In the advanced technology program radioisotope heat sources were incorporated into an Integrated Radioisotope Catalytic Monopropellant Hydrazine Engine designed to maintain the catalyst bed above 200F in an earth orbiting space environment. The impact of ambient temperature starts is thus reduced without requiring additional electrical power. A limited development effort was conducted to upgrade a 5-pound thrust engine design originally developed during a TRW IR and D program. Iterations of the injector and headspace designs and variations to the catalyst bed were evaluated. Accelerated life testing of the selected design revealed a headscreen deformation problem and verified the design improvement incorporated to prevent recurrence.