A Case Study in NASA-DoD - The Black Vault

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Changes required to make the AEM compatible with SGLS are summarized
in Table C-2.
DESCRIPTION OF MMS AND COMPARISON WITH STPSS
The MMS is a large NASA multimission modular spacecraft. Like
the STPSS, the C&DH system is capable of transmitting high data rates
and has a computer on board for data processing and formatting. However,
as is shown in Table C-1, the MMS and STPSS C&DH systems differ
substantially because of the STDN-SGLS incompatibilities. The uplink
frequency, uplink subcarrier modulation, antenna polarization, communication
security protection, and command format differences necessitate
the following changes:
1. Replace the STDN transponder with an SGLS transponder.
2. Replace the phase-shift keying (PSK) demodulator with an
SGLS single conditioner (includes PSK demodulator).
3. Modify the signal conditioner output, modify the command
decoder input, or add a suitable piece of equipment between
the two to make the signal conditioner and the command decoder
compatible.
4. Redesign the MMS omni antenna.
Further details on interchanging STDN/SGLS communication components
are summarized in Table C-3. While the differences between the two
C&DH systems are substantial, it is possible that proper preliminary
design of the spacecraft would enable communication black boxes to be
interchanged with minimal impact. However, if a decision is made late
in the design cycle, substantial problems will most likely occur.
Available STPSS equipment could be used directly on the MMS. Capabilities
are similar, so sizes, weights, and power requirements should be
also.