karn@allegra.UUCP (Phil Karn) (03/04/84)
Posted: Sun Mar 4, 1984 1:57 PM GMT Msg: AGIE-1731-3276
From: MSWEETING
To: AMSAT
Subj: UoSAT-2 Status report
** UOSAT-2 SPACECRAFT OPERATIONAL STATUS **
4th March 1984 0800 gmt
Following a flawless launch on DELTA 174 from Vandenberg Air
Force Base, Ca., UOSAT-2 separated from the launcher at approx
19:11 gmt over Turkey and in range of the Command Station at
Surrey. A lengthy series of instructions was transmitted to
the spacecraft to establish the initial operating conditions
and then the s/c computer was instructed to switch the 145.825
MHz downlink on for 10 secs to check housekeeping data and
ensure that outgassing of the beacon did not give rise to
corona. The spacecraft responded perfectly first time and good
data was received & decoded at Surrey. The 145 MHz beacon was
then activated for several minutes, under computer control,
and further data gathered which confirmed that the spacecraft
was in very good shape. Just prior to LOS at Surrey, the
computer was instructed to activate the beacon once more for a
further 4 minutes and good data was received as the spacecraft
disappeared over the horizon.
On orbit #2 the 145 MHz beacon was re-activated by
abreviated computer instructions and the short and long bursts
of telemetry repeated - data indicated everything on the
spacecraft to be entirely nominal and so the computer was
instructed to keep the 145 MHz beacon active in check-summed
telemetry at 1200 bps for the next 80 minutes.
The spacecraft arrived at UoS silent (as expected) at AOS
on orbit #3 and the short and long bursts of telemetry data
process was repeated - data again indicated the spacecraft to
be entirely nominal and so the computer was instructed to
activate the 145 MHz beacon for the next 10 hrs whilst the
spacecraft was out of range of the Surrey station.
With all having proceeded perfectly to plan thus far, the
UoS team relaxed (collapsed?) and waited for telemetry reports
from around the world!
The first indications that all was not well came from the
printer when Larry Kayser wanted to know why he could not hear
UO-11 followed by t/m from Phil Karn etc. The UoS Command Team
were 'revived' and awaited the first pass of the day, orbit
#8. The spacecraft was silent (again as expected) at AOS,
however repeated attempts to re-activate the 145 MHz beacon
using the s/c computer failed as did direct command. Heated
analysis of the situation resulted in the preliminary theory
that the 'Watch-Dog' timer (a device that de-activates the 145
& 435 MHz beacons after 21 days if no commands have been
detected from the ground - remember UO-9!) may have been
incorrectly initialised and thus may have terminated
transmissions prematurely. The 'Watch-Dog' can be reset by
command and this, and re-activation of the 145 MHz beacon,
were attempted on orbit #9 - however with no success.
Continued attempts on orbit #10 yielded nothing and things
began to look rather grim. At that time no reason could be
found for the premature shut-down of the beacon and the
prevailing theories tended towards cataclysm. Additionally,
t/m 'went down' and we had to resort to phoning around to
gather more pieces of the picture! Data from G.Ratcliffe via
phone from Australia confirmed that the spacecraft systems
were functioning nominally when he tracked UO-11 just before
termination of transmissions. The spacecraft was in very good
shape!
Detailed examination of the s/c computer software used
during the first few passes shewed that the timing had been in
error - the timing clock selected had been running at 8 times
that required - resulting in premature shut-down of the beacon
on both orbit #2 and #3 entirely in agreement with
observations! This now veered the theories away from the 'Big
Bang' and towards some sort of spacecraft systems problem.
Lack of feedback from the spacecraft keeps us effectively
blind and all we can do is postulate the most likely theories
based on pre-launch experience. The current theory is that
there may be a problem with the 145 MHz beacon causing it to
fail to operate correctly and generate wide-band noise and
block the command receivers. This theory is based on
observations of the performance of the beacon during test
where some problems of this nature were encountered but were
later believed to have been fixed. The Surrey Command Station
are continuing to attempt to command the 145 MHz beacon OFF
and the 435 MHz beacon ON - so far without success. If the 145
MHz beacon is ON but not operating correctly, it should be
possible to observe it with high gain antennas and spectrum
analysers etc. Should this prove to be the case, then it may
be most profitable to attempt to command the spacecraft using
the 1.2 GHzcommand uplink as this uplink is the most
independant of the VHF/UHF systems.
All we can do is try out various theories - we tend not to
favour total system failure or spontaneous detonation at
present rather some more limited scenario. We shall keep you
posted as to our thoughts and progress. Needless to say,
everyone here is somewhat disappointed after the efforts of
the last months and such a flawless start to UO-11's life!
We still have faith, though!
Martin Sweeting UoSAT Programme Manager
+ UoS Team