karn (03/26/83)
Recently, the idea of a solar-powered rocket engine for orbital maneuvering was proposed within AMSAT (the amateur radio satellite group) as a way of making an inherently safe engine for a payload (the PACSAT amateur packet radio satellite) deployed from the space shuttle. The idea is really quite simple: you carry tanks of water, preheat them with the proper solar coatings on the (external) tanks, and vaporize the water into steam with electrical power from the solar cells. Specific impulse is quite low, 125-150 sec, but the big advantage here is that it is MUCH easier to sell to a jittery NASA concerned about "amateurs" flying hazardous fuels on an expensive manned vehicle. It turns out that the major limitation for our purpose of a standard GAS (getaway special) can is volume, not weight, so we can afford to use a lot of water. About 40-50kg would be needed to maneuver from the polar orbit provided by the Landsat Recovery Mission (STS-V2) up to a reasonably stable one, approximately 800-900 km. Phil