KING@KESTREL (12/28/82)
From: Richard M. King <KING at KESTREL> It's pretty clear that you can't reach L5 from LEO without traveling sunward (unless you launch in a polar orbit, but this is silly because in that case you won't travel AWAY from the sun, either). Solar sails will tack. If they reflect (almost) all of the light that strikes them, the thrust will be (almost) perpendicular to the surface. (however the thrust is proportional to the sine of the angle the sail makes with the illumination. This quantity can go negative - if the sun strikes what you consider to be the back of the sail, you get negative thrust.) You'll have to spiral outwards. So what? the mechanical parts have to be able to move the sail at will, but that will be necessary anyway. I would suggest a small but robust sail for two reasons: 1) don't push technology - it would be awfully embarassing to have your large, extremely thin sail evaporate or something equally greusome. 2) we're going into stormy seas. The L5 "point" is very large and contains a lot of guck (probably). 3) what's the hurry? If we can get even .0001G it should only take nine months to get a delta-V of 20 KM/sec, which should be adequate. My last comment is that the tidal force of Earth is by no means constant. It declines with the CUBE root of the distance. I don't know whether we can get to L5 without getting close enough to the moon to have it exert significant tidal influence. I would recommend using the leading trojan point for this reason. Maybe mini-sails would be better stabilizers than a tidal pendulum, at least after reaching a certain distance from Earth. Dick -------