High Density Hall Thruster Propellant Investigations

Abstract

Multiple high density propellant alternatives for Hall Effect Thrusters were investigated experimentally. The metals magnesium and zinc showed promise for high specific impulse applications. The halogen iodine showed great promise for general use, with measured performance similar to xenon and lower plume divergence. The metal bismuth showed promise for missions requiring high thrust to power. All of the high density options could substantially increase the change in velocity available to spacecraft when discharge potential and propellant volume are fixed or limited. NomenclatureB = magnetic field E = electric field e = charge of an electron, 1.6 x 10 -19 C F = thrust Φ = potential difference 0 g = gravitational constant at Earth's surface, 9.81 m/s 2 I = current, subscripts b for beam, c for cathode, d for discharge, m for magnet sp I = specific impulse j = current density m = mass, subscripts p for propellant, 0 for initial m = mass flow rate, subscript a for anode M = ion mass P = power, subscript d for discharge p = pressure, subscript s for sensor, x for xenon q = ion charge R = radial direction d V = discharge potential v = exhaust, particle, or beam velocity V ∆ = change in spacecraft velocity Z = axial direction η = efficiency, subscript t for thrust

Mission and System Advantages of Iodine Hall Thrusters

“…6 The thrust peaked at 25mN at a discharge power of 500W, and performed at 12-14mN under the nominal 200W operation. A thrust-to-discharge power ratio of 75mN/kW was demonstrated with 150V discharge and 65mN/kW under nominal conditions.…”

“…6 To avoid bulk accumulation of I 2 on surfaces, the removal rate must exceed the arrival rate. The flux away from a surface may be estimated from the I 2 vapor pressure.…”

“…Test results also indicate a reduction in plume divergence with iodine. 6 Thrust is typically measure directly with an inverted pendulum, "Null" type thrust stand. 8 Specific impulse is defined by…”

Iodine Plasma Propulsion Test Results at 1–10 kW

“…Testing from the BHT-1000 focused on both performance and the plume [16]. Plume divergence was measured at multiple operating conditions.…”

A Calcium Aluminate Electride Hollow Cathode

“…Iodine has recently attracted interest as an alternative electric propulsion propellant [17]- [20]. It has an atomic mass similar to xenon with slightly larger ionization cross sections (for both I and I 2 ).…”