

Ever seen a radiometer? or hear about the radiation pressure equation?

This is a common misconception... one that even Maxwell mistakenly believed. Apparently along with the folks at Encyclopedia Britannica as well.

Pay attention to which way a radiometer turns. If it were turning due to radiation pressure, it should act as if a force were pushing on the white side of the plates. Since the white plates reflect the light, there should be twice as much pressure on them as there is on the black plates which absorb the light. (It takes a greater transfer of momentum for something to bounce off of you than for you to catch it... think of the conservation laws).

The problem with the radiometer is that it turns the wrong directions... it acts as if something is pushing on the black side of the plates. And there is... air pressure. The black side will reach a higher temperature than the white side, and then due to the thermal transpiration, the gas near the edges moves from the hot side to the cool side, and in doing so it pushes the blades along.

Radiometers are in a near vacuum, but there is enough air pressure inside to allow this effect to happen.

Re:Solar sail

[RedWizzard]

Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exerting equal force on the sails. With no fuel it is doomed to slow down and be 'blown' around in space.

As others have pointed out, they are directional. But aside from that, when you are halfway from one star to the next you'll want to start slowing down anyway.

Re:Solar sail

[serutan]

The article was short on technical details. A lot more info can be found easily on the net, such as here.

To clear up one point, solar sails are not powered by the solar wind, which is a stream of particles. They are powered by light, which exerts several thousand times more force than the solar wind.

The sail is not direction. It is affected by light coming from all directions, but it "blows" in the direction of the prevailing light, which would come from the brightest/closest star. To change direction a solar sail ship must change the angle of the sail in relation to the nearest star.

At the start of a journey the sail would be ahead of the ship, towing the ship behind it. Sometime between stars the ship could use small maneuvering jets or something to flip itself around and put the sail behind it. The increasingly strong light from the destination star would gradually slow it down.

More likely though, the sail would be retracted or jettisoned in mid-journey, when the light from the destination star equalled the light from the original star. This is when the ship would be at its maximum velocity. It would then coast at that speed for the rest of the trip and use the gravity of the destination star or planets to decelerate much more quickly.

Re:Solar sail

[Phanatic1a]

What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.

They don't need to. Any holes punched by micrometeorits will be, even in the aggregate, infinitesimal compared to the total sail area.

Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exerting equal force on the sails.

The article's claims aside, solar sails are an abysmal technology for interstellar travel.

Re:Solar sail

[zmollusc]

Erm, unless your target star is *much* brighter than the sun, you will need to start braking at the halfway point. After all, you accelerated flat out till then, so your braking distance will be equal.

Re:Solar sail

[Stephen H-B]

The idea of cooking with the sun was actually used in some science fiction books (I forget which ones, maybe Larry Niven). The general idea was a huge array of mirrors in orbit around the sun, when the {insert generic evil alien empire} ships invaded, all the mirrors were turned upon them and they promptly exploded. viola.. free superweapon!

Re:Solar sail

[Dusabre]

The sail will have a momentum at the time that it reaches the point between stars where their solar wind is of equal force. It doesn't grind to a stop because an equal force is exerted from front and behind - they balance out and momentum is retained. After that point, it will start decelerating - braking.

To balance differing wind speeds - a variable sail would be used. Stronger destination star - sail gets smaller over the journey.

It won't get blown around

Re:Solar sail

[JohnPM]

Nice post, but one detail has to be wrong. If you could use the destination system for gravity braking then you would be able to equally use our own system for gravity acceleration. The only way the destination is more effective is if you actually slam into it (or perform aerobraking).

The speeds involved in inter-stellar are so high that gravity assisted decelleration is probably out of the question. Aero-braking in an atmosphere is certainly not an option. There have been some proposals for braking on interstellar hydrogen I believe (ramjet concept).

Re:Solar sail

[Phleg]

You'd have to play one hell of a ping-pong game with the gravitational force of planets in order to shed off the kinds of speed we're talking about with intergalactic travel.

It's better just to keep pointed in the direction of that system's star. If both sides are reflective, you'll slow down as you approach.

Re:Solar sail

[fiannaFailMan]

It's easy. Just reconfigure the main deflector dish to emit a coherent tetreon pulse that will generate a de-facto tachyon surge ahead of the ship and miraculously save the ship with one second left on the timer.

Re:Solar sail

[Chuck1318]

For interstelar travel, you can't rely on the sun. You need big honking lasers in your home system. The light from the lasers will be much stronger than the light from the target star, at least until the probe gets rather close.

Coincidentally, the next story posted on /. (about SETI) talks about lasers 10000 brighter than the sun.

Re:Solar sail

[Tenebrious1]

What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.

That's why the Japanese are busy working on manufacturing "solar duct tape"...

What Solar Sails Are

[SlashChick]

In case you, like me, didn't know that much about solar sails, there's a great article at How Stuff Works about them: How Solar Sails Will Work. Looks like a pretty interesting technology!

Re:What Solar Sails Are

[Cecil]

Wow, that surprised me. I thought they actually used the solar wind to power them, not light. But that is not so. The article says the light produces 9 newtons per square mile (3.5 newtons per km^2) whereas by my calculations, an average strength solar wind stream of 1 proton per cm^3 at 500km/s would only produce about 0.0004 newtons per km^2.

Kind of counterintuitive. I thought the unbelievably small mass of a proton would still outweigh the nearly infinitesimal mass of a photon. But I guess our star puts out enough photons to make it count.

Cool, anyway.

Re:What Solar Sails Are

[Efreet]

Also, photons tend to lose less energy than protons as you get farther away from the sun, since they have a lower mass to energy ratio. Or another way to think about it is that they move faster, spending less time being pulled on by gravity before getting out here to Earth.

Re:What Solar Sails Are

[snake_dad]

The huge solar flare of last year gave a nice example of that. Its passing was noted by Cassini and other spacecraft, and it significantly slowed down the farther out from the sun it travelled.

Physics

[caitsith01]

Anyone care to fill us in on the rate at which the energy received by a surface decreases with distance? I imagine that, given the incredibly weak force applied by light, it would take one HUGE sail to get anything like meaningful acceleration for space travel. Surely be the time you are a few million kilometres from the Sun the amount of force being applied will have dropped off by a huge amount?

Anyway, we should get to Mars and back a few times before we try to get to the stars... baby steps.

Re:Physics

[CrankyFool]

The amount of force exerted on the sail decreases as a square of the distance (since the amount of light reaching the sail decreases by a square of the distance). We're not talking about 'meaningful acceleration' in anything like our current thinking of space travel -- this isn't "get on this space yacht and a few months down the road you'll get to the other star," but rather "put something on this vessel and several hundred/thousand years from now it'll get to where you wanted it to get."

This isn't about travel.

Either way, the Japanese are trying to make this look cool by saying it's star-faring technology. Probably true, but only because we're not likely to put humans on this thing -- so it's possible we'll do this before we get to Mars, because the expense and risk could be vastly lower.

Re:Physics

[symbolset]

This takes you to the Kuyper belt. From there, ion drive takes you the rest of the way.

Re:Physics

[vantango]

Why wouldn't it be meaningful acceleration?
If the resistance in space is less than the force exerted on the sail, it should result in positive acceleration.

Remembering that the ship is already moving pretty quickly when it enters space, its velocity will continue to increase until the force exerted on the sail equals the resistance of space (a long time).

Re:Physics

[Jetson]

Anyone care to fill us in on the rate at which the energy received by a surface decreases with distance?

I'm no scientist, but wouldn't the thrust follow the same inverse-square law as radiant light?

To make best use of a solar sail, it would probably make sense to use a conventional rocket to establish a highly eccentric (parabolic) orbit around the sun and then pop the sail open after perihelion where the sail would contribute the most energy to the orbit.

I think aiming the spacecraft (on the outbound journey) would be the hardest part.

Re:Physics

[Beryllium Sphere(tm)]

The acceleration is very low but it operates continuously. Given a choice between a few minutes of using a rocket before it's out of fuel, versus months of gradual acceleration on a solar sail, you can actually get more speed from the sail.

For the foreseeable future the real applications would be inside the solar system.

Re:Physics

[rippleone]

We need to remember to always ask the question do we really need to go to another planet when we can't seem to get along with each other here. We don't even use our natural resources with the level of accountability that we should given that for right now this is it for us. We have yet to even mine an asteroid. We really need to work out just a few issues before we start littering the solar system with McDonalds wrappers.

Re:Physics

[CrankyFool]

The ship is absolutely NOT moving 'pretty quickly' when it enters space. It may be moving pretty fast compared to, say, planes -- escape velocity is about 25KMPH, which would be about Mach 32 if it was at sea level.

But when it comes to interplanetary distances, 25KMPH is ... barely pokey.

Closest star to us is Proxima Centaury -- about 4.2 light years, or 2.5 * 10^13 miles.

Well, this explains it much better than I can. Basically, the Japanese mission is using 7.5um film; the NASA document posits that, if we were able to use sail of only a few nanometers (actually, a few thousand times lower areal density than we can currently achieve), we could see acceleration of up to .3m/s/s, and terminal velocity of around 671KPH. Estimated trip to closest star: About 2693 years.

Don't hold your breath.

Re:Physics

[Phanatic1a]

It can actually be quite meaningful acceleration, depending upon what sort of payload you're talking about. Keep in mind that Deep Space One was a useful space mission, and its ion engine provided a maximum thrust of about .09 Newtons. At 1 AU from the sun, you're going to get about 100 times that force exerted on each square mile of sail.

That's quite acceptable, especially because it scales so well. This would be admirably suited for interplanetary bulk cargo transportation, ferinstance. Sure, it might take each particular sail/cargo unit a while to get moving, but you could set up a series chain of them and get a pretty darned good throughput.

Re:Physics

[vandan]

That's a damned good point. I often think the same thing when the issue of searching for alien life comes up.

Imagine if an alien intelligence were watching us. Do you think they'd be keen to make contact with us after witnessing our war-torn past? Even over the last couple of years, we've invaded Afghanistan and Iraq, destroying what was left of both places ( and of course we're to blame for the state they were in to start with ).

I think an alien intelligence would stay well clear of us until we proved we were mature enough to interact with them.

Yes there are far more important things for us to worry about than going into space. In fact I think a lot of our current problems exist specifically because our technology has matured faster than our society has.

Re:Physics

[Phanatic1a]

we could see acceleration of up to .3m/s/s,

And that's an entirely meaningful acceleration, because it's so constant. Your payload will be an enormous fraction of your total mass, instead of the tiny fraction of total mass it is with chemical rockets, so you're not wasting energy hauling around fuel. .3m/s/s may not sound like much, but since it's constant, it adds up quick. Remember, v(t)=at+v(0), so that .3m/s/s gets you to rather incredible speeds pretty rapidly.

Hell, cut it by a factor of 1,000, and it's still tremendously useful. The engineering difficulty is in actually producing large sails, not in being able to put them to good use once we can build them.

Re:Physics

[Jedi Alec]

i'd say that not getting along just gives us all the more reason to move to another starsystem ;-)

Re:Physics

[Jeremi]

I'd say we need to go to another planet precisely because of the reasons you state. Having all of our eggs in one basket like this is too risky.

