Development and calibration of a passive space dust collector for low earth orbit

Observation of dust and debris in the near Earth environment is a field of great commercial and scientific interest, vital to maximising the operational and commercial life-cycle of satellites and reducing risk to increasing numbers of astronauts in Low Earth Orbit. To this end, monitoring and assessment of the

flux of particles is of paramount importance to the space industry and wider socio-economic interests that depend upon data products/services from orbital infrastructure. A passive space dust detector has been designed to investigate the dust environment in LEO-the Orbital Debris Impact Experiment (ODIE). ODIE is designed for deployment in LEO for ~1 year, whereupon it would be returned to Earth for analysis of impact features generated by dust particles. The design emphasises the ability to distinguish between the orbital debris (OD) relating to human space activity and the naturally occurring micrometeoroid (MM) population at millimetre to submillimetre scales. ODIE is comprised of multiple Kapton foils, which have shown great potential to effectively preserve details of the impacting particles' size and chemistry, with residue chemistry being used to interpret an origin (OD vs. MM). LEO is a harsh environment-the highly erosive effects of atomic oxygen damage Kapton foil-requiring the use of a protective coating. Common coatings available for Kapton (e.g., Al, SiO2, etc.) are problematic for subsequent analysis and interpretation of. OD vs. MM origin, being a common elemental component of MM or OD, or having X-ray emission peaks overlapping with those of elements used to distinguish MM from OD. Thus palladium coatings are proposed as an alternative for this application.

To develop this technology to a flight-ready level much testing and calibration of the instrument is required to ensure it retains impactor residue and size whilst being exposed to the LEO environment. In this thesis the ODIE detector foils, Kapton coated with palladium, are evaluated to find the optimum thickness of Kapton and palladium that survives both hypervelocity impact and exposure to atomic oxygen. The hypervelocity impact experiments were performed with the Light Gas Gun at the University of Kent at 1 and 5 km/s and showed that the 25 µm Kapton foil established the best relationship between the size of the projectile and the size of the impact feature created on impact. The palladium coating was found to delaminate at thicknesses great than 30 nm and hence coatings thinner than 30 nm are recommended for remaining adhered to the Kapton post-impact. The 25 µm Kapton foil with various thicknesses of palladium coating were exposed to atomic oxygen and, based on the mass loss of the samples due to exposure, the 75 nm palladium coating performed the best with the least mass lost during exposure, although the defects on the surfaces of the foils may have affected this result.

For the ODIE detector to be deployed in LEO, a Kapton foil thickness of 25 µm and a palladium coating thickness of 30 nm are the recommended parameters for the detector to address the flux of the sub-millimetre orbital debris and micrometeoroid populations.