Improved Thermo-Mechanical Design of the VASIMR RF Coupler

The proposed work on Phase II involves the design, manufacture, and test of a full-scale embedded RF Coupler for the plasma heater stage of the VX-200SS VASIMR rocket core. The RF Coupler is a critical power component of the engine and, specifically, the heater stage RF Coupler delivers the largest fraction of the power to the VASIMR plasma. In 2021, an earlier innovation to the design of the RF Coupler-GCT assembly, called the Trapped Coupler, enabled the VASIMR VX-200SS test article to reach thermal steady-state at a company record of 80 kW. With the Embedded Coupler design, the proposed innovation in Phase II of this SBIR, and the knowledge obtained from Phase I, the Ad Astra team looks to increase that power to 100 kW, an objective relevant to the Phase I Solicitation Subtopic, High-Power Electric Propulsion Thrusters for Mars-Class Missions. In a Trapped Coupler, all heat coming from the ceramic must pass through its inner diameter surface. In contrast, the Embedded Coupler uses its walls as two additional surface heat pathways. Theoretical estimates conducted by the Ad Astra team show that the heat transfer area in the embedded design increases by roughly a factor of 3 and results in a lower steady-state temperature for the GCT. To accomplish this, the RF Coupler will be machined-in-place in a high-purity copper vein pattern cast on a ceramic GCT host. The coolant within the coupler flows along two stacked counter-flowing channels, a feature required by the current RF electrical circuit. Other potential designs for this channel structure are possible and being explored outside of this SBIR but, in all cases, the manufacture requires a high-precision welding technique that Ad Astra has developed in-house and successfully demonstrated in the Trapped Coupler configuration. - The new RF Coupler assembly design enables better heat transfer within the rocket core, allowing high-power (>100 kW) operation of the rocket consistent with NASA’s goals. - A new manufacturing technique for this critical engine component has been identified and developed in Phase I. - The innovation reduces risk in the technology maturation of the VASIMR engine. 1.Demonstrate manufacturing technique developed in Phase I in a new host material. 2.Produce a full-scale RF Coupler assembly on the new host material. 3.Test the thermal performance of the new assembly with a high-power heater in vacuum. 4.Compare experimental and theoretical thermal performance data of the new RF Coupler assembly. 5.Compare experimental thermal performance of the new and current RF Couplers. 6.Test the new RF Coupler in the VX-200SS™ rocket core and validate its performance. 7.Evaluate alternative material and manufacturing options for the new RF Coupler design.

- 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 - 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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