Re:Physics

[CrankyFool]

I entirely agree with you but will point out two things:
A) We're talking _interplanetary_, not interstellar; and
B) Bulk cargo transportation is definitely doable here -- but we're not talking about travel.

In other words, this isn't "travel to the stars" on two accounts. It's not that this isn't _useful_ (or cool), it's just useful for intrastellar transportation, not interstellar travel.

Re:Physics

[Errtu76]

baby steps will get us nowhere. I like the idea of individual organizations (non-gov) exploring space, which will only push the leading space explorers to work harder. What we *should* do is just go! I mean, 35 years later and we STILL can't claim more than just 'we put a man on the moon'. No colonies on the moon yet. No other planets explored (by man). Seems like a very slow-learning baby to me.

Re:Physics

[Hockney Twang]

As others have pointed out, a solar sail does not accelerate directly away from the sun. It orbits the sun and uses the energy from the sun to accelerate its propulsion. So you can actually stay quite close to the sun and build up a great ammount of speed, then your orbits gradually get bigger as a result, until you're far enough away to break out of orbit and zip along at high speed. It takes a long time to get to it, but once it's there, you're going pretty fast.

Re:Physics

[Squiddl3]

>No other planets explored (by man

others than which?

I can't remember men explored any planet except earth. And look what happened :o

Moon to earth is in no reasonable comparison from moon to another planet (like mars). Its like comparing walking to the supermarket and walking to australia.

Re:Physics

[TeraCo]

Don't worry about this guy too much, he has trouble extracting his political axe from his favourite grinder.

Re:Physics

[vandan]

Their religious system has nothing to do with it.
In both cases the previous regime was installed and supported by the US.

Where does religion come into it?

And how do you explain the nation-wide co-ordinated resistance to the US occupation?

Re:Physics

[vandan]

Hey arsewipe!

Been defeated by one too many of my comments, eh?
How about giving some constructive arguments instead of complaining generally about my political inclinations?

Of course it is obvious that for me to upset you, you must also have a political axe to grind. But you carefully forgot to mention your own extreme right-wing bias, eh?

Re:Physics

[TeraCo]

What axe? I'm actually a swinging voter, but of course there is no room for people to make informed choices in your world eh?

You don't particularly upset me, but I have decided to try and point out to you how god damned stupid the extremist left is.

[Just as stupid as the extremist right when it comes down to it, but there are less extreme rightists on this site.]

Now, just try and relax, and admit that supporting religious fundamentalists, just because they are anti-US is a mistake.

Re:Physics

[vandan]

There are religious fundamentalists and then there are religious fundamentalists. Take the US government for example - the strongest supporters of the Christian fundamentalists to date.

And as for it being wrong to support religious fundamentalists just because they are anti-US ... we don't look at it like that. We support any group who tries to free the Iraqi people from their current oppressors. If they happen to be religious fundamentalists, then fine. The Iraqi people should be free to choose whoever they want to run the place, whether you label them religious fundamentalists or not. This is the secret to self-determination. The fact is that they have widespread popular support, and according to our democratic values, therefore earn the right to government.

Re:Physics

[TeraCo]

We support any group who tries to free the Iraqi people from their current oppressors.

This is your biggest mistake. You should be more choosy about who you cuddle up to, lest it come back to make you look like an idiot later. For bonus points, name the major sponsor of Afghani militants in the 80's.

The Iraqi people should be free to choose whoever they want to run the place, whether you label them religious fundamentalists or not. This is the secret to self-determination. The fact is that they have widespread popular support, and according to our democratic values, therefore earn the right to government.

But these religious fundamentalists are responsible for the genocide of various social groups in Iraq. Surely that makes them more 'oppressive' than the current Iraqi leadership which, to my knowledge haven't yet done that.

The question is, if these religious fundamentalists have popular support, why don't they just wait for the elections, and win those, rather than blowing up the very people they are trying to rule over with car bombs. The answer is of course, that they don't want that sort of government, with all of the relevant oversight that comes with it. They would rather be able to cause people to disappear in the middle of the night, like the good old days. You honestly can't expect me to believe that the average Iraqi citizen wants this.

Iraqi Citizen: Cool! Reign of terror! I hope my family and I disappear in the middle of the night like the good old days.

Re:Physics

[vandan]

For bonus points, name the major sponsor of Afghani militants in the 80's.

Don't know about the 80's. How about the 90's? The Taliban, which was set up by the CIA and backed at every turn by the US and UK governments.

The question is, if these religious fundamentalists have popular support, why don't they just wait for the elections, and win those, rather than blowing up the very people they are trying to rule over with car bombs.

How about because all political opposition who state that they want to run in the next election ends up in Abu Ghraib prison? Don't know honestly think the US are going to let a stupid little thing like national elections get in the way of their plans for the middle east? Look at how the current US government got into power - by stealing the election and having the courts 'appoint' them winners. And who were the judges on the panel? Why they were all appointed by Bush's brother, who just happens to be the governor of Texas! And who funds the Bush family? The Bin Laden family! Do you really think democracy will prevail in Iraq? If you do, you are incredibly naive. We haven't even got it right here yet. I laugh whenever people try to tell me that our 2-party system and our once-every-four-years vote-for-one-donkey-over-the-other is supposed to be the height of democracy.

Iraqi Citizen: Cool! Reign of terror! I hope my family and I disappear in the middle of the night like the good old days.

You forget that Saddam ( like Bin Laden ) was trained by the US and installed by the US and backed by the US. In fact he was one of their closest allies until 1991. I'm not saying that Iraq should return to what they had before. In fact, that is what you are saying by approving of the so-called 'elections'. Elections under the supervision of the US forces and the current interim government will only produce another Saddam. And that's exactly what the US wants.

Re:Physics

[TeraCo]

You forget that Saddam ( like Bin Laden ) was trained by the US and installed by the US and backed by the US. In fact he was one of their closest allies until 1991. I'm not saying that Iraq should return to what they had before. In fact, that is what you are saying by approving of the so-called 'elections'. Elections under the supervision of the US forces and the current interim government will only produce another Saddam. And that's exactly what the US wants.

Don't know about the 80's. How about the 90's? The Taliban, which was set up by the CIA and backed at every turn by the US and UK governments.

PS: Yes, this was my point. Today's allies can be tomorrows people who are loading people into ovens just because they come from the wrong village. You're going to feel like a bit of a tool for supporting them then, surely. Or maybe you won't, because it was all in aid of hating the US.

This is why you are wrong, because you can't look over your hatred of the US to see the real situation. [For bonus points, read something that isn't Green Left Weekly]. Well, riddle me this? How the hell is militants derailing the election process going to produce a democracy? I'm not saying that the US way is any more likely to succeed.. but at least it isn't driving car bombs into buildings full of people.

Re:Physics

[TeraCo]

Crap, my response to your first paragraph was eaten by HTML voodoo. Rest assured it was very insightful!

Re:Physics

[vandan]

Well, riddle me this? How the hell is militants derailing the election process going to produce a democracy?

It's called a revolution. It starts small, with targeted attacks on visible symbols of the oppressors. It ends in everyone standing up and saying "Yes. Enough is enough. Down with the current system. We'll take over now."

Of course every time a country attempts this the CIA rock up and make sure it fails ( that is unless they instigated it themselves ... they do this quite a bit too ). But successfull revolutions do happen. Yugoslavia had one. The US will claim it was their surgical-precision carpet-bombing of civilians that brought regime change. But if you talk to ( or find quotes from ) people who were there, they will tell you that it was the people who all came together to overthrow their oppressor that won the day.

One quote I saw on a film recently from a uni student in the former Yugoslavia:

The people have won the day! And if the US ever wants to save us with their bombs again, PLEASE don't bother; we did it ourselves today, and we will do it again when needed

Now I have a question for you. And I want you to demonstrate that you have considered it seriously.:

You must have seen the most recent uprisings in Iraq, where hundreds of thousands of people went into the streets to protest the current US puppet regime. Clearly the interim government has NO support. How exactly are you going to get a democratic outcome by telling the Iraqis to go home and just deal with the US puppet regime and forget about all their family and friends and political leaders who have been imprisoned, tortured and killed in Abu Ghraib prision and others. Do you really think Iraq is on the verge of democracy ? Look at the democracy that the US has set up in Afghanistan? How about the democracy that the Palestinians are entitled to in their own country? The US is not interested in democracy - just in making people think they want democracy, because they think people will agree with them if they claim to be the champions of democracy. The sad thing is that 50% of the people are gullible enough.

Re:Physics

[TeraCo]

It's called a revolution. It starts small, with targeted attacks on visible symbols of the oppressors. It ends in everyone standing up and saying "Yes. Enough is enough. Down with the current system. We'll take over now."

Everyone? Or just the militants. This strikes me as naive in the extreme. Mainly because I can't see how 'everyone' is going to assume control. Someone has to have authority, and it's not going to be Joe Iraqi off the street.

Re:Physics

[vandan]

That's what unions, religious groups and other non-government organisations are for.

When things get bad enough ( as history teaches us time and again ), this ( a revolution ) is exactly what happens. And Iraq isn't far at all from one. I only hope they have the perseverence to stick it out, or the US will take the hint and start on the next in the 'axis of evil' or 'war on terrorism' or 'enemy of the free world' or whatever else they dream up that George Dubya can manage to pronounce.

Re:Physics

[TeraCo]

Well, there are no unions or other non-government organizations.. except for Joe Terrorist who certainly doesn't have Joe Iraqi's best interests at heart.

Re:Physics

[vandan]

You think all they want is destruction?
Do you really think there are people who think like this, or perhaps this is just what the neo-conservatives would like us to believe so we don't think that there are decent people in Iraq who want the US gone.

I'll let you in on a little secret. Terrorists are ordinary people in extraordinary situations. The fact that they turn to violence of such a nature surely points to the stress that they are under. There are no Iraqis that go out and blow things up for fun, or even because they are religious fanatics. They do it because it's the only way they know of sending a message that they are serious about getting the US out. You're "Joe Terrorist" is just one of the many of these people. They are not after death and destruction. They've had plenty of that under the occupation already. They want the US out, and they want control of their own destiny. Just like we would if someone invaded us.

Re:Physics

[TeraCo]

You think all they want is destruction?

Hell no, they are pretty indifferent to destruction when it comes down to it. What they want is to be able to run the country according to their own whims, not caring about the US, the UN, or Joe Iraqi living down the street.

If the US pulled out tomorrow, I suspect Iraqi would dissolve into civil war instantly, with a wide variety of factions going for it.

Re:Physics

[vandan]

What they want is to be able to run the country according to their own whims, not caring about the US, the UN, or Joe Iraqi living down the street.

Absolutely right apart from that bit about 'Joe Iraqi down the street'. People in Iraq care as much about their neighbours as the rest of us.

If the US pulled out tomorrow, I suspect Iraqi would dissolve into civil war instantly, with a wide variety of factions going for it.

This is a lie that is perpetrated my the mass media and our governments. The truth is that the Iraqi people are not on the virge of a civil war, and are quite unified in what they want. I've been to forums where people who had actually been to Iraq recently spoke briefly about their experience. We had former human shields, Red Cross workers, and I think a telecommunications contractor. They all said the same thing - that the Iraqi people are all uniting around a common goal: democratic control of their country - and that all the talk we hear of fighting between different religious groups is a myth.

