and heat sinks 20 and 26 this common path eliminates the need for individual paths that would pose a space and weight problem for the system which is intended for remote space surveillance applications the figure illustrates an optional second symmetrical thermal switch 28 shortened which would be identical and connected for redundancy fig3 illustrates a heat sink 20 which has the form of a prior art heat pipe which dumps heat collected from the heat pipe array 14 this structure is more fully described in u s pat no 4 470 451 issued on sep 11 1984 to the present assignee the body of heat sink 20 includes a main body 27 extending perpendicularly from a flange 30 within the body exists a first channel 32 having circular cross section and which serves as a vapor channel the wall of the vapor channel contains a multiplicity of circumferential grooves 34 which are schematically illustrated these grooves extend along the length of the vapor channel over which heat rejection takes place cryocooler 22 is mounted to flange 30 and heat transfer occurs between the metallic body 27 of the heat sink 20 and the cryocooler 22 when the cryocooler is operating the body 27 of the heat sink 20 further has a second channel existing in parallel spaced relationship to the first channel and having a somewhat smaller diameter the second channel is a liquid channel 36 and is interconnected with the vapor channel 32 via passageway 38 in the event that cryocooler 22 is operative in the system vapor in channel 32 will condense and the resulting condensate liquid will flow into the circumferential grooves 34 then into the connecting passageway 38 and then into the liquid channel.