Space and ground-based studies of orbital atomic oxygen effects using silver film detectors

Harris, Ian Laurence (1996) Space and ground-based studies of orbital atomic oxygen effects using silver film detectors. University of Southampton, Doctoral Thesis.

Abstract

Atomic oxygen, formed by the photodissociation of molecular oxygen, is the most abundant atmospheric species at altitudes of between 150km and 650km, a region occupied by low Earth orbiting satellites. This oxygen reacts with many spacecraft materials, degrading their performance and risking equipment failures.

A review of space experiments reveals that the majority have relied on the retrieval of samples from orbit, which has limited the number of experiments and the range of environmental conditions investigated. A technique for the remote, in situ measurement of oxygen concentrations and effects has therefore been developed and tested. This technique is based on the oxidation of a thin conducting silver film in atomic oxygen flows; the resulting resistance increase of the film is used to monitor the progress of the reaction.

Experiments in a ground-based simulation facility have observed that the reaction of the silver sensor with fast atomic oxygen is linear/parabolic. Rates have been obtained for these processes and the effect of some exposure conditions on the reaction investigated. Other phenomena, such as the break-up of the sensors' conduction path and continued oxidation after the oxygen flow has ceased, are also reported and discussed.

Some sensors have been overlayed with additional materials (polyethylene, PTFE, carbon and silicon dioxide). The behaviour of these sensors is reported and the erosion of the coatings compared with that of bulk samples of the materials.

A space experiment based on the silver film sensor is described. Results from this experiment, flown on the microsatellite STRV-1a, correspond closely with those obtained from the ground-based testing. This has permitted estimation of the STRV-1a orbital environment.

Suggestions for the improvement of the sensor design are made. The most common problem in both space and ground-based experimentation was that of sensor contamination, which introduced reaction delays in some cases and probably prevented oxidation in some others.

Experiments conducted in another facility did not produce the expected oxidation, so an investigation into the possible reasons for this was conducted. The conclusions are presented and recommendations for upgrading the facility are made.

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