I remember one particular incident - where a mosque was bombed, and the media here grabbed it and paraded it around as an example of the barbaric nature of Iraqis and how they needed our military guidance for them to achieve piece. What they didn't say in the report was that the bombing was by a right-wing terrorist group that is linked to the current interim government, and that immediately after the bombing, people from all religious backgrounds came together to help the injured, and then later came together to mourn the dead. After the mourning was over, they marched down the street with shouting slogans like "Down with the US". The couple that I saw interviewed ( on SBS ) said that they knew the mosque was bombed to provoke fighting between different religious sects, but that they had seen it for what it was, and were instead insisting that the blame lies soley with the US and their supporters.

Re:Physics

[TeraCo]

This is a lie that is perpetrated my the mass media and our governments.

Uhh... what about the.. you know.. genocide?

Re:Physics

[vandan]

Uhh .. what about the ... you know ... US?

The genocide was as a direct result of the US giving Saddam chemical weapons and telling him to test them, in much the same way that the US now give chemical and nuclear weapons to Israel. The US benefitted directly from Iraqi and Israeli testing of their chemical weapons. US military experts and well as representatives of US chemical companies who manufactured the weapons oversaw most of their use.

The fact that Saddam targetted the Kurds in no way proves that the Iraqi people in general are torn by religious or racial hatred. The only thing it proves is that the US shouldn't have given Saddam chemical weapons when they knew exactly what he would do with them.

You jumping up and down about genocide is ridiculous in light of the fact that the US was more to blame than any other entity on the planet apart from the Ba'ath party and Saddam himself. You certainly can't blame the Iraqi population for the killing of the Kurds. How exactly is your Joe Citizen supposed to stop the Ba'ath party with their US-donated weapons and ammunition?

Re:Physics

[TeraCo]

But that's the thing.. your anti-USism is getting in the way again. Just because the US killed a whole lot of people DOESN'T MAKE IT RIGHT when someone else does it.

Re:Physics

[vandan]

???

But by the same token you can't support the US by saying:

Yeah sure the US have killed tens of thousands by invading Iraq ( or millions through trade sanctions ), but just look at the hundreds that have been killed by resistance fighters since they invaded

That's what you get for bombing the fuck out of the country and completely destabilising the Middle East. Are you obsolutely certain that the US have the high moral ground here? Do you really think the handful of people killed in the struggle for independance measures at all against the number that were killed even in the initial 'shock and awe' campaign? You have to keep things in perspective and keep in mind who started what.

I'm absolutely certain that the US does not have the high moral ground in this case. And while I don't encourage violence of any kind, I am realistic enough to point out that the so-called 'terrorists' in Iraq are merely everyday citizens in extraordinary circumstances. They have been betrayed by the US and by the whole world for decades and now that US forces are on their soil, they're fair targets. And anyone who sides with them are also fair targets. I don't even live there and I can see their point of view perfectly. The US's actions should have a large number of people being investigated for war crimes. The actions of the resistance fighters simply do not compare, and are even defensible when you hear their stories. Instead of me googling around for a story, I'll just let you imagine one. Do it now. Imagine you were in Iraq. Imagine the past 20 years of your life. Now finish it off with the US killing half your family in their shock and awe campaign, and locked up the remaining men and raped and tortured them. What do you do? Welcome them with open arms?

I was not born with my 'anti-USism'. I have accumulated it over the years by watching and learning.

Take Afghanistan.
Or Iraq.
Or Cuba.
Or Venezuela.
Or Palestine.
Or the Phillipines.
Or Indonesia.
Or Vietnam.
Or Chille.

The US talks of 'freedom' and 'democracy' and saving the world from the horrors of war. In reality, they are the antithesis of everything they claim to be fighting for. So I make no apology for being anti-US. I will change my tune when they change theirs.

Wrong

[HeghmoH]

...it is the only technology now in existence that can one day take us to the stars.

Orion can take us to the stars, and it can be done with today's technology, not something that's just starting to enter the very earliest test phases. But it's nuk-yu-ler, so it doesn't count.

Re:Wrong

[gilroy]

Blockquoth the poster:

Orion can take us to the stars, and it can be done with today's technology, not something that's just starting to enter the very earliest test phases.

Because Orion needs to carry its fuel, its period of acceleration is necessarily limited. If you count Orion as a star-faring technology, then you need to count chemical rockets, too... Just ask Pioneer 10.

Re:Wrong

[ByteSlicer]

Uhm... I think you make some wrong assumptions here. What about this:
To get from speed 0 (on Earth) to light speed, using an acceleration of 1g (one time the normal gravitational acceleration), we would need 3.0e+8/(1*9.8)/(3600*24), which is about 354 days.
The human body would do just fine under those conditions.

Re:Wrong

[mati]

I don't follow. Just accelerate at 1g for 5 times as long (around a year) and everyone's comfortable. Accelerating the other direction at Alpha Centauri would be another year and you're still well under a decade for a one-way trip.

Re:Wrong

[div_B]

I don't follow. Just accelerate at 1g for 5 times as long (around a year) and everyone's comfortable. Accelerating the other direction at Alpha Centauri would be another year and you're still well under a decade for a one-way trip.

The problem (aside from energy considerations...) is time dilation. That 1 year is 1 year in the spaceship. It's a whole lot more in the frame of say, earth. I *think* it works out that it takes infinite time in the frame that was coincident with the spaceship's frame before it began accelerating.

Actually I'm pretty sure thats right; consider the spaceship at 0.9c, after 319 days of acceleration. On that day, the ship adds another day's worth acceleration to it's speed, however time dilation is now more than 2x, so that change in speed occurs over (more than) 2 days, as observed in the other frame. As the ship's speed approaches that of light, time dilation approaches infinity, and as such the acceleration as observed in the other frame approaches zero.

The moral of the story being, you can accelerate a massive object to the speed of light (neglecting energy considerations, which aren't something you can really neglect in this case :) ), however the universe will end before it gets there.

Re:Wrong

[famebait]

And you get free earth-style gravity on board too!

Re:Wrong

[RamboCalrissian]

That's the last thing we need. Space pirates going around on nuclear ships. This whole solar sail business is already too much.

Re:Wrong

[caswelmo]

I, like most I assume, have never really gotten a firm grasp of the reality of time dilation. Basically, here's my own practical implementation: The faster you go, the longer it seems that you take to people that aren't going with you (stayed on Earth).

So, you get to make the choice: 1) Get there fast so that it doesn't take your whole life. 2) Get there slow so that someone you know might be around when you get back.

Here's an interesting question for you physicists out there:

Is there an "optimal" speed for minimizing the time that Earth would perceive you as being gone?

If you're doing a science mission for Earth, that would seem to be the time that would matter for the greater good.

Re:Wrong

[at_18]

'' Is there an "optimal" speed for minimizing the time that Earth would perceive you as being gone?''

Yes, go as fast as possible. The time perceived on Earth is the one that results from your speed, as measured from Earth. So, if you are doing a 10 light years trip going at 0.5 c, it will take 20 years in Earth's time, and a bit less in yours. If you go at 0.9c, it will take about 11 years in Earth time, and much less for you.

The correct version of your 1 and 2 choices should be in the distance axis:

1) go somewhere relatively near, so that when you come back someone you know might still be around
2) go very far away, see the universe, and say goodbye to everyone before leaving.

In both cases, the faster you go, the less time will take for Earthlings to see you back, and also the less time will seem to you. The latter goes down much faster. The total time, measured from Earth, is time = distance / speed, no need to use relativity. That's for when you compute time for people aboard the ship.

Re:Wrong

[MarsDefenseMinister]

Something else that needs to be considered is that the feasibility of Orion is theoretical. In the real world I think that production of the nuclear explosives would be tremendously difficult. The number of nuclear explosives required would present a large production problem. We have mass produced nuclear explosives in the past, but not on the scale required. We took decades to produce all that we currently have. And that production was extremely costly particularly to the environment. Orion might be something that only requires technologies available today for the spacecraft, but the fuel production would be really difficult for us right now.

Re:Wrong

[HeghmoH]

I don't follow. Using Orion technology, starting today, we could build a starship that would put living humans around Alpha Centauri in a bit over a century. We couldn't do that with chemical rockets at all with what we know, no matter how much money you spend on it.

Re:Wrong

[cheesybagel]

You have H-Bombs (fusion), so you do not need to mine as much Uranium to make a device with a similar explosive energy. Besides, these bombs will be smaller than the usual megaton city busters, more like tactical nukes (to blow up bridges, etc) used to be.

You could recycle old nuclear weapons to make the Orion propulsion devices, there are a load of these stockpiled right now. There are also other interesting ideas for how to make a fusion bomb without using a messy fission device as a trigger (using heavy powered lasers, chemical explosives, plasma guns, anti-matter, etc). Interestingly most of these ideas also apply to useable fusion power generation. Read about the NIF (National Ignition Facility) of the US and similar facilities in France and elsewhere for more on this matter.

Of course these other ideas are violently opposed by Greens and other similar people because they would make nuclear weapon proliferation a bigger issue in their view. Their way of thinking is, since the nukes would be cleaner, they would be used more widely. I think this issue is bogus. You do not use a stick of dynamite to kill a fly. It is a matter of economics. And if we do go into global thermonuclear war someday, wouldn't it be nicer if the weapons actually were cleaner? Sheesh.

Re:Wrong

[MarsDefenseMinister]

How about some quantities here. Saying that we could recycle old plutonium and/or uranium is good, but Orion would require huge amounts of the stuff. Perhaps more than we already have on hand.

The production of materials is expensive and the environmental costs are also expensive. The fallout thing is a non-issue, because Orion operates outside of Earth's ecosphere. But cleaning up a production site is expensive. See Hanford for more information.

Re:Wrong

[mantera]

Man, you're gonna upset hippies who'll be totally against the idea of us poluting virgin space with our radiation-emitting scrap. *tongue-in-cheek*

Re:Wrong

[cheesybagel]

The project Orion design most people remember was for a huge vessel built like a battleship (it was even made of steel) to carry along a manned crew. You have to remember this was originally designed in 1958, hence this sort of design.

If you just want to make a robotic probe, it would be smaller. Of course, if it is interstellar range (Proxima Centauri is 4.2 light years away) you want, it will still be positively huge if you want to get there in reasonable timescales. The Wikipedia page has some numbers.

There is no way around this size problem, according to known science, except if you put the fuel outside the ship. Which is what laser beamed solar sails are all about. If they can get them to work reliably...

But for manned deep space exploration, nuclear propulsion is still the best bet. Solar sails would be too frail and low thrust.

Re:Wrong

[div_B]

I, like most I assume, have never really gotten a firm grasp of the reality of time dilation. Basically, here's my own practical implementation: The faster you go, the longer it seems that you take to people that aren't going with you (stayed on Earth).

Someone has posted a nice answer to your question already, although I feel I might be able to clarify this bit for you.

As the sister post to this states, if you travel 10 ly away from earth and back, it will take you 20 yrs minimum, as observed from earth. It's more informative to consider what's observed in the spaceship.

