A Performance Comparison of Xenon and Krypton Propellant on an SPT-100 Hall Thruster (Preprint)

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)10-08-2011 REPORT TYPE Conference Paper DATES COVERED (From -To) TITLE AND SUBTITLE 5a. CONTRACT NUMBER A Performance Comparison of Xenon and Krypton Propellant on an SPT-100 Hall SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)Air Force Research Laboratory (AFMC) AFRL/RZS SPONSOR/MONITOR'S Pollux Drive NUMBER(S)Edwards AFB CA 93524-7048 AFRL-RZ-ED-TP-2011-342 DISTRIBUTION / AVAILABILITY STATEMENTApproved for public release; distribution unlimited (PA #11558). SUPPLEMENTARY NOTESFor presentation at the 32 nd International Electric Propulsion Conference, Wiesbaden, Germany, 11-15 Sep 2011. ABSTRACTThe use of krypton as an alternative to xenon for Hall thruster propellant is an interesting option for satellite system designers due to its lower cost. However, this cost-savings comes at the expense of thrust efficiency. Reduction in efficiency can be caused by energy losses from Joule heating, radiation, and the ionization process as well as degradation of plume quality from an increase in velocity distribution spread (most often from an increase in multiply charged ion populations) and geometric beam divergence.1 In order to quantify this performance reduction for the case of the flight model SPT-100 HET (1.35 kW), an ongoing series of experimental measurements is being conducted to measure how various thruster efficiency terms change with propellant and operating condition. This study will combine thrust measurements with plume data from electrostatic probes. This paper presents the results of performance measurements made using an inverted pendulum thrust stand. Krypton operating conditions were tested over a large range of operating powers from 800 W to 3.9 kW. Analysis of how performance is impacted by propellant and operating condition is presented. A simple mission analysis was done based on these measurements to evaluate the practicality of krypton propellant for an SPT-100 subsystem using krypton propellant for north-south station keeping (NSSK) for a typical communications spacecraft in geosynchronous orbit.. SUBJECT TERMS

Background Pressure Effects on Ion Velocity Distributions in an SPT-100 Hall Thruster

“…The operating conditions for this study are outlined in Table 1. The nominal condition was chosen to match the applied discharge voltage and anode mass flow rate during previous testing of the SPT-100 at the AFRL [20]. The overall setpoint of the thruster had a slightly lower discharge current than in previous testing due to various factors including extensive operation of the available thruster before use in this study (greater than 200 h), use of laboratory power supplies and mass flow controllers rather than flight model equipment, and operation in a different vacuum chamber (Chamber 1 at the AFRL, which is smaller and operates at higher background pressure).…”

Luminescence Measurements of the Kr+/Kr2+ + Kr Collision Systems

“…Emission of Kr I from 1s to the ground state could not be observed in this work due to the extremely short wavelength (~120 nm) at which these transitions occur. The Kr II emissions in this spectral region are all assignable to 5s  6p (standard electronic notation) transitions from both the 3 Luminescence spectra taken at E cm of 50 eV, 100 eV, and 300 eV are presented in Figure 3. As the collision energy is increased, the intensity of the spectral features also increases, most notably in the NIR and 400-500 nm regions.…”

“…1,2 Traditionally, the propellant of choice has been the rare-gas xenon (Xe), whose relatively low ionization potential, high atomic mass, storage compressibility, and chemical inertness have made it an ideal propellant. Worldwide production of xenon appears to be limited to 6000 m 3 per year owing to the low concentration of xenon in the atmosphere (87 ppb). 3 Xenon is finding increasing use in electric propulsion systems, high efficiency lighting and windows resulting in significant price variation.…”

“…Worldwide production of xenon appears to be limited to 6000 m 3 per year owing to the low concentration of xenon in the atmosphere (87 ppb). 3 Xenon is finding increasing use in electric propulsion systems, high efficiency lighting and windows resulting in significant price variation. This cost results in HET ground-testing becoming increasingly expensive.…”

“…Compared to Xe, Kr has a smaller atomic mass (84 amu) and higher ionization potential (14.0 eV) which results in lower thrust but potentially greater specific impulse. [3][4][5] The operation and integration of HETs on spacecraft lead to a number of potential complications that can affect the propulsion systems' lifetime and effectiveness. The generation of high energy ions can result in erosion of the walls of acceleration channels.…”