Thermal management of modern electronics has become a problem of significant interest due to the demand for power and reduction in packaging size. Requirements of next-generation microprocessors in terms of power dissipation and heat flux will certainly outgrow the capability of today’s thermal control technology. LHPs, like conventional heat pipes, are capillary pumped heat transport devices. They contain no mechanical moving part to wear out or require electrical power to operate. But unlike heat pipes, LHPs possess much higher heat transport capabilities enabling them to transport large amounts of heat over long distances in small flexible lines for heat rejection. In fact, a miniature ammonia LHP developed for a NASA space program is capable of transporting 60W over a distance of 1 meter in 1/16”O.D. stainless steel tubing. Therefore, miniature LHPs using water as the working fluid are excellent candidates to replace heat pipes as heat transports in electronic cooling systems. However, a number of operational issues regarding system performance, cost, and integration/packaging must be resolved before water LHPs can become a viable option for commercial electronics.
This paper presents a mathematically rigorous, subspace projection-based reduced-order modeling methodology and an integrated framework to automatically generate reduced-order models for spacecraft thermal analysis. Two key steps in the reduced-order modeling procedure are described: first, the acquisition of a full-scale spacecraft model in the ordinary differential equation, and differential algebraic equation, forms to resolve its dynamic thermal behavior; and second, reduced-order modeling to markedly reduce the dimension of the full-scale model. Specifically, proper orthogonal decomposition in conjunction with a discrete empirical interpolation method and trajectory piecewise-linear methods are developed to address the strong nonlinear thermal effects due to coupled conductive and radiative heat transfer in the spacecraft environment. Case studies using NASA-relevant satellite models are undertaken to verify the capability and to assess the computational performance of the reduced-order modeling technique in terms of speedup and error relative to the full-scale model. Reduced-order modeling exhibits excellent agreement in spatiotemporal thermal profiles (less than 0.5% relative error in pertinent timescales) along with salient computational acceleration (up to two orders of magnitude speedup) over the full-scale analysis. These findings establish the feasibility of reduced-order modeling to perform rational and computationally affordable thermal analysis, develop reliable thermal control strategies for spacecraft, and greatly reduce the development cycle times and costs. Nomenclature A = conduction exchange matrices C = thermal capacitance matrix D = scatter matrix of thermal loads Q = heat flux R = radiation exchange matrices T = temperature vector, K t = time, s U = projection space u = independent thermal inputs Subscripts r = quantity in reduced dimension space s = thermal links between the nodes and the isothermal objects t = time-varying quantity
Diane ThiesLockheed M a r t i n Space Operations AbstractThe Terra spacecraft is the flagship of NASA's Earth Science Enterprise. It provides global data on the state of atmosphere, land and oceans, as well as their interactions with solar radiation and one another. Three Terra instruments utilize Capillary Pumped Heat Transport System (CPHTS) for temperature control: Each CPHTS, consisting of two capillary pumped loops (CPLs) and several heat pipes and electrical heaters, is designed for instrument heat loads ranging from 25W to 264W. The working fluid is ammonia. Since the launch of the Terra spacecraft, each CPHTS has been providing a stable interface temperature specified by the instrument under all modes of spacecraft and instrument operations. The ability to change the CPHTS operating temperature upon demand while in service has also extended the useful life of one instrument. This paper describes the design and on-orbit performance of the CPHTS thermal systems.
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