Precise Thrust Actuation by a Micro RF Ion Engine

The NASA Science Mission Directorate has plans to launch high-performance advanced space telescopes for astrophysics missions that require precision formation flying for synthetic aperture telescopes. These formations dictate the capability for precise alignment, synchronized maneuvers and reconfigurations. In order to accomplish the stated tasks, precise and low-noise micro-thrusters are needed. Busek Co. Inc. is proposing to continue the development of a micro RF ion engine propulsion system. Propulsion system is emphasized here because we believe we have all the building blocks needed to complete the system. The RF ion engine will operate in a dual thrust mode or low thrust, nominally 5-30 microNewtons (micro-N) for very precise, long duration missions and have the option to operate at high thrust, nominally 100 micro-N, for short applications such as spacecraft tip-off. This combination of thrust ranges from the same thruster is a unique and mission enabling technology. Busek has a flight qualified carbon nanotube field emission (CNTFE) cathode that is a near perfect fit for neutralizing the ion beam. The CNTFE is propellant-less and very low power, order of 1 Watt. Busek proposes to utilize a slightly modified microvalve for precise microflows. DC and RF electronics and control complete the system.

Potential commercial applications include any micro and nano-satellite missions that would require precision thrust, drag-free flight or incondensable propellant. Terrestrial applications for the micro RF ion thruster include a micro machining and semiconductor fabrication by nano focused ion beams. The microvalve has many applications where precise control of micro flows is required. The miniaturized valve has potential in many ion engines including small Hall effect thrusters as well as gridded ion thrusters, miniature chemical thrusters typical of ACS or mini spacecraft propulsion. The CNTFE cathode has already shown applications in the colloid propulsion system Busek delivered to JPL in 2008. In addition, Busek is investigating CNTFE cathodes for terrestrial applications.

Applications of micro RF ion engines include many currently planned and future NASA missions that require precisely controlled and highly throttle-able thrust for formation flights. These missions include Laser Interferometer Space Antenna (LISA), Space Interferometer Mission (SIM), Submillimeter Probe of the Evolution of Cosmic Structure (SPECS), Space Astronomy Far Infrared Telescope (SAFIR), Terrestrial Planet Finder (TPF) and Stellar Imager. Furthermore, micro RF ion engines can serve as tip-off control for formation flying satellites. Not only applicable to formation flight applications, micro RF ion engines are also the prime candidate for missions calling for zero drag. Zero drag can be achieved by varying thrust to counter the drag force measured from minute deceleration of the spacecraft. The thrust must be rapidly responsive and precise, which are the special features of RF ion engines.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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