Solar Sail Launch Date Set

smooth wombat writes "Get out your PDAs and set aside March 1, 2005. That is date the solar sail, named Cosmos 1, is set to be launched from a submerged Russian submarine in the Barents Sea. If the sail cannot be launched on that date the launch window extends to April 7. The goal of the mission is to be the first controlled solar-sail flight. The project is being undertaken by The Planetary Society, which was co-founded by Carl Sagan. Space.com also has a writeup about the launch. The announcement of the launch date coincided with Carl Sagan's birthday. Sagan would have been 70 years old. He served as President of The Planetary Society until his death in 1996."

Comments

How controlled is controlled

[delta_avi_delta]

Do they simply plan to test the technology in a straightforward drag-test away from the sun, or is it "truely" controlled - will they send it away from earth and then bring it back?

Re:How controlled is controlled

[MindStalker]

I seriously doupt this thing could sail into the sun even at an angle without some serious modifications. Its not that kinda sail.

Re:How controlled is controlled

[Councilor Hart]

How can they brink it back?
The sail catches the particles emitted by the sun, and is driven forward by them.
Inside the solar system, the direction of these particles is outward. Their speed/impuls is larger than that of extra solar system particles coming in.
Anyway, the net effect is a wind blowing out of the solar system.
No way to bring it back in the same way it got there.

Can anyone tell me what's up with /. these days? I have been gone for 3 months, and now it's damn slow and infested with 503's.

Re:How controlled is controlled

[delta_avi_delta]

Well, if you take the "wind" metaphor, and the "sail" metaphor, I was wondering if someone had figured a way to metaphorically "tack"

Re:How controlled is controlled

[madaxe42]

Tacking is, theoretically, possible, however consider the following:

All the wind is coming from one central point.

Your sail is *huge*, and not rigidly supported. In order to tack, you need to be able to hold a sail at 45 degrees to the wind, while holding your vessel pointing towards the wind, with a predisposition to move in that direction (supplied by the hull/daggerboard) which, while feasibly possible with a solar sail, would be an engineering feat, to say the very least.

Re:How controlled is controlled

[pragma_x]

But even a sailboat cannot sail directly /into/ the wind.

It might be able to to sail (indirectly) towards the sun, if it uses gravity to tack. This is akin to how a sailboat tacks by using its keel as an opposing force to the wind. Also, positioning the sails perpendicular to the solar wind will also allow it to use a local gravity well (Earth, Venus, Saturn, etc) more effectively.

Re:How controlled is controlled

[Retric]

The thing is orbiting the sun at a high rate of speed. All they need to do is angle sail such that it's acceleration reduces the sail's orbital speed and it will enter a lower orbit.

It would take a while but the best way to get a solar sail out of the sun's gravity well is to give it a vary eliptical orbit and then acsellerate as fast as it can on the last pass by the sun.

Re:How controlled is controlled

[merlin_jim]

How can they brink it back?
The sail catches the particles emitted by the sun, and is driven forward by them.
Inside the solar system, the direction of these particles is outward. Their speed/impuls is larger than that of extra solar system particles coming in.
Anyway, the net effect is a wind blowing out of the solar system.
No way to bring it back in the same way it got there.

That would be true if everything didn't orbit the sun.

Which it does.

Remember, when you're orbiting, if you increase velocity in the direction of orbit, you move out. If you decrease velocity in the direction of orbit, you move in.

How do you do that with a solar wind that blows in neither direction?

Same way that landsails go three times the speed of the wind that drives them; vector math.

Put more appropriately, the vector force on the craft is related to the incident angle at which the particles impact the sail. Tilt the sail, tilt that angle. By reflecting the solar wind partially ahead of you, you slow your orbital velocity, causing your orbit to shrink.

That's how a solar sail navigates in a solar system. Remember that if you thrust straight away from the sun, you just make your orbit more and more elliptical until you reach escape velocity. You can't just catch the solar wind and ride it out, you have to use it to increase your orbital velocity.

