Environmental Engineering Reference
In-Depth Information
6.4.2 Dynamic Schedule Adjustment Driven by Calibration Status
For spacecraft with high performance and accuracy requirements but very
stable calibration longevity (both science and engineering), a ground schedul-
ing system will be able to schedule science observations well in advance with
a high degree of reliability. This confidence is due to the knowledge that if
calibration accuracy degrades prior to execution of a key scheduled observa-
tion, the degradation will occur gradually and gracefully, leaving the ground
scheduling system ample time either to insert a re-calibration activity to re-
store nominal spacecraft function or to re-schedule any extremely performance
sensitive observations for a later time.
However, if calibration stability is extremely dynamic, the “half-life” of the
ground scheduling system's spacecraft state knowledge may be significantly
less than the lead time on execution of many of the scheduled targets, in which
case a prescheduled canned observing sequence will experience many obser-
vation failures and poor overall eciency. An alternative to this is to couple
realtime calibration status monitoring directly into planning and scheduling
of both science observations and re-calibration activities.
For example, the ground could uplink to the spacecraft a target list having
a label attached to each science target defining the level of telescope calibra-
tion needed to make the science observation worthwhile. The planning and
scheduling agent could then elect to schedule only those list targets (or goal
generated targets, as discussed later) compatible with the spacecraft's current
state of calibration (as determined by the monitor-and-trending agent). After
all such targets are exhausted, the agent could schedule a re-calibration ac-
tivity (as created by the calibration agent) to bring the spacecraft back up to
specifications, following which the remaining list targets could be observed.
Alternately, utilizing another label supplying priority information, the pres-
ence of any target with a high priority designation could be sucient to cause
planning and scheduling to order a re-calibration activity immediately.
Although this example primarily illustrates the cooperative behavior
of planning-and-scheduling, data monitoring-and-trending, and calibration
agents, a somewhat lower degree of participation by several other agents
(including attitude/orbit determination, attitude/orbit maneuvering, SI
commanding-and-configuration, and SI data processing) may arise as a
requirement.
6.4.3 Target of Opportunity Scheduling Driven by Realtime
Science Observations
For most TOOs, the ground system, due to its access to data from other space
and ground observatories, will be best positioned to designate appropriate
TOOs for its spacecraft and adjust the observing schedule accordingly. Also,
for those TOOs identified by processing SI measurements from the spacecraft
itself, as long as those TOOs do not have a short lifetime and as long as
