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This paper shortly summarises the experimental results obtained since 2011 bya large European academic consortium for the scientific conceptualisation, thedefinition of the technical requirements, the generation of experimental data,and the validation of a numerical code, for the Pulsating Heat Pipes (PHP)experiment on the International Space Station (ISS). The PHP is a passive,wickless thermal device, whereby a two-phase fluid, forming liquid plugs andvapour slugs, moves with a pulsating or circulating motion inside a meanderingtube or channel. The PHP may have a very broad range of geometries (flat,tubular, 3D structured), it can dissipate heat from large areas, and it can besuitable for high power applications with low/medium heat fluxes. PHPfunctioning is based on the capillary effect, which provides the existence ofliquid plugs completely filling the channel cross-section, in a way that anyexpansion or contraction of the vapour slugs will naturally generate a movementof the fluid along the channel axis. For this, it is important that the channelhas a cross-section size below a given threshold, which depends on the liquidsurface tension and (for a static fluid) on the gravity acceleration. In space,when only residual accelerations are acting, such a static size threshold isvirtually infinite, while a finite dynamic threshold exists even in the absenceof gravity. The concept of a ''Space PHP'' was originally developed in 2014 bythe team, and from then 17 Parabolic Flight Campaigns (PFC) and 3 SoundingRocket (SR) experiments have been carried out to generate the data for thepreparation of an experiment targeting a Low Earth Orbit (LEO) mission. Both atubular and a flat plate PHP have been successfully tested in reduced gravityand on ground, by using different combinations of fluids and buildingmaterials. The need for having an experiment on a LEO environment is mainlybecause, during a PFC, only 22sec of reduced gravity are possible, which is aperiod below the characteristic time for reaching a steady state condition foralmost all of the tested devices. Instead, a steady state was reached using theSR campaigns: in this case however, only one experimental condition wasachievable, and long-duration data of the PHP performance still remains beyondreach. Several measurement methodologies have been used to characterise theSpace PHP, like infrared analysis, high-speed camera visualisation techniques,with data processed with different techniques, from wavelets to inverse heattransfer problem solution. The results clearly showed that PHPs are veryinteresting for space applications due to their simplicity of construction, thecapacity to transfer heat up to several hundred watts, a high power/weightratio, their geometrical adaptability, and, in particular, the Space PHP willbe a breakthrough technology for space thermal management.

Toward Low Earth Orbit (LEO) Applications: the Scientific Journey of the ''Space Pulsating Heat Pipe'' Experiments