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

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: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

[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.