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Solar Sails And Space Propulsion
Doomie writes "The Economist has an interesting article about solar sails. It talks about the Russian ICBM that will launch Cosmos 1 (mentioned previously on /.) 'The first craft powered by solar-sail technology to orbit the Earth', and the link between this technology and interplanetary travel. Cosmos 1 will orbit Earth starting on June 21st and could, in theory, reach '200,000kph after three years of acceleration' due to the fact that 'particles of light, or photons, that strike a surface give it a tiny push'. The official homepage of the project has more details." Update: 06/18 18:57 GMT by Z : While space trains would be cool, that wasn't the intent of the story. Changed rails to sails.
Sail of the century
Jun 16th 2005
From The Economist print edition
One small step into orbit may be one giant leap for interplanetary travel
Rick Sternbach, The Planetary Society
ON JUNE 21st, a Russian nuclear submarine is due to launch an intercontinental ballistic missile (ICBM) from beneath the surface of the Barents Sea in the Arctic Ocean. Fortunately, this will not be the opening volley in a global thermonuclear war. Rather, it is intended to open up a new age of space exploration.
The ICBM's payload is Cosmos 1, an experimental spacecraft being launched by the Planetary Society (a space-advocacy group founded in 1980), in conjunction with NPO Lavochkin (a Russian firm which built the craft) and the Makeev Rocket Design Bureau (which modified the ICBM). If the mission, which will cost $4m and has been paid for entirely by private subscription, is successful, Cosmos 1 will become the first craft powered by solar-sail technology to orbit the Earth.
Solar sails rely on the fact that particles of light, or photons, that strike a surface give it a tiny push. Ideally, such sails should be as big as possible, to maximise the amount of sunlight collected, and as reflective as possible, because a photon bouncing off a perfectly reflective sail produces twice as much thrust as one absorbed by a non-reflective sail. Even so, the thrust generated is tiny: a sail with an area of one square kilometre would feel the same force that a kilogram weight exerts on a table on Earth. But there is no air resistance in the vacuum of space, and the sun shines continuously. Slowly but surely, the light-propelled tortoise outruns the rocket-driven hare, reaching 200,000kph after three years of acceleration.
The Planetary Society has details of the forthcoming launch of Cosmos 1. The Makeev Rocket Design Bureau modified the ICBM which will carry the craft.
Solar sails would thus be especially useful for journeys to distant planets or vastly more distant stars, as they do not need to carry any fuel with them. But while they have lived in the imaginations of scientists and science-fiction writers for over a century, their track record in real life has been limited. The Japanese Aerospace Exploration Agency has tested the unfurling of solar sails on sub-orbital rockets, but no one has put solar sails into orbit. Cosmos 1 should change that and, if it works, it will prove the feasibility of the technology for future missions.
Eight triangular sails arranged like the petals of a flower will propel the craft. Each of the sails is 15 metres long, and in total they span 600 square metres--roughly the size of the penalty area on a football pitch. During launch, the sails will be rolled up like so many sleeping bags. Once the ground crew has decided that the craft is in a stable orbit, though, a series of tubular "masts" will be inflated that will unfurl the sails as they expand.
Solar sails require special materials if they are to reflect sunlight efficiently while weighing as little as possible. They must also be able to fold up easily into a small space. Cosmos 1's sails are made from plastic sheets just five microns (millionths of a metre) thick. That is about a quarter of the thickness of a plastic dustbin liner. The plastic in question, Mylar, is coated with aluminium to make it reflective. Mylar is perhaps more familiar from its use in helium-filled party balloons.
If all goes as planned, the spacecraft will go into an orbit that flies over the Earth's poles. Four days later, the sails will be deployed. Once this has happened, the team will monitor Cosmos 1's altitude. The sails are able to swivel slightly, and the ground crew can tilt them individually in order to catch the most sunlight. The resulting increase in the altitude of the orbit will indicate that the sails are indeed feeling the sun's push.
Provided all this works well, the team will then try one last experiment. In order to use solar sails to travel to the outer planets, where the sun's l
The similarities are striking, in that with both solar rails and solar sails, you don't have much option what direction you want to go.
Yeah, I noticed that, too. Also incorrectly stated:
Cosmos 1 will orbit Earth starting on June 21st and could, in theory, reach '200,000kph after three years of acceleration' due to the fact that 'particles of light, or photons,
Actually, "in theory", the thing will fall apart in months because the mylar is not designed to withstand long-term solar exposure. A spacecraft designed for lasting longer could, in theory, reach those speeds.
Did he just go crazy and fall asleep?
Darn, I was in the middle of preparing a submission on Cosmos 1 when I saw this. Anyways, I have a little more info which people might find interesting, so I'll go ahead and paste it below:
Countdown to First Solar Sail Spacecraft
The Planetary Society's Cosmos 1, the first spacecraft to be propelled by a solar sail, has just been loaded onto a converted ICBM in preparation for its launch from a Russian submarine this Tuesday, June 21. This is the first mission by a non-profit space advocacy group and is being funded by private donations. Project Operations Assistant Emily Lakdawalla is posting a running description of events on the official blog. Videos and animations describing the mission are available, including commentary from the Planetary Society's Vice President, Bill Nye the Science Guy. Downloadable print-out model kits are also available.
One of the many neat things about this project is that if the first phase of regular solar sailing is successful, they'll run a later experiment with focusing a microwave beam on the sail to see how well it propels the craft. I wish the Planetary Society the best in this high-risk endeavour.
I think it's important to note that this spacecraft will never reach these speeds because it's only designed to last a month or so, as can be read here:
http://www.planetary.org/solarsail/timeline.html
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.
The idea of rail-guns for launching vehicles came about because on other planets there wasn't enough atmosphere for aerodynamics to work or for jet engines to work. The relative vacuum and low gravity was an advantage for anything that didn't need to carry its own fuel. The rail gun would use electromagnetic fields to accelerate the vehicle to beyond escape velocity.
However, for Earth, you need a take off velocity of at least 7 miles/second (or 25,000 miles/hour). And that doesn't take into air friction. Assuming you could build such an aerodynamic capsule, you would need a considerable acceleration for a period of the launch phase.
To minimize the amount of energy you need to use, you'd want to travel straight up, and to generate enough energy you would probably have to burn gallons of hydrocarbons or run a whole chain of nuclear reactors. Since energy is most efficient when you use the least number of conversion stages, you really end up with a vertical rocket launch with solid or liquid fuel.
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Yes, that extra energy is given by the pressure created by the photons striking the mirrors. A photon has no mass however it still transfers momentum. They derived this stuff from playing with equations. For example the momentum for light is p = hf/c where h is Planck's constant, f is frequency and c is the speed of light. So therefore the momentum is transferred from the photon to the sails.
See you don't understand how light is actually reflected. The photons are first absorbed which means that the energy is absorbed. This causes the electrons to move up in its orbit. When the electron moves back down, cause it wishes to be stable, it releases a photon. This works exactly like a regular engine. By having thrust going in the opposite direction the ship goes forward. Well same thing here but instead it is light. See how it works now? For every action you have an equal and opposite reaction. It's the same principles just being applied to light so it's a bit harder to understand.
Now as for this actually working, well I don't know. Everything in physics says it should but physics has said a lot of things should work or fail and has been wrong many times. Hope this has helped you to understand