AO-40 Future Rests on Reducing Spin, Regaining Attitude Control

Space Bulletin 004 ARLS004

From ARRL Headquarters

Newington, CT February 6, 2001

To all radio amateurs




SB SPACE ARL ARLS004


ARLS004 AO-40 Future Rests on Reducing Spin, Regaining Attitude Control



The key to a successful AO-40 recovery effort continues to be a
matter of reducing the satellite's spin and regaining the ability to
adjust its attitude from the ground. ''The current problem is the
lack of accurate AO-40 attitude data,'' AMSAT News Service said.
Accurate data are not available because AO-40's sun sensor is not
seeing the sun because of the satellite's attitude.



Only when ground controllers can accurately determine the
satellite's attitude will it be possible to change it and correctly
aim AO-40's high-gain antennas for optimal reception on Earth--and
that's assuming the transmitters are functioning on bands other than
2.4 GHz. Ground controllers have had no luck hearing AO-40's
transmitters on the omnidirectional antennas on 2 meters, 70 cm or
1.2 GHz. Since the satellite's computer was reset and telemetry
resumed December 25, the AO-40 ground team has been analyzing
telemetry sent via the 2.4 GHz beacon--the only transmitter now
operating.



AMSAT-Germany described AO-40 as ''in the fog'' because its high
angle with respect to the sun temporarily prevents the sun sensors
from providing attitude data.



Ground controllers have been pinning their hopes on a previously
announced ''de-spinner'' programming routine that would permit AO-40
spin control without having to rely on the sun sensors. The
satellite's current spin rate is reported to be 17.7 RPM. But even
if the programming fix fails, ''it's no cause for panic,'' AMSAT-DL
said. By April, controllers reason, the satellites sensors will
again see the sun and ''thanks to magnetorquing, spin and attitude
can be actively improved upon the rising tide.'' Once the spin is
reduced, sun angle improved, and antennas pointed, testing can
resume. Still outstanding are tests of the VHF and UHF transmitters,
the arc-jet motor, and the reaction wheels, among others.



Both AMSAT-DL President and AO-40 Project Leader Karl Meinzer,
DJ4ZC, and AMSAT-NA President Robin Haighton, VE3FRH, have continued
to be optimistic that AO-40 will have a useful life of Amateur Radio
service. Command stations James Miller, G3RUH, Stacey Mills, W4SM,
made a long-term prediction of AO-40's new orbit. They say that even
after last year's incident--which silenced the satellite for nearly
two weeks--and the resulting decrease of perigee, AO-40's orbit will
be stable, although perigee will oscillate by several hundred
kilometers.



AMSAT-DL says the recovery effort has been slowed somewhat because
of limited access time on the part of the command team, due to
AO-40's current orbital parameters.



Discussions of the future of AO-40 are expected to dominate the
eighth AMSAT-DL Symposium on March 17, AMSAT-DL said.