A Case Study in NASA-DoD - The Black Vault

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Appendix C
COMMUNICATIONS AND DATA HANDLING SUBSYSTEM:
A COMPARISON OF AEM. STPSS. AND MMS
by
P. A. CoNine
Table C-i summarizes the communications and data handling subsystems
for the AEM, the MMS, and the STPSS. It can readily be seen
that the three C&DH systems are substantially different and not compatible.
Major differences include frequencies, modulation, formats,
data rates, polarization, and security equipment. None of the C&DH
equipment on the three spacecraft is beyond or even pushing the state
of the art. Most of the equipment on the AEM and STPSS has been used
on previous spacecraft. While some of the MMS equipment will be new,
the overall spacecraft is in the latter stages of development. Because
the STPSS missions are not concerned with cross-linking data to another
spacecraft, it is not necessary to pay any further attention to the TDRSS
transponder.
DESCRIPTION OF THE AEM
The AEM spacecraft is currently being built by Boeing in two versions:
the HCMM and the SAGE. The HCMM has a VHF command and housekeeping
telemetry system and an S-band telemetry unit for experimental
data; the SAGE vehicle has all communications at S-band frequencies.
The command and telemetry formats are compatible with the NASA-STDN
satellite tracking and telemetry system. The HCMM spacecraft is the
only one in this study with a VHF command receiver and housekeeping
transmitter; however, the communication system has been designed so
that it can become S-band-compatible (as on the SAGE) merely by changing
the transponder/transmitter-diplexer units. No further consideration
will be given to the VHF system.
The AEM telemetry system has a low data rate of 1 or 8 kbps, although
on the SAGE tape recorder playback can be as high as 1 Mbps.
The command rate is a low 600 bps. The memory is small and is used