If the spaceship was travelling at the speed of light, then the time dilation is infinite. What this means, is that time has stopped on the spaceship. However much time passes on earth, and NO time passes on the spaceship. Also, length contraction is infinite. What this means, is that a distance as measured from earth's point of view, say the 3000 lys (?) to Andromeda, is measured to be ZERO distance by the spaceship. Both are complimentary views of the same effect: at light-speed, the ship sees itself as travelling at infinite speed across the universe, while the earth sees it as travelling at the speed of light.

This is the extreme relativistic limit, and it's easy to see that at 0.99c or whatever, very little time passes on the ship, and the distance becomes very small, but both remain finite.

I'm sure most of us have looked up at the night sky and thought 'wow, that light I'm seeing left that star however many million years ago, and I'm looking into past, etc'. Consider the photons in light (pun not intended) of what was discussed above: the photons have travelled say, 1 million lys, in 1 million yrs, from your point of view. However, the photons live in the extreme relativistic limit, hence they have experienced no time passage at all, they appear at your retina instantly. Hence, if photons were unstable, and decayed with some half-life, we'd never know, because all photons exist for an infinitesimally short span of time. Understand that, and space-time diagrams, delineated by the paths of light rays, begin to make some sense (the operative word being 'some').

All this is explained in terms of Special Relativity, which deals only with motion at a constant velocity (ie in an 'inertial frame'). Acceleration is covered by General Relativity. Any 'return trip' away from earth is going to involve a change in direction (an acceleration), which can be approximated under SR by a constant velocity away, and then a constant velocity back.

If you really want to damage your brain, consider that if the spaceship is receding from earth at light-speed, then from it's point of view earth is receding from it at light speed, and that therefore the same arguments made for the spaceship could be made for the earth, (ie that earth experiences no passage of time while the spaceship does), right?

The paradox is broken by including the effect of the turn around. As the spaceship must change direction, it no longer exists in only one inertial frame (ie one with no acceleration). The spaceship is what changes direction, the earth doesn't, hence the earth, being in only one inertial frame, is what will age compared to the ship, not vice versa. (Of course you could argue that from the ship's point of view, the earth changes direction, but the acceleration is really at the ship's end, as it experiences the applied force, ie effect of the retro-rockets, or the solar-sail, which is a real acceleration, not a 'relative' one).

Re:Wrong

[Ohreally_factor]

Keep your goddamn radiation out of space, man! For the sake of the children! We don't want them inheriting a solar system full of radiation! =)

Obvious Answer

[rf0]

Solar Anchor :)

Rus

Re:Obvious Answer

[fiftyfly]

I think they cal it 'Sol'

Repairing micro-meteorite holes

[metachor]

What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.

This is pure speculation on my part, but perhaps some future form of nanotechnology could be used to make self-repairing sales. Implanted sensor arrays would detect discontinuities in the sail-surface and delegate molecular assemblers to patch it.

Re:Wrong-A "glowing" recommendation.

[HeghmoH]

Sorry, but that is incorrect. There is a design from the late 60s for an Orion starship that could get to Alpha Centauri in 130 years, for the whopping cost of $1 trillion. Thats much faster than a solar sail could ever hope to do.

Going to Sol

[anactofgod]

You just have to tack into the solar wind. *grynn*

You heard it hear first -- America's Cup 2200.

---anactofgod---

Re:Going to Sol

[name773]

sounds kind of... tacky.
:)

Re:Going to Sol

[gilroy]

Blockquoth the poster:

You just have to tack into the solar wind. *grynn*

You probably think you're being funny, but this is in fact exactly right.

Re:Going to Sol

[Beardydog]

Well, that's not so much tacking into the sun as it is allowing yourself to fall into the sun. Decreasing angular momentum = shrinking orbit. But it is a far better idea than falling into the sin -without- a giant shiny parachute.

Re:Going to Sol

[Efreet]

Almost, but not quite.

You see you can tack with a solar sail, but you can only tack to go in different directions [i]downwind[/i]. You can't tack upwind without the equivalent of a keel, something thats sort of hard to come by in space.

Re:Going to Sol

[Anonymous Coward]

Well the analogy to sailboats breaks down a bit but you get the same effect as tacking into the wind with a solar sail. The sail can be oriented to direct some of the force tangential to your current orbit around the sun. So depending on the orientation you can either spead up (which increases your orbit by spiraling out) or slow down (which causes you to spiral towards the sun).

To go back to to the boating example. Imagine a boat, without a keel, but with an anchor fixed to a shallow lake. The anchor is attached by a rope to a winch on the boat. You have a constant wind eminating from above the anchor in all directions (ok so this is a stretch but bare with me). The winch will increase or decrease the length of the anchor rope in proportion to the tension on the anchor rope.

You could sail directly away from the source of the wind (above the anchor), but you could also sail in a circle and even expand or decrease the radius of that circle. So you don't need keel to sail around the sun!

Re:Going to Sol

[Chuck1318]

You see you can tack with a solar sail, but you can only tack to go in different directions [i]downwind[/i]. You can't tack upwind without the equivalent of a keel, something thats sort of hard to come by in space.

The analogy with sailing on water is not perfect, but when the analogy breaks down, it does not mean the solar sail does not work, but just that you have to deal with the real physics of the situation, rather than reasoning from analogy. If a solar sail vehicle is in orbit around the sun, by tilting the sail to make the reflection go toward the forward direction of the orbit, you slow its orbital speed, causing it to descend into a lower orbit closer to the sun.

How romantic

[syousef]

We'll sail to the stars.

Please. One poster has already pointed out that this only works within the limit of a star's solar wind. It's also a very slow mode of transport. If you want to send your decayed remanants (even the bones will have disintegrated) HALF way to the stars this is definitely the way to go!

For travel within the inner solar system however, as a secondary form of propulsion it may have its uses.

Re:How romantic

[syousef]

Until acted on by another force, such as that from the solar wind of another star.

Don't lecture me on inertia let alone as an AC.

Re:How romantic

[syousef]

I'm suggesting that it would be pushed back and forth until it reached an equilibrium point between the 2 stars, if they were the only 2 forces acting (which they would never be).

You'd get pretty close to the other star, then the sail would act as a parachute. Okay you say so you want to slow down when you get to the other star. Without controlled propulsion just try and do it.

PERHAPS you could try shutting down the sail to insert yourself into a stellar orbit using the star's gravity for breaking. I think even that would be far fetched.

This is not a good controlled way to travel between stars.

Mind you I _COULD_ be very wrong. I just doubt it.

Re:How romantic

[syousef]

The light from Sol would keep pushing it at least until it passes the heliopause, and after that, probably have little effect. At that time, the target star would not have much effect on the sail. When the sail is getting closer to the other star, it would start to slow down.

Yes, after the heliopause much less effect, which equates to a slow slow ride relying on inertia built up while in the heliosphere.

Of course it's far fetched to use the target star's gravity in order to slow down while approaching it! The gravity would not exactly stop you from falling towards it, would it?

You can definitely use the gravity of a large body to either slow down or "slingshot" you to speed you up. A great many probes use planets to do just this, so that they don't require inpractical amounts of fuel to do this.

Re:How romantic

[syousef]

My god, the guy gets corrected and specifically told the reason he was wrong and still doesn't get it. When you reach the half way point you've already been accelerating for all that time, you'll start deaccelaerting but you sure as hell wouldn't stop right there like you claim with your "HALF" in capital letters.

For heaven sakes people I was NOT suggesting that it would literally stop mid way, even if my wording is inprecise. I do know what inertia is. What I was suggesting is that if you had a solar sail being blown around by 2 stars and they were your only form of propulsion you'd:

A) Only accelerate for a little while, and take a very long time to get there
B) Be blown back by the stellar wind of the other star once you reached the boundaries of its solar wind. If this was your only form of propulsion you'd have to have a retractable sail and calculate when to put it out to break adequately.
C) Find this a very impractical way to get between stars.

Why don't you stop posting as AC and get a clue.

Only if you're sending sails to super-bright stars

[Anonymous Coward]

If the destination star has about the same amount of solar wind (or whatever sails use; I forget what exactly) as our sun, the point where it reverses course would be about 1AU from the destination star. I'd say that's close enough to be considered "reaching another star".

Not a working solar sail as such

[bigsteve@dstc]

Quote from article:

ISAS succeeded in deploying a big thin film for solar sail in space for the first time in the world. ISAS launched a small rocket S-310-34 from Uchinoura Space Center in Kagoshima, Japan, at 15:15, August 9, 2004 (Japan Standard Time). The launch was the culmination of a historic new technology, the world-first successful full-fledged deployment of big films for solar sail.

My interpretation of this and the rest of the article is that they were testing deployment mechanisms for sail material, rather than deploying a working solar sail.

The pictures in the article which show the test sail deployed immediately behind the launch vehicle imply the same thing. The following text says that the launch vehicle reentered and splashed down 400 seconds after liftoff. This can only mean that both the LV and the sail experiment were in ballistic flight when the latter was deployed. For a solar sail to work, it would need to be deployed after orbital insertion (or after escaping the magnetosphere.) The article does not mention orbital insertion, nor was there time for this to occur.

Re:Not a working solar sail as such

[Chuck1318]

My interpretation of this and the rest of the article is that they were testing deployment mechanisms for sail material, rather than deploying a working solar sail.

Makes sense to me. I sure would want to test the deployment mechanism before going to the expense of a real mission, putting it into orbit along with an expensive scientific probe.

Turning around...

[anactofgod]

Actually, to be a bit serious, I seem to recall through clouded memory from college days long gone by that flipping the sail around was one method to decelerate the rocket on approach to the target star. In this scenario, the rocket would have maximum velocity somewhere around the mid-point between the source and destination stars.

So, unless one had other means of propulsion to facilitate a return to Sol, one would have to change one's mind a whole heck of a lot sooner than ~half-way to Alpha Proxima, otherwise it'd just be easier to just keep on truckin'.

---anactofgod---

Good to see

[T.Hobbes]

It's very good to see this branch of space technology getting funding. I'd rather travel in a starship with warp drive, but until then we need some feasable way to get to other stars. There's no reason, in my mind, why we shouldn't send a few of these off to nearby stars with the sole purpose of taking some close-in measurements and somehow getting the data back here (getting the data back would probably be harder than getting the spacecraft there in the first place). The very fact that it would take hundreds or thousands of years for them to get there is the best reason to start sending them now.

Let's all raise a glass of Sake to the engineers behind this project!

Re:Good to see

[DupyMcCopy]

I forget what the theory is called but if we deploy the probes now. later, we will develop faster probes. The faster probes will over take the older slower ones. Another question is that will we be around to hear from the probe and will anyone back here remember to listen for it.

Not so fast...

[Bill_Royle]

"Because it carries no fuel and keeps accelerating over almost unlimited distances, it is the only technology now in existence that can one day take us to the stars."

This may be true, but it'll take another technology to take you there safely: brakes.

This whole "keeps accelerating" schtick concerns me from a self-preservation point of view...

Re:Not so fast...

[imaginate]

Umm... turn around.

I hope that was intended to be funny.

Re:Not so fast...

[Bill_Royle]

And how do you plan on landing? In a pretty little spiral?

Re:Not so fast...

[gilroy]

Blockquoth the poster:

This may be true, but it'll take another technology to take you there safely: brakes.

