Environmental Engineering Reference
In-Depth Information
be made. Finally, using onboard SAA contour information and spacecraft
ephemeris, the FSW could have determined the time at which those PCA
observations could commence relative to earth occultation and SAA entrance
times. Although this capability was not flown on RXTE, it has been imple-
mented successfully and is the key to satisfying the rapid TOO response time
The third item among the list of autonomy features implemented
prelaunch - the antenna manager - enabled de-coupling of science and com-
munications scheduling. For missions where HGA selection is preplanned by
the ground, a change in target attitude due to inclusion of a TOO can induce
changes in HGA commanding for that target observation period and even
future target observation periods downstream. Further, for ground algorithms
that optimize TDRS switchover times and HGA selection choices in order to
maximize total TDRS contact time, relatively small changes in the attitude
profile can cause major changes in desired TDRS schedule. By contrast,
RXTE's antenna manager allowed the FSW to determine in realtime which
was the best HGA to use to close the link with the scheduled TDRS space-
craft, based on the FSW's realtime knowledge of its attitude and the relative
orbital positions of RXTE and TDRS (derived from onboard orbit models).
Also, knowing the TDRS schedule, RXTE's FSW could autonomously deter-
mine when HGA transmitters should be turned on and when playbacks from
the solid state recorder (SSR) should start. These autonomous features were
used routinely with great success until a transponder failure eliminated the
two-HGA capability.
RXTE and the Tropical Rainfall Mapping Mission (TRMM) also provided
enhanced flexibility in telemetry formatting via their telemetry filter tables.
In practice, the same amount of planning effort (the most laborious part of
the job) would be required to make major changes to its standard telemetry
configurations (identified as operationally necessary prelaunch) as would be
the case for earlier approaches to telemetry formatting, but once determined,
the modified telemetry formatting could be implemented via a simple table
uplink as opposed to a FSW change.
RXTE and TRMM also flew a more sophisticated version of TMON, called
TSM (originally developed for the Solar Anomalous and Magnetospheric Par-
ticle Explorer (SAMPEX) mission), which supported all the functionality of
TMON, i.e., monitoring telemetry points, performing limit checking, and ini-
tiating stored command sequences and associated event messages on limit
failure. In addition, TSM maintained statistical data for each monitor point
and accepted FSW reconfiguration commands. Statistical information gener-
ated includes telemetry-point current value and time, minimum and maxi-
mum values seen with associated times, average value, and number of times
the monitor point has been seen. TSM was particularly useful to the RXTE
mission as a means to deal with star tracker problems experienced inflight
without having to implement major changes in the flight code itself.
