Message-ID: <301@petrus.UUCP>
Date: Sun, 3-Mar-85 22:18:19 EST
Article-I.D.: petrus.301
Posted: Sun Mar  3 22:18:19 1985
Date-Received: Mon, 4-Mar-85 20:35:47 EST
References: <61@pbear.UUCP> <823@ames.UUCP>
Organization: Bell Communications Research, Inc
Lines: 56

> With all this talk about solar sails on the net I thought you might like
> to know that the World Space Foundation is actually building one and
> expects to fly it.  The have built two prototypes, one full size, and have had
> an upper stage donated to them.  They still need a launch - either shuttle
> or Ariane - and I don't think they've started on the flight article.
> They main players are experienced people from JPL, they know what 
> they're doing.  
> 
> I don't know how far they've got on control, but the 
> last I saw there were two small rotatable sails on the end on one of
> the booms for pitch and roll control.  There is also a movable mass near
> the center of the sail for yaw.
> 
> If anyone has the address available, why don't you post it?  Most of
> their labor is volunteer.  If you want to help, contact Robert Staehle (sp?)
> at JPL in Pasadena, CA.

The World Space Foundation is indeed a serious group. They have approached
AMSAT, the radio hams who build amateur communications satellites and
have proposed a joint venture in which AMSAT builds the communications
hardware to fly on their sail. They get command, telemetry and tracking
facilities, something that AMSAT can do well, and we (AMSAT) get a slow
but free ride for a transponder into a useful communications orbit, something
that AMSAT is always looking for.

We were all impressed with their technical knowledge of the subject, and
they seem to have a viable organization. A possible joint project
is only in the very preliminary stages at the moment, but one thing that
can make it emerge into reality very fast is for volunteers to step forward
and actually take on part of the design job.  The primary contact person on
the AMSAT side for the project is Dr. John Champa, K8OCL. John recently moved
to Michigan and I don't have his new address handy, but mail to him can be
forwarded via the AMSAT address (PO Box 27, Washington, DC 20044).  Feel free
to contact him if you think your interests might lie in the electronics
side of such a project. Here's YOUR opportunity to do something "up there"
besides talk about it idly on net.space!

Regarding photon pressure and spinning toys: AMSAT-Oscar-7, launched in
1974, made practical use of this phenomenon. In those days, amateur
satellites had no propulsion systems or active attitude control systems,
but something had to be done to keep them from tumbling uncontrollably.
The end-over-end motion was easy enough, you just stick a big bar magnet
along the main axis of the spacecraft. Within days after launch the
whole thing aligns itself with the earth's magnetic field and the satellite
turns end-over-end slowly twice per orbit (this is a polar orbit).
The remaining problem was to control roll about the magnet axis, and for
this task photon pressure was used. The satellite had four antenna elements
bent towards one end, which were fabricated out of ordinary carpenter's
rule (the kind that's yellow or white, with inch markings). One side of
each element was painted white, the other black.  The result was a net
torque from radiation pressure that slowly rolled the spacecraft about
its magnet axis at almost exactly the predicted rate. Very simple, very
effective.

Phil Karn
Asst. VP Engineering, AMSAT