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The near-term potential for iodine propellant in Hall thrusters is explored. The merits of iodine with respect to other propellants are presented. Recent performance measurements are summarized, and new measurements taken with an 8 kW thruster are presented. Thruster discharge power exceeded 10 kW, and peak measured anode efficiency exceeded 65%. Spacecraft interactions issues are also addressed and relevant data taken with a 1 kW thruster are presented. Plume data showed lower divergence with iodine than with xenon, and that a plume shield could effectively attenuate the far field plume. Material samples placed in the plume showed a strong reaction with iron, but little reaction with typical spacecraft materials. System level benefits, including low storage pressure and extremely high density, are also discussed. All results so far indicate iodine is a viable propellant for electric rockets, and for some missions is superior to xenon.

The plasma plume from a low-power Hall-effect thruster fueled by iodine vapor was characterized with several wetted plasma probes. The plasma source included a laboratory propellant feed system and a laboratory model Hall thruster powered by a breadboard power processing unit. The hollow cathode was fed with xenon. Iodine and xenon ion velocity and energy distributions were measured with an ExB probe, an electrostatic analyzer, and a combined electrostatic analyzer/ExB probe. Multiply charged species were detected in the plume when the thruster was operated with iodine and xenon. Diatomic iodine ions were also detected. The dimer fraction was found to vary with thruster operating conditions and probe location in degrees from the center of the beam. The dimer fraction was also found to decrease as discharge current and voltage increased. With the thruster operating at a discharge potential of 250 V, the fraction of the high-energy ion flux comprised of dimers exceeded 10% over a broad region of the plume at low power. Significant dimer fractions could increase thrust to power by useful amounts at the cost of some overall efficiency. Nomenclature B= magnetic field E = electric field e = charge of an electron, 1.6 × 10 −19 C f = species current fraction F c = centripetal force g = species number fraction g 0 = gravitational constant at Earth's surface, 9.81 m∕s 2 h = species number fraction I = current I sp = specific impulse j = current density M = ion mass _ m = mass flow rate n = number density P d = discharge power q = ion charge r = radial direction or distance T = thrust V d = discharge potential v = velocity Γ = flux η = efficiency ξ = thrust to power factor ϕ = electric potential

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