Environmental Engineering Reference
In-Depth Information
telemetry fields are reserved for FSW-calculated products (and FSW inter-
mediate calculation parameters) deemed to be of value by the FOT and other
analytical support staff. As engineering and housekeeping downlink bandwidth
typically is in short supply due to optimization of communication hardware
trades relative to weight and cost, the allocation of telemetry slots and the
frequency with which they are reported is usually a rather dicult process as
individual subsystem information needs are traded to avoid exceeding com-
munication bandwidth limits.
However, in the event of an inflight anomaly or the scheduling of a special
activity such as an instrument calibration, at times the nominally optimized
engineering/housekeeping telemetry contents may not be adequate to support
the immediate needs of the ground. In such cases, the FOT can utilize a
capability provided by the FSW to modify telemetry contents. In the past,
this was achieved by “flying” several predefined telemetry formats, with the
current one in use being that selected by the ground. In response to changing
inflight conditions, the ground could simply command the use of a different
telemetry format more appropriate to current needs. The weakness of this
approach lay in its inflexibility, i.e., a telemetry format needed to be defined
and be onboard already for it to be used. So if some unexpected conditions
occurred requiring an allocation of telemetry slots and frequencies different
from that supported onboard, not much could be done immediately to address
the problem.
By contrast, the filter table approach utilized by recent spacecraft affords
much more flexibility. In principle, any desired presentation of telemetry-
accessible data points can be achieved. Of course, given a limited bandwidth,
increasing the frequency of a given telemetry item can crowd out other impor-
tant data items, so a careful trade must always be performed before changing
filter table settings. However, at least the higher degree of flexibility ensures
that any single FSW-accessible data point can, in principle, be viewed by the
ground as frequently as desired.
Flight Autonomy Enablers of Lifecycle Cost Minimization
As budgets for overall lifecycle costs steadily decrease, mission plan-
ners increasingly look to FSW as a means to reduce continuing costs of
operation. Many current onboard autonomous capabilities, though originally
implemented to satisfy mission-specific objectives or to promote enhanced
spacecraft H&S, in fact also reduce the work load of operations personnel,
thereby enabling the reduction of stang levels without the loss of eciency
or increased risk. For example, for decades, spacecraft have autonomously
maintained attitude control, calibrated gyro-drift biases, propagated their or-
bital ephemeris, managed battery charging, maintained thermal constraints,
packaged and stored science and engineering data, checked for limit vi-
olations, and (on detection of any violations) either fixed the problem or
placed the spacecraft (or localized element) in a benign state pending ground
