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Loop heat pipe
Compared to the ordinary heat pipe, which is a rigid, monolithic structure with continuous internal capillary wick structure, the Loop Heat Pipe (LHP) needs only capillary wicks at the evaporator and the reservoir.  
Principle of a loop heat pipe
Principle of a Loop Heat Pipe
The LHP technology has since 2000s gained wider acceptance and is baselined as heat transfer element for the deployable radiators (for example for future telecommunication spacecraft) which need some structural flexibility for the deployment as well as long heat transport lines to transport heat from remote satellite payloads to the large radiating surfaces. The use of several LHPs could also replace the relatively complex three-dimensional heat pipe networks for the thermal control of bulky and highly dissipative satellite payloads not directly mounted behind the satellite radiator surfaces.
COM2PLEX experiment
COM2PLEX experiment
Like heat pipes, the LHPs operating with ammonia as working fluid are currently the most popular thermal products for the thermal control of high powered telecommunication satellites (it is an enabling technology for the two-phase deployable radiator). LHP operating at the temperature range lower than that of ammonia is also considered as an enabling technology for some scientific satellites with highly limited power budget by exploiting the loop shut down feature.
Minitherm experiment on-board FOTON M2
Minitherm Experiment on-board FOTON M2
ESA is currently funding the development and flight experiments of high performance LHPs, LHP-based deployable radiators, the flight experiment of miniaturised LHP as well as the lower and upper extension of the LHP operating temperature range, flat LHP evaporator (instead of the classical cylindrical evaporator body) and novel composite wicks.
Minitherm experiment on-board FOTON M2
Minitherm Experiment on-board FOTON M2
A very successful flight experiment COM2PLEX took place in early 2003 where three different LHP designs were tested in microgravity conditions for nearly 15 days onboard the US Space Shuttle.
Last update: 27 March 2007

Related links
ARTES-8 High performance loop heat pipeARTES-8 Lightweight deployable radiator structureDeployable radiator flight experiment on-board AlphasatThermal analysis developments for the Large Platforms Mission ProgramBroadband data relay flight experiment using LHP on-board AlphasatFOTON M2 - Minitherm flight experiment (1)FOTON M2 - Minitherm flight experiment (2)FOTON M3 - TEPLO flight experiment (1)FOTON M3 - TEPLO flight experiment (2)COM2PLEX flight experiment
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