ATS-6 Flight Performance of the Advanced Thermal Control Flight Experiment

The Advanced Thermal Control Flight Experiment (ATFE) was launched aboard the Applications Technology Satellite-6 (ATS-6) on May 30, 1974. ATFE is designed to demonstrate the thermal control capability of a thermal diode (one-way) heat pipe, a feedback-controlled variable conductance heat pipe (FCHP) and a phase-change material (PCM). The experiment has been in almost continuous operation since launch. Flight data for the different operational modes are compared to ground-test data, and the performance of the individual components is analyzed. The system´s performance with and without feedback control is also compared. Finally, the ATFE´s behavior from launch through May 31, 1975, is presented. All thermal control components are performing as predicted for the existing flight environment. However, the daily reservoir and radiator temperatures during peak solar input are greater than those experienced in the ground acceptance tests. These increased temperatures have resulted in a loss of control by the FCHP for several hours around the period of maximum insolation. The higher temperatures are apparently due to contamination and/or degradation of the second surface mirrors which cover the reservoir and radiator.