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Advanced thermal management systems are one of the key technologies needed for future applications within the framework of the NASA Authorization Act 2005. This Act specifies that a programme shall be established to develop a sustained human presence on the Moon, including a robust pre-curser programme to promote exploration, science, commerce and US pre-eminence in space, and as a stepping stone to future exploration of Mars and other destinations. This paper will elucidate the development of two-phase thermal management systems for Moon and Mars applications, using data obtained from experiments with terrestrial scale-model systems, built according to the thermal-gravitational modelling and scaling laws (derived from dimension-analytical similarity considerations). It will include also important supporting issues, like the compilation of flow pattern maps at various gravity levels and writing down the constitutive heat and mass transfer equations for these maps.

Two mechanically pumped two-phase test rigs were built at NLR in order to experimentally study critical issues of spacecraft two-phase thermal management systems: a 5 kW, 31 mm ID, freon loop, focusing on the critical components of the ESA Two-Phase Heat Transport System. a 300 W, 4.93 mm ID, ammonia loop, to support the development of the ESA Capillary Pumped Loop Experiment (for the in-orbit demonstration of two-phase heat transport system technology) and to experimentally support two-phase thermal modelling and scaling activities. The rigs are described in detail. Typical test results are presented.

In order to demonstrate two-phase heat transport system technology in orbit, the Dutch-Belgian Two-Phase eXperiment TPX was successfully flown as Get Away Special G557, aboard STS60, February 1994. Based on TPX conclusions and lessons learned, a reflight experiment TPX II is being developed in order to usefully fill the time gap between TPX and possible future full-scale Capillary Pumped Loop flights. The characteristics of TPX II, intended to fly early 1998, are discussed in detail: configuration and component changes, updates of objectives/scenario, current status, results of pre-launch (components) testing and outlook.

Two-phase heat transport systems are currently considered for the thermal management of future large power spacecraft. The monitoring of the quality, being the relative vapour mass content, of the two-phase mixture at various locations in the system, is valuable - possibly indispensable - for the proper operation of such a system. This paper reviews concepts for quality monitoring. Only a few concepts turn out to be suitable for spacecraft applications. Promising concepts are based on the capacitance, sonic velocity and index of refraction. These concepts are described and quantitatively analyzed. Applicability, advantages, restrictions and some hardware aspects are discussed.