A Coupled Approach to the Design Space Exploration of Nuclear Thermal Propulsion Systems

Summary

Nuclear Thermal Propulsion (NTP) systems have been a technology of interest to space exploration since as early as the 1950s due to their potential for improved efficiency as compared to traditional propulsion systems while being able to produce comparable amounts of thrust. More recently, NTP system have been identified as a promising candidate for future manned and un-manned missions to Mars by NASA in the Mars DRA 5.0 document. Moving towards a sustainable human presence on interplanetary destinations, there is a need to support such analysis with appropriate tools and capabilities. One such capability is design space exploration which allows mission and vehicle designers to explore a continuum of possible mission and vehicle alternatives in a manageable manner.

The study of NTP systems is particularly challenging due to the highly coupled nature of the nuclear reactor to the surrounding propulsion subsystems and components. As a result, the conventional approach to the analysis of such systems tends to tackle the problem in a decoupled fashion where the reactor and the surrounding subsystems are treated seperately. Such an approach presents significant limitations due to the sensitivity of the reactor to the surrounding systems. The objective of this research project was to develop and demonstrate a novel methodology which allows for the coupled analysis of NTP systems, and using the resulting model to enable rapid design space exploration.

My Contribution

• Created a structure and plan for the development of a coupled NTP system model. I worked with various members of the student team as well as representatives from NASA-MSFC and Georgia Tech's School of Nuclear and Radiological Engineering to scope the project and identify associated deliverables.
• Created a code for the simplified cycle analysis of an NTP system to envelope the boundary conditions of the nuclear reactor within the NTP system. Using simplified thermodynamic relationship paired with various literatures values intended to be reflective of a real NTP system, I developed a MATLAB code to bound the design space that the nuclear reactor model would operate within for this project.
• Created and executed a Design of Experiments on the NTP NPSS model and used the outputs of this DoE to generate surrogate models. I then processed the DoE consisting of 20,513 simulation runs using the JMP software package to create surrogate models. These surrogate models were then used to enable a design space exploration exercise through the prediction profiler or the contour profiler methods.
• Created a code that uses the outputs of the NTP system model to provide insight with regard to the performance of a hypothetical NTP powered crewed Mars Transfer Vehicle (MTV) launched on SLS Block 2 or Starship. Using the architecture proposed in the NASA Mars DRA 5.0 document, I created this tool to perform the 1st order sizing of a crewed MTV for a variety of heavy launch vehicle options.
• Published and presented the work completed as part of this paper to the 2020 AIAA Propulsion and Energy conference as first author.

Design Space From Surrogate Models

Output MTV from Sizing Code

Paper Abstract

Nuclear Thermal Propulsion (NTP) is identified as one of the preferred propulsion technologies for future manned missions to Mars and other interplanetary destinations. NTP systems can improve the returns and mitigate the risks of such missions by reducing travel time and improving payload capacity as compared to traditional chemical propulsion systems. Due to the complexity and tightly coupled nature of the nuclear reactor and surrounding NTP subsystems, the traditional decoupled approach to NTP system analysis is inadequate. A new approach is needed to enable a high-fidelity design space exploration exercise for NTP systems. The approach outlined in this paper will address an integrated model of the reactor and supporting subsystems. This model, along with the incorporation of Design of Experiments and Surrogate Modeling, will allow for the exploration of the performance of a large number of NTP system designs with respect to metrics such as specific impulse and thrust to weight ratio. The subsystems analysis is handled by Numerical Propulsion Systems Simulation (NPSS) while reactor modeling is conducted using various numerical codes. This paper proposes and demonstrates a coupled design space exploration approach for NTP systems and uses these findings to consider vehicle-level implications.