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

[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

[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.

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.

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

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.