Environmental Engineering Reference
In-Depth Information
Power Management
The flight system plays a role in electrical power management at three levels:
positioning solar arrays (SAs), managing battery charging and discharging,
and overall power monitoring and response. For celestial-pointing spacecraft
having movable SAs, the FSW will select the appropriate SA position for
each attitude that produces the desired energy collection behavior. Usually
the position is chosen to optimize power generation, though for missions where
over-charging batteries is a concern, the FSW may offset the SA(s) from their
optimal position(s). For earth-pointing spacecraft, the FSW will rotate the SA
to track the Sun as the spacecraft body is rotated oppositely so as to maintain
nadir pointing. The FSW will also autonomously control battery discharging
and charging behavior consistent with algorithms defined prelaunch and re-
fined postlaunch by operations personnel. While carrying out these functions
on an event-driven basis, the FSW also actively monitors the state-of-charge
of batteries. If power levels fall below acceptable minimums, the flight system
will autonomously transition itself (or individual, selected components) to a
state or mode of reduced functionality (usually a safemode) with correspond-
ingly lower electrical power demands.
Data Storage and Downlink Bandwidth
Onboard data storage utilization and downlink bandwidth allocation typi-
cally fall out of trade studies for ground system operations costs. The ground
system will plan its observations to ensure that adequate space is available
to store any science data collected during an observation. Similarly, FSW
development personnel will design the formats of all telemetry structures to
ensure that operations personnel have access to key performance data at re-
quired frequencies and to guarantee that customers receive their science data
packaged appropriately for ground system processing. However, even in these
cases dominated by prelaunch considerations, the flight system has its own au-
tonomous realtime role to play. Specifically, the FSW must monitor free space
availability on the storage device and, in the event of a potential overflow,
determine (based on ground-defined algorithms) priorities for data retention
and execute procedures regarding future data collection. It also must contin-
uously construct the predefined telemetry structures and insert fill data as
necessary when data items supposed to be present in the telemetry structure
are unavailable. Further, to ensure that the necessary link with the ground
is maintained to enable successful telemetry downlink, the flight system must
appropriately configure transmitters and orient movable antennas to establish
a link with the ground antenna.
Angular Momentum and Propulsion
The last two onboard resources, angular momentum (for reaction wheel-
based spacecraft) and propulsion subsystem fuel, can be viewed as physical
