Experimental study of hypervelocity impacts on space shields above 8 km/s

This paper deals with hypervelocity impacts of millimeter size space debris on space structures at velocity regime between 6 and 15 km/s. Millimeter size debris present a real threat to space structures since they cannot be tracked nor detected by radars. At the opposite, for larger debris, 5-10 cm size, avoidance manoeuvre can be conducted remotely from earth to shift the space structure from the threat trajectory. A lot of works (tests and simulations) have been done for debris smaller than 5 cm size. For debris smaller than 1 cm, the maximum impact velocity reachable with available facilities is mainly up to 8-8.5 km/s. As a result, the ballistic limit equation (BLE) for single plate, whipple shield and honeycomb structures are only based on analytical and numerical investigations for higher threat velocity. There is no efficient facility available to generate hypervelocity impacts in the 8-12 km/s regime for millimeter size projectile. To fulfil this need, the French space agency CNES granted a R&T contract to Thiot Ingenierie company for performing hypervelocity tests between 8 and 12 km/s. The contract specified Thiot Ingénierie for performing the analysis and the development of a special hypervelocity device that will be able to propel 1 to 3 mm aluminium sphere at this high velocity regime. With this innovative launcher, impacts of 1 mm sphere diameter at a speed of 10km/s and above is now reachable. The present study presents hypervelocity impacts on different types of targets: single plate, whipple shield and honeycomb structure have been tested. Impact velocities ranging from 7 to 10 km/s have been reached. Specific diagnostic tools (very high speed camera, X-rays flash photography …) are used to analyse the tests. Results, in terms of ejecta projection, post-impact damage are presented. The effects of ejecta tunnelling in the case of honeycomb shield is highlighted.