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

Abstract

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 feedbackcontrolled variable conductance heat pipe (FCHP) and a phasechange 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.The Advanced Thermal Control Flight Experiment (ATFE) is providing the first zero-g flight data for the performance of a thermal diode heat pipe [9] and an electrical feedback-controlled heat pipe [6]1. The temperature stability derived from the melting and freezing of octadecane is also being evaluated. Experiment ObjectivesThe ATFE is designed to demonstrate the thermal control capability of a thermal diode (one-way) heat pipe, a phase-change material (PCM) for thermal storage, and a feedback-controlled variable conductance heat pipe (FCHP). The experiment permits evaluation of these components on an individual basis and as an integrated temperature-control system. In addition to developing flight-qualified hardware for future thermal control applications, specific ATFE performance objectives were as follows.1) Thermal diode: Demonstrate reverse-mode diode operation (determine shutdown energy and OFF conductance), determine effect of zero-g environment on diode shutdown characteristics, and demonstrate forward-mode heat pipe operation (determine forward-mode thermal conductance).2) Phase-change material: Demonstrate temperature stability derived from melting and freezing of a PCM, determinie the stability of the melting and freezing points in the zero-g environment, and evaluate the effect of the zero-g environment on the thermal conductance of the PCM package.3) Feedback-controlled heat pipe: Demonstrate the ability of the FCHP to provide temperature stability with variations in heat load and effective sink temperature, demonstrate the ability of the FCHP to perform as an ON/OFF thermal switch, and establish its variable conductance behavior in flight. Experiment Description