Public reporting burden for this collection ol Infomiatlon Is estimated to average 1 hour per response, Including the time for reviewing Instructions, searching easting data sources, gathering and maintaining the data needed, and completing and reviewing this collection of infomiatlon. Send comments regarding this burden estimate or any other aspect of this oolleotlon of information, Including suggestions for reducing this burden to Department of Defense, Washington Headquarters Serwoes, Directorate for Infomiatlon Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204 Ariington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for falling to comply v»ith a collection of information If It does not displav a currently valid 0MB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY) 19 ABSTRACTIn recent teste the plume current density profile, plume ion energy, and radiated EMI were characterized for Pratt & Whita^'s T-220HT Hall Effect thruster. The T-220HT is a high power (6-20 kW) thruster designed for maximum peak thrust. Tests covered a power range jfrom 8-10 kW and discharge voltages of 300 and 600 V. Plume measurements at Air Force Research Laboratoiy (AFRL) facilities demonstrated plume widths narrower than typical Hall thrusters. Halfangles containmg 90% of the integrated plume flux were in the range of 27-29°. Radiated electromagnetic emissions were measured over a frequency range from 200 MHz to 60 GHz at The Aerospace Corporation. For discharge voltages at or below 300 V, EMI was below MIL-STD 461E limits except at a single peak below 1.4 GHz, v^ere the limit was exceeded by only about 5 dB. Increasing flie discharge voltage ID 600 V noticeably increased emissions in this frequency range, but these were still generally below MIL-STD 461B. Plume ion ener^ spectra were also characterized at The Aerospace Corporation's facility.An RPA (Retarding Potential Analyzer) was mounted at a downstream distance of 1 meter and was varied in position from 20° to 100° from tiie thruster centerline. Measuremente generally confirmed tiie plimie profile data taken at AFRL. Energy spectra confirm fliat the flux at high angles is dominated by low eneigy chargeexchange ions.

Publicreporting burSen 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)2. REPORT TYPE The Aerospace Corporation, El Segundo, CA AbstractThe United States Air Force Research Laboratory's Electric Propulsion Space Experiment (ESEX) was launched and operated in early 1999 in order to demonstrate the compatibility and readiness of a 30-kW class ammonia arcjet for satellite propulsion applications. As part of this flight, an array of on-board contamination sensors was used to assess the effect of the arcjet and other environments on the spacecraft. The sensors consisted of microbalances to measure material deposition, radiometers to assess material degradation due to thermal radiation, and solar cell segments to investigate solar array degradation. Over eight firings of the ESEX arcjet (and 33 min. 26 sec operating time), the following preliminary results are reported. The microbalances show no measurable deposition from the arcjet, in agreement with predictions. The radiometer near the thruster, viewing the arcjet plume and body, experiences a change in the thermal properties of its coating from the firings. Radiometers with no view of the arcjet, or a view of only the plume, show no change. During firings, the solar cell segments, near the thruster, show decreasing open-circuit voltage; probably attributable to an additional electrical load provided by the plume plasma. The solar cells also exhibit a 3% decrease in non-firing, solar-illuminated short-circuit current over the eight arcjet firings, attributable to decreased solar transmission of the cover glass. However, no effects associated with the arcjet are observed on the spacecraft solar arrays. These data are in good agreement with model predictions, where available. In general, contamination effects are observed only on sensors near the thruster exhaust nozzle, a location unlikely to be used in an operational high-power electric propulsion system. No contamination effects are observed in the backplane of the thruster. For future programs, while engineering measures may be needed for spacecraft equipment in the immediate vicinity of the thruster body, the arcjet environment is generally benign.

No 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)2 ABSTRACT A quadrature heterodyne interferometer is augmented with a Herriott Cell multi-pass reflector to increase instrument resolution and enable a separation of the phase shift due to neutral density from room vibrations. In addition, the use of the Herriott Cell enables variations in the multi-pass laser-beam geometry that optimizes the diagnostic for small scale length measurements or for planar measurements. Ray tracing analysis is used to illustrate retro-reflective planar measurement geometries attainable with the instrument.Analysis is performed to show that phase front degradation and loss of scene beam intensity, concomitant with the large number of reflections from the Herriott Cell mirrors, does not introduce a systematic measurement uncertainty. The diagnostic capability is demonstrated with measurements of the electron and neutral densities in the plasma exhaust from electric propulsion thrusters. Experimental data with up to 18 passes through plasma demonstrates that the instrument resolution to electron and neutral density increases almost linearly with number of passes. However, measurement uncertainty associated with room vibrations is shown to remain constant as the number of passes is increased. Therefore the Herriott Cell can be used to increase the signal of neutral density phase shifts relative to the noise of the phase shifts due to room vibrations. For the Pulsed Plasma Thruster plasma exhaust used to validate the instrument, the addition of the Herriott Cell reduces the density measurement uncertainty to equal or less than the uncertainty due to discharge irreproducibility. When used on plasma sources with higher reproducibility, the Herriott Cell interferometer should be an effective tool for high resolution electron and neutral density measurements.

A Herriott cell consists of two concave mirrors positioned on opposite sides of plasma so as to create multiple laser paths through the plasma. Added to a traditional interferometry diagnostic, the Herriott cell multiplies the effective path length through the medium and thereby increases instrument resolution. Previous work used a planar geometry to validate the use of Herriott cells in interferometer applications where the numerous mirror reflections will significantly degrade the phase front quality. The current work extends the Herriott cell capability to a point configuration. In this geometry the multipass beams converge near a single point within the plasma, useful for performing density measurements in very small scale length plasmas. Ray tracing analysis is used to illustrate example measurement geometries attainable with the instrument. It is shown that the configuration results in two convergence points for the laser paths, which somewhat complicates the interpretation of the experimental data. In addition, the multitude of passes through the high density, small scale length passes increases the likelihood for deleterious refractive effects. The diagnostic capability is demonstrated with measurements of the electron and neutral densities in the plasma exhaust of a Micro Pulsed Plasma Thruster. The measurements are validated with similar, lower resolution measurements, obtained using a single-pass interferometer.