VASIMR Engine

[Vahe231991]

Former astronaut Franklin Chang Diaz said last February that a 100 kW test of the VASIMR engine is planned for this year.

[Nighthawk117]

PRESS RELEASE 041525, April 15, 2025
AD ASTRA ROCKET COMPANY SUCCESSFULLY DEMONSTRATES INNOVATIVE
DESIGN OF CRITICAL VASIMR® SYSTEM UNDER NASA RESEARCH CONTRACT
[Webster, Texas – for immediate release]

Ad Astra Rocket Company (Ad Astra) has successfully
completed a 30-month contract with the National Aeronautics and Space Administration (NASA), to develop an
advanced thermomechanical design of the radiofrequency (RF) coupler for the VASIMR® rocket engine. The
innovative design was experimentally demonstrated in late March 2025, during sustained plasma tests of the
 VX200SS™ VASIMR® engine prototype at Ad Astra’s Texas laboratory. The innovation produces up to 28%
reduction in the steady-state operating temperature of the RF coupler, an improvement that would enable the
engine to operate at higher power.

The RF couplers (each engine needs two) are highly integrated, electromechanical assemblies that handle
virtually all the power of the engine. They launch RF waves into the engine’s magnetized central core. These
waves produce and heat a plasma – a superheated gas – to millions of degrees. The plasma internal energy is
converted to rocket thrust by the engine’s magnetic nozzle.

The RF couplers are critical elements of the engine’s architecture. By their power handling function and
location close to the plasma, they are naturally subject to substantial heating. During normal operation, they must
remove up to 10-15% of the engine power as waste heat. While the present RF couplers work well at power levels
up to 80 kW, at higher power, they hover uncomfortably close to their temperature limit. The new design, featuring
advanced materials and innovative manufacturing, runs significantly cooler than the present system and opens a
higher power range for the engine.

Phase I of the project began on July 25, 2022, and ended on January 25, 2023. Four months later, Phase
II initiated on May 22, 2023, and ended on March 31, 2025. Over the 30-month effort, the Ad Astra team
developed unique and innovative manufacturing techniques and in-house materials test capabilities for rapid
prototyping to explore multiple materials combinations and manufacturing protocols.

“It is exciting to see the incredible amount of innovation of our team in engineering solutions and
manufacturing techniques,” said Dr. Franklin Chang Díaz, Ad Astra CEO; “I am proud of their awesome creativity
and hard work in bringing technical concepts like this quickly to reality,” he added.

These system improvements are designed to increase the robustness and ultimate power of the VASIMR®
engine and set the stage for advancing the engine’s Technology Readiness Level (TRL) from its present TRL 4-5
to TRL-6; namely, a system capable of being field tested in space.

https://www.adastrarocket.com/wp-content/uploads/2025/04/AdAstra-Release-041525_Final-1.pdf

[InterestedEngineer]

The RF couplers are critical elements of the engine’s architecture. By their power handling function and
location close to the plasma, they are naturally subject to substantial heating. During normal operation, they must
remove up to 10-15% of the engine power as waste heat. While the present RF couplers work well at power levels
up to 80 kW, at higher power, they hover uncomfortably close to their temperature limit. The new design, featuring
advanced materials and innovative manufacturing, runs significantly cooler than the present system and opens a
higher power range for the engine.

They carefully did not say what that new power range was.

80kW is ion engine territory, you might as well use an ion engine.

A couple of MW might be much more useful, but would have to keep in mind the mass-power ratio, as in all these systems the dry mass is the biggest impediment to high deltaVs.

The ion engine folks keep improving the mass-power ratio, VASIMR will have a hard time keeping up.

[InterestedEngineer]

| Engine             | Type               | Power (kW) | Mass (kg) | W/kg |
|--------------------|--------------------|------------|-----------|------|
| Starlink V2 Mini   | Argon Hall         | 4.2        | 2.1       | 2000 |
| NASA NEXT          | Ion (Xenon)        | 7.0        | ~8.0      | 875  |
| VASIMR VX-200      | RF Plasma (Argon)  | 200        | ~500      | 400  |
| Busek BHT-6000     | Hall (Xenon)       | 6.5        | ~10.5     | 620  |
| Airbus T6          | Gridded Ion        | 4.5        | ~10.0     | 450  |
| NASA HiPEP         | Ion (Xenon)        | 20         | ~60       | 333  |


or for a putative mission of 100kW power and deltaV of 10km/sec:

| Engine           | Isp (s) | Dry Mass (kg) | Fuel Mass (kg) | Total Mass (kg)     | Mass Ratio |
|------------------|---------|----------------|------------------|------------------|-------------|
| Starlink V2 Mini |  2500   | 50.0           | 25.2             | 75.2             | 1.503       |
| NASA NEXT        |  4190   | 114.3          | 31.5             | 145.8            | 1.275       |
| VASIMR VX-200    |  3000   | 250.0          | 101.2            | 351.2            | 1.405       |
| Busek BHT-6000   |  2750   | 161.3          | 72.4             | 233.7            | 1.449       |
| Airbus T6        |  3800   | 222.2          | 68.4             | 290.6            | 1.308       |
| NASA HiPEP       |  9600   | 300.3          | 33.6             | 333.9            | 1.112       |