Re:How controlled is controlled

[merlin_jim]

In order to tack, you need to be able to hold a sail at 45 degrees to the wind, while holding your vessel pointing towards the wind, with a predisposition to move in that direction (supplied by the hull/daggerboard) which, while feasibly possible with a solar sail, would be an engineering feat, to say the very least.

not feasibly possible the way you describe it. There is no hull, there's no viscuous medium. Sailboats tack by transferring momentum to the water through the keel or whatever.

Solar sails can't do that. If we could build a solar sail that could do that, we could build a warp drive, because what you're talking about is a reactionless thruster.

Now what we CAN do is in fact even easier. Through out the sailboat metaphor. You've got a flat sheet with a significant amount of radiation pressure on it, with a central mass with quite a bit of orbital inertia.

You *can* tack against that orbital inertia, using the radiation pressure to keep the sail taut. Change the lengths of the cables connecting the sail to the inertial mass and you can change the direction that the radiation pressure is thrusting you in, up to about 45 degrees away from out in either direction.

See my other post in this story for a discussion of how to use that thrust to move closer to the sun.

Re:How controlled is controlled

[Councilor Hart]

Ah crap.
I should have realised I was talking to tight a turn. (I hope that's a correct english expression.)
It might make a nice programming exercise for my astrophysics class next term.
I have to much theoretical knowledge and far to little practical.
Thanks for the correction.

Re:How controlled is controlled

[dingbatdr]

Sailboats can tack because there is a keel on the bottom of the boat that keeps it going in a line. There is no equivalent of a water surface with a solar sail. It may be possible to tack into the wind with a solar sail, but I don't see how.

dtg

Re:How controlled is controlled

[WalksOnDirt]

You (and others) are misusing the term "solar wind". The solar wind is composed of particles (mostly protons), and is mostly absorbed and not reflected. The proposals I've seen for using it for propulsion involve large magnetic bubbles. They are quite interesting but a long way from being ready to test in space, I believe. See http://spacescience.com/headlines/y2000/ast04oct_1 .htm for example.

The Cosmos craft is a solar sail, which uses the light from the sun, not the solar wind, to maneuver as you describe.

Re:How controlled is controlled

[Anonymous Coward]

it's acceleration

"its".

Re:How controlled is controlled

[Anonymous Coward]

As the GP wrote, use gravity as a "keel".

Boy will they be surprised

[AtariAmarok]

Boy will Gul Dukat be surprised when this thing pulls up to Cardassia Prime.

It stays in orbit

[jangobongo]

According to the official website:

Cosmos 1 will orbit the Earth at an altitude of over 800 kilometers. It will gradually raise its orbit by solar sailing -- the pressure of light particles from the Sun upon its luminous sails.

Also in another section of the website:

For a while after deployment the giant blades will be kept in a fixed position, giving mission controllers a chance to carefully observe the spacecraft's behavior. Only after a few days will the Cosmos 1 team begin shifting the blades' angles towards the Sun or perpendicular to it, in a controlled program to increase the orbit energy. Gradually, the continuous pressure of reflecting sunlight will raise the spacecraft into a higher orbit above the Earth.

The flight of Cosmos 1 will not last long. Within a month the mylar sails will begin to degrade in the harsh sunlight, and the tubes supporting the blades will be losing pressure. It is possible that by this time the spacecraft will have risen to a high enough orbit that it will remain there, forever orbiting the Earth. It is more likely, however, that the orbit will slowly decay, and Cosmos 1 will end its days as a fireball in the Earth's atmosphere.

Re:control (Deorbiting, not tacking)

[G4from128k]

The sailboat analogy is deeply flawed because sailboats can sail up wind by transferring momentum from the wind to the water. Lift generated by the keel acts in combination with lift generated by the sail to create a net forward force even as the sailboat moves upwind. A solar sail has no equivalent second fluid to act against in order to move upwind. But a solar sail can move "upwind" by deorbiting.

For a mirrored sail, the force acts perpendicular to the sail surface. By canting the sail in the right direction (angling it to reflect sunlight forward), the force on the sail can act to deorbit the satellite. Thus, a solar satellite does not tack in the sailboat sense, but uses the suns energy to drop into an orbit closer to the sun.

Cheap Shot

[Anonymous Coward]

A launch date of March 1 was scheduled, with a window to April 7, but the actual liftoff date will be determined by the Russian navy.

