Issue A&A Volume 483, Number 3, June I 2008 Page(s) 941 - 947 Section Astronomical instrumentation DOI http://dx.doi.org/10.1051/0004-6361:200809414 Published online 19 March 2008

A&A 483, 941-947 (2008)
DOI: 10.1051/0004-6361:200809414

Meteoroid and space debris impacts in grazing-incidence telescopes

J. D. Carpenter, A. Wells, A. F. Abbey, and R. M. Ambrosi

Space Research Centre, Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK

(Received 17 January 2008 / Accepted 25 February 2008 )

Abstract
Context. Micrometeoroid or space debris impacts have been observed in the focal planes of the XMM-Newton and Swift-XRT (X-ray Telescope) X-ray observatories. These impacts have resulted in damage to, and in one case the failure of, focal-plane Charge-Coupled Device (CCDs) detectors.
Aims. We aim to quantify the future risks of focal-plane impacts in present and future X-ray observatories.
Methods. We present a simple model for the propagation of micrometeoroids and space debris particles into telescopes with grazing-incidence X-ray optics, which is based on the results of previous investigations into grazing-incidence hypervelocity impacts by microscopic particles. We then calculate micrometeoroid and space debris fluxes using the Micrometeoroid and Space Debris Terrestrial Environment Reference model (MASTER2005). The risks of future focal-plane impact events in three present (Swift-XRT, XMM-Newton, and Chandra) and two future (SIMBOL-X and XEUS) X-ray observatories are then estimated on the basis of the calculated fluxes and the model for particle propagation.
Results. The probabilities of at least one impact occurring in the Swift-XRT, XMM-Newton, and Chandra focal planes, in a one year period from the time of writing in November 2007 are calculated to be ~5% and ~50% and ~3%. First-order predictions of the impact rates expected for the future SIMBOL-X and XEUS X-ray observatories yield probabilities for at least one focal-plane impact, during nominal 5-year missions, of more than 94% and 99%, respectively.
Conclusions. The propagation of micrometeoroids and space debris particles into the focal planes of X-ray telescopes is highest for Wolter optics with the largest collecting areas and the lowest grazing angles. Telescopes in low-Earth orbits encounter enhanced particle fluxes compared with those in higher orbits and a pointing avoidance strategy for certain directions can reduce the risk of impacts. Future X-ray observatories, with large collecting areas and long focal lengths, may experience much higher impact rates on their focal-plane detectors than those currently in operation. This should be considered in the design and planning of future missions.

Key words: instrumentation: detectors, -- meteors, meteoroids -- X-rays: general -- space vehicles: instruments -- telescopes

© ESO 2008

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