C4.5 A Review of the High-Isp / High-Voltage Hall Thrusters

Claude Martin BRITO

Project Manager, Future and Advanced Projects, Safran Aircraft Engines

France

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For space missions where transit times is not a major constraint, such as comet chasers (Deep Space 1), asteroid rendezvous missions (Psyches spacecraft), and generally interplanetary missions, a high speci c impulse (Isp) is crucial. In the near-Earth environment, there are several missions where e cient propulsion systems are also essential from propellant consumption point of view. These include long-term drag compensation in LEO and VLEO (GOCE), long-term formation ight (for space-to-space communications), high-precision missions (LISA Pathnder), and interferometry missions (LISA). High Isp can also bene t commercial space applications, such as orbit corrections, slow plane change, orbit repositioning for commercial space debris removal (ADRAS-J) and potentially for the upcoming OSAM missions. Despite Hall E ect Thrusters (HET) having been studied since the 1960s and extensively used since the 2000s, a technological barrier appears to be emerging around 3000 seconds of Isp. Although theoretically, the potential for increasing the Isp in HETs is limitless by raising the discharge voltage or reducing the mass of the propellant species, these adjustments lead to signi cant impacts on both the thruster (plasma properties) and the system (power supply units capable of handling high voltage levels). This review o ers an exhaustive overview of HETs operating at high-voltage / high-Isp, by covering a relevant set of thrusters developed over the past 10 years (across all TRLs), data results from characterization tests or partial life-span test campaigns, and Safran Spacecraft Propulsion (SSP) own activities. This state-of-the-art analysis describes the technical solutions proposed for optimizing the magnetic eld, managing thermal loads, and optimizing the discharge channel geometry using various materials. Drawing on SSP experience, additional topics are addressed, such as the inuence of di erent channel materials, the homogeneity of the anode mass ow-rate, ceramic beveling, and thruster aging on maximum critical discharge voltages. The review study underscore the need to explore new high-voltage tolerant ceramics for the discharge channel, increase the magnetic eld intensity without compromising life-span or plasma stability, optimize the geometry of the discharge channel, design thrusters with better thermal management, and develop robust high-voltage wiring, connectors and electronics at PPU level. SSP is actively engaged in these challenges: several technological building blocks are currently being tested through an improved version of the PPSR5000, and high-voltage dedicated laboratory models are currently under test. These activities will provide signi cant insights into the functional triad (performance, stability and life-span) of highvoltage HETs and prepare the next steps toward a high-voltage DM thruster.