In August, 1995, the TOPEX/Poseidon satellite completed its third year in orbit and met its operational life requirement. The satellite TCS is performing as expected with the telemetry indicating that all components are operating within their allowable temperature ranges during normal mission modes. This paper assesses the performance of TCS from the start of the mission through 3 years in orbit at 1335 km altitude and 66.25° inclination. This orbit is in the Van Allen Belt in which few spacecraft fly. Specific attention is paid to environmental, operational, and attitude control conditions and their effects on the satellite thermal performance. The thermal telemetry data of each satellite module is discussed with respect to thermo-optical property degradation and the effects of varying orbital sun angles.