Environmental Engineering Reference
In-Depth Information
errors caused by cosmic rays. As the observation continues, the SI data-storage
agent will progressively build the observation file so that, by the end of the
activity, a complete, coherent record of the observation will have been com-
piled for downlink as a unified file under the authority of the SI data-storage
and communications agent.
When “data-take” at this target has been completed, the planning and
scheduling agent determines that a survey observation can be performed con-
veniently and schedules the necessary slew to the target. Processing flow then
proceeds as described above for the earlier target, except following comple-
tion of data collection from the survey activity, the SI data processing agent
processes the survey data and identifies several point-targets of interest.
These targets are reported to planning and scheduling, which then adds
them to the target list for immediate revisits, with observations to be per-
formed according to canned, ground-specified scripts. The targets are then
visited in an order defined by the planning and scheduling agent. At the end
of this activity, the SFDDIC (using data from the look-ahead modeling agent)
determines that a momentum dump is required. Planning and scheduling is
notified, which decides that the dump should be performed now, and issues
the necessary directive to the orbit maneuvering agent, which also handles the
thruster commanding for momentum reduction. As with the attitude control
agent, the orbit maneuvering agent must forward its thruster commands to the
executive agent, which in turn relays them to the FSW backbone, which then
performs its QA and communicates directly to the thrusters to cause the
thrusters to fire in the manner specified. Finally, by this time the ground sta-
tion antenna has become visible to the spacecraft (or
vice-versa
, depending
on one's point of reference), and an electronic handshake between the ground
station's and spacecraft's communications agents is established. The hand-
shake is initiated by the ground station agent, but downlink of the science
data onboard, including the recently built ground-specified and opportunistic
survey files, is managed by the onboard communications agent. The lights-out
ground system autonomously validates each file as it is downlinked. As trans-
mission of a file is deemed to be successful, the ground system notifies the
onboard communications agent and SI data-storage agent that the onboard
addresses associated with that data are free to be overwritten.
This completes the narrative illustrating the mutual communication and
interaction of FSW subsystem agents (along with some interaction with
ground system agents) in nominal performance of inflight activities of a typical
science mission. In reality, the description provided is highly oversimplified:
the communication flow in the example is quite sequential, whereas in real-
ity, there will be many parallel conversations in progress at any given time.
Also, the assumptions specify a model of a far lower level of complexity than
would be characteristic of a real mission. So the example provided should be
viewed as simply a token of what would obtain in an actual application.
