Thermal modeling for the Triton Hopper

Abstract

NASA is currently designing a conceptual vehicle to explore the surface and atmosphere of Triton, Neptune’s captured Kuiper Belt Object, under a NASA Innovative Advanced Concepts (NIAC) Phase 2 study. This tholin-rich moon is dynamic, with an atmosphere, active geysers, and a unique “cantaloupe” terrain. Based on observations from Voyager-2, the surface of Triton is at temperatures between 33 and 38 K and it has a slight atmosphere that varies in pressure depending on location between equator and pole. A vehicle is being proposed which relies on scavenging solid and gaseous nitrogen and for use as a propellant. Under the current conceptual design, nitrogen is collected, liquefied, gasified, pressurized, and then fed into warm gas rocket nozzles to provide thrust to hop from one location to the next. Gaseous nitrogen is collected using cryopumping. This paper presents the design and analysis of the passive thermal system for the collection tank and active cryocooler system used to cryopump nitrogen from the rarified atmosphere to a tank. Models are developed for parasitic heat leak, multi-layer insulation heat leak, and structural heat leak to determine the required cryocooler power and mass as a function of multiple parameters.