LABORATORY DEMONSTRATION MODEL ACTIVE CLEANING TECHNIQUE DEVICE

摘要

This report describes the work accomplished under the development phase of NASA Contract NAS8-28270. The objective of this program was to develop a laboratory demonstration model (LDM) of an active cleaning technique (ACT) device for space use. The principle of this device is based primarily on the technique for removing contaminants from optical surfaces which was developed under NASA Contract NAS8-26385. This technique utilizes exposure to a plasma to remove contaminants from a surface. The laboratory demonstration model incorporates both plasma cleaning and ion sputtering modes of operation.nDuring the design study phase of the present program a prototype device was developed and a preliminary design was established based on tests of the prototype device. One major problem remained unsolved after completion of the design study phase. The plasma tube development was based on the earlier assumption that plasma cleaning was caused by atomic oxygen reacting with the contaminant 'to form volatile products. This assumption proved to be erroneous since the plasma tubes, developed for operation at high vacuum (<10-5 torr) conditions, produced atomic oxygen but did not produce measur¬able contaminant cleaning. Plasma cleaning under the companion contractn(NAS8-26385) was accomplished at relatively high chamber pressures (10-3 to 10-2 torr) which resulted in a plasma discharge throughout the vacuum chamber.nSince the problem of producing active cleaning species at high vacuum (<10 torr) conditions remained unsolved after completion of the design study phase, a major effort of the present program was to develop a suitable plasma tube for the laboratory demonstration model. After considerable experimental effort a plasma tube was developed which provides the active cleaning species at high vacuum conditions. It was shown that plasma cleaning occurs in the region of a visible plume which extends from the end of the plasma tube.