Environmental Engineering Reference
In-Depth Information
survey work in selected regions of the celestial sphere. Knowing those portions
of the celestial sphere targeted for survey work, the total percentage of time
allocated to surveying, and guidelines regarding how much time should be
spent on surveys within, say, a week-long interval, the scheduling agent could
identify opportunities to “piggy-back” survey observations following successful
ground-specified targets at approximately the same attitude.
6.4.5 Opportunistic Science and Calibration Scheduling
The previous discussion of goal-driven scheduling cited an example that could
also be considered opportunistic scheduling, i.e., piggybacking a goal-specified
survey observation on top of a specific ground-specified point target. However,
opportunistic scheduling need not be goal-driven.
For example, while the spacecraft is executing attitude slews commanded
for the purpose of acquiring targets and collecting science as specified by the
ground, a calibration Remote Agent could keep a running tally of “miss”
distances derived by comparing star-tracker-computed attitudes with gyro-
measured angular separations. After collecting an adequate amount of data,
the agent could calculate new gyro scale factors and alignments to maintain
slew accuracy within performance requirements. The calibration computa-
tions would be done in the background on a nonimpact, computational time-
as-available basis relative to ongoing science or higher priority engineering
support activities. Should representative slew data of a specific geometric va-
riety be lacking, the calibration agent could request that the scheduling agent
reorder the target list or consult its targeting goals to see whether a target
could be “created” that would enable the collection of necessary engineering
data as well. Failing that, the scheduling agent could simply add a slew of the
required type to complete the calibration activity, if the FDC agent (using
data provided by the monitoring and trending agent) indicated that a re-
calibration needed to be performed in the near future to maintain spacecraft
slewing accuracy requirements.
6.4.6 Scheduling Goals Adjustment Driven by Anomaly Response
This operational capability highlights cooperative behavior between the Re-
mote Agents performing scheduling and fault-correction. Suppose that the
review, by the fault-detection agent, of the fault monitoring-and-trending
agent's spacecraft-state analysis has generated an error flag, which the fault-
isolation agent has associated with a solar array drive. Suppose further that
the fault-diagnosis agent has determined that continued nominal use of that
drive mechanism will lead eventually to failure of the mechanism, and in re-
sponse, the fault-correction agent rules that the solar array should be slewed
to its safemode orientation and not moved from that position until instructed
by ground command.
