Environmental Engineering Reference
In-Depth Information
4.
GEO earth pointers
5.
Survey missions
6.
Lagrange point celestial pointers
7.
Deep space missions
8.
Spacecraft constellations
The following subsections discuss these in more detail.
6.6.1 LEO Celestial Pointers
For LEO celestial pointers, the intermediate- and short-term scheduling prob-
lem is quite complex due to the many time-dependent constraints charac-
teristic of near-earth orbits. The ground system component responsible for
that function must be large and expensive, embodying many complex space-
craft and environmental models. But, since the dominant input to optimizing
scheduling is not realtime measurements, there is little advantage in migrat-
ing short-term planning to the spacecraft, given that communications with
the ground can be expected to be regular, frequent, and of long duration. It is
even unclear that event-based scheduling would win a cost-benefit trade with
conventional ground preprogrammed absolute time-based scheduling, given
the need for look-ahead to maintain high scheduling eciency. An exception
to this general statement would be realtime support for TOOs, where the spe-
cial onboard processing would not schedule the TOO itself, but instead simply
make platform and payload housekeeping adjustments, as necessary, to sup-
port the change in the plan. So the planning and scheduling area probably
is not a productive application for agent formalism for LEO celestial point-
ers, and similarly, SI commanding and configuration is likely to be limited in
carrying out ground instructions, probably via templates stored onboard to
reduce uplink data volume.
On the other hand, one can easily imagine additional calibration func-
tions being migrated to the flight system for LEO celestial pointers. For ex-
ample, as miss-distance data from slews are collected onboard, the current
state of calibration could be monitored autonomously and a background task
could re-compute the gyro scale factors and alignments (supported by back-
ground fine-attitude and orbit-determination background tasks). Whenever
fault detection determined that the current calibrations no longer were ac-
ceptable, fault correction would direct use of the current “latest-and-greatest”
computed values. Implementation of each of these functional areas in the Re-
mote Agent formalism via the design structure described earlier in this sec-
tion would greatly facilitate the cooperative behavior described above without
adding risk to the maintenance of platform and payload H&S via the FSW
backbone.
Summarizing, implementing the following additional onboard functions
as Remote Agents would be consistent with the lights-out control center
philosophy:
