Advanced Heat Pipe Technology for Space Heat Transport and Rejection Technologies G. Y. EASTMAN, D. M. ERNST, R. M. SHAUBACH & J. E. TOTH Heat transfer considerations have a major impact on the viability and practicality of spacecraft and future space missions. Heat transport subsystems will carry primary heat from a heat source (nuclear or solar) to an electrical energy converter, unconverted heat to a radiator, and accomplish the radiant loss of this heat to space. Similarly, as the electrical power from the converter is changed back to heat in the power consuming systems, this low temperature heat must be transported and radiated. In systems envisioned to date, the mass of the heat transport subsystem has ranged from 25% to more than 50% of the power generation system mass. For example, in SP-100 thermoelectric power system currently in ground demonstration, approximately 1350 kg of the total system mass of 4580 kg is attributed to the heat transport and rejection subsystem. A failure of the heat transport subsystem either constitutes, or results in, a complete spacecraft powerplant failure. In short, the heat transport subsystem is one of several critical components that will determine the efficiency, life, reliability and success of a space power system. We believe that heat pipes will withstand their attack by the naysayers, promoting liquid droplet radiators, rotating belt radiators, balloons and other heat transport and radiator concepts and will increasingly be employed in future spacecraft to accomplish heat transport and heat rejection with low mass and low delta-T (high effectiveness). Furthermore, the state-of-the-art of heat pipes is in a period of rapid change, so that it is important to impart knowledge to a broad audience beyond the narrow community of heat pipe developers. The purpose of this paper is to present some of these recent developments and comment on their potential for future applications. High Evaporator Power Density An improved understanding of liquid and vapor flow within heat pipe wick structures, especially nonhomogeneous ones, has led to the demonstration of evaporative power density capability of tens of kilowatts per square centimeter with liquid metals as working fluids, and tens to hundreds of watts per square centimeter with less potent, lower temperature fluids. In general, the new trends of performance are from two to a hundred times those previously demonstrated and accepted. For example, the tungG. Y. Eastman, D. M. Ernst, R. M. Shaubach & J. E. Toth, Thermacore, Inc., 780 Eden Road, Lancaster, PA 17601, USA.
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