Fusible heat sink for a cryogenic refrigerator

Claim 1

In combination with a missile guidance assembly having an outer skin forming the outer surface of the missile guidance system; said outer skin being adapted for securing to a missile; a detector, for the guidance system of the missile, within the outer skin; a cooling system, for said detector, including a cryogenic refrigerator having a hot cylinder, a cold cylinder, a crank system interconnecting the hot cylinder and the cold cylinder and a crankcase surrounding the crank system and a heat pipe system for transferring heat from the crankcase to the missile skin; apparatus for removing heat from the crankcase when the heat pipe system is inoperative, comprising: a heat sink, within the missile guidance skin; said heat sink including an annular housing member; said housing member being secured to the crankcase with a portion of the crankcase forming a wall of a heat sink housing; a fusible material, having a melting point within the range between 242° F. and 271° F., within said housing; means within said housing for providing a good heat transfer between the fusible material and the crankcase.