Nuclear thermal propulsion for crewed interplanetary travel is being thoroughly evaluated for its conversion to low-enriched uranium fuel. Previous studies successfully found that, at the full-scale level of 16kblf and greater, a nuclear thermal rocket fueled with LEU is possible without necessitating a significant mass increase. Up to this date, however, LEU has not been evaluated at smaller thrusts, which may be a desirable size for purposes such as small-scale qualification testing. Preliminary efforts during the Nuclear Cryogenic Propulsion Stage Program found that a 7.5kblf engine is the smallest size an HEU core could reasonably reach before more than halving the thrust-to-weight ratio. As LEU-NTP is inherently limited by its lower enrichment, and therefore lower U-235 density, the belief holds that LEU-NTP can only sustain comparable system masses at the higher thrust levels, where thermal hydraulic requirements limit the minimum size of an HEU core. Nevertheless, the point of diminishing returns for LEU-NTP relative to minimum thrust has yet to be concretely defined. The following paper begins progress towards this effort by attempting to convert the previously mentioned 7.5kblf HEU core to low-enriched uranium.
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