Debris production from solar array surface impact spallation: Results from the Hubble Space Telescope

Impacts on exposed spacecraft surfaces generate vapour, liquid and solid ejecta particles. Unless this encounters other parts of the spacecraft it escapes into space. On the HST spacecraft, meteoroid and space debris impacts produced thousands of craters visible to the naked eye (spallation diameter > 100 mu m) on the solar arrays. On the front surfaces these craters liberated solid spall-type glass fragments with dimensions up to similar to 40% of the maximum spallation diameter. Pictorial evidence from the HST solar array impacts is presented, indicating that the largest fragments produced are in the millimetre size range and are due to impacts from the rear. Using the HST data an estimate of the fragment size distribution, production rate and total mass loss is presented. On the thin HST arrays rear impacts dominate the mass loss being an order of magnitude above that due to front impacts. Consideration of the ballistic coefficients of these sized particles under atmospheric drag indicates that they could remain for up to a year in orbit after release.