Deep space missions are becoming more prevalent, and yet current propulsion technologies are not fit for them. Nuclear electric propulsion is one of the possible propulsion methods, however currently at a rather low efficiency (in addition to other problems caused by nuclear).
The paper proposes a deep space probe with nuclear electric propulsion that utilises an advanced thermoelectric generator power conversion system. Experimentation thus shows 20-50x electrical conductivity increase, which results in much higher efficiency.
The idea uses the model mission of travelling to Europa to illustrate its feasibility. Called SPEAR (Swarm-Probe Enabling ATEG Reactor), the mission should utilise the novel NEP to fly a probe to Europa, which then launches a swarm of cubesats to analyse and study the Jupiter's moon for signs of life in its subterranean ocean. The advanced TEG approach allows for reduced mass and reduced power levels, thus less propulsion.
Their proposed NEP has many advantages – it is cost-effective, the available power does not degrade (as is the case with solar panels) and the available power exceeds traditional radioisotope power sources. SPEAR estimated power in deep space is 3kW electric power.
The nano-reactor uses low-enriched uranium, which makes it accessible also to industry and academia by avoiding the limitations and regulations of high-enriched uranium. The reactor is 15kW with 3kW electrical 12kW thermal energy. Lithium hydride is used in the core to keep the weight down. This also decreases the temperature.
Thermoelectric generators comprise of thermoelectric materials that form a couple. Multiples of couples are strung together and current is produced based on the temperature change between the materials. What is proposed in this paper is to raise the conductivity of the materials by radiation from the reactor. The radiation ionises atoms in the target material, freeing up electrons, which in turn raises electrical conductivity.
While performing experiments, the study concluded that even small changes in conductivity greatly enhance efficiency and figure of merit. ATEG performance must be researched and validated further, but it can be said with confidence that ATEG conversion technology with nano-reactor paves the way for deep space exploration.
Source:
(2021) Novel Deep Space Nuclear Electric Propulsion Spacecraft, Nuclear Technology, 207:6, 866-875, DOI: 10.1080/00295450.2020.1832814