Um, no. As you approach the destination star, its light pressure will start to counteract your velocity and slow you down. The "brakes" are built in.

Re:Not so fast...

[imaginate]

Obviously the spacecraft that's being dragged by the sail (presumably with the intersteller travelers in it) needs to have some kind of lander if that's your intent... but we've already been there, done that; there's not even a need for new tech.

Re:Not so fast...

[Dusabre]

I see you haven't thought your 'insightful' comment through.

You start to approach another star, you turn the sail around and its light decelerates you.

Re:Not so fast...

[isorox]

Assuming the star is the at least as bright as our Sun

Could this be used with other rockets?

[JazzXP]

Would it be possible to have a rocket as well as a solar sail? The rocket for the inital acceleration, then use the solar sail to keep accelerating (much more energy efficient).

Re:Could this be used with other rockets?

[StarsAreAlsoFire]

Yes, but sadly it is somewhat self-defeating. You get the most benefit from solar particles the closer you are to the sun (the flux is more dense).

Although if you did use an initial boost to push you into a sun-skimming orbit, that would help a lot. Not *TOO* close, obviously, but doing a gravity assist off mercury (yeah, not a big boost) would put you in position to grab ton of extra delta V from both being near the sun, and you can time it for pretty much any other flyby combo you want (mercury is 'fast' WRT setting up for flybys). Dunno if getting much closer to the sun that Mercury is feasible; a dark spot on your mirror would be pretty tragic even that close.

None of this is new; I only regurgitate Scifi books and orbital mechanics classes. Mostly scifi.

CG?

[xoboots]

Is just me or do those press photos look like they are CG? Circa Doom II.

Exactly - robotics competition coming too

[apsmith]

At the SPS 04 meeting we heard about a planned launch in a couple of years of something very similar - a suborbital rocket with 20 minutes or so in space at zero gravity, which will deploy a large triangular mesh intended to resemble a possible structure for a solar power satellite. Then two or three teams of robots will be competing to maneuver about this mesh under vacuum/zero-g conditions, and see how far/fast they can go, and what they can do. One of the teams involved spoke - they seem to have previously had something to do with playing Robotic Soccer.

Interstellar travel it wasn't.

[Alsee]

They deployed a sail less than two minutes after launch, had it in place less than two minutes, threw it away, deployed a second sail, then less than three minutes later it crashed into the ocean.

Total trip, liftoff to crash-down, less than 7 minutes.

-

Not wind!

[Anonymous Coward]

Just to clarify what people seem to be mistaking, the sail is *not* powered by Solar Wind, it is powered by the light of from the sun. The idea is that each photon of light that reflects off of the surface of the sail transfers a little bit of it's momentum to the sail.

Re:Not wind!

[StarsAreAlsoFire]

While it is within the sphere of influence of the sun, will it not also be boosted by the 'solar wind' (all those juicy massive charged particles)?

Would seem pointless to not set up the tiny bit of photovoltaics you would need to make the sail a mag sail in addition to the whole light sail thing. Most of your acceleration would be within the first few dozen light minutes of earth anyway.

Solar sailing

[antikarma]

It won't be a viable method of transportation between solar systems until it has an anti-pirate defense system. Giant solar sails just scream "come and get me space pirates."

Re:Solar sailing

[isorox]

It won't be a viable method of transportation between solar systems until it has an anti-pirate defense system.

It's ok, we'll use some form of DRM

Re:Solar sailing

[Snowhare]

A few square kilometers of concentrated sunlight makes a great weapon.

2 questions (Earth altitude, Sol heliosphere exit)

[MMHere]

1. Did they get high enough above Earth to enter the inter-planetary "void," and thus avoid the significant effects of Earth's atmosphere? 100, 230, and 400 seconds after liftoff hardly seem "high enough."

2. What happens to such sails when they cross the heliosphere of a regionally prominent star such as Sol? Is it all chaotic photons and miscellanous radiation in the interstellar "void?" Or are conditions regulated by the nearest stellar bodies?

-- In other words, how would one navigate effectively once the prominent wind from Sol fades and is replaced by other forces? Are you doomed to follow your trajectory mainly established by Sol once you leave its heliosphere, possibly modifed by various minor (uncontrollable) forces from other winds in the void? Can you take advantage of such extra-Solar winds to go where you want?

Just a question...

[ScottZ]

How do you run against the solar wind? What are the appropriate forces to run your 'keel' against when you want to track across a solar system (say, to somewhere useful)?

Anyone got any pointers?

Re:Just a question...

[gracefool]

Answer: You tack.

Re:Just a question...

[radtea]

Short answer: gravity.

Long answer: sail-boats sail upwind by creating a composite force vector from wind on the sails and hydro-dynamic forces on the keel that has a net up-wind component.

There are two cases to consider for solar sails: transfer orbits, and free flight. For transfer orbits, which we'll use to get from Earth to Mars, say, the sail can be used to either increase or decrease the orbital angular momentum of the spacecraft.

If the sail is tilted at 45 degrees to the solar radius such that the reflected light is pointed in the direction of orbital motion, the spacecraft will lose orbital angular momentum and fall inward toward the sun. Tilt the sail in the opposite direction and the opposite will happen.

For a spacecraft not in a closed orbit, things are more complicated, and I don't think it has quite the same freedom of motion. I'd guess that you'd want an interstellar solar sail to spiral out from the sun until it achieved solar escape velocity, and then have it point straight back at the sun for as long as possible. At some point you'd want it to turn over and point at the target star, which, due to deterioration of the sail etc, you'd probably want to be a good deal brighter than the sun, unless you were just going to pass on by.

In practical terms, solar sails may be used to send (very small) instrument packages out to local stellar systems in our lifetimes. It's very unlikely they'll ever be used for human travel. Of course, in 1945 it was very unlikely anyone would build a rocket large enough to send people to the moon.

--Tom

Interplanetary uses

[AnotherScratchMonkey]

The light weight and lack of propellant make this an ideal platform for interplanetary endeavors, even for lifting satellites into high Earth orbit cheaply. Much of the cost of a mission is getting the weight out of Earth's gravity well, and the weight of boosters for that must be lifted by the lower stages.

Limitations of Solar Sails

[Lifix]

First of, I am not a trained professional. I am a high school senior but I believe that I understand the principals behind this technology. The term solar sail is a modern misnomer. Solar sails are only capable of accelerating away from a star. This is because the sail is powered by reflecting solar radiation/solar wind. (I'm not sure, but I believe that this is limited by the inverse square law, which means that every time you double the distance between you and the source of the radiation, you decrease it's power 4 times. AKA it's power decreases exponentially as you travel away from it.) This means that in the expanse between stars, there will be essentially no acceleration, and in fact, depending on the size of your sail, some drag. Because space is not really empty (one hydrogen atom per square meter, which would add up if you need to travel light years with fully deployed several KM wide solar sails.) While the best way to use solar sails would be to put human power behind them, that is to fire lasers at the sails to continue powering them past the heliopause, enabling them to continue accelerating past our solar system. The simple option for travel would be to have a craft capable retracting it's sail, retract its sails once it leaves the area of acceleration, and then deploy them once it arrives in it's target solar system, slowing it down. Solar sails are also impractical for travel in a solar system (with the exception of traveling from an inner plannet straight out to a planet more distant from the sun.) Solar sails can not function like sails on an ocean. The reason sails work on an ocean is because boats have centerboards, solar sail craft do not have centerboards (because space doesn't have the matter to support one) they would simply drift away from the sun. Conclusion: Solar sails, while wonderful and interesting, will never have a practical use transporting humans simply because it would take hundreds of thousands of years to travel between stars. I also believe that if we begin constructing solar sail craft to travel to distant stars, we should (if we don't we are doing something wrong) be able to travel to the star and back before a solar sail craft would get there to begin collecting data. If I screwed up anything flame me as much as you want.

Re:Limitations of Solar Sails

[Lifix]

Well my formatting died, sorry guys. Take two:

First of, I am not a trained professional. I am a high school senior but I believe that I understand the principals behind this technology.

The term solar sail is a modern misnomer. Solar sails are only capable of accelerating away from a star. This is because the sail is powered by reflecting solar radiation/solar wind. (I'm not sure, but I believe that this is limited by the inverse square law, which means that every time you double the distance between you and the source of the radiation, you decrease it's power 4 times. AKA it's power decreases exponentially as you travel away from it.) This means that in the expanse between stars, there will be essentially no acceleration, and in fact, depending on the size of your sail, some drag. Because space is not really empty (one hydrogen atom per square meter, which would add up if you need to travel light years with fully deployed several KM wide solar sails.)

While the best way to use solar sails would be to put human power behind them, that is to fire lasers at the sails to continue powering them past the heliopause, enabling them to continue accelerating past our solar system.

The simple option for travel would be to have a craft capable retracting it's sail, retract its sails once it leaves the area of acceleration, and then deploy them once it arrives in it's target solar system, slowing it down.

Solar sails are also impractical for travel in a solar system (with the exception of traveling from an inner plannet straight out to a planet more distant from the sun.) Solar sails can not function like sails on an ocean.

The reason sails work on an ocean is because boats have centerboards, solar sail craft do not have centerboards (because space doesn't have the matter to support one) they would simply drift away from the sun.

Conclusion: Solar sails, while wonderful and interesting, will never have a practical use transporting humans simply because it would take hundreds of thousands of years to travel between stars.

I also believe that if we begin constructing solar sail craft to travel to distant stars, we should (if we don't we are doing something wrong) be able to travel to the star and back before a solar sail craft would get there to begin collecting data. If I screwed up anything flame me as much as you want.

Re:Limitations of Solar Sails

[Anonymous Coward]

Ugh, too much wrong with your post to even break it down and comment. Read this.

Re:Limitations of Solar Sails

[frizzbit]

Solar sails are also impractical for travel in a solar system (with the exception of traveling from an inner plannet straight out to a planet more distant from the sun.) Solar sails can not function like sails on an ocean.

Solar sails can be used to travel in any direction just like ocean-going vessel sails can, it's called "tacking" and for solar sails it involves tilting the sails away from the sun to change the direction of the reflected photons. Obviously this means that the greater the angle away from the sun the less area exposed to incident photons so that reduces the acceleration that can be achieved but that hardly makes it any particular destination impractical.

Re:Limitations of Solar Sails

[pjt33]

I'm not sure, but I believe that this is limited by the inverse square law, which means that every time you double the distance between you and the source of the radiation, you decrease it's power 4 times. AKA it's power decreases exponentially as you travel away from it

Nonono. A.k.a its power decreases quadratically. Exponential decay would mean that the power decreased by a fixed ratio (e.g. 4 times) every time it travelled a fixed distance (e.g. 1 million km).

Re:Limitations of Solar Sails

[Ronny Cook]

Solar sails can be used to move towards or away from a star. The trick is that the sail is not generally perpendicular to the star but at a 45 degree angle, so that light is reflected behind the vehicle (to accelerate), in front of it (to slow down) or at some sideways angle (for a sideways vector).

If you accelerate, you move into a higher orbit (and move away from the star). If you decelerate you move into a lower orbit (towards the star). Sideways vectors are used to change the plane of your orbit.

