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The Flight of the Solar Sail
N3wsByt3 writes "After months of uncertainty, the final verdict has fallen: The Planetary Society has reveiled that it will launch its Cosmos 1 on June 21. Cosmos 1 will be the first non-governmental spaceship that makes use of solar sails as main propulsion mechanism - it is pushed along by light particles from the Sun, instead of bringing its fuel along for the ride - which makes this a unique experiment in more then one way." This was supposed to have happened already, so here's hoping things get off the ground this time.
planetary.org is the Planetary Society, the people who are, you know, launching the sail. As the sail the Society is launching will be the first solar sail, you won't find any government solar sails.
The sail ideally will reach 0.1c exiting the solar system. After that point, the sail does ditttysquat and can be removed from the craft the sail is bearing. Combining solar sails with conventional space manuvering systems isn't all that difficult; this would allow all the steering one would like.
As the sail would approach another star, the sail would slow if both sides of the sail were mirrored. This would merely mean that were we traveling to another star, we could actually stop rather than keep on going. Doesn't that kinda sound handy at all?
As the solar sail travels the solar system, it would slowly accellerate, reaching approximately 0.1c exiting the system, according to Carl Sagan's wife, who is funding the project.
This is the first spacecraft propelled completely by solar wind.
You could use a solar sail to go from Earth to Mercury if you wanted.
Angle it so that thrust is opposite the orbital motion of the earth. You slow down relative to the sun. You fall to a lower orbit. Nifty, huh?
If you're really in a hurry to slow down you detach a reflector, let it fly in front of you, and have a planet-based launching laser fire at the reflector, bounce back to you and slow you down.
The Voyagers took advantadge of a very special and unfrequent planetary relative position that allowed to accelerate the probes by gravitational assistance "jumping" from planet to planet in a spiral path.
A solar sail could, theoretically, pass the Voyagers in less than a week. That's the advantage of having continuous thrust along the way, rather than one impulse at the start and then coasting as the Voyagers did.
The Voyagers are now at a distance of about 13 light-hours from the sun. A thin and lightweight solar sail would quickly accelerate to almost the speed of light, so it's possible to cover that distance in a few days at most.
"as you approach it, it will start to slow down, and eventually stop"
It may seem counterintuitive, but sailboats here on Earth can actually sail against the wind. Not directly -- most sailboats can point about 45 degrees into the wind (i.e., if the wind is blowing from north to south, a sailboat can travel northeast or northwest as well as anything more southerly than that). When sailing against the wind, the sails (which are allowed to curve) become airfoils and "pull" the boat upwind in exactly the same way that airplane wings pull a plane up despite gravity.
That said, I don't think a photonfoil approach will work for solar sails since I don't think photons will develop a pressure differential like molecules do. You could should be able to tilt the sails to get a vectoring effect, though, and you could use this to slingshot around a few handy planets and get additional velocity to reach your destination even though it is "upwind".
DRM 'manages access' in the same way that a prison 'manages freedom'
first of all, there's no such thing as a perfect reflector, so there's always going to be be some loss. but there's a grand tradition of frictionless planes and other such things in these though experiments, so we'll give you that.
second, unless you have perfectly coherent light (super laser), you'll have dissipation of the beam. we'll spot that, too (see above).
once those have been taken care of, the dealbreaker is going to be that the reflected photons are red-shifted when they bounce off each sail.
the energy of a photon (E) is equal to Plank's constant (h) times the frequency (f).
the increase in kinetic energy of the sail is conserved conserved due to a lower frequency of the reflected photon.
Fermat's other theorem: "I have a simple proof, but I can't write it down as I fear it's a DMCA violation to discuss it"
For one thing, almost by definition you can't travel towards a star on this thing because as you approach it, it will start to slow down, and eventually stop.
From the Planetary.org solar sail FAQ
9 . Can a solar sail only provide thrust away from the sun?
No, thrust can be generated inward or outward with respect to the sun. By turning the sail at different angles, we can add or subtract velocity to the spacecraft. When we add velocity, the sail flies away from the Sun. When we subtract velocity, its orbit spirals inward.
Curiosity was framed. Ignorance killed the cat.
Yeah, replying to my own post, but there's another misconception a lot of people here seem to have that needs addressed.
Also from the Planetary.org Solar Sail FAQ
5. Does a solar sail fly on the solar wind?
No! The solar wind is made up of ionized particles ejected by the Sun. These particles move much slower than light. A solar sail does not stop or reflect them, although they also may impart some of their momentum to the solar sail. However, the force from the solar wind is less than one percent of that from light pressure.
Curiosity was framed. Ignorance killed the cat.