Nuclear propulsion and space microreactors
Creators: name: Elshater Mohamed, Shady
Publisher: name: ETH Zurich
Year: 2023
Subjects: Nuclear fission
space propulsion
nuclear propulsion
Aerospace
neutronics
microreactor
space power
info:eu-repo/classification/ddc/620
Engineering &amp; allied operations

description: This thesis started with the goal of developing SPARTACUS, a toolbox to assess the feasibility of a  space mission propelled by nuclear electric propulsion (NEP) or nuclear thermal propulsion (NTP), and how they compare with classical chemical rocket propulsion. While NEP uses a very high specific impulse (ISP) electric thruster powered by a nuclear fission reactor to generate low-thrust for long periods of time, NTP uses a fission reactor core to heat up and push a propellant through a nozzle generating a high-thrust impulse. Chemical propulsion is also based on high-thrust impulses, although with about half the ISP of NTP.

In the first phase, low-thrust and high-thrust orbital trajectories based on a simple two-body model were generated in order to obtain the propellant and power requirements as a function of the duration of flight. Both low-thrust, obtained with a numerical direct solver and two heuristics, and high-thrust, obtained with a Lambert solver, solutions were validated with literature references. Further, the different types of propulsion and their specifications were discussed. Some important features not implemented due to time constraints are solar electric propulsion (SEP) transfers and gravity assists.  

In the second phase, the basics of a nuclear fission microreactor, needed to power a NEP system but also usable for fission surface power, were presented. A survey of past space microreactors in the kWe to MWe range was followed by a more detailed analysis of its main components, namely reactor core, shielding, power conversion, and radiator. Since the ultimate goal will be to assess a NEP mission powered by a custom-designed fission reactor, it was decided to first validate the neutronics analysis of the reactor core and shielding with the LANL reactor "KRUSTY" as reference. Fission spectrum, reflector worth, fuel-temperature reactivity, dose behind shielding, and other relations, showed a good level of agreement with literature values. Many pieces are still missing in order to model and design a complete reactor, also due to the different design options existing.

Finally, the developed SPARTACUS tool, in the form of a web app with UI, was used to compare the capabilities of NEP, NTP, or chemical propulsion for missions to Mars, Jupiter, and Saturn, as a function of the reactor specific mass and several other parameters. Additional tools such as plotting the optimal ISP or the maximum reactor specific mass for a mission are also implemented. The results highlighted the strengths of NEP, suited for long high-Delta V missions requiring high payload mass ratios, and its weaknesses, such as the inefficiency of low-thrust when first escaping from the strong gravitational pull of a planet during a so-called escape spiral. A possible mitigation is the use of a bimodal system, which can alternate between high-thrust NTP and low-thrust NEP in a single core.