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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.""
...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.
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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.
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.
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.
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.
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.
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You just have to tack into the solar wind. *grynn*
You heard it hear first -- America's Cup 2200.
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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.
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.
You use on board rockets to help steer as you draw close to your destination.
File under 'M' for 'Manic ranting'
There is also a sequel but I will leave that up to you as a project to find out what it is.
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.
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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.
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 ?
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.
The Mongrel Dogs Who Teach
"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.
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.
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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:
w orks
http://en.wikipedia.org/wiki/Sailing#How_sailing_
Cheers!
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.
Rest Mass from Wikipedia
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
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).
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
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.
http://blog.nexusuk.org
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.
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...
-- The universe began. Life started on a billion worlds...
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far beyond what solar energy would of provided
It's would have, you blithering idiot.
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.
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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.
c at ,5,,11,science,831
http://www.imdb.com/title/tt0273608/
http://www.bbcshop.com/invt/bbcdvd1090&bklist=i
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)
(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
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.
Serious? Seriousness is well above my pay grade.
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).
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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.
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
.09 Newtons from DS-1's ion engine was managing?
.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.
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
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
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.
# ssh -l neo the_matrix; killall -9 agent_smith
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.
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Keels are there to counter-balance the mast in a gravity environment. I don't think there's much chance of that in space.
"Give a man fire, and he'll be warm for a day; set a man on fire, and he'll be warm for the rest of his life
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.)
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.
You are either part of the solution or part of the precipitate!
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.
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.
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.
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.