# solar energy in space

by geordief
Tags: energy, solar, space
 P: 72 Is it possible to use solar energy to provide locomotion in Space? I appreciate that Solar sails have been mooted but is there any way that the energy from the sun can be used in such a way as to approach the source of the light?
 Mentor P: 9,588 If you can eject some mass (using solar energy, if you like), it is possible. If you can find some way to catch and accelerate solar wind, it might be possible, but the density is very low.
 P: 660 A solar sail can bring you anywhere more or less. This results from space mechanics, where you go farther from the Sun (or the attracting body) by accelerating on the orbit, and nearer by braking along the orbit. So in the typical use, a solar sail "tows" and is inclined 45° to the orbital speed and to the Sun's direction, in order to brake or accelerate. Much more efficient, even to go away from the Sun, because paths in a gravity field are very much a matter of kinetic and gravitation energy, but the means used give a speed, so this speed acts far better if it combines parallel with the existing big speed (30km/s for Earth on its orbit!) to produce the V2 effect. Because Sunlight is stronger nearer to the Sun, a Solar sail is in fact better to reach the inner planets or orbits. One Japanese craft presently uses it that way. I also computed that a Solar sail spacecraft, with very reasonable assumptions, would have reached a Solar polar orbit within two years and have stayed there indefinitely: compare it with Ulysses http://en.wikipedia.org/wiki/Ulysses_(spacecraft) which took years to fly by Jupiter because our rockets can't provide 40km/s for a polar Solar orbit. And then, Ulysses flew once over each pole in many years, then all was over. A sail goes there in two years, stays there, changes the distance and inclination at will... Checkmate! I had some thoughts at Solar sail technology there http://saposjoint.net/Forum/viewtopic.php?f=66&t=2102 I'm not pleased with the beams I imagined, but other ideas are good to my eyes: how to thin the polymer film, how to test the unfurling... To go far and fast away from the Sun, say to the heliopause in few years, a sail would first brake to go near, and from that better position, accelerate and escape our Solar system easily. There are "amateur" websites especially for that topic, very interesting, with advanced thoughts. What a sail can't do well is brake when it arrives at an outer planet like Uranus or Neptune. But well, maybe we could have rockets for that purpose, combined with Oberth effect and capture using massive moons. I consider every space agency should have very active and concrete projects on this topic. This technology IS feasible and brings a lot. ----- The Solar wind is extremely weak, much more so than Sunlight pressure. It diminishes less than Sunlight with distance but should remain fainter. It has been proposed only because, as being composed of charged particles, it could be deflected by a huge (really) loop of current whose immaterial area weighs nothing. A wire was considered, an electron beam as well, curved by the Sun's induction. ----- To get more thrust, Sunlight can heat an ejected working fluid, in a "Solar thermal rocket". This is technology at grasp. ESA has a reasearch project for a craft from from Low-Earth-Orbit to geostationary, towing a satellite that has brought the necessary hydrogen, and back to LEO for the next customer, within a few weeks. Perfectly feasible and very useful. I have thrown a few thoughts at it there http://saposjoint.net/Forum/viewtopic.php?f=66&t=2164 including a very low-pressure chamber and a windowless hole in the chamber to let the concentrated light in. I will throw more thoughts at it. Some day. I consider this is the proper way to transport people to Mars and back. Chemical rockets and hardware preset in Martian orbit would permit a shorter trip to Mars or a short stay on Mars; Solar thermal rockets enable both at the same time. http://saposjoint.net/Forum/viewtopic.php?f=21&t=1954 ----- Other combinations are possible, like Solar electricity that powers an ion thruster and its variants, but they need much more light collecting area than the Solar thermal engine without saving global mass on a big mission like manned Mars. On a smaller mission, for instance hopping from one asteroid vicinity to an other, this has been done by JPL with huge success.

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