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This paper will discuss thermal control examples, which were considered to be (very) promising in the past, whose further developments were stopped due to number of reasons, but which currently are regaining attention resulting in a re-start of R&D activities, which must lead to applications in real spacecraft. The various issues are electro-hydrodynamic and electro-osmotic control of heat pipes and of capillary and mechanically pumped single- and two-phase thermal control loops, switching by electro-hydrodynamic, electro-osmotic, and the novel electro-wetting control, vapour pressure driven thermal control loops, thermal-gravitational modelling & scaling, and controlled rotating radial heat pipe joints. The revival of the old activities and the start of novel activities are considered to be important for near-future spacecraft thermal control applications.

A concise survey is given of international research done in the last decades for developing spacecraft-oriented (variable conductance) two-phase thermal control systems, based on passive or active control of fluid manipulation. The various methods of variable conductance heat pipe control are discussed, focusing on control using non-condensable gas. The historical development is given, including the arguments why these relatively simple two-phase thermal control systems often have been and will be the preferred solution to meet the large variety of different restrictions, induced by the typical requirement specifications of many, relatively low power (up to 5 kW) applications in space. The paper briefly mentions alternative control approaches considered in the past, while focusing on those that are regaining attention, i.e. systems, based on electro-hydrodynamics and electro-osmosis. It touches also a novel switching/pumping control alternative based on electric wetting.

The classic design of a loop heat pipe (LHP) usually includes a cylindrical evaporator design, where the heat generated at the wall has thermal/hydraulic contact with the surface of a cylindrical porous wick structure. Such a design is characterized by good technological and physical bases and a well-proven theory. It is capable to solve many practical tasks. However, also attempts to design a loop heat pipe with flat contacting surfaces between the heated wall and wick are of practical interest for applications for which the effective heat inputs to cylindrical evaporator surface is hardly realizable, or for which mounting surfaces require contact over a flat surface only. World wide there is only limited development of flat evaporator loop heat pipes [1]. Therefore this study can be called a novelty. Besides of technological development the basis for physical modeling of such loop heat pipe should be elaborated.

This paper discusses the thermal modeling activities as a design and development tool for the Tracker Thermal Control System, the mechanically pumped, carbon dioxide thermal management system for the AMS-2 Silicon Tracker. Main modeling topics are: radiator sizing and condenser development, set-point control and pre-heating issues with respect to the spatial and temporal temperature gradient requirements of the Tracker.

As two-phase flow and heat transfer is expected to strongly depend on the gravity level, a Two-Phase eXperiment has been developed for ESA to demonstrate two-phase heat transport system technology in orbit. TPX, a reduced-scale capillary pumped two-phase ammonia loop with a flat and a cylindrical capillary evaporator and an actively controlled reservoir for loop temperature setpoint control, included downscaled components of mechanically pumped loops: multichannel condensers, vapour quality sensors, and a controllable 3-way valve for vapour quality control exercises. The presented detailed evaluation of the experiment results obtained during the TPX flight on STS60, clearly proves the viability of two-phase technology for space.

Mechanically pumped two-phase heat transport systems are currently developed to meet the high power and long transport distance requirements of thermal management systems for future large spacecraft. Capillary pumped systems are being developed for applications with special requirements concerning microgravity disturbance level, temperature stability and controllability. As two-phase flow and heat transfer in a low-gravity environment is expected to differ from terrestrial behaviour, two-phase heat transport system technology has to be demonstrated in orbit. Therefore the Dutch-Belgian Two-Phase eXperiment TPX has been developed within the ESA In-Orbit Technology Demonstration Programme. TPX is a two-phase ammonia system, flown in the 5ft3 gaseous nitrogen filled Get Away Special canister G557, aboard STS-60.

Mechanically and capillary pumped two-phase heat transport systems are currently developed to meet the high power and long transport distance requirements of thermal management systems for future spacecraft. Compared to existing single-phase systems, two-phase loops offer important advantages: reduced overall mass and pumping power consumption, virtually isothermal behaviour, adjustable working temperature, insensitivity to variations in heat load and sink temperature, and high flexibility with respect to the location of heat sources within the loop. As two-phase flow and heat transfer in low-gravity environment is expected to (considerably) differ from terrestrial behaviour, the technology of two-phase heat transport systems and their components is to be demonstrated in orbit. Therefore a Dutch-Belgian Two-Phase experiment has been developed within the ESA In-Orbit Technology Demonstration Programme.

Mechanically and capillary pumped two-phase heat transport systems are currently developed to meet the high power and long transport distance requirements of thermal management systems for future spacecraft. As two-phase flow and heat transfer in a low-gravity environment is expected to (considerably) differ from terrestrial behaviour, the technology of two-phase heat transport systems and their components has to be demonstrated in orbit. Therefore a Dutch-Belgian two-phase experiment (TPX) is being developed within the ESA In-Orbit Technology Demonstration Programme TDP1. TPX concerns a two-phase ammonia system in the (5ft3, gaseous nitrogen filled) Get Away Special canister G-557. The system is a downscaled capillary pumped two-phase loop. It includes downscaled versions of mechanically pumped two-phase loop components: multichannel condensers and vapour quality sensors (plus a controllable 3-way valve for control exercises). The Critical Design Review status of TPX is discussed.