Thermal, Avionics, and Power Considerations for Designing a Nuclear Thermal Propulsion Flight Demonstrator

As part of the Appropriations Bill passed by the US Congress in February 2019, NASA was instructed to develop a nuclear thermal propulsion (NTP) flight demonstrator by 2024. [4] In response to this directive, the Advanced Concepts Office (ACO) at Marshall Space Flight Center (MSFC) was tasked with beginning concept studies for the flight demonstration (FD) mission. During the NTP study formulation, two philoso- phies emerged with regards to FD concept design. The first, Flight Demo 1 (FD1), strictly observes the 2024 schedule requirement at the expense of lower engine performance than expected of theoretical NTP engines. The second concept, Flight Demo 2 (FD2), relaxes the schedule requirement to allow for higher engine performance and more traceability to future operational systems. Both the FD1 and FD2 concepts present considerable challenges for subsystem design, specifically in the areas of thermal control, avionics, and power. To guard against undesired graveyard orbits, a requirement to keep the NTP engine and the reaction control system (RCS) separate was put in place. As a result of this requirement, the avionics subsystem must provide separate command and data handling (CDH) and instrumentation for each propulsion system. In-space instrumentation and monitoring of a NTP system has never been done before, necessitating the development of novel strategies and unique hardware. The heating rates produced by the NTP engine are extremely high, leading to difficulties with thermal control. The FD1 concept utilizes high-pressure gaseous hydrogen (GH2), which is largely insensitive to temperature fluctuations. The FD2 concept, however, utilizes cryogenic liquid hydrogen (LH2) which must be kept stable near 20 Kelvin. A high-performance thermal control system (TCS) will be required to ensure all components and subsystems are maintained within their operational temperature ranges. This paper will highlight the thermal, avionics, and power solutions required for the full scope of challenges for a NTP flight demonstrator.