5 Responses

1. Yes, that’s been worked on for years

   http://en.wikipedia.org/wiki/Solar_sail

   http://en.wikipedia.org/wiki/Laser_propulsion

2. Yes. Solar sails actually exist, and they work. Build a large sail, and have the light from the Sun “push” against it, propelling you away from the Sun.
   Photonic drives would probably work, but the technology to build them doesn’t exist yet. You would have to build a giant laser, and then fire light beams out behind you. Newton’s Third Law means that the light will push you forwards. But we don’t have power sources anywhere near powerful enough for this to work.

3. Solar sails are a surprising efficient way of using light as a propulsion method. Think of a craft with a huge (many kilometers in size) ‘parachute’ unfurled in FRONT of the craft. The sail catches the photons and ‘pulls’ the craft behind it. Given that the craft is weightless the whole craft can attain a significant fraction of c if started close to the sun and directed outwards.

   Hope this helps to visualize…

   > Jimmer <

4. A solar sail gets about 4.6 newton of thrust per square kilometer of surface when the same distance from the sun as Earth. Ten times farther from the sun, it will get 1/100th as much thrust. At some point, it would provide more aerodynamic drag than thrust. This makes it only marginally useful within the solar system and totally useless in interstellar space.

   Laser drive powered by matter-antimatter might some day be useful for interstellar missions lasting many years. A 300 Gigawatt laser (100 times the max output of the world’s largest nuke plant) has a thrust of 1000 newton. If you could get that much power on a spacecraft with a total mass of 1000 tonne, including fuel, you could accelerate at .001 m/s². If the conversion of matter-antimatter to laser power were 100% efficient, your fuel consumption would be 3.33 milligram per second. In one year, you would use up 105 kg of fuel and accelerate to 31.5 km/s.

   As the fuel gets used up, the acceleration increases. As you approach the speed of light, you need to use the relativistic formulas. So I won’t calculate the time required to reach the stars. You can simplify the calculation of speed by the fact that momentum of the ship (in Earth coordinates) is equal and opposite the momentum of the laser beam (in ship’s coordinates). And momentum of the laser beam in ship’s coordinates is mass of fuel consumed times the speed of light.

   Suffice it to say, you would need a very long time or a lot more thrust. To reach the nearest star in a lifetime, you might need to start out with more matter-antimatter fuel than the remaining mass of the ship.

   Be careful where you aim that laser. You wouldn’t want to PO the rest of humanity by slicing the Earth in two on your way out!

   EDIT: Solar sail in the news: http://www.spaceflightnow.com/news/n1101/22nanosail/

5. Yes. The typical approach is known as a ‘light sail’, that is to say, you use an enormous, extremely thin mirror that catches light from the Sun the way a sailing ship catches wind. It would also be possible to build our own artificial array of lasers that could be used to push the sail from some fixed location.

   In addition, I have heard a proposal to use quantum physics to ‘teleport’ a laser beam from the ground up into a spaceship and have it drive the spaceship. I’m not sure how feasible this really is though.