All this acceleration lasts as long as you have light. So even if the sail only gives you 0.001g of acceleration, after three hours that's as much acceleration as a one second, one gee burn... but you have not used any fuel. This can carry on for many months, and at the end of that time you have as much "fuel" as you started with.

I actually agree that, barring powerful lasers to "push" the sail, solar sails are not an interstellar technology; they don't build up enough speed quickly enough. However it's not true that interstellar debris will slow the sail down substantially. The amount of interstellar material is just not enough to affect it. The density of the local interstallar medium is actually around 10^5 atoms per cubic metre. That is an *incredibly* hard vacuum. One hydrogen atom is about 1.67x10^-27 kg; a 1km square sail will hit 10^14 of these for each kilometre of travel. The sail will have to travel roughly 6x10^12km to encounter one kilo of hydrogen. Alpha Centauri is about 4x10^13km away; in getting there you'll encounter about six kilograms of material.

That's simplifying a bit, as matter is much denser than that before you hit the heliopause. On the other hand, once radiation pressure becomes negligible, turn your sail sideways to the interstellar medium and it won't hit *anything*.

Within a solar system, they are an incredibly efficient means of transportation, because they give constant acceleration with no fuel cost. Outside of the solar system, they are much less useful without the aid of lasers boosting your radiation pressure.

Robert Forward's "Rocheworld" (AKA Flight of the Dragonfly) is SF but covers interstellar use of solar sails fairly well. The SF short "The Wind from the Sun" by Arthur C Clarke (I think I have that title right) gives a good overview of use within a solar system.

Re:Limitations of Solar Sails

[I7D]

"Because space is not really empty (one hydrogen atom per square meter, which would add up if you need to travel light years with fully deployed several KM wide solar sails.)"

AFIAK, that 1 hydrogen atom per square meter is an average of the universe - including dense molecular clouds and stars.

"that is to fire lasers at the sails to continue powering them past the heliopause, enabling them to continue accelerating past our solar system."

No laser on Earth would give the sail any decent help compared to our sun (and moon for that matter).

Re:Limitations of Solar Sails

[nutshell42]

No laser on Earth would give the sail any decent help compared to our sun (and moon for that matter)

That's not necessarily right. Of course no existing laser has the required power and none is focussed enough. But let's assume we could build a laser which spreads its light only a few km per light-year then suddenly even a rather weak laser would be more powerful than the sun because the light of the sun will be distributed over approximately 10^26 km^2 by then

Re:Limitations of Solar Sails

[nutshell42]

No they can't. With space ships you can never get closer to the origin of the radiation (with radiation power! see below) while you can do that with ocean-going ships

The way to navigate in an arbitrary direction within a solar system is to change your orbital speed. You're on earth and want to go to Jupiter? Spread your sails and go there. You're on Earth and want to improve your tan on Mercury? Use the sail to reduce your tangential speed (tangential to the sun) and your orbit will drop. Add some nifty fly-by maneuvers and you can go wherever you want.

In interstellar space you'll always be able to plot a course that ensures that the acceleration points in the right direction because there are many radiation sources available

Re:Limitations of Solar Sails

[frizzbit]

With space ships you can never get closer to the origin of the radiation (with radiation power!

I believe this is wrong - maybe you mean you cannot accelerate directly towards the source of radiation. That's true but it is not necessary to do so. For example if you tilt your sail so that the incident sunlight makes a 10 degree angle with the plane of the sail you will experience an acceration along a direction only 20 degrees away from sun - which is pretty close to directly towards it.

The way to navigate in an arbitrary direction within a solar system is to change your orbital speed.

I agree with this point. This is true for any currently feasible spacecraft, solar sail or not. The difference lies in the acceleration achieved by different propulsion methods.

A traditional rocket is able to achieve several Gs of acceleration. This means it only needs to burn for a few minutes to achieve a net acceleration of a few kilometers per second. This changes its orbital speed such that it is effectively in a different orbit - one that will hopefully take it where it needs to go. After the burn is done the craft coasts the rest of the way along its new orbit.

A solar sail OTOH can only achieve much smaller accelerations. Since no actual craft has been built let's assume a 5 micron thick mylar sail 10 by 10 metres square propelling a craft with a total weight of 70kg of which 1 kg would be the sail. Such a sail could achieve about 120 microGs. This might seem small but over 24hours it would add up to a change in speed of 100 metres per second. Over the period of two or three months it could easily match the boost that the current chemical rockets provide. Unlike them it would be constantly changing its orbit while travelling along it.

In interstellar space you'll always be able to plot a course that ensures that the acceleration points in the right direction because there are many radiation sources available

Using the stars as propulsion sources would require truly gigantic sails because they are so much fainter than the sun! For example, in the example above the sails would have be 1000km by 1000km to achieve similar accelerations.

Here you go:

[Anonymous Coward]

Rest Mass from Wikipedia

Re:Here you go:

[ahfoo]

Cool, that was a good read for anybody who wants to comment on this story. I read it and I found a typo at the end of the page that I took the opportunity to edit. Wow, I'm so glad I could contribute. What an honor. Wiki plus Slashdot. What a combo.

Ortw

[Keith McClary]

A clover type deployment was started at 100 seconds after liftoff at 122 km altitude, and a fan type deployment was started at 169 km altitude at 230 seconds after liftoff

Re:Wrong-A "glowing" recommendation.

[BerntB]

Orion starship that could get to Alpha Centauri in 130 years [..]. Thats much faster than a solar sail could ever hope to do.

I'm a big fan of the Orion project. (And that design would use megaton fusion bombs! Cool!)

But a laser pumped solar sail could be faster. Those big laser will be a big investment, though... and the "misuse" applications should be about the same as for lots megaton bombs! (It's mentioned e.g. here.)

Deployment and size

[AnotherScratchMonkey]

I didn't see anything in the article saying how big the test sails were. Large ultralight structures have to be pretty ungainly to handle even in zero-g, and designing effective deployment and handling systems can't be easy. Imagine what it takes to steer a fragile gossamer object like that!

We already have sol here!!

[zoloto]

Microsoft has currently installed Sol on our computers even up to a decade ago.

Hit WINDOWS KEY + R type in SOL ENTER

Sol is right here, no need for travel!

Obligatory Star Wars reference

[Zog The Undeniable]

Didn't Count Dooku - aka Darth Tyrannus - have one of these? Probably not the fastest vehicle for escaping Yoda's army of clones, but maybe it leaves no heat signature or something ;-)

Solar Parachute?

[pt99par]

Looks more like a solar parchute.. Compared to a sail on a sailing boat that can actually sail back to the location from which it came.. how are they going to get back with that thing. Thinking of how we use resources on earth maybe their isn't anything worth coming back to..

Solar vs. wind sail

[anno1602]

If I understand solar sails right, they are actually pretty different from the way wind sails work. Contrary to what your NASA links is telling us, most of the force from the sail does *not* come from the wind trapped in the sail pushing it along. Rather, under the pressure of the wind, the sail takes the form of a wing, and Bernoulli forces propel the boat along. This also enables sailing (up to a degree depending on the craft and the rigging) against the wind. I do not see how Bernoulli forces would appear on a solar sail (as the light can't go faster on one side of the sail than on the other).

Re:Solar vs. wind sail

[CrowScape]

Where wind sails have Bernoulli to work off of to go against the wind, solar sails have Newton. What the gp is saying is you start off in orbit around a star. If you want to get away from that star, you angle your sail +45 degrees, which reflects the light back along your orbit. Thanks to conservation of momentum you gain tangental velocity which propells you in a spiral outwards as you slowly break the sun's gravitational pull. If you want to go towards that star, you angle your sail -45 degrees, reflecting the light forward along your orbit. You lose tangental velocity and the sun's gravitational pull reels you in. You're right, completely different principles are at work, but you get a similar result.

Re:Solar vs. wind sail

[chancycat]

Awesome - good stuff. Thanks for the insight.

Re:Solar vs. wind sail

[uslinux.net]

Thanks to conservation of momentum you gain tangental velocity which propells you in a spiral outwards as you slowly break the sun's gravitational pull.

If it's anything like spinning in circles in my front yard when I Was a kid I think I'll pass. Vomiting in space seems even less enjoyable than here on earth.

Re:Solar vs. wind sail

[anno1602]

Okay, thank you. I guess I was misled by bad analogies. Oh, BTW: Sail boats can actually go faster than the wind... can light sails go faster than light? ;-)

Re:Solar vs. wind sail

[Ohreally_factor]

In space, no one can see you scream.

Does anyone know...

[Izago909]

how they are going to produce an untra-thin and ultra-light solar sail on such a gigantic scale? I forgot the ratio but it's going to take an ernormous sail to propel even a few kilograms. The only reasonable analogy I've heard is painting wax with a silver pigment and then melting the wax away, but that still leaves an important issue: The smalest speck of interstellar dust will leave a sizable hole in a sail so thin and light. How far can something like thins make it? Even space isn't a truly zero friction environment.

Re:Does anyone know...

[digitalunity]

There is an even better way to do it. It's called Chemical Vapor Deposition. Basically, you pump gaseous material(precursor) into a furnace. The molecules break down, depositing the desired material onto a base surface(substrate) and the leftover gases are pumped out. There are a variety of uses for CVD in semiconductor manufacturing(metal,amorphous silicon,silicon dioxide deposition) as well as astronautical uses(complex shape production where casting and forging isn't possible).

CVD is incredibly useful for creating free-standing thin films. You take your substrate, CVD your desired chemicals onto it, and then chemically remove the substrate.

A little about CVD

A PDF about rocket combustion chambers and nozzles of Iridium/Rhenium by NASA/assorted US military

Personally, if it were me, I would investigate the posibility of using a CVD thin-film of polished amorphous silicon on a organic polymer substrate. It has a lot of advantages in strength and rigidity as well as the silicon CVD process being a thoroughly tested process. It would also present an anvantageous surface area/weight metric.

So maybe we could just

[Anonymous Coward]

Send Texas and the Middle East to another planet? That would satisfy both sides, right?

Origami in space!!!

[Keith McClary]

A clover type deployment was started at 100 seconds after liftoff at 122 km altitude, and a fan type deployment was started at 169 km altitude at 230 seconds after liftoff

Oops, I meant to title this "Origami in space!!!", not "Ortw" but I accidently hit "Enter" and Slashdot's unforgiving code irrevocably posted it.

DS9 episode

[TheRealStaunch]

This reminds of the Deep Space 9 episode in season 3 where Sisko builds a primitive Bajoran sail ship and attempts to fly to Cardassia with it.

Re:DS9 episode

[seb249]

oooh i just realised how sad i am!

i remember that episode and was thinking of it myself!!!!!

calculations from NASA

[gentoo4ever]

These solar sails are pretty useless. Here http://solarsails.jpl.nasa.gov/introduction/design -construction.html are calculations from NASA guys. It looks like this Japanese sail has acceleration of few mm/s^2 and is not able to get out of sun gravitational field (and, of course, the Earth's one). It would take solar sail 100 years to get to alpha centauri if it had acceleration 10 m/s^2 (table 3 in the above link, there is "-" in the table for 5 m/s^2 and less , that is it will never get away from sun ). There was a good idea though to build a huge mirror to focus sunlight on such sail. This would effectivly increase surface area of a sail and pressure would not drop as square of the distanse from the sun.

