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The thermal design of a high-power C-band phased array with integral solid-state amplifiers, and its integration into a three-axis-stabilized spacecraft, are discussed. A thermal design has been developed employing fixed-conductance heat pipes and an embedded heat pipe radiator panel. The design tradeoffs and problems encountered in removing 2,000 W from a 1-m-diameter array are described, and possible solutions are presented. The highly concentrated heat source associated with solid-state amplifiers has emphasized the importance of minimizing MMIC chip internal thermal resistance in terms of the overall thermal control subsystem weight. Thermal test verification issues and concerns with 1-g operation in integrated spacecraft testing are also addressed.

The embedded heat pipe radiator panel is the thermal foundation for the present and future-generation three-axis-stabilized, geosynchronous communications spacecraft. This paper discusses design guidelines and analyzes the thermal performance of some commonly used heat pipe/panel configurations. Among the designs considered are an in-plane design with heat pipes bonded to each other in overlapping sections, an in-plane design with heat pipes crossing on two levels, and externally mounted heat pipes. The thermal performance parameters are quantified and compared as a function of radiator area and weight.

The heat dissipated during various rates of charge, overcharge, and discharge of a nickel-hydrogen (Ni/H2) cell was measured using a radiative-type calorimeter. A flight configuration-type Ni/H2 cell was prepared for this study by wrapping the 4-in.-wide cylindrical portion with heater tape and insulating the two dome ends with 10 layers of aluminized Mylar. The radiating surface was limited to the cylindrical portion of the cell. The calorimeter consisted of a liquid-nitrogen-cooled copper chamber arranged inside a vacuum jar. Since the experiments were not performed under isothermal conditions, the term was included in the equation used to calculate heat dissipation. Experimentally measured heat values were compared against those calculated using a thermoneutral potential of 1.51 V.

The thermal dissipation of a 48-Ah nickel-hydrogen (Ni/H2) battery cell has been derived by testing it in a controlled radiative environment. Temperature profiles and corresponding cell thermal dissipations are presented for different battery discharge/charge cycles. A comparison between test results and theoretical predictions for battery dissipation is presented. The thermal capacitance of a Ni/H2 cell is computed from both test data and tabulation of individual cell component weight and specific heat.

An INTELSAT-funded experiment to determine the solar absorptance of optical solar reflectors (OSRs) as a function of incidence angle has confirmed the initial findings from flight data reduction on the COMSAT COMSTAR Beacon experiments. The OSR solar absorptance is shown to increase with increasing sun incidence angle. The magnitude of the increase for a body-stabilized spacecraft in geosynchronous orbit during peak solar illumination and a 66.5° incidence angle is 20 percent larger than the value normally derived from spectrophotometer measurements. These results help to explain the increases in spacecraft temperature and OSR degradation observed on many spacecraft immediately after launch which heretofore have been attributed to outgassing effects.