Eureka! We've invented the reactionless drive!

[Steve VanDevender <stevev@efn.org>]

Kevin's invention of a momentum-absorbing structure will be one
of the great inventions of history, if it pans out.  That's
because it could be used to create a reactionless drive.

Put Kevin's parasail and a powerful laser inside your ship, and
just shine the laser at the parasail.  You'll start moving in the
direction opposite the direction the laser is pointing.  The
structure doesn't have to be exposed to space or anything; you
could just have a box in the engine room containing the
parasail-laser assembly.  You can even use the parasail's
absorber to power the laser (with some auxiliary generator to
compensate for inefficiency losses).

Here's what would happen:

The laser turns on, and generates forward momentum in the ship in
reaction to the backward momentum of the laser light.

The laser light is absorbed by the parasail, producing some
smaller amount of backward momentum than the forward momentum the
ship got in reaction to the laser.  There's more forward momentum
than backward momentum, so the box produces net forward momentum
without reaction mass.

A lower-tech solution could involve a bunch of BB cannons
shooting at a more sturdy version of the parasail assembly.  

The best part is that if the parasail recovers most of the energy
directed at it, you can keep pumping that energy back in to the
laser or BB cannons or whatever is providing the thrust; if you
can make this efficient enough, you can get huge amounts of
momentum for small quantities of energy.