High-Temperature Resistojets for All-Electric Spacecraft

Abstract

Electrothermal propulsion systems for spacecraft consist of an electrically powered heat exchanger, which increases the enthalpy of a propellant. Enthalpy is traded for kinetic energy through a gas dynamic expansion process to produce a high-velocity exhaust jet via a converging-diverging nozzle producing thrust. The performance is quantified by the specific impulse (Isp), which increases proportionally to the square root of the stagnation gas temperature. By increasing the stagnation temperature, the amount of propellant required on board of the spacecraft to accomplish a specific mission decreases or greater total impulse is provided for a fixed quantity of propellant. Surrey Satellite Technology Limited (SSTL) has used a low power hot gas system, known as a resistojet, since 2002, which uses either butane or xenon as propellant. This system has flown on 21 spacecraft including the European GPS Galileo Testbed GIOVE-A validation satellite. A collaborative development programme between the University of Southampton and SSTL is currently proceeding to develop a high-temperature resistojet which nearly doubles current ISP performance. Selective Laser Melting (SLM) manufacturing is being utilised to build a novel complex thin-wall concentric cylindrical heat exchanger (HE) as a single component, for this reason, this thruster has been named Super-high Temperature Additive Resistojet (STAR). High-resolution micro-Computed Tomography (CT) is used as a tool for non-destructive inspection since the HE of the thruster is closed preventing visual inspection. The CT volume data is used to determine a surface mesh to perform coordinate measurements, nominal/actual comparison and wall thickness analysis. STAR is designed to increase the stagnation temperature of the propellant to approximately 2,500K with a resulting Isp for xenon propellant above 80 s. Presently, the driver of the high-temperature resistojet technology is a requirement for the all-electric propulsion spacecraft bus. Geostationary telecommunication satellites typically use chemical propulsion for attitude control as well as orbit–raising and station-keeping. The benefit of using STAR is in fuel mass savings, cost savings in launch vehicle option for lighter spacecraft and further reduction of costs by eliminating the use of hazardous propellants. This research presents the design, construction and performance evaluation of the first proof of concept thruster, STAR-0, through vacuum testing with Ar propellant at the University of Southampton facility. The prototypes are made of stainless steel, which limits the maximum gas temperature to approximately 1,000 K. A set of multiphysics simulations is validated against the experimental results and the numerical investigation is extended to high-temperature refractory metals, which will enable the construction of an engineering model.

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Identifiers

ORCID for Federico Romei: orcid.org/0000-0003-2283-4658

ORCID for Hugh Lewis: orcid.org/0000-0002-3946-8757

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