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Retention of Sputtered Molybdenum on Ion Engine Discharge Chamber SurfacesGrit-blasted anode surfaces are commonly used in ion engines to ensure adherence of sputtered coatings. Next generation ion engines will require higher power levels, longer operating times, and thus there will likely be thicker sputtered coatings on their anode surfaces than observed to date on 2.3 kW-class xenon ion engines. The thickness of coatings on the anode of a 10 kW, 40-centimeter diameter thruster, for example, may be 22 micrometers or more after extended operation. Grit-blasted wire mesh, titanium, and aluminum coupons were coated with molybdenum at accelerated rates to establish coating stability after the deposition process and after thermal cycling tests. These accelerated deposition rates are roughly three orders of magnitude more rapid than the rates at which the screen grid is sputtered in a 2.3 kW-class, 30-centimeter diameter ion engine. Using both RF and DC sputtering processes, the molybdenum coating thicknesses ranged from 8 to 130 micrometers, and deposition rates from 1.8 micrometers per hour to 5.1 micrometers per hour. In all cases, the molybdenum coatings were stable after the deposition process, and there was no evidence of spalling of the coatings after 20 cycles from about -60 to +320 C. The stable, 130 micrometer molybdenum coating on wire mesh is 26 times thicker than the thickest coating found on the anode of a 2.3 kW, xenon ion engine that was tested for 8200 hr. Additionally, this coating on wire mesh coupon is estimated to be a factor of greater than 4 thicker than one would expect to obtain on the anode of the next generation ion engine which may have xenon throughputs as high as 550 kg.
Document ID
20020038847
Document Type
Technical Memorandum (TM)
Authors
Sovey, James S. (NASA Glenn Research Center Cleveland, OH United States)
Dever, Joyce A. (NASA Glenn Research Center Cleveland, OH United States)
Power, John L. (NASA Glenn Research Center Cleveland, OH United States)
Date Acquired
September 7, 2013
Publication Date
December 1, 2001
Subject Category
Spacecraft Propulsion and Power
Report/Patent Number
IEPC-01-086
NAS 1.15:211319
NASA/TM-2001-211319
E-13130
Meeting Information
27th International Electric Propulsion Conference(Pasadena, CA)
Funding Number(s)
PROJECT: RTOP 755-B4-04
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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