money is in short supply

Am 27.02.2011 07:16, schrieb Al Globus:
>
> On Feb 25, 2011, at 9:46 PM, Frank wrote:
>
> > The sail foils used for the SSPS-spacecraft would just feature a
> > mass of 32 kilograms.
> > Not so much, to give up the advantage of better production capacity
> > on Earth to save
> > a part of this 32 kg.
>
> Where does this figure come from? Including thin-film solar cells I
> calculate that a system based on the Ikaros satellite would probably
> weigh around 45 g/m^2 for the energy production alone. See
> http://space.alglobus.net/papers/SSI2010SSPpaper.pdf
> for details.
>

Hi Al,
I like Your paper. Seems that my design resembles Your
proposal of a thin film based
"One-Launch Operational PowerSat".
(for the One-Launch deployment part see US patent
application of a
"Solar-Sail-Launch-System" US 11614081 .)

The 32 kg are only the mass of the solar cell foils, not the structure.
The figures for the solar cell-foils came from Kevin Reed, who heads the
Welsom Space Consortium.
He claims that he can deliver thin film solar cell foils for one tenth
of the price
of regular solar cells for space applications.

Even as the SSPS looks like a Heliogyro, it isn't.
My design needs structure, which is heavier as the sail foil.
There are 12 telescoping masts instead none compared to
a Heliogyro and compared to the 4 (lighter) masts of a square sail.

The system needs also 3 electric motors and 2 electric winches per mast and
a foil roll which carries the solar cell foils and electric thrusters
with fuel.

The higher mass compared to a Heliogyro SSPS is the weakness of the System,
it's strength lies in the ability to provide fuelless high precision
attitude control,
station keeping and pointing adapted to and combined with Solar-electric
propulsion.
You could switch seamlessly from Roller-Reefing attitude control to
SEP-attitude control
using the same turning axles as shown on page 13 of the presentation
http://www.solar-thruster-sailor.info/PresentationISSS2010V13.pdf.

With additional mobile dockingable thruster units,
http://solar-thruster-sailor.info/figs/fig16.html
it is also possible, to refuel the
craft just by casting off the old thruster unit and dock in again a new one.
A separate tanker mothership could deliver those refueling daughter units.

The 500 kw available for this sample design would allow to power one
DS4G ion engine
http://www.daviddarling.info/encyclopedia/D/DSG4_ion_engine.html,
which allows exhaust speeds of about 210 km/sec., which is about 7 times
better as regular ion engines. So this engine would use only one seventh of
the fuel needed for the same thrust produced with a regular ion engine.

When the mobile main engine is switched off, 20 % of the systems capacity
would be also able to power the 100 kw solide state laser for power beaming
You mentioned in Your paper.

By the way, the system would be scale able by enhancing the number of
telescopic mast segments of each mast and/or the volume of the launcher
payload department.

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.

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

Best wishes

Frank