Ground-Based Investigations of Atomic Oxygen Interactions with Space Station Surfaces

摘要

High strength to weight ratio fiber organic epoxy materials are primary candidates as structural members for Space Station construction but preliminary STS exposure experiments have shown that many of these materials experience extensive etching by oxygen atoms present in low earth orbit (LEO). Oxygen atoms colliding with ram directed surfaces have energies of 5 eV (due to 8 km/s orbital velocity) and produce etching rates of 0.1 micron/orbit, i.e., 10% of the incoming O-atom flux reacts with organic based surfaces causing surface recession; while ram surface reflected O-atoms (thermal), react with rates 3 to 4 times lower. In order to investigate this problem ground-based simulation and testing facilities have been developed which include a high kinetic energy O-atom source, a sample exposure chamber and a high sensitivity molecular beam apparatus. The sample exposure chamber is suited for surveying materials for their O-atom reactivity through weight loss measurements. The high sensitivity molecular beam apparatus will be used for determining reaction mechanisms through measurements of reaction product identity, translational and internal state of products, and angular distribution of reaction products. The O-atom source, based on the use of a laser sustained discharge, has demonstrated O-atom translational temperatures of 8 to 9000 K and is presently operating with 50% oxygen in argon using 500 watts of CO sub 2 laser power which is expected to produce velocities of 4 to 5 km/s. One hour exposures of kapton, two types of fiber glass epoxy materials, and MgF sub 2 coated optics have been accomplished and preliminary results indicate that the coated aluminium optics have very low reaction rates while kapton has the highest rate. (ERA citation 10:037162)