Telemetry, tracking, and commanding (TT&C) link considerations for a LEO Sat

Telemetry, tracking, and command are very important functions necessary for the proper operation of a satellite. It becomes a critical issue for the LEO-Sat program, however, when the command and control is provided from a small ground station with limited capabilities (low transmit EIRP and receive G/T), and when the satellite is in a contingency mode of operation, such as tumbling (antennas off pointed). Previous link analyses have shown that the satellite link would be adequate when commanding from large remote tracking stations (RTS) with a larger antenna (45- or 60-foot dish). This paper deals with command and control of this new LEO-Sat in its early orbit, using a small remote tracking station (RTS), with a 33-foot antenna. Our analyses have proven that the uplink and downlink can be closed even with a small RTS station with a 33-ft antenna. The details of these analyses are given in this paper. The communication link performances, both during normal operations as well as in contingency tumbling mode of operations, are presented here. Both the SNR (signal to noise ratio) and the threshold techniques were shown side-by-side, in the link analyses, for normal and anomalous tumbling cases, with similar results. The conclusion in Section 5 summarizes the analyses. Aerospace personnel and the satellite contractor came to a similar conclusion: that the uplink and downlink (to and from the satellite) using small RTS stations with a 33-ft antenna have adequate link margin. In normal mode, worst-case LEO-Sat and nominal small RTS station parameters were used in the analysis. In contingency mode or tumbling mode, the worst worst-case parameters for LEO-Sat and for a small RTS station were used. A summary of the results of the analyses performed for the uplink and downlink communication paths are given in this paper.