Improved Design of the VASIMR Radio Frequency Transmission Line

The proposed Phase I work addresses the subtopic “High-Temperature, High-Voltage Electric Propulsion Harnesses Connectors and Cables” and aims to deliver an improved design of the VASIMR® “Rhino Horn,” the low impedance section of the engine’s 2nd stage RF transmission line. Lying deep in the rocket core assembly, this component carries the largest fraction of the RF power. The Rhino Horn must withstand kV-level reactive voltages and be actively cooled to remove hundreds of watts of Joule self-heat and additional heat conducted from its proximity to the rocket core. Three generations of Rhino Horns have preceded the proposed design, each improving over the previous one. Generation-3 (Gen-3), the most recent operational design, enabled the VX-200SS™ VASIMR® prototype to demonstrate, in July of 2021, thermal steady state at 80 kW in an endurance test lasting 88 continuous hours. The fourth generation (Gen-4) Rhino Horn presented here, features innovations in thermal management, high-voltage insulation, integrated manufacturing and ease of assembly and installation. In this proposal we aim to complete the Gen-4 Rhino Horn design to Critical Design and validate its assumptions in a sub-scale Rhino Horn experimental assembly to be built and tested in vacuum. Also, a numerical “twin” of the Gen-4 Rhino Horn will be developed, validated with the experimental results, and used to predict the thermal behavior of the Gen-4 Rhino Horn at power levels > 100 kW. While the proposed work focuses on Rhino Horn improvements, the innovation is systemic and relevant to the low impedance RF line driving the first stage “ionizer” as well. That section has not exceeded thermal limits at the power levels explored thus far; however, being also a high current-carrying component, it is likely to do so at higher rocket power when the system demands more from the “ionizer”. Like the Rhino Horn, the Helicon RF line must maintain insulator integrity to kilovolt potentials in a cramped space.

Lunar resupply missions with high-power solar and nuclear electric propulsion (SEP/NEP) Fast interplanetary robotic science missions with high-power NEP Cislunar NASA in-space transportation with high-power SEP/NEP Planetary defense missions with high-power SEP/NEP Orbital debris mitigation (could also be non-NASA) Multi-MW-class human fast interplanetary missions with high-power NEP

Lunar resupply missions with high-power SEP/NEP In-space "mining" missions with high-power SEP/NEP Cislunar commercial in-space logistics with high-power SEP/NEP DoD cislunar robotic applications with high-power SEP/NEP Commercial mission extension, resupply, maintenance and repair vehicles with high-power SEP/NEP Reboost and orbit maintenance of large space stations in LEO with high-power SEP

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