The Drexler lightsail

Marcel wrote:
>
> SOLAR SAILING By Eric Drexler
>
> The name of the game, then, is to maximize
> acceleration by minimizing the mass per unit area of the mirror.
>
> People have looked at this problem, off and on, for about 20 years.
> They set themselves the problem of stuffing about a square mile of
> folded reflecting surface into the nose of a rocket, of launching it,
> and of making it unfold and stretch into a reasonably flat surface in
> space.
>

One more way to get a very large solar sail into space from Earth
without folding the sail cloth would be
to divide it into many rows of sail foils each smoothly furled onto a roll.

The rolls could be used to steer the spacecraft by "Roller Reefing"
(unfurling and furling the steering foils).

If you have a stiff frame like an Outer (pipe) Ring, it can hold ion
thruster devices
for additional propulsion and steering and the sail foil rolls.

Having also an Inner Ring structure in the sail craft`s center, would
enable to use this
structure as a payload and docking station, were several daughter units
above and under
each other can dock in the mother ship.

For such a "RingCraft"-design take a look at
http://solar-thruster-sailor.info/figs/fig13.html

The principle of fuel less steering that sail is described at
http://solar-thruster-sailor.info/figs/fig18.html

I do agree with Eric Drexler that constructing such a sail in space
(even using space materials)
would be the best way to build a solar sail.
The sail-foil on rolls idea however could be used for both, Earth launched
or space constructed solar sails.

Here is a design for an Earth launched mothership-spacecraft with solar
sail and ion propulsion, station keeping
and steering http://solar-thruster-sailor.info/figs/fig19-21d.html
It could be launched from Earth with several already docked in daughter
units, like asteroid landers, communication
and observation units, making a complete asteroid sample mission feasible.

As the mothership can reef the sail foils it could deliver the landers
with the asteroidal materials back to the ISS
where those samples could get analyzed.
(Solar sails without roller reefing would get in trouble at the ISS
because the atmospheric rests would slow them down to much).

Regards

Frank