Environmental Engineering Reference
In-Depth Information
(I/O) channels that has provided the ground system a relatively stable envi-
ronment for the development of standardized COTS products, which, in turn,
has enabled dramatic reductions in ground system development costs.
Second, it is the responsibility of the FSW to respond to events that the
ground system cannot deal with because of the following:
1.
The spacecraft is out of contact with the ground
2.
The response must be immediate
3.
Critical spacecraft or payload issues are involved, or
4.
The ground lacks key onboard information for formulating the best re-
sponse
Historically, the kinds of functions allocated to FSW for these reasons were
ones such as the attitude control subsystem (ACS), safemode processing and
transition logic, fault detection and correction, target acquisition logic, etc.
Third, the FSW can be used to streamline (at least in part) those (pre-
viously considered ground system) processes where an onboard, autonomous
response is cheaper or more ecient. In many of these cases, routine processes
may first be performed manually by operations personnel, following which au-
tomated ground software is developed to reduce costs. After the automated
ground process has been fully tested operationally, the software or algorithms
may then be migrated to the flight system where further cost reductions may
be achievable.
Fourth, the process may be performed onboard in order to reduce demand
on a limited resource. For example, downlink bandwidth is a valuable, limited
quantity on most missions, either because of size/power constraints on space-
craft antennas/transmitters, or because of budget limitations on the size of
the ground antenna. In such cases, FSW may be used to compress the out-
put from payload instruments or prune excessive detail from the engineering
telemetry stream to accommodate a smaller downlink data volume.
As can be seen from even casual consideration of these few examples, the
demands placed on FSW have a widely varying nature. Some require high
precision calculation of complex mathematical algorithms. These calculations
often must be performed extremely quickly and the absolute time of the calcu-
lation must be accurately placed relative to the availability of key input data
(here, we are referring to the data-latency issue). On the other hand, some
FSW functions must process large quantities of data or must store and manage
the data. Other functions must deal with intricate logic trees and orchestrate
realtime responses to anomalies detected by self-monitoring functions. And
because the FSW is the key line of defense protecting spacecraft H&S, all
these functions must be performed flawlessly and continuously, and for some
missions (due to onboard processor limitations), must be tightly coupled in
several processing loops.
