Martin Ploner

Attitude and Spin Period of Space Debris Envisat Measured by Satellite Laser Ranging

The Environmental Satellite (Envisat) mission was finished on April 8, 2012, and since that time, the attitude of the satellite has undergone significant changes. During the International Laser Ranging Service campaign, the Satellite Laser Ranging (SLR) stations have performed the range measurements to the satellite that allowed determination of the attitude and the spin period of Envisat during seven months of 2013. The spin axis of the satellite is stable within the radial coordinate system (RCS; fixed with the orbit) and is pointing in the direction opposite to the normal vector of the orbital plane in such a way that the spin axis makes an angle of 61.86° with the nadir vector and 90.69° with the along-track vector. The offset between the symmetry axis of the retroreflector panel and the spin axis of the satellite is 2.52 m and causes the meter-scale oscillations of the range measurements between the ground SLR system and the satellite during a pass. Envisat rotates in the counterclockwise (CCW) direction, with an inertial period of 134.74 s (September 25, 2013), and the spin period increases by 36.7 ms/day.

The search for debris in GEO

Abstract The debris population in and near the geosynchronous ring (GEO) is still poorly known. Most of the observational effort has been concentrated on low altitude regions where the spatial density of debris objects is higher than the estimated figures for GEO. However, the GEO ring is a unique environment for science and for commercial applications, and there is no natural removal mechanism in this region. Recent optical surveys with the NASA CCD-Debris-Telescope (CDT) and the ESA 1m telescope in Tenerife (Canary Islands) confirmed the existence of a previously suspected large population of small, uncatalogued debris objects in GEO. The number of detected debris per size class is steadily increasing down to the current observational limit of about 20 mag, corresponding to objects of 0.1 to 0.2 m in diameter. In total this new population outnumbers the catalogued population by a factor of two.

Optical surveys of space debris in GEO

Abstract Optical observations in astronomy have been revolutionized by the use of solid state CCD detectors. Their enhanced sensitivity combined with digital image processing opened new prospects for automated sky surveys. Such techniques may be used for space debris surveys. Ground based optical surveys of the geostationary ring and the geostationary transfer orbit region outperform Radar observations in terms of minimum detectable object size, even when using telescopes of moderate size. On the other hand, automated optical surveys — given the large data volume produced by the sensors — ask for a high degree of on-line processing. Furthermore carefully planned observation scenarios are mandatory. We discuss different detection techniques and survey types. Optical surveys may yield a wide variety of results. In the simplest case a correlation with catalogued objects on the basis of observed positions is performed. It is also possible to aim for precise orbits, visual magnitudes, albedo, geometrical size, attitude motion, etc. The techniques will be illustrated by results from three surveys conducted with the 1 m Zimmerwald Laser and Astrometry Telescope (ZIMLAT) in the geostationary orbit region.

Determination of resonant geopotential terms using optical observations of geostationary satellites

The ellipticity of the Earths equator causes a resonant librational motion of geostationary satellites. Combining astrometric observations of Meteosat satellites from Zimmerwald (Switzerland) and Graz-Lustbuhel (Austria), the resonant geopotential terms C22 and S22 were determined. The accuracy of the parameters provided by the limited campaign is close to that achieved in JGM-3. The comparatively simple observation and reduction technique offers a useful alternative method to monitor the values of the resonant geopotential terms C22 and S22 in order to determine possible time variations or to assess upper limits for variations.