Spacecraft telemetry link performance in a transfer orbit

There are several critical periods early in the mission of a geo-stationary communication satellite. The first is the period from launch vehicle ignition until the upper stage final successful burn. The second is after the above span until the vehicle reaches its final altitude of a synchronous orbit. For a nominal low thrust apogee boost ascent subsystem during that later time, almost continuous telemetry is mandatory. This is especially true during the crucial periods of main engine burns and attitude correction phases. Maintaining a strong telemetry link throughout this phase requires an adequate RF signal link from the spacecraft to a ground station in the telemetry RF channel. An analysis of this link performance during each orbit until final position has two major aspects. One, the location of the spacecraft in relation to the ground tracking station at each moment in the mission is a matter of geometry and Keplerian physics. The other is the RF signal and its supporting subsystems, both on the ground and aboard the vehicle. The fundamental theoretical considerations or both the orbit parameters and radio link components are examined and then the individual parameter sensitivities are analyzed. Next, a nominal cast for a generic mission is studied. This survey considers the telemetry performance during each major stage of the flight from the launch through the transfer orbit to the postinjection period to the final orbit. Then abnormal situations due to both orbit and RF faults are examined. Finally, some design and operation concepts which may lessen the impact of the previous anomalies, are presented.