light weight PowerSats

On Feb 28, 2011, at 1:17 AM, Frank wrote:

> I don't think, that a pure HelioGyro as in Your paper would work as a
> GEO-SSPS.
> As You know, JAXA had problems to steer the Ikaros solar sail
> spacecraft
> because of the high momentum of the rotating foils, so they looked
> also
> into decreasing the rotation speed.
> I think, that because the blades of a HelioGyro SSPS have to point
> allways towards Sun,
> the Sun pressure would push them away of the Sun, if the rotating
> speed is
> not pretty high.

I've added the IR system to my design using fiber lasers. It turns
out that, with some reasonable assumptions, the fiber lasers provide
enough stiffness to get rid of the rotation. This simplifies the
system quite a bit.

I've submitted the paper to ISDC with this analysis and hope to
present it there. In any case, it will show up on space.alglobus.net
in the relatively near future.

>
> Also the Craft, which orbits around Earth but has to point towards
> Sun has
> to change it's attitude constantly.

It does not have to change it's attitude much. Just point towards the
sun and make sure you don't have major gravity gradient issues --
which is not a big deal at GEO anyway. You just need to rotate about
1 degree a day to maintain sun pointing (360 degrees/year).

If you want to point at Earth you have to change attitude 360 degrees
in a day. Of course, if the sail is sun pointing the power beam needs
to rotate to keep on target.

> So a pretty good attitude control System is so important, best a
> fuelless one,
> because a SSPS would stay years in orbit and need a lot of fuel
> delivered to
> GEO over the years.

It's not clear it needs much fuel. I've done simulations of 100 g/m^2
PowerSats using STK that suggest that you only need to correct for
inclination creep and a little bit of orbital decay. The
eccentricity goes to 0.2 but then back to zero in the course of a
year. There may be clever ways to use the sail to stay more-or-less
where needed, but I don't know what they are (yet). The sat does
wobble around initial location, but the beam needs a lot of pointing
capability anyway so I think one can just live with it and compensate
with beam pointing.

This will, hopefully, be the topic in a third paper on the system.

In a late 2004 talk, Rutan made the following predictions:

1) Within 5 years 3,000 tourists will have been to space -- this did
not happen.
2) Within 15 years sub-orbital tourism will be affordable, and 50,000
people will have flown.
3) Within 15 years the first, expensive orbital tourist flights will
have happened.
4) Within 25 years orbital tourism will be affordable.

There have been a lot of wild claims in this business, but Rutan may
know what he's talking about. His privately financed SpaceShip One was
piloted into space three times in 2004, and Rutan has a contract with
Virgin Galactic to build a true sub-orbital tourist vehicle.

Al Globus
http://alglobus.net

Views expressed in this email are only my opinions and are not the
position of any organization I'm familiar with.