Re:calculations from NASA

[achurch]

These solar sails are pretty useless.

That's because they weren't designed to be useful--they were designed to gather data for the purpose of eventually building useful ones. This particular article is light on details, but the report I saw on the news here had someone from JAXA explicitly saying they are in a preliminary data-collection stage.

Re:calculations from NASA

[Phanatic1a]

These solar sails are pretty useless. Here http://solarsails.jpl.nasa.gov/introduction/design -construction.html are calculations from NASA guys. It looks like this Japanese sail has acceleration of few mm/s^2

And a few millimeters per second per second is useless, why?

3 millimeters per second squared, and after a week you're moving at 1.8 kilometers per second. After a month, 7.2 kilometers per second. After 2 months, you've already exceeded Earth's escape velocity from the surface, let alone from orbit. Solar escape velocity at 1 AU is about 48 kilometers per second, so it would take you half a year to get fast enough to escape the solar system altogether. Actually, less than that, because as you're accelerate you're moving outward and so the solar escape velocity from your present position is continuously decreasing, but I'm in no mood for calculus right now.

These accelerations seem small, and hell, sure, they are small, but when you're applying even tiny accelerations constantly, over an extended period of time, that acceleration adds up to meaningful speeds. What kind of acceleration do you think the .09 Newtons from DS-1's ion engine was managing?

It would take solar sail 100 years to get to alpha centauri if it had acceleration 10 m/s^2

That's damned fast. Sustained 1g acceleration is pretty much up in indistinguishable-from-magic, though.

table 3 in the above link, there is "-" in the table for 5 m/s^2 and less , that is it will never get away from sun

No, that's ridiculous. As long as you have the thrust to move away from the sun, you'll "get away from the sun," because as I mentioned, the further out you are, the lower the solar escape velocity at your current position is. Hell, even the .3m/s sail listed in that table has a 'terminal velocity' of 671 kilometers per second, and solar escape velocity from the surface of the sun is only 618 kilometers per second.

Re:calculations from NASA

[Johnny Vector]

3 millimeters per second squared, and after a week you're moving at 1.8 kilometers per second. After a month, 7.2 kilometers per second. After 2 months, you've already exceeded Earth's escape velocity from the surface, let alone from orbit. Solar escape velocity at 1 AU is about 48 kilometers per second, so it would take you half a year to get fast enough to escape the solar system altogether. Actually, less than that, because as you're accelerate you're moving outward and so the solar escape velocity from your present position is continuously decreasing, but I'm in no mood for calculus right now.

Except you're losing thrust faster than the escape velocity decreases. Escape velocity goes as 1/sqrt(r), whereas the light intensity (hence thrust) goes as 1/r^2. Solar sails probably aren't the best way to go interstellar. But then, neither is anything else we can imagine at the moment. sigh

And now, safely buried in the comments because I have limited bandwidth...

Photos of the Uchinoura Space Center, from back when they called it Kagoshima Space Center. (Kagoshima is the prefecture, Uchinoura is the town. Nobody in Japan has heard of Uchinoura, so they called it Kagoshima Space Center until with the increased level of joint projects with a certain American space agency they decided 'KSC' was too easy to confuse with Kennedy Space Center.)

Re:calculations from NASA

[gentoo4ever]

ok, you are right ;) I was to hasty, sorry :(( Here http://www.pioneerastro.com/USSIT/ussit.html is the original paper on which NASA is referring. It explains much more. Still, it states that anything less then 10 m/s^2 is unpractical for the interstellar flight.

Re:calculations from NASA

[ediron2]

These solar sails are pretty useless...It would take solar sail 100 years to get to alpha centauri...

As opposed to our current ETA for Proxima Centauri: A big whoopin' Never?

I'll take 100 years, thanks.

Seriously, between costs, technological limitations, and the 20 years of creeping along that it took our first probes to leave the solar system... and don't even get me started on the POLITICS... I'm doubtful we'll get to Mars in 30 years, let alone to Proxima in 100. So, in my book, the X-prize, Chinese attempts, Japanese sails... any alternative is great.

Spoilsport

[Beardydog]

The Gripping hand

I can't tell if they were terrible books, or great books, but either way I really enjoyed them.

Re:Spoilsport

[Diag]

Yeah, Larry Niven's books taught me, or rather made me properly grasp the concept, that interstellar travel would require long period of acceleration towards your target, then the same period of deceleration, or acceleration away from the target.

Bullshit!

[logicnazi]

Yes, it keeps accelerating over long distances....but I can make a rocket do the same thing by asymptotically slowing down the rate of fuel burn. A solar sail is doing nothing differnt, while the sail will keep accelerating the accelaration will fall off with the radiation pressure (about 1/r^2).

Personally, I tend to believe things like ion drive are actually much more efficent and likely to work well with stare exploration (ion drive is just a fancy way of saying you shoot very small amounts of mass out the back going very fast. This is important because it means you can get more thrust from the same amount of fuel weight if you have something like a nuclear power source to accelerate the ions).

Re:Bullshit!

[Saluton_Mondo]

Personally, I tend to believe things like ion drive are actually much more efficent

Maybe for satellite operations (e.g. station keeping, etc.), but I think ion drives are unlikely to be used for serious long-distance spaceflight (at least for the transport of humans). There are also many problems with using ion engines in this way: inability to perform ground launch, inability to accelerate quickly, etc., etc.

Babelfish Link

[oddmake]

For the first time in the world in thin film sail development for "Solar sail" success (Uchinoura)

# Sorry, but I have no time to translate manually

Yikes!

[payndz]

Those pictures make it look like Vejur, coming to cleanse the carbon-unit infestation from the Creator's planet...

Re:Yikes!

[gooser23]

uh... that's VGER as in VoyaGER (6, IIRC)

Re:Yikes!

[payndz]

Well, the novelisation of ST:TMP, written by Gene Roddenberry himself*, spells it 'Vejur', so I'm going with the Great Bird.

*(And yes, I know Alan Dean Foster actually wrote it. I'm just being annoyingly literal for comedic effect - hey, I'm a Trekkie!)

Not that much time difference

[Anonymous Coward]

to the crew on board, it'd be like
mere hundreds or even tens of years

Not according to general relativity: they need
to accelerate when leaving, and decelerating when
arriving to destination. Decelerating will almost
reverse any time compression from the
relativistic speed...

Re:Not that much time difference

[antimatt]

No. Relativistic time dilation isn't based on acceleration at all, but on velocity (with respect to some "fixed" point of reference).

The formula for calculating t', the time experienced by the moving body, is: t' = t0*(1/sqrt[1-(v^2/c^2)]), where t0 = time experienced by the fixed reference point.

Acceleration isn't in the equation. You cannot "undo" time dilation simply by stopping your motion.

Never been camping?

[Exiler]

One rule I've observed is that it doesn't matter WHAT you strap to your flashlight, or how many spares you bring, by the end of the week you WILL be in the dark.

Featured in a BBC documentary

[O0o0Oblubb!O0o0O]

For those of you who are - like me - not experts in physics, this technology was featured in the BBC documentary "Space" presented by Sam Neill.

http://www.imdb.com/title/tt0273608/

http://www.bbcshop.com/invt/bbcdvd1090&bklist=ic at ,5,,11,science,831

One of the chapters discusses how travel to other stars would be possible. As far as I remember there is another technical solution in discussion which would involve nuclear detonations as part of a propulsion system. (I might have confused something there, though)

A reference

[AllenChristopher]

Niven was slyly referring to when Archimedes actually DID that. Archimedes used a burning mirror to defend the harbor of Syracuse against the Romans.

Not the only way t o the stars.

[TheNarrator]

This website has a list of many advanced propulsion technologies under devleopment by JPL. Considering that we are using chemical rockets which have been known about since the 30's it's good to see that people are looking into new propulsion tech. These systems, some of which can reach the speed of light, include Advanced Chemical Propulsion, Nuclear Propulsion, Antimatter Propulsion, Electric Propulsion, Micro Propulsion, Beamed Energy, Sails, Gravity/AeroGravity Assist, Chemical and Electromagnetic catapults, Tethers Skyhooks and Towers,Extraterrestrial resource utilization,etc.

Re:Not the only way t o the stars.

[Skavookie]

Some of which can reach the speed of light? Ok, I'll resist the urge to ask what you're smoking and instead give you the benefit of the doubt and ask: Huh? Could you explain that, please?

solar wind

[N3wsByt3]

Solar sails do not use (or not primarely, exept maybe when close to the star, in the beginning) solar wind to propel itself. It uses the reflection of the sunlight; thus, photons, rather then ions.

It's also not correct that solarsails can't be used to reach other suns, because the sun there gives an oposite force. It's quite trivial, when using adaptive (rotating) solarsails, which have only one higly reflective side, to slow down or accelerate when nearing a solarsystem. And even withing a solarsystem; for an interesting project in that regard, see the planetary society where they plan to launch the first non-gov solarsail-powered probe.

Been There, Done That

[Anonymous Coward]

Count Dooku has had a bitchin' solar sail for years now. Old news.

dumb shmuck...

[Anonymous Coward]

What the hell is wrong with you? You hear of a well-thought-out idea developed, examined, and approved by physicists, and without looking into it, you dismiss it with your first couple of off-the-top-of-your-head thoughts.

OF COURSE it's not shining laser light into the sails from the ship itself, like a sailboat with a fan on it, you unbelievable moron. And as for getting "worse and worse with aim", you DO NOT TRY AND POINT THE LASER AT THE FAST-MOVING AND LIGHT-YEARS-DISTANT SPACESHIP, AND DO COURSE CORRECTIONS BY MOVING THE LASER, you just keep the laser pointed at the destination, and do course correction at the ship.

The problem here is not so much that you completely misunderstood the whole concept, it's that you so vastly overestimate your intelligence and knowledge that you didn't recognize your stunning incapacity to evaluate this suggestion.

So let's review:
1- you're not as bright as you think
2- other people are brighter than you think
3- other people have often evaluated things a lot more thoroughly than you are capable of doing in 30 seconds
4- if you don't understand something, it's more likely your own defect than a problem with the expressed idea
5- sit down and shut the fuck up, you arrogant ignoramus

Now that that's out of the way, there certainly are practical issues with this method of space travel. It's just that they have absolutely nothing to do with what you thought they were.

Re:dumb shmuck...

[Paradise Pete]

I wish you'd posted under your account. I'd be your fan. (Sailboat not included, of course.)

Re:dumb shmuck...

[Bishop]

What a beutiful flame. The best part is that the dumb shmuck was modded as insightfull.

The Wind from the Sun

[Insipid Trunculance]

Hasnt anybody read this story by Arthur C. Clarke about an Earth to Moon race in solar sail powered space ships.

A beautiful story with an excellent description of some problems which may exist.Read the story,i will spare the spoilers.

Confirmation?

[aallan]

I can't find anything about this in the main stream media, the only story Google News finds (at least at the moment) is this which is talking about NASA and a recent on-the-ground test deployment.

Anyone actually got any more hard facts about this one?

Al.

Actually, this does exist!

[commodoresloat]

...in Japan.

