As NASA continues the exploration of deep space, there is a need for safe, reliable, and long-lasting source of energy. Solar cells, which are useful at the inner solar system, cannot provide adequate power for a spacecraft once it has passed beyond Jupiter's orbit. For missions to the outer planets, NASA has relied on radioisotope thermoelectric generators (RTGs) using 238Pua s a heat source. RTGs are an excellent power conversion technology but, unfortunately, 238Pu is a potential environmental hazard. In the past, the use of 238Pu has generated much controversy and turmoil. Its use in future missions is doubtful because of environmental concerns. This paper presents calculations performed with MCNP for a power source that will take advantage of the low temperatures found in deep space
