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Capillary Pumped Loops (CPL) are projected to be the primary heat transport device for the next generation spacecrafts and satellites. The major shortcoming of a traditional CPL system has been its inability to tolerate vapor and/or non-condensible gas (NCG) bubbles when they are present in the liquid side of the loop. The vapor/NCG bubbles ultimately caused the capillary pumps to fail. A novel CPL design concept, called Advanced CPL or A-CPL, was introduced to create deprime resistant capillary pumps. The main idea of the A-CPL was to generate a liquid flow through the capillary pump core to flush out vapor/NCG bubbles.

Like other spacecraft subsystems, the thermal control system had to comply with the following requirements: (i) robust/reliable in harsh environments, (ii) minimal power consumption, (iii) compact/lightweight, and (iv) long life even without maintenance. For this reason, passive two-phase heat transport technologies such as heat pipes, Loop Heat Pipes, and Capillary Pumped Loops became popular among spacecraft engineers. Future thermal requirements may outgrow the capabilities of the existing devices. The US Naval Research Laboratory is leading a research and development effort to produce advanced technologies for the thermal management of the Navyapos;s next-generation spacecraft and satellites.

Loop Heat Pipes have proven as reliable heat transports for spacecraft thermal control systems. NASA Goddard Space Flight Center in collaboration with NASA Jet Propulsion Laboratory recently proposed a miniature dual pump/condenser LHP system for use in future Mars missions. Results of a ground test program indicated that the dual pump/condenser LHP performed very well, but in a complicated manner. No analytical model was available to facilitate the design/analysis of this emerging technology. A generalized LHP theory will be presented in this paper along with the derived governing equations and solution scheme. Model predictions were made and compared with test data for validation.

The Loop Heat Pipe has become increasingly popular among spacecraft engineers for its operational reliability and robustness. At first glance, the LHP seems like a simple capillary-pumped heat transport device. In reality, the thermodynamics and fluid dynamics in the LHP form a complex system, especially during transient operation. The LHP performance varies with power input and sink temperature, but perhaps more importantly, with transitions from one condition to another. In addition, when multiple LHPs are thermally coupled, a change in one LHP can result in a detrimental effect on another. In this paper, model simulations of a thermal control system having two LHPs will be presented to show the system performance during the expected on-orbit thermal conditions of low Earth orbit.