Impacts on Hubble Space Telescope solar arrays: Discrimination between natural and man-made particles A.T. Kearsley a, * , G. Drolshagen b , J.A.M. McDonnell c , J.-C. Mandeville d , A. Moussi d a Department of Mineralogy, The Natural History Museum, Exhibition Road, London SW7 5BD, UK b ESA/ESTEC, Keplerlaan 1, NL-2200 AG Noordwijk, The Netherlands c Planetary and Space Science Research Institute, The Open University, Milton Keynes MK7 6AA, UK d ONERA/DESP, 2 Avenue Ed. Belin, 31055 Toulouse, France Received 30 September 2004; received in revised form 16 May 2005; accepted 16 May 2005 Abstract A Post-Flight Investigation was initiated by the European Space Agency to analyze impacts on solar arrays of the Hubble Space Telescope (HST), exposed to space for 8.25 years at approximately 600 km altitude. The solar cells deployed during the first Service Mission (SM-1 in December 1993) were retrieved in March 2002 as part of Service Mission 3B (SM-3B). A sub-panel of 2 m 2 was cut from the arrays for subsequent selection and removal of individual solar cells for analysis. Six cells (4.8 · 10 3 m 2 ) were surveyed for flux of all craters of sizes greater than 5 microns. Analytical scanning electron microscopy was used to analyse residues in 111 fea- tures of 3–4000 micron conchoidal detachment diameter (D co ), examined on 23 solar cells. Eighty three show identifiable residue: 38 are Space Debris impacts and 45 Micrometeoroid impacts. Of the remaining 28, 2 contain residue of ambiguous origin, 1 is probably a minor manufacturing flaw, 1 is obscured by contamination, and 24 are unresolved, lacking recognizable residue. The majority of space debris impacts on the SM-3B cells are less than 80 microns D co , dominated by Al-rich residue, probably of solid rocket motor origin, although three may be due to sodium metal droplet impacts. Three larger features include paint pigment and binder, ferrous alloy, and possible carbon-fibre composite material debris. Micrometeoroid residues are found across the entire crater size range and dominate features of between 100 and 1000 microns, their residues are similar to those found in earlier SM-1 surveys. Fe- and Mg-rich silicates dominate; Fe sulphides are common and there are occasional vesicular Ni- and S-bearing mafic silicates of hydrous phyllosilicate origin. A single sodium aluminosilicate res- idue and one Fe Ni metal residue were found; as well as enigmatic Mg- and S-bearing residues, all considered as probably of micro- meteoroid origin. A few Fe-, O- and C-bearing residues were classified as of ambiguous origin. Ó 2005 Published by Elsevier Ltd on behalf of COSPAR. Keywords: Space debris; Micrometeoroids; Hubble Space Telescope; Hypervelocity impact; Analytical electron microscopy; Solar array 1. Introduction and aims The retrieval of both solar arrays (wings V2 and +V2 of Fig. 1) from the Hubble Space Telescope (HST) and their return to Earth by the shuttle Orbiter Columbia provided an opportunity to document the current flux of particle impacts in low Earth orbit (LEO). The exposure of the solar arrays for 8.25 years in LEO provided a large number of impacts, available for comparison with the flux from SM-1 (3.6 years in LEO). An extensive survey of impact numbers, crater morphology and dimensions was performed under European Space Agency (ESA) contract 16283/02/GD/ ESTEC and is reported in Moussi et al. (2005). The chemical composition and likely origin of the microme- teoroids impacting on SM-1 and SM-3B cells is ad- dressed in detail within Kearsley et al. (submitted to 0273-1177/$30 Ó 2005 Published by Elsevier Ltd on behalf of COSPAR. doi:10.1016/j.asr.2005.05.049 * Corresponding author. E-mail address: antk@nhm.ac.uk (A.T. Kearsley). www.elsevier.com/locate/asr Advances in Space Research 35 (2005) 1254–1262