Ion thrusters are high-efficiency, high-specific impulse, advanced-electric space propulsion systems that are being proposed for ambitious deep-space missions that can require thruster operational lifetimes measured in years. One of the primary components of an ion thruster is the discharge cathode assembly (DCA). The DCA can include a hollow cathode with a surrounding keeper and is responsible for initiating and sustaining ion thruster operation. Unfortunately, wear-test and extended-life test results of a 30-cm ion thruster show that a molybdenum (Mo) keeper DCA can last only 3 years due to ion bombardment erosion. Therefore, contemporary Mo keeper DCAs utilized in ion thrusters are incapable of satisfying the 7-14 year mission requirement.
Researchers at the University of Michigan have developed a gas-fed hollow cathode keeper, which can reduce ion bombardment erosion by expelling gas through the keeper faceplate. The expelled gas effectively creates a high-pressure “shield” around the keeper such that bombarding ions suffer energy-reducing collisions before impacting the keeper. As the bombarding ion energy is reduced enough, the erosion is eliminated since sputtering is a threshold phenomenon. By protecting the discharge cathode from this erosion damage, which involves minimal changes to the established, space-rated designs, the cathode lifetimes may be extended to fulfill the critical 7 - 14 year timeframe to allow operation for long-duration missions.
Applications and Advantages
- Ion thruster
- Other plasma applications including Hall-nl-thruster systems and non-electric propulsion-nl-applications
- Semiconductor industry to maintain pristine-nl-plasma environment
- Erosion-resistant cathode keeper
- Minimal changes to the established, space–nl-rated designs, requires no new components