Nuclear Electric Propulsion (NEP) has been considered for crew and cargo class missions to Mars for more than six decades based on fuel efficiencies 10 to 20 times greater than is currently achievable with conventional propulsion. An NEP system is comprised of five technology elements that include: the reactor and coolant subsystem, Power Conversion Subsystem, Power Management & Distribution Subsystem, Electric Propulsion Subsystem, and the Primary Heat Rejection Subsystem. However, recent independent assessments by the National Academy of Science, Engineering, and Medicine (NASEM) and NASA Engineering and Safety Committee (NESC) have concluded that all five elements remain at low technology readiness levels. Both studies urged Research and Development (R&D) to reduce the uncertainty that exists regarding each element’s contribution to overall system specific mass per unit power (a, kg/kWe), a key measure determining if an NEP architecture closes. The Primary Heat Rejection Subsystem (PHRS) is the largest and most massive NEP technology element, with a radiative surface area greater than 2,500 m² and constituting 40-60% of the total NEP mass.

In previous mission architectures, ground rules mandate stowage of the entire NEP system (reactor, truss, electric propulsion, propellant) under a single launch shroud. This forces employment of massive, folding radiator arrays with complex mechanisms to achieve the necessary radiating surface area. These conceptual PHRS designs and commissioning schemes (commissioning defined here as: the achievement of an operational PHRS in-line with reactor startup) are acknowledged as non-optimal. They constrain architectural flexibility, limit vehicle performance, and have been identified by Glenn Research Center (GRC), the Space Nuclear Propulsion (SNP) project, and NASA Headquarters as a major NEP architectural risk driver. By including the advantages of in-Space Assembly (iSA) to the design process it is expected the constraints will be removed.

The Modular Assembled Radiators for NEP Vehicles (MARVL) will transform the NEP PHRS from a relatively fixed mass element with little margin for improvement into a powerful lever for mass, cost, and development risk reduction by:

1. Developing a rigorous analysis framework to evaluate PHRS commissioning schemes including deployable systems, robotic In-Space Assembly (iSA), and a combination thereof.
2. Developing an integrated simulation framework to evaluate full-scale PHRS commissioning operations and performance in relevant space environments.
3. Designing a high-temperature radiator array module based on lightweight radiator technologies (e.g., heat pipes, panel materials) previously developed at GRC.
4. Designing a high-temperature fluidic interface capable of heat transfer with the reactor liquid metal trunkline (e.g., module-to-module, module-to-trunkline).

As stated in the Moon-to-Mars (M2M) Architecture Definition Document (ESDMD-001), the first development challenge of any Mars architecture is the transportation system that can deliver crew and cargo to Mars and back. MARVL impacts M2M objectives including developing transportation systems for crew operation to Mars (TH-5), delivering large surface elements to Mars (TH-6), and returning large cargo mass from Mars to Earth (TH-12). MARVL’s developments in Mars transportation, iSA, heat transport, and heat rejection align with both NASA and national technology goals and objectives. Further, the inclusion of In-space Servicing, Assembly, and Manufacturing (ISAM) as proposed aligns with the White House’s ISAM national strategy. Based on direct conversations with NASA Principal Technologists (PT), MARVL will contribute to the closure of seven key STMD capability gaps.

MARVL will also foster new NASA technical expertise in space-rated high-temperature fluid interfaces, which currently does not exist in industry or within NASA and will be necessary for future systems. This technology could be infused into future Lunar and Martian surface-based nuclear power plants; the Fission Surface Power (FSP) project has expressed great interest in this technology. Additionally, SNP is highly integrated with the Department of Defense (DOD) and other government agencies with interests in nuclear propulsion that would benefit from, and likely leverage, MARVL-developed capabilities. The simulation framework will be reused as the NEP design is iteratively updated, and the individual MARVL subsystem models developed could be applied towards simulating other in-space concepts (e.g., cislunar tugs, other transit vehicles, etc.).