First astrometric observations of space debris with the MeO telescope

The MeO (for Metrologie Optique) telescope is the Satellite and Lunar Laser Ranging (SLR) dedicated telescope of Observatoire de In Cote d'Azur (France) located at plateau de Calern. The telescope uses an altazimuth mount. The motorization of the mount has a capability of 6 deg/s allowing the follow up of Low Earth Orbits (LEO) satellites, as well as Medium Earth Orbits (MEO) and geostationary (GEO) satellites, and the Moon. The telescope has a primary mirror of 1.54 m. It uses a Nasmyth focus equipped with an EMCCD camera. The telescope field of view, defined by the equivalent focal length and the size of the camera, is currently 3.4 arcmin x 3.4 arcmin. Space debris observation with an optical telescope ideally requires a large field of view, accurate pointing, a fast slew rate, a high sensitivity, accurate astrometric positions, and a precise method for orbit propagation. The challenge is to obtain accurate orbits for all debris without compromising the field of view. The MeO telescope has a larger diameter than the ones habitually used for space debris tracking. It should improve the current accuracy of observations in the GEO region. For LEO, such sensitivity should allow observations of small pieces of debris at low altitudes. This paper presents the preliminary experiments carried out to benefit from the high astrometric quality of the instrument, namely the method developed to extract and to compute the astrometric positions of LEO and MEO satellites, as a test of the capabilities of such an instrument (very small field of view, but large aperture) for space debris tracking. Furthermore, we analyse the ability of MeO to keep track of an object for which only a preliminary orbit (computed by the Laplace method from previous observations) is known, so that high precision measurements can be obtained and the object can be catalogued with an updated orbit. The feasibility of our astrometric methods was tested throughout 2010. This paper presents the methods used and the difficulties encountered. The originality of our paper does not strictly reside in the methods used but in their adaptation to a telescope presenting such a small field of view. We discuss our first results obtained for LEO and MEO satellites. In particular, we give an estimate of the astrometric errors for the geodetic satellite Lageos-1 by comparing its positions deduced from our reduction strategy with those obtained from a reference orbit. We also present research to use the Laplace method to produce preliminary orbital elements. In this context, we discuss a novel improvement to the Laplace method. To put it in a nutshell, this article provides original results covering all fields of orbit estimation, from satellites tracking to preliminary orbit determination. (C) 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.