Environmental Engineering Reference
In-Depth Information
attention. Trying to perform any of these functions with ground personnel
“in the loop” would not only be less ecient and less safe, but also be far
more expensive than delegating the responsibility to the flight system.
Recently, more elaborate flight-autonomy capabilities have been intro-
duced specifically to reduce operational costs. For example, to break linkages
between spacecraft target-pointing and communications (antenna pointing),
the Rossi X-ray Timing Explorer (RXTE) mission introduced an autonomous
antenna-manager function responsible for selecting the appropriate high gain
antenna (HGA) that can be used compatibly with the current spacecraft
attitude. This capability not only supported greatly reduced lead times on
changing targets to observe a TOO, but also reduced staff efforts (and costs)
in scheduling TDRS contact times by eliminating couplings between TDRS
scheduling and onboard antenna selection, which often is a factor when opti-
mizing communications contact time.
And for JWST, the use of an onboard event-based scheduler could reduce
overhead time (in turn, raising observing eciency) and reduce both ground-
system modeling costs as well as the need for spacecraft “hand holding.” And
further in the future, increased onboard processing of science data may not
only enable increased capabilities to exploit TOOs detected in real time on-
board, it could for some missions also permit a reduced science data downlink
volume, with associated operations cost reductions, as the science commu-
nity gains confidence in the accuracy and reliability on the onboard processed
product.
It should be noted that these reductions in operations costs do not them-
selves come without a cost. The development of new FSW functionality typ-
ically is an expensive undertaking, both from the standpoint of coding the
new capability and the testing required to ensure that no inadvertent harm is
done to the spacecraft. The impact of these software costs, however, is less-
ened when the new autonomous function is implemented for a long duration
mission where the costs can now be traded relative to the, say, 10 years of op-
erational effort that the FSW replaces. Similarly, when several missions can
use the new capability, the up-front development costs for the first mission can
be seen as a long-term investment yielding savings both on that mission and
downstream missions. Hopefully as the expense of developing FSW continues
to decline and as greater FSW reuse becomes possible, the trade of continuing
operations costs for new FSW autonomy will be an increasingly favorable one.
3.2 Brief History of Existing Flight Autonomy
Capabilities
In the previous sections, the reasons for developing flight autonomy and the
flight autonomy capabilities that were developed in response to those needs
were discussed in some detail. In the following sections, those flight autonomy
capabilities will be grouped in accordance with the general time periods in
