This section describes the performance drivers for the contact functions of Telemetry, Commanding, and GSS Processing and describes a reasonable distribution of the required functionality on hardware platforms. The Telemetry and Commanding appendices (B and C, respectively) contain detailed analysis of processing loads in each area. Analysis of GSS load is included in Appendix B, since status data can be processed like telemetry data. Several telemetry and commanding architecture options are presented in Appendix B (Figure B-9) and Appendix C (Figure C-9). Each option varies the allocation of functions across platforms, as shown in Figure 9. Functions for Telemetry processing, Commanding processing, and GSS processing are listed.
As discussed in Appendix B, the Telemetry load is bounded by the satellite PCM rate, which ranges from 75 bps to 5 Mbps, the data expansion factors associated with telemetry processing, and the telemetry processing and display requirements. The higher telemetry rates, (e.g., 1.024 Mbps to 5 Mbps), consist primarily of mission data, with little or no embedded SOH data. Therefore, not all measurands in the 5-Mbps stream are processed for SOH assessments, which is the SSCS responsibility. A maximum SOH embedded rate of 128 Kbps and a maximum dedicated SOH stream rate of 128 Kbps are assumed for the worst case SOH load.
The Commanding load is driven by the commanding rate (which ranges from 75 bps to 28.8 Kbps), amount of real-time constraint checking performed, and complexity of real-time command verification. Commanding performance loads are detailed in Appendix C.
At lower telemetry and commanding rates, GSS data processing becomes an additional loading factor. This data is used as input to the command constraint checking process and in determining both the quality of the satellite telemetry data and the vehicle state. Thus, the processing load for GSS data is included in the calculation of total contact load. The GSS data rate is assumed to range from 3.1 Kbps to 6.8 Kbps (see Appendix B).
To illustrate the variation in processing load allocations across platforms, two cases with specific data rates are analyzed. For high data rates, the maximum Telemetry, Commanding, and GSS data rates (1.024 Mbps mission, 256 Kbps SOH, 28.8 Kbps commanding, and 6.8 Kbps GSS) are assumed. For nominal data rates, 8 Kbps SOH, 1 Kbps commanding, and 6.8 Kbps GSS are assumed.