SPHERICAL RADIOISOTOPE THERMOELECTRIC GENERATORS - AN APPROACH TO HIGH SPECIFIC POWER DEVICES.

A concept for attaining high specific power radioisotope thermoelectric generators (RTG's) is described which features the close packing of thermoelectric elements around the surface of a spherical heat source, thereby reducing the need for conventional thermal insulation systems. Eliminating the thermal insulation allows the thermoelectric element length (and associated thermopile weight) to be reduced without incurring excessive bypass heat losses. An attendant advantage accrues by the elimination of the thrmal insulation as a source of overall system gaseous impurities. One of the design constraints is that the spherical heat source volume must be sized to match the surface heat flux requirementimposed by the thermoelectric converter which envelops the heat source. A preferred embodiment of the spherical RTG concept is described along with component weight breakdowns for output power levels ranging from 250 to 575 watts including weights for the heat source, thermal and impact protection members, thermoelectric converter, outer shell and spring assembly hardware, and radiator. The results of design optimization analyses are described and indicate that specific power levels of four to six watts(e) per pound are attainable using the TPM-217 thermoelectric alloys operating between 225 and 800 C.