Small Business Innovation Research/Small Business Tech Transfer
Ultra-Compact Center-Mounted Hollow Cathodes for Hall Effect Thrusters
Project Description
The proposed innovation is a long lifetime, compact hollow cathode that can be mounted along the axis of a 600 W-class Hall effect thruster. Testing at kilowatt power levels and above has shown that the thruster axis is the optimal position for thruster throttling and plume divergence. It also minimizes the impact of background conditions upon ground based performance measurements, reducing programmatic and technical risk to the end user. The proposed compact cathode will extend these benefits to low power Hall thrusters. The cathode will be compatible with iodine as well as with noble gases. Hollow cathodes are a critical, life-limiting component for Hall effect thrusters and gridded ion engines. Failure mechanisms include degradation, poisoning and evaporation of the electron emitter, keeper and emitter tube orifice erosion, and heater failure. To achieve >10,000 hr lifetime, compact cathode will use a hexaboride (LaB6 or CeB6) electron emitter. Hexaborides degrade more slowly than state-of-the-art barium oxide impregnated tungsten emitters at equivalent current densities. Hexaborides are also resistant to contamination from oxygen and other impurities. The cathode also includes a new, high temperature heater. To minimize keeper and orifice erosion, the design will be optimized through testing and plasma measurements. In Phase I, Busek shall design, built and test the compact cathode. The plasma plume will be interrogated with an emissive probe to determine spot and plume mode operating regimes on xenon and iodine. An integrated cathode-thruster test will also be performed to determine the cathode's performance with a thruster. The Phase II test program will include duration testing of the cathode and thruster-cathode system with a fully modified BHT-600, thermal cycling and plasma modeling. At the end of Phase II a cathode will be delivered to NASA for testing with a 600W-class Hall thruster.
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Anticipated Benefits
Topic S3.02 seeks to mature and demonstrate in-space electric propulsion technologies, specifically calling for long-lifetime hollow cathodes for use with iodine propellant and high specific impulse thrusters. Hollow cathodes are used in Hall Effect Thrusters (HETs) and ion engines, two types of high specific impulse electrostatic spacecraft propulsion that can be used for unmanned planetary exploration and support secondary payload options. The compact cathode directly supports several Hall effect thrusters currently being developed at Busek and NASA, including the xenon fueled Busek BHT-600, an iodine compatible version of the BHT-600 and JPL's experimental MaSMi thruster. These thrusters may propel NASA Discovery, New Frontiers and Explorers Class science missions. Traditionally, these mission classes would use xenon propellant; however, iodine propellant would expand the mission envelope without increasing the mission cost. Iodine yields performance comparable to xenon but provides many additional benefits at the system level. In addition, a fully fueled, non-active system may be stored on the ground or on orbit for long periods of time, which facilitates spacecraft spares and minimizes down-times in the event of a failure. This program will ultimately lead to flight hardware to support iodine-fueled missions.
Hollow cathodes are used in Hall effect thrusters, a type of electric propulsion that is attractive for military and commercial missions due to high performance, small size, low mass, and relatively low cost. Low power all thrusters can accomplish all required in-space propulsion functions including orbit raising, orbit circularization, inclination changes, station-keeping, repositioning, and end-of-life de-orbiting. The design will specifically support small spacecraft with power levels up to 1 kW. The next stage for commercial users is the all-electric satellite, where apogee insertion and on-orbit functions are both handled by electric thrusters. The low plume divergence enabled by an axial cathode of the type being developed minimizes spacecraft interactions, which is critical for geosynchronous spacecraft with operational lifetimes of 10-15 years. The thruster and cathode would be also very well sized for an ESPA-class (180 kg) spacecraft flown as a secondary payload on an Air Force Evolved Expendable Launch Vehicle (EELV). More »
Hollow cathodes are used in Hall effect thrusters, a type of electric propulsion that is attractive for military and commercial missions due to high performance, small size, low mass, and relatively low cost. Low power all thrusters can accomplish all required in-space propulsion functions including orbit raising, orbit circularization, inclination changes, station-keeping, repositioning, and end-of-life de-orbiting. The design will specifically support small spacecraft with power levels up to 1 kW. The next stage for commercial users is the all-electric satellite, where apogee insertion and on-orbit functions are both handled by electric thrusters. The low plume divergence enabled by an axial cathode of the type being developed minimizes spacecraft interactions, which is critical for geosynchronous spacecraft with operational lifetimes of 10-15 years. The thruster and cathode would be also very well sized for an ESPA-class (180 kg) spacecraft flown as a secondary payload on an Air Force Evolved Expendable Launch Vehicle (EELV). More »
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Primary U.S. Work Locations and Key Partners
| Organizations Performing Work | Role | Type | Location |
|---|---|---|---|
| Busek Company, Inc. | Lead Organization |
Industry
Women-Owned Small Business (WOSB)
|
Natick, Massachusetts |
| Jet Propulsion Laboratory (JPL) | Supporting Organization | FFRDC/UARC | Pasadena, California |
Primary U.S. Work Locations
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California
-
Massachusetts
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