Environmental Engineering Reference
In-Depth Information
Of course, there are certain requests that just cannot be fulfilled. It is the
executive's job to notice these, come up with the “closest fit” to the request
issued from the human controller, and report back with the closest fit to ask
for a go-ahead on that schedule.
When all of the planning has been performed through the negotiation,
the executive satellite could issue the plan to all image gathering satellites.
The satellites will receive their plans, and internally they will schedule their
own control (perhaps via an internal agent network for subsystem control)
for setting up their imaging systems, recording the image, and transmitting
it. The satellite will pass over the section of the planet in due course, record
the images, and transmit them back to the executive satellite. The executive
satellite will assemble the images when the whole spectrum has been covered,
and transmit them back to the human controller at the next appropriate
opportunity.
This scenario is a perfect illustration of a negotiating agent network. Al-
though it is hypothetical, it unifies the concepts of hierarchical parsing net-
works between spacecraft, and within spacecraft.
B.6 Scenario Issues
One aspect of the presented design concepts that could create problems in
flight is the layering of communications engendered by the FSW backbone.
Commands, status messages, and data often must go through several check-
points before they reach their intended hardware destination in order to
guarantee platform and/or payload H&S, no matter what anomaly or fail-
ure conditions may obtain with the Remote Agents. There are two potential
problems arising from this security paradigm. First, some commanding has
associated with it very severe timing requirements. For example, in the case
of HST, in order to satisfy its pointing accuracy and stability requirements,
reaction wheel commands must be executed within 7 ms of receipt of the gyro
data from which the commands are derived. For this case, a data latency prob-
lem engendered from the time delays in relaying commands to the reaction
wheels potentially could jeopardize meeting a fundamental mission require-
ment, unless the OBC and bus infrastructure are adequate to support the
design. Second, the multiplication of messages and commands, especially if
receipt of one always triggers an acknowledgement, could create a blizzard
of trac on the bus (or busses), leading to loss of information or even pro-
cessing lock-up, again, unless the OBC and bus infrastructure are adequate
to support the design. In other words, the presented design concepts, involv-
ing communications-and-computation-intensive negotiation processes between
multiple agents, imply the need for research into new spacecraft architectures
and the crucial need for certain minimum levels of performance of future on-
board communications and computing resources.
