Proceedings Article | 1 February 1992
KEYWORDS: Contamination, Atomic force microscopy, Sensors, Crystals, Particles, Microscopy, Scanning tunneling microscopy, Polymers, Oxygen, Quartz
On the STS-32 Space Shuttle mission, a flight experiment provided an understanding of the effects of the environment on the long duration exposure facility (LDEF) from rendezvous with the shuttle until removal from the payload bay at the Orbiter Processing Facility (OPF) at NASA/KSC. The interim operational contamination monitor (IOCM) is an attached shuttle payload that has been used on two earlier flights (STS 51C and STS 28) to quantify the contamination deposited during the course of the missions. The IOCM can characterize by direct measurement the deposition of molecular and particulate contamination during any phase of flight, i.e., prelaunch, ascent, on-orbit operations, descent, and ferry flight of the shuttle. Measurements are made continually during these periods. Two types of particulate collection sensors are employed in order to avoid efficiency of collection uncertainties. In addition to these principal measurements, the IOCM actively measures the optical property changes of thermal control surfaces by calorimetry, the flux of the ambient atomic oxygen environment, the incident solar flux, and the absolute ambient pressure in the payload bay. The IOCM also provides a structure and sample holders for the exposure of passive material samples to the space environment, e.g., thermal cycling, atomic oxygen, and micrometeoroids and/or orbital debris, etc. One of the more salient results from the STS-32 flight suggests that the LDEF emitted a large source of contamination (mainly particulates) after berthing into the shuttle. The source emission rate of LDEF averaged 2.5 X 10-12 gr/cm2-sec for a period of eighty hours following berthing, falling off to a rate of 4.1 X 10-13 gr/cm2-sec just prior to re-entry. Post flight obscuration ratios on IOCM surfaces were measured at 2.4 percent. An atomic force microscope (AFM) was used to perform post-flight characterization of the IOCM sensors. The AFM is a new instrument capable of ultra high (atomic) resolution without coating the surface or exposing it to vacuum. This paper discusses the results observed by the IOCM during the retrieval of the LDEF, the operational capabilities of AFM, and the unique results acquired in assessing the data.
