Preliminary analysis of contamination measurements from the ESEX 26 kW ammonia arcjet flight experiment

Abstract

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.

Flight plasma diagnostics for high-power, solar-electric deep-space spacecraft

“…The PDP-E reverse biases both photodiodes and measures the photocurrent and temperature. This type of Photometer has flight heritage with several USAF missions [1], [6], [11].…”

“…The PDP-E monitors both temperatures. Radiometers of this type have flight heritage with several USAF missions including ESEX, TacSat-2, AEHF-2 [1], [6], [11].…”

“…The specific type of solar cell would be a matched version (single element) to the ARRM main solar arrays. Diagnostic inflight solar cell elements have flown on ESEX [1], TacSat-2 [11], and AEHF-2 [6].…”

“…Plasma plumes from high-power electric thrusters are known to interact with solar arrays and other materials commonly found on spacecraft surfaces [1]- [6]. Satisfactory characterizations of these potentially adverse effects are beyond the capabilities of ground-based test facilities because (1) the background pressure in vacuum chambers is typically orders of magnitude higher than in flight ( [2], [6]) and (2) energetic thruster ions sputter the chamber walls, generating a deposition environment [7] not present in space.…”

A Proposed On-Orbit Demonstration of an Advanced Pulsed-Plasma Thruster for Small Satellite Applications

“…The most successful technique to assess this impact (derived from the ESEX flight experience) is to use a series of radiometers with different spacecraft materials such as thermal paints, radiator materials, or optical coatings. A description of the radiometer operation is detailed elsewhere [19], but the basic technique involves measuring the temperatures at the surface and the base of the sensoryand deriving the change in the radiated heat flux as the surface thermal properties are changed by deposited material. The on-orbit radiometer temperatures are compared to the known degradation of the materials under the satellite orbital conditions.…”