Abstract: A high efficiency deployable heat radiator system for radiating heat generated at a source of heat aboard an orbiting spacecraft or like vehicle is described which comprises a first subsystem for circulating liquid heat exchange medium into heat exchange relationship with the heat source and for conducting vaporous medium generated at the heat source to a manifold; one or more interconnected movable radiator panels each including a pair of spaced wall members defining heat radiating surfaces; a plurality of heat pipes each having an elongated condenser end disposed between wall members of the radiator panels and in heat exchange relationship with the heat radiating surfaces; a manifold for conducting vaporous medium from the source into heat exchange contact with the evaporator ends of the heat pipes; an interface structure interconnecting the evaporator end of each heat pipe with the manifold and including a tubular member enclosing each evaporator end for conducting vaporous heat exchange medium into contac