The helical VHF command antennas are also located at Wallops. The commands and incoming telemetry are relayed between GSFC and Wallops through a communications satellite. The OCC has ultimate responsibility for the health and safety of the spacecraft and for all spacecraft engineering functions 24 hours per day. The OCC staff is in continuous voice communication with the Wallops tracking station technicians who operate the command and receiving antennas. IUE's orbit is frequently monitored to provide accurate pointing predictions for the ground commanding and receiving antennas.
Gravitational perturbations cause the gradual westward precession of the orbit's semi-major axis.
At this time, the large hydrazine jets are fired to slightly modify the semi-major axis so that the orbit drifts eastward again.