Gridded ion thrusters provide excellent thruster performance and have successfully been implemented on both geocentric and heliocentric missions. While ion thrusters have a substantial number of attractive technological attributes, they are often classified as inherently low thrust density devices. This manuscript details an ongoing collaborative effort among the NASA Glenn Research Center, the University of Michigan, and The Aerospace Corporation investigating ion engine design modifications for high thrust-density/high thrust-topower operation. Measurements were performed at The Aerospace Corporation in a 2.4-m diameter × 9.8-m long cryopumped vacuum chamber on an engineering model NEXT engine with a reduced interelectrode gap. The perveance, discharge losses, and far-field current density were characterized at operating conditions consistent with high thrust-to-power operation. The total voltage needed to achieve a given beam current was reduced by a factor of 10% with the reduced grid-gap optics, which is in close agreement with the Child Langmuir equation. The thrust loss correction factor ranged from 0.961 to 0.979 and was consistently higher than the predicted values. The discharge losses decreased with increasing beam current, with a minimum value of 150 W/A at a beam current of 5.50 A.
Nomenclature= ion charge thrust loss correction factor I sp = specific impulse, s β = beam divergence thrust loss correction factor j b = beam current density, A/m 2 δ = current density divergence angle relative to thruster centerline l g = interelectrode gap, m i = discharge losses, W/A m = ion mass, kg ζ = probe angle relative to the ion optics perforated edge NEXT = NASA's Evolutionary Xenon Thruster η u = propellant utilization efficiency P in = input power, W θ = probe angle relative to ion optics centerline PM = prototype model ψ = probe angle relative to the thruster centerline at the center of the spherically-domed ion optics * Research Engineer, In-Space Propulsion Systems Branch, 21000 Brookpark Road/MS 301-3, AIAA Member. † Sr. Technologist, Propulsion Division, 21000 Brookpark Road/MS 301-3, AIAA Sr. Member.