Abstract: A locking mechanism for securing together two separable pieces, such as two components of a spacecraft during launch. An elongated rod of heat contractible material provides a single active member which changes from a locking length to a contracted length upon application of sufficient heat to raise the temperature of the rod from below to above its transition temperature. Mounting and housing structures are provided for mounting and heating this transducer rod and an apertured member or recessed stop is provided for engaging a projecting portion thereof. Heating may be provided by redundant, electrically actuated heating coils surrounding a major portion of the rod length. At least a major portion of the transducer rod may be made of 55-Nitinol.