[net.space] L5 Sailing

dps (12/23/82)

Question about sailing to L5 and then matching speed with L5 and family:

Can this be done so that probe is always sailing "downwind"?  I would
imagine that a solar sail would work mainly on "push" instead of
"lift", so that the probe would be unable to "point" above a beam reach,
if that far.  (Lift on earth sails comes from a surface effect deflection,
and then apply newton: dp/dt = -ma.  If the equivalent effect exists with
the solar sail, I would expect the mass deflected to be too small to be
of practical use, and likely cancelled out by something else (gravititional
irregularities?))

It may be possible, by choosing point of launch (from LEO) appropriately.
The point I'm thinking will be trickiest is transition from travel to 
station keeping.

silver (12/25/82)

Not sure if you realized this, but you can sail "upwind" in space.
The "wind" normally comes from a gravity source; if you turn the sail
right, you can LOSE orbital energy with respect to the source and fall
toward it.  This is overly simplified, but... (Anyone disagree?)