Environmental Engineering Reference
In-Depth Information
2.2.2 Executive and Task Management, Time Management,
Command Processing, Engineering and Science Data Storage
and Handling, Communications
Command and data handling (C&DH) includes the executive, time man-
agement, command processing, engineering- and science-data storage, and
communication functions. The executive is responsible for coordinating and
sequencing all the onboard processing, and separate local executives may be
required to control lower level processing within a subsystem. The command
processor manages externally supplied stored or realtime commands, as well as
internally originated commands to spacecraft sensors, actuators, etc. Again,
depending on the design, some command management may be under local
control.
The C&DH also has management responsibility for engineering- and
science-data storage, in the past via tape recorders, but nowadays via solid
state storage. Depending on the level of onboard sophistication, much of the
bookkeeping job may be shared with the ground, though the trends are to-
ward progressively higher levels of onboard autonomy. Telemetry uplink and
downlink are C&DH responsibilities as well, though articulation of moveable
actuators (such as high gain antenna (HGA) gimbals) as well as any sup-
porting mathematical modeling associated with communications (e.g., orbit
prediction) are typically the province of the ACS.
2.2.3 Electrical Power Management, Thermal Management,
SI Commanding, SI Data Processing
Critical H&S functions like spacecraft electrical power and thermal manage-
ment are usually treated as separate subsystems, though the associated pro-
cessing may be distributed among several physical processor locations (or
located in the spacecraft bus processor) depending on the design of the flight
system. This distribution of subfunctionality is particularly varied with re-
gard to SI commanding and data processing, given the steadily increasing
power of the SIs' associated microprocessors. Currently, any onboard process-
ing that is associated with a spacecraft's Optical Telescope Assembly (OTA)
falls within the context of the SI functions, though as OTA processing becomes
more autonomous with the passage of time, it could well warrant independent
treatment.
2.2.4 Data Monitoring, Fault Detection and Correction
The processing associated with data monitoring and FDC is even more
highly distributed. Typically, the checking of individual data points and the
identification of individual errors (with associated flag generation) are done
locally, often immediately after the measurement is read out from its sensor.
On the other hand, fault correction is typically centralized, so responses to
multiple faults can be dealt with in a systematic manner.
