path thermosyphon a high conductivity carbon fiber material a high conductivity metal or the like heat storage subsystem 203 employs a phase change material 204 housed within sealed case 208 which changes phases e g from solid to liquid at a threshold temperature in response to heat input thereby acting as a heat storage unit or heat capacitor phase change material 204 is preferably selected based on among other things its fusion or transition temperature more particularly in a preferred embodiment phase change material 204 is selected such that its transition temperature is less than the maximum operating temperature of the heat source being cooled i e the source of heat input 110 in fig1 and greater than the steady state temperature of the heat source at its nominal heat emitting state depending upon the application acceptable phase change materials include for example various salt hydrates such as magnesium nitrate sodium acetate etc paraffin water methanol liquid nitrogen liquid ammonia and polyalcohols such as pentaglycerine and neopentylglyol sealed case 208 may be configured in any suitable shape and may be fabricated using a variety of materials e g plastics such as polypropelene epdm and polyolefin and or metals such as steel stainless steel copper aluminum and the like fins 206 are thermally coupled to the heat transfer subsystem 202 and are preferably distributed evenly and efficiently within sealed case 208 so as to reduce large open areas the fins may comprise any suitable material for example copper aluminum carbon fiber etc in the illustrated embodiment fins 206 are thin discs suitably bonded to heat pipe 202 which extends axially through.