baalke@mars.jpl.nasa.gov (Ron Baalke) (02/06/91)
ULYSSES STATUS REPORT
February 4, 1991
As of 9 AM (PST), February 4, 1991, the following data was taken on
the Ulysses spacecraft:
Distance from Earth 103,283,902 miles (166,219,328 km)
Distance from Jupiter 318,755,081 miles (512,986,577 km)
Velocity relative to the Sun 63,353 mph (101,956 kph)
Velocity relative to the Earth 69,108 mph (111,218 kph)
Tape recorder operations based on recovering data acquired during the 16
hours out of view periods are continuing on a routine scheduled basis.
Experiment reconfigurations have been carried out as required.
An average of 93% data recovery was achieved during this reporting period
due to the problem reported below. On January 29, a data loss occurred while
the spacecraft was being tracked by the DSN (Deep Space Network) station at
Madrid. Since the station was not aware at the time of any ground problem,
it was feared that nutation had commenced again and was the cause of the data
loss. Consequently, a Conscan maneuver was initiated which removed the small
Earth pointing error which existed by design at that time (the spacecraft
antenna is permitted to off point by small amounts to minimize the number of
required corrections).
As a result of this maneuver the link was re-established. No evidence of
nutation existed in the telemetry data received on the ground; therefore, the
Madrid station was requested to check again if anything was non-nominal on the
station. Further investigation has shown that a procedural error at the
ground station gave rise to a ground antenna off pointing which was just
sufficient to give rise to this data loss but which was brought within the
threshold by optimizing the spacecraft Earth pointing. Steps are being taken
to avoid a repetition of this error.
On February 1, problems were experienced with uplinking block commands to
the spacecraft to configure for tape recorder operations for February 2 and 3.
Following some diagnostic analysis the other onboard command decoder was
selected and the block commands were transmitted successfully. The problem is
currently under investigation.
The spacecraft is currently configured with receiver 2 as the prime unit
fed via the High Gain Antenna and with receiver 1 as backup fed through the Low
Gain Antenna (LGA-F). However at the uplink power of 20KW currently being
radiated, receiver 1 is locking on to one of the command sub-carriers. This
could result in a randomly generated but legal command passing through to the
command decoders. Consequently, the uplink power has been reduced to 10KW to
prevent receiver 1 from locking up on this sub-carrier. As the spacecraft
distance from the Earth increases this phenomena will eventually cease to be a
problem.
A close watch is being kept for the possible return of nutation and
procedures are available to control it should it occur.
___ _____ ___
/_ /| /____/ \ /_ /| Ron Baalke | baalke@mars.jpl.nasa.gov
| | | | __ \ /| | | | Jet Propulsion Lab |
___| | | | |__) |/ | | |___ M/S 301-355 | It's 10PM, do you know
/___| | | | ___/ | |/__ /| Pasadena, CA 91109 | where your spacecraft is?
|_____|/ |_|/ |_____|/ | We do!