Environmental Engineering Reference
In-Depth Information
as they are generated. Data passing validation can then be routed to onboard
storage, while data failing validation can be deleted, saving onboard storage
space, downlink bandwidth, and ground system processing effort. In practice,
a requirement of many science missions is that all the raw science data be
downlinked; so often this potentially available flight capability is not imple-
mented or exercised. Even for those missions, however, lossless compression
of data may be performed onboard (usually in hardware), yielding significant
savings in onboard space and bandwidth (as much as a 3-to-1 reduction in
data without loss of information content), while at the same time affording
the science customer full information, even to the point of backing out the
original raw science data. Finally, the flight system can play a valuable role by
exploiting the realtime availability (onboard) of both science and engineering
data to synchronize time-tagging and even to package data into organized files
tailored to the needs of the customer for whom those data are targeted.
Flight Autonomy Enablers of Ecient Resource Management
In addition to these fundamental applications (command execution, pointing
control, and data storage) that are the primary components of conducting
science, the flight system must also support auxiliary applications associated
with managing limited onboard resources, including computing power, inter-
nal data transfer, electrical power, data storage, telemetry downlink band-
width, angular momentum, and rocket/thruster propellant.
Computing Power and Internal Data Transfer
The first two items, computing power and internal data transfer, are man-
aged both through the design of the FSW and realtime monitoring of FSW
performance. Traditionally, at its high level design, FSW functions have been
carefully scheduled so as to ensure that adequate computational resources are
available to permit the completion of each calculation within timing require-
ments without impacting the performance of other calculations. Although the
FSW may often be operated below peak intensity levels, the FSW is designed
to be capable of handling worst case demands. Similarly with respect to inter-
nal data flows, the bus capacities are accounted for when analyzing the feasi-
bility of moving calculation products, sensor output, and commands through
the flight data system. To deal with anomalous or unexpected conditions caus-
ing “collisions” between functions from either a CPU or I/O standpoint, the
flight system monitors itself in realtime and, in the event of a conflict, will
autonomously assign priority to those functions considered most critical. If
an acceptable rationing of resources is not proved to be possible, or if the
conflict persists for an unacceptably long period of time, the flight system
(or a major component of the flight system such as an individual SI) will
autonomously transition itself to a state or mode of reduced functionality
(usually a safemode) with correspondingly lower CPU and/or I/O demands.