Other Existing Technology

[Edward Faulkner]

There is another existing technology that could travel interstellar distances. NASA's Orion project designed a starship propelled by nuclear weapons and a big pusher plate. And yes, the crew can be properly shielded.

Of course what we really should be working on is actual nuclear rockets - controlled nuclear burn instead of explosives. Nuclear gas core rockets are really not beyond present technology, their exhaust is cleaner than the space shuttle's, and they're so powerful you can build big, heavy, safe vehicles.

Re:Other Existing Technology

[Rakishi]

The problem with the later is that it's still not useful for interstellar travel. It needs to carry fuel to heat up and shoot out the back, and to gain a decent speed it needs A LOT of fuel.

Crucial problem

[SleezyG]

Okay, everyone. Let's calm down. The Japanese, or any other Earthlings, will not have to worry about changing their velocity at Alpha Centari anytime soon. The fact is, all they accomplished was opening two differently shaped pieces of foil above Earth over a 400 second period.

Please. I used to launch Estes rockets with shiny parachutes. Prove to me that it WASN'T photons reflected from the Earth into my solar parachute that were slowing my rocket's descent. So NASA, ISAS, and 14-year-old model rocket enthusiasts have simply proven that gravity will pull anything you launch into the sky back to Earth.

Re:Solar Parachute

[nitehawk214]

No, the parent is saying that if you want to push off of something to stop you at that rate of speed, it will need to be very massive.

I would think that you could just rotate the entire assembly around once you get close to the destination to slow down, turing your solar sail into a "solar parachute".

Limited directions?

[wikdwarlock]

Can someone in the know answer me this:

Since a solar sail needs light pressure to accelerate, can it only accelerate in a direct line away from a star?

also

Isn't there a problem, once the sail gets far enough from its original star, that pressure from other stars will interfere w/ the path?

Meteorites

[ajdecon]

What you're missing here is how big this sail would have to be. To get a meaningful acceleration, you'd probably have a big, flimsy sail several thousand square kilometers in area; and once you have that, who cares if you lose a few square kilometers now and then?

The other factor is that once you get outside the solar system, the matter density should go way down; not much dust, virtually no chance of large rocks. Sure, they're out there... but odds are that you'll never hit anything capable of taking out a major percentage of the sail.

Slingshot effect?

[RetiredMidn]

...you flip yourself around so that the sail is pointing towards the destination, and you use the radiation pressure from that star to kill your velocity.

Another option is to use gravitational effects; i.e., the same "slingshot effect" used to boost Galileo to Saturn. IANARS, but I'm pretty sure the same principle can be applied to kill off velocity. (Takes a long time, but what's a couple of years after an interstellar voyage?)

There's also aerobraking, if you know there's a planet with an atmosphere available. Although I'm not sure I'd want to kill off that much speed with friction. Ouch.

All of this assumes a awfully fine degree of maneuvering precision using just a sail. It's hard enough with sailboats on water, and they have the benefit of a rudder and keel. I suspect some kind of reaction-based propulsion system (ion drive?) would be desirable for the end game.

Quantum teleportation propulsion

[PIPBoy3000]

I ran across this novel form of propulsion the other day that looks promising if it pans out.

The idea is to entangle two cesium atoms, then send one up into space. Back on earth, excite the one that remains and the one in space will do the same. In theory that could be used as an ion drive while keeping the bulk of your engine back on the ground.

Re:Quantum teleportation propulsion

[stj]

The problem with this as with any other quantum mechanism, is that here they are talking about singular atoms, while in practice QM works statistically and there is a huge (exponential) impact of the distance on the effectiveness of QM mechanisms.

Ort clound anyone?

[d474]

Have fun using this "sailing" vessel to traverse the Ort cloud. Try crossing ice berg infested waters at over 70,000 mph!

I know from experience: Have you ever played Asteroids while at full thrust!? You last about 15 seconds tops. Now just add a big friggin' sail to act like a drift net and you've got a gourmet recipe for disaster.

I'd rather try my luck playing golf in a thunderstorm.

Argh

[narl]

Thank you for ruining my day. Every time I'm reminded of the Orion project I get pissed off.

If we could have just tried Orion, we could have landed full-scale bases on the moon, mars, and wherever else we wanted them with only a handful of launches. And we would have done this more than 20 years ago.

We've lost the tooling now to even make more of the Saturn V rockets we used to have. The only reason NASA can even do as much as it does anymore is because they can take advantage of miniturization to fit more in their tiny payloads. That and having Russia save our butts on the station.

It makes me sick.

Massive solar sail

[Clith]

Read the parent again:

That sail would have to be pretty massive, like the mass of a planet, in order to counteract years of acceleration so you could push it away from yourself to slow down

100 grams is not massive enough to slow you down. Of course, a high-mass solar sail is a waste, as it would have an extremely low acceleration. Probably faster to get out and push.

Hmm, along the lines of SETI@Home, we could ask everyone to point a $3 laser pen at a solar sail to help it go faster. The difference in acceleration could even be measured and posted to a website, live. Hah!

Re:Wrong-A "glowing" recommendation.

[yakovlev]

How do you stop at the other end? It's obvious with Orion or a normal solar sail, but where does the energy come from with a laser pumped solar sail?

How to slow down when lasers are used?

[chitownIrish]

If you use a stationary laser to push the ship away from the solar system, how will it be able to stop when it gets to its destination? Presumably the laser provides greater acceleration than the solar wind, and so you wouldn't be able to slow down as fast as you sped up.

Re:How to slow down when lasers are used?

[Chuck1318]

In The Mote in God's Eye the method used was to dive close to the destination star, so the much more concentrated light pressure would bring the ship to a stop. One of the characters suggested that they could have gone past, electrically charged up their ship to make a u-turn by the galactic magnetic field, and come back toward the destination star from the opposite direction, and had the lasers back at their home add their power to the destination star's light.

How do you steer it?

[smallfeet]

You can't tack without a keel so you would need to be on a broad reach away from the sun. You would have to have some fuel or you would most likely miss your destination, which adds to the mass you need to accelerate. The further from the sun you get the less acceleration you would have until at some point you would need to drag the sail in and drift.
Has anyone calculated what the maximum speed for one of these would be? There must be a limit on how large you can make the sail and still deploy it in a reasonable amount of time. I guess you could shot it toward the sun before deploying the sail.

Is it out on its way to the stars?

[kanweg]

Having read TFA, I noticed that the two sails were deployed at heights of only 122 km and 169 km altitude. Which means they'll probably be orbiting the earth (or with not enough tangential speed, they dropped down). But are they making it to another planet or (a couple more slashdot stories later) to the stars? I think it will take many rounds before they can leave the earth's gravity, stop circling around the earth, and be on their way. And how many other satelites will they mop up on their ascent to higher orbit? Questions, questions...

Bert
Who is probably posting this too late to get a response

Won't work

[bobv-pillars-net]

I'll probably get modded down again, but I'm personally waiting for the scientists to conclude that solar sails just don't work, since they violate the law of conservation of energy.

Unless somebody is hypothesizing that photons exhibit a red-shift when they bounce off of a mirror?

Re:Won't work

[Chuck1318]

Unless somebody is hypothesizing that photons exhibit a red-shift when they bounce off of a mirror?

Sure. Think of the light as a wave train. One peak hits, and bounces away (at the speed of light, of course). The next peak hits, but by this time the sail has moved a tiny bit away, so the wave peaks are a tiny bit further apart. Longer wavelength = red shift = lower energy. Where did the energy go? Into accelerating the sail.

Re:Won't work

[bobv-pillars-net]

So the red-shift depends on the velocity vector of the mirror in the direction away from the source of light? That would imply that the faster the mirror moves, the greater the red shift, and presumably, by your theory, the greater the energy transfer into the mirror. Has this actually been measured in a laboratory? I googled unsuccessfully, but perhaps I used the wrong keywords.

Re:Won't work

[Chuck1318]

It's a Doppler effect. Police radar works on the Doppler wavelength shifting of the reflection from the moving car, and the microwaves of radar are a part of the electromagnetic spectrum along with light.

Stupid question: Where is it going?

[boo pixie]

What is it's mission?

Huh? Re:Won't work

[hacksoncode]

Ummm. Photons have momentum. For this *not* to be transferred to the solar sail would be a violation of conservation of momentum.

"Shop or Compare Prices"?

[roesti]

Strangely, according to its table of contents, the article on Howstuffworks has a chapter called "Shop or Compare Prices".

I couldn't find any prices for a solar-sail-powered spacecraft, though. I guess if you have to ask, you probably can't afford it.

Solar wind not sunlight would be propelling this

[drg55]

Its fairly obvious that the solar wind, not sunlight would be propelling this object in the inner solar system. The solar wind is made up of ions expelled by the Sun http://science.nasa.gov/headlines/y2001/ast31jan_1 .htm

Not Just for Exploring the Stars

[Zentakz]

Though Solar Sails are often associated with interstellar travel they have many extremely useful applications in Earth orbit and local solar system exploration. Most potential applications take advantage of the continuous thrust and zero fuel payload of a solar sail. Near Earth, Solar Sails are particularly suited for high orbital inclination satellite missions. Weather forecasting and global positioning systems would directly benefit from satellites orbiting the poles. Most satellites take advantage of the natural speed of Earth's rotation to boost them into an orbit relatively close to the equatorial plane. Changing the plane requires a large fuel burn for a conventional rocket and greatly increases launch costs. With its small but continuous thrust, a solar sail can reach polar orbits without a massive fuel payload, making them more accessible to scientific research. Away from Earth, Solar Sails offer a number of other interesting options. Missions have been proposed for asteroid rendezvous, travel to the inner planets (yes, solar sails can travel toward the sun), and an interesting idea using Lagrange points. More advanced solar sails could use their continuous thrust to enlarge the regions where they are able to "hover" well away from Earth. This allows much better observation of solar activity. Solar sails not only have an appealing sci-fi flair, but appear to be quite practical as well. I hope to see the technology develop rapidly.

Cosmos 1

[Chuck1318]

The Planetary Society is planning to launch their Cosmos 1 solar sail later this year. It was built in Russia, and will be launched from a Russian submarine, aboard a converted SS-N-18 ballistic missile. The Cosmos 1 solar sail has multiple triangular vanes, and looks a little like a windmill.

Damn the sig maximums!

[BerntB]

Damn the maximum lengths of sigs... Point 1-4 from this would look good .

The bad part is that the "dumb shmuck" is modded down to 0, so it looks like he comments on my post above. :-)

well besides that, this:

[Madcapjack]

Well besides that I think this is some really cool stuff...

ISAS succeeded in deploying a big thin film for solar sail in space for the first time in the world

(a quote from the article)

"first time in the world" doesn't quite seem an appropriate expression...now does it?

So, Japan goes Crazy Eddie?

[SqueezeBox]

Can anyone confirm that the sails are in orbit? (or not) Whilst watching for Perseids tonight (in the UK) I spotted something which appeared to be a satellite, but it's brightness was varying from "quite bright" to "invisible". My first thought was "rotating/tumbling satellite" but the variations were not regular. Viewing conditions were reasonable, with some high misty clouds, but not enough to account for my losing sight of the object. It occurs to me that a sail in orbit might produce this effect. First time I've seen anything like that in many years of skywatching! (Oh, and I saw half a dozen good Perseids too :) )