Lightweight Nuclear Electric Space Propulsion With Ten Times the Power

The Swarm-Probe Enabling ATEG Reactor, or SPEAR, is a nuclear electric propulsion spacecraft that uses a new, lightweight reactor moderator and advanced thermoelectric generators (ATEGs) to greatly reduce overall core mass. This will subsequently require a reduction in operating temperatures and reduce the total power levels achievable by the core. However, the reduced mass will require reduced power for propulsion, resulting in a small, inexpensive nuclear electric spacecraft.

The ATEG system they previously proposed would have 15,000 watts of thermal energy about 3000 watts of electrical energy. The best RTG that NASA has flown was about 300 watts. GPHS-RTG or General Purpose Heat Source — Radioisotope Thermoelectric Generator, was used on Ulysses, Galileo, Cassini-Huygens, and New Horizons missions. The GPHS-RTG has an overall diameter of 0.422 m and a length of 1.14 m. Each GPHS-RTG has a mass of about 57 kg and generates about 300 Watts of electrical power at the start of mission (5.2 We/kg), using about 7.8 kg of Pu-238 which produces about 4,400 Watts of thermal power.

The phase I effort showed that a low mass probe was feasible and that key component- the ATEG conversion system- had extremely high potential for efficient, solid-state power conversion.

The Phase II effort will build on these findings to demonstrate a functioning ATEG unit and show the increased efficiency in a working unit. This will be done by creating a boron based ATEG and operating it at a test reactor at KSU to simulate the radiation field created by the SPEAR. The ionizing radiation will improve the material properties of the TEG feet (as demonstrated in phase I) and show unequivocally that the performance improves.

The major tasks in this phase will include:

Demonstrating performance of the improved ATEG units.
Improving the computational model for the ATEG performance prediction so that new combinations of materials can be used in the future.
Optimizing the SPEAR reactor to minimize mass and cost.
Identifying detailed trajectory and mission info for orbital insertion and Cubesat orbits to gather data from Europa plumes.
Creating a low mass NEP system will open many new opportunities for research in the future. Using smaller rockets will provide flagship class results with much smaller missions. Additionally, the development of the ATEG units and small reactors can provide power to other rovers, surface bases, satellites, or a number of other missions.
Development of the SPEAR probe will show that inexpensive, effective nuclear technologies can be achieved for future space exploration.

Prior Work on Space Nuclear Power and Propulsion

Here is a 2015 presentation – Radioisotope-Based Propulsion System Enabling Exploration with Small Payloads. Nuclear and Emerging Technologies for Space 2015, Albuquerque, New Mexico