RE: starship-design: Sail types

["L. Parker" <lparker@cacaphony.net>]

Nels,

Solar sails CAN sail exactly like a sailboat. More, since they can also use
gravity, they can do things that sailboats can't, like sail into the wind.
Solar sails don't use the Solar wind for propulsion however, they use the
photon pressure of solar light itself which is MUCH greater. The solar wind
is far too weak for what you are thinking of.

If you can figure out how to build a directed relativistic particle beam
capable of providing enough particles to push a sail, you don't need the
sail. Put it on the ship and use IT for the drive. The problem with current
particle beam drives is low thrust. They are extremely efficient and high
ISP but their net thrust is low because we can't produce enough particles to
do any good for bulk cargoes.

Solar sails don't have a return problem, if they can accelerate enough to
get there, they can decelerate enough to stop and then reaccelerate to get
back, etc. The problem is that the best solar sail proposal going will only
achieve around .3c and it used a gravity assist maneuver to do it. Said
gravity assist was around the Sun and the heat and g forces associated with
it would likely kill any living cargo...since you used gravity assist for an
initial acceleration boost you will need to provide some extra deceleration
thrust at the other end now. Solar aero braking anyone?

Lee