Environmental Engineering Reference
In-Depth Information
trending agent to identify those clusters that can be observed successfully
given the current state of SI calibration. Monitoring and trending reports
back that current calibration accuracy is insucient to support successful
observations at the nearest cluster, but is satisfactory at the remaining clus-
ters. Planning and scheduling determines that the ground-specified priority
attached to the nearest cluster is not high enough to justify scheduling an SI
calibration update at this time, and instead directs that the attitude control
agent generate appropriate commanding to produce a slew to the first target
in the next nearest cluster.
To effect a slew to the next target requires reaction wheel commanding,
so the attitude control agent's commands must pass through an executive
agent that interfaces with the FSW backbone. The backbone accepts the slew
directive from the agent community and interfaces with the reaction wheels to
effect the slew. Following successful completion of the slew (as determined by
the SFDDIC Agent), the ACS software in the backbone facilitates entry into
fine-pointing mode by activating the quaternion star trackers (QSTs) and fine
error sensor (FES). Once the necessary QST and FES data are available, the
fine attitude determination agent begins computing high accuracy attitude
products. The data are simply stored in a file associated with the observation
(managed by the SI data-storage agent) and may be accessed by all users
requiring the information. At the same time, and regularly before arrival at
the target, the orbit determination agent has produced a steady stream (once a
second) of spacecraft, Solar position and velocity vectors, and trends position
and velocity vectors, again in support of applications needing the information.
In particular, the attitude control agent uses both the high accuracy at-
titude and orbit data to generate high precision attitude control commands
that, again, are passed through the executive agent to the FSW backbone,
which in turn interfaces with the reaction wheels (after the backbone quality
assures (QAs) the commands) to produce the desired pointing performance.
Having established a stable platform at the target attitude, the planning and
scheduling agent directs the acquisition of the science target by the SI and
initiation of the science observation specified by the ground. To this end,
it notifies the SI commanding-and-configuration agent to effect the neces-
sary SI adjustments required to perform the desired science activity. The SI
commanding-and-configuration agent generates the associated commanding
and forwards it to the executive agent, which communicates the hardware
changes to the FSW backbone so it can directly command the SI. All data
output from the SI, whether from the target acquisition or execution of the
science observation itself, is stored in the science observation file.
Specialized processing of the first SI data is performed by the SI data pro-
cessing agent to support target acquisition. Once the target has been acquired
successfully, the activity proceeds to the science observation itself, which is
processed onboard to support compact packaging prior to downlink. For exam-
ple, lossless compression will be performed, and possibly processing to reject
