To meet the requirements of large flagship-type missions, the NASA Glenn Research Center has developed the next generation ion propulsion system.  The NASA Evolutionary Xenon Thruster (NEXT) is a 40 cm diameter ion engine, double the beam extraction area of the NSTAR ion engine.  The NEXT ion engine development followed the “derating” philosophy used for the NSTAR engine.  The NEXT engine consists of a stainless steel semi-conic discharge chamber with a ring-cusp magnetic field geometry.  Hollow cathodes are employed for electron emission in the discharge chamber and to neutralize the ion beam.  The ion optics are dished grids with the same geometries as NSTAR.  The engine was designed to be throttled from 1.1-6.1 kW to adjust for varying available power resulting from solar panel degradation over the life of the mission.  The NEXT ion engine has been demonstrated over a throttling range of 1.1 - 6.9 kW, specific impulse range of 2210 – 4100 s, with resulting thrust of 50 - 237 mN.

The fourth Laboratory Model NEXT engine, referred to as LM4, was built at the NASA GRC with the intention of conducting detailed mappings of the discharge plasma via electrostatic probes and Laser-Induced Fluorescence (LIF).  LM4 was completed in October 2003 and transported to PEPL where it will undergo the aforementioned testing.

The University of Michigan and the United States Air Force Research Laboratory have designed and built a 5 kW Hall thruster for research purposes designated the P5. This thruster has a discharge chamber outer diameter of 173 mm and was designed to emulate the characteristics of commercial Hall thrusters. Measurements taken in the LVTF (see AIAA-98-3503) using the thrust stand have shown that this thruster does have performance characteristics comparable to commercial models. This thruster will be available for long term research projects at the University of Michigan. It will also be available for modification to test the effects of changes in thruster configuration and to allow for internal diagnostic access.

Ion thrusters are electrostatic electric propulsion engines. Ions (typically Xenon or Krypton) are efficiently produced in a discharge chamber via collisions between neutral atom and energetic electrons generated by a hollow cathode in the discharge chamber. The ions are accelerated through two fine grids with roughly a 1300 V difference between them for 2.3 kW operation. The ion beam is "neutralized" by electrons emitted from a second hollow cathode external to the discharge assembly. The NASA Solar Electric Propulsion Technology Application Readiness (NSTAR) program developed the 2.3 kW ion engine for use as a primary propulsion engine for orbit transfer and intra-solar system trajectories. The NSTAR engine is the primary propulsion for the Deep Space 1 (DS-1) probe currently in route for comet and asteroid rendezvous.

The functional model thruster (FMT) was the immediate predecessor to the engineering model (EMT) NSTAR thrusters which themselves led to the flight engines and remain the principal ground test engines. They differ primarily in the FMT’s extensive use of 1100 grade aluminum. FMT2 was assembled and modified at NASA GRC specifically for use at PEPL. The modifications included the addition of large windows for optical access to the discharge chamber. The discharge cathode and ion optics are identical to those used in the EMT’s.

In December, 1998, PEPL became the first university to run an ion engine at power levels greater than 1 kW. The discharge and overall engine performance of the FMT at PEPL was nearly identical to that of the flight engine over the entire throttling range of the NSTAR thruster.

The Linear Gridless Ion Thruster (LGIT) is a two-stage device that is designed to incorporate the efficient ionization process found in gridded ion thrusters with the high thrust density and crossed-field acceleration mechanism of Hall thrusters. It is convenient to think of this thruster as the ionization stage of an ion thruster combined with the acceleration stage of a Hall thruster.  Learn more about the LGIT by viewing a powerpoint presentation or a PDF.  The following reference is the original paper describing the thruster development:

Beal, B. E., Gallimore, A. D., "Development of the Linear Gridless Ion Thruster," AIAA-2001-3649, 37th Joint Propulsion Conference, Salt Lake City, UT, July 8-11, 2001.

Hydrogen arcjet plume firing at PEPL.  Runs on H2, N2, or a mixture, at about 12A, 1 kW, peak around 600s I_sp, (20-30% efficiency).

1.35 kW MAI Hall thruster

SPT-100 Hall thruster

PEPL-70 Hall Thruster