Verification and Validation of a Cold Gas Propulsion System for the TALARIS Hopper Testbed

Abstract

The TALARIS (Terrestrial Artificial Lunar And Reduced gravIty Simulator) hopper is a small prototype vehicle currently being flight tested as an Earth-based testbed for guidance, navigation, and control algorithms that will be used to explore lunar and other planetary surfaces remotely. It has two propulsion systems: (1) a system of four electric ducted fans to offset 5/6 of the Earth's gravitational force, and (2) a cold gas propulsion system which uses compressed nitrogen propellant to impulsively emulate the lunar propulsion system and flies in an environment dynamically similar to that of the Moon. This paper is a follow-up to the SPACE 2010 paper entitled "Development of a Cold Gas Spacecraft Emulator [CGSE] System for the TALARIS Hopper." It focuses on the second of the aforementioned propulsion systems. This paper reviews the history and design of the CGSE, describes the testing characterization process, compares actual and predicted results, and discusses the CGSE performance in the context of closed-loop vehicle control. Special focus is given to emergent behaviors. NomenclatureA e = exit area of a converging-diverging nozzle, m 2 A t = throat area of a converging-diverging nozzle, m 2 F = thruster force, N γ = ratio of specific heats m  = mass flow, kg/sec P b = back pressure in a converging-diverging nozzle, Pa P c = chamber pressure in a converging-diverging nozzle, Pa P e = exit pressure in a converging-diverging nozzle, Pa R = specific gas constant, J/(kg-K) T c = chamber temperature in a converging-diverging nozzle, K V e = exit velocity in a converging-diverging nozzle, m/sec V i = entrance velocity in a converging-diverging nozzle, m/sec