Environmental Engineering Reference
In-Depth Information
SI specified “peak-ups” to facilitate realtime target acquisitions inside SIs
having narrow FOVs. However, the formalism of Remote Agents enables more
elaborate interactions.
For example, suppose a spacecraft's SI complement included an instru-
ment with a movable component (say, for survey scanning). Depending on
the mass/motion of the component and the mission jitter requirements for
fine pointing, the attitude perturbations induced by the component's motions
could threaten satisfaction of the jitter requirement. To deal with this poten-
tial problem, the agent embodying the SI could inform the attitude control
agent of its intended motions in advance, so that the pointing control law
could compensate for the disturbance in advance, so as to protect a precision-
pointing fixed-boresight SI observation from blurring. If the attitude agent
determined it could not compensate for the effect, the fault correction and
scheduling agents could be brought into the “discussion” to resolve the con-
flict, perhaps by giving priority to the precision pointing SI.
A more interesting solution would be for the more demanding SI to “an-
nounce” to an SI executive agent when it needed a particularly steady plat-
form, and then have the executive agent prohibit motions by the lower priority
scanning instrument during such periods. Similar restrictions would also apply
to other moving structures such as gimbaled antennas.
Another application for SI/agent direction of platform behavior is SI cal-
ibration. At its least elaborate, it would be straightforward to automate the
process of periodically placing an SI in self-test mode (using its internal test
source), comparing the output relative to a nominal signal, and passing on
any discrepancy information to an SI calibration function. This could be a
purely internal SI implementation. A more sophisticated example would in-
volve periodic re-observations of a baseline target for the purpose of checking
whether SI performance has remained nominal (and this example would en-
tail agent collaboration with the attitude-control and scheduling agents). This
example would also include the option for recalibrating the SI or optical tele-
scope assembly (OTA) if a significant degradation has occurred (where the
re-calibration would be the job of the calibration agent).
6.4.9 Beacon Mode Communication
For missions where contact with the ground is expected to be irregular and
where down-link requirements are driven by the spacecraft's need to inform the
ground only of the results of science observations processed onboard (triggered
by event messages from an onboard processing agent), it would be appropriate
for the spacecraft to control communications. Similarly, if contact is driven
by the spacecraft's need to confer with the ground regarding some problem
experienced onboard (also triggered by an agent message), it would be most
ecient/least costly for an onboard communications agent to “dial up” the
ground's agent. In its extreme form, contact responsibility totally migrated
to the spacecraft is referred to popularly as beacon mode, which can include