Translation: the submarine will probably break down en route.

Acceleration

[clonan]

Has anyone found out what kind of acceleration they are expecting?

How much will it have to accelerate to get into the stable orbit they were talking about?

Re:Acceleration

[Tsalg]

Forget about solar wind - have a laser shooting at it. Some plans involve banks of lasers or microwave transmitters in orbit around the Earth or the Sun or even on the lunar surface to accelerate the craft, rather than using solar photons. With that you could reach 1/10th of the speed of light (about 300,000 km/sec), though there are other, rather more optimistic, suggestions that as much as half the speed of light could be obtained.

One of the major problems with these designs are the lasers would have to be prohibitively large to prevent the beams diverging at great distances. Further to this laser technology would have to be greatly improved to hit moving targets millions of kilometres away.

more about that on solar sails webpage

Re:Acceleration

[pu'u_bear]

Of course, the real technical difficulty in this plan is the breeding and training of the huge friggin' sharks that can survive in vacuum.

Re:Acceleration

[novakyu]

One of the major problems with these designs are the lasers would have to be prohibitively large to prevent the beams diverging at great distances.

Not to mention very massive (compared to the craft), so that the laser itself doesn't get accelerated to maybe 3,000 km/sec in the process due to conservation of momentum.

Are these real "plans" or are they just made up (er, on the spot)? Lasers, maybe, but microwave transmitters? Microwave has frequency (and thus, momentum per photon) much lower than visible light (in fact, it's right between radio frequency and infrared), and, although I don't know too much details about microwave, simple knowledge (which, I fancy, I possess) of basic physics should say that something with that long a wavelength cannot be focused very well.

In any case, energy conservation (in case of elastic collisions, and for inelastic collisions, well, it's even worse) demands that as much energy as would be needed for a conventional rocket be used to propel those rockets--so, how is that any more effective than what we have now? At least for solar sail, the idea is to harness the energy of the sun, much of which goes wasted, but unless the laser system, on top of being prohibitively large and cost-ineffectively massive, utilizes photovoltaic cells to "continuously recharge themselves" (er... in Data's words in 'Insurrection'), I don't see what the benefit of even considering those plans.

So far, the only human-powered (i.e. non-solar-sail) next generation space rocket idea I heard that makes sense is the one that uses, er, fission explosion at the rear to propel itself.

Re:Acceleration

[Anonymous Coward]

The point being, you dont have to carry the propellant (photons) and the fuel on the craft, which is an enormous improvement on long-distance travel.

Interstellar travel, with en-route times of less than a couple of thousand years, are just plain impossible with anything that carries propellant and fuel on-board. This is because the amount of mass you need to eject from your ship to accelerate to interstellar speeds is millions of times more than the weight of the payload. Add to that the need to accelerate the propellant on-board too, and you get such obscene numbers it's not even funny. For a chemical rocket with payload of some tens of tons to reach Proxima cetauri in less than 900 years would take more propellant than there is mass available in the entire universe. And you still need to decelerate after that... One chance is a particle accelerator pointed to rear of the ship ejecting stuff at near-lightspeed, but how would you power it? Nuclear reactor is worthless for electricity production in space unless you can use something to cool down the ship so you can produce energy from the temperature difference.

Re:Acceleration

[clonan]

You forget radiant energy.

At any real difference from the sun you can radiate away the extra heat....

This massive radiator can function as a solar sale when close to a star (Launching and arrival)...double duty :-)

Or you can use the heat to vaporise the fuel material before your particle accelerator spits it out.

Re:control (Deorbiting, not tacking)

[Anonymous Coward]

So once you get going, you can't stop?,

Jane! Jane! Stop this crazy thing!

Oops

[pragma_x]

correction: positioning the sails parallel to the solar wind will also allow it to use a local gravity well more effectively.

Only $4 million

[UnapprovedThought]

The cnn article says:

The mission, costing just under $4 million, will attempt the first controlled flight of a solar sail.

Maybe this technology could be used someday to boost light satellites so they don't fall out of orbit? In any case the investment to find out sounds like it's well worth it.