a passive thermal control enclosure for transporting and storing payloads in earth orbit includes an inner box - like enclosure surrounded by an outer box - like enclosure with insulation in the space between the enclosures . the walls of the inner enclosure are fiber - matrix composite skins with honeycomb sandwiched therebetween . each enclosure has its own door latched closed by releasable latches formed in opposed pairs that can be operated without any net force on the operator . packs of phase change material are placed into the inner enclosure with the payload . the pcm is contained in flexible packages . the packs of pcm are removed when they melt and replaced with fresh packs , and the melted packs preferably are re - frozen on - board the orbiting spacecraft . freezing preferably is carried out such that the freeze front moves substantially in only one direction from one end of the pack to the other .