Development of carbon-based atomic oxygen sensors
This work focuses on the development of a hyperthermal, neutral atomic oxygen (AO) sensor that can be used on a wide variety of spacecraft platforms and in ground-based atomic oxygen environment simulators. Carbon has been identified as the sensitive medium for sensing the AO and one of the most important aspects of this work was selecting the most appropriate type of carbon for a particular AO dose. This work fabricates carbon films by physical vapour deposition (PVD) and screen-printing techniques to provide different thicknesses and erosion rates, which affect the sensitivity and life of the sensor. Screen-printed films provided a useful means of detecting large AO doses (fluences), whilst the thinner PVD films provide a more sensitive film for smaller AO fluences. Attempts are also made at interpreting the data to measure the rate of AO (flux). A combination of characterisation techniques confirm that the carbon films react by chemical removal of the carbon, which is also detected by measuring changes in electrical resistance. This work also postulates that the disorder of the carbon films (measured by Raman spectroscopy) can have an effect on the erosion rate of the material. Results from this work will eventually be compared with two low Earth orbiting spacecraft experiments: STORM on the International Space Station and CANX-2. These experiments are described and engineering details relevant to the sensors are also included.