Satgen 557  Incapacitated Orbiters  by GM4IHJ (BID SGEN557) 1999-11-27

Recent reports regarding the state of two well known satellites ,
suggest that one , could be classified as blind , while the other
might be said from appearances, to be drunk.

Satgen505 of Nov 98, warned of the imminent failure of the 3rd of the
Hubbles Space Telescopes gyroscopes/inertia wheels. Leaving Hubble
with just 3 out of 6 , working. This being the minimum number required
to keep the satellite pointing accurately at its celestial targets. A
warning vehemently denied by one radio amateur who claimed to have a
special line to NASA. 

Despite that amateur denial, the 3rd gyro duly failed in Feb 99, and
NASA began organising an Emergency repair mission for October 99. A
mission now unfortunately delayed by Space Shuttle wiring problems
until December next. Unfortunate, because a 4th gyro has now failed.
So Hubble has had to be closed down to safe mode, and will be blind
until a complete outfit of replacement gyros can be fitted by the
Emergency repair team.

Meanwhile another excellent satellite, Amsat Oscar Ten. Much loved by
radio amateurs who got their first taste of super sat DX on it 16 long
years ago. Has been producing some very odd signals. Signals whose
random walk characteristics as seen on an FFTDSP spectrum analyser,
would certainly call for a charge of driving whilst under the
influence of drugs or drink , if any one of us tried it on the
highway.

Viewed on an FFT display Ao10s beacon signal has a remarkable pattern
of swings and swirls, repeating roughly every 6 minutes. At first
sight the pattern appears complely random. But this is not the case.
There are 3 bumps every 6 minutes , with the middle hump of one 6
minute sequence reaching a level of 15 dBs over noise , whilst the
following 6 minute sequence exhibits a lower signal level than its
predecessor, or its successor.

If you have access to FFT software , run it with a long integration
time so that you get about 18 minutes of signal on screen at anytime.
. Then see if you can work out what might be causing this sequence.
Noting that as the aspect of the satellite versus your station changes
over several hours, the pattern slowly modifies, further confusing the
issue. It is distinctly possible that some of the changes, ie the 3
humps every 6 minutes correspond to one revolution of the satellite in
which its antenna is alternately shielded by , or, clear of, the 3
points of the satellites body structure. As each satellite corner
rotates in turn across the line of sight to the receiving station, one
corner going by every two minutes , But there must also be other
tumbling motions , including one where the signal is almost lost
completely for two minutes in every 12 minutes. Here the clues seem to
point to something not present all around the orbit, only occuring
when the satellite is viewed in certain parts of its orbit. Please
take a look for yourself if you can, and see if you can figure out
what is happening up there.