Public reporting burden for this collection of information Is estimated to average 1 hour per response, Including the time for reviewing instructions, searching exdsting 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 Arcjet thrusters employ an arc discharge to heat propellant, which expands through a nozzle to produce thrust Spacecraft designers who desire to exploit the enhanced specific impulse of arcjets have expressed concern about the electromagnetic environment produced by the thrusters. Laboratory tests were performed to investigate the electromagnetic environment produced by a 26-kW ammonia arcjet in the frequency domain from dc to 10 Glrz using antennas intended to characterize electric and magnetic fields. Results obtained with a 30-cm monopole antenna exposed to the arcjet plume correspond to those of similar ground tests at lower power. When the antenna was shielded from electrical contact with the plume by a Pyrex® cover, signal levels dropped sharply at all frequencies. With a covered 30-cma monopole antenna near the arcjet plume, arcjet-on signals exceeded ambient levels over the frequency range 10 kHz-5 MHz. The maximum signal level typically exceeded the ambient level of 40 dBuV/MMHz by approximately 27 dB/.tV/MHz near 200 k-z. A likely explanation for'the sharp reduction in signal level once the antenna electrode is covered is that electrons and ions from the plume are collected on the exposed antenna but not on the covered antenna. Signals on the shielded antenna may be interpreted as the result of propagating electric fields, but considerable uncertainty remains about the field source and the effects of the facility on the measurements. Although the electromagnetic fields produced by an arcjet operating as part of a satellite are probably lower than previously expected, these results raise new concerns about the character and spacecraft compatibility of the plasma=from an arcjet plume.

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