Search

Abstract: The Astronomical Institute of the University of Bern was and is conducting several search campaigns for space debris in the geostationary ring (GEO) and the geostationary transfer orbit (GTO). First tests to build up a catalogue of satellites and space debris were performed recently. As the discovery observations of an object usually cover a time interval of a few minutes only, the first orbits determined are assumed to be circular. For GEO objects a circular orbit is a rather good approximation. This is certainly not the case for GTO objects. Nevertheless, a circular orbit seems to be an acceptable approximation for a short time interval around the observations. The first orbits can be used to acquire follow-up observations, which allow the determination of elliptical orbits. The maximum allowed time span between the detection and the follow-up for a successful recovery is found using simulated GTO orbits and observations. Further follow-up observations are simulated in order to study the orbit improvement process and the required force model. The accuracy of orbits needed to build up a catalogue is studied. The simulations are compared to the results achieved with observations acquired by the 1m telescope on Tenerife. [Copyright &y& Elsevier]

During the preceding years, the Astronomical Institute of the University of Bern (AIUB) was conducting several search campaigns for space debris in the geostationary ring (GEO). The optical observations were performed with a 1-m Ritchey–Chrétien telescope on Tenerife. A substantial population of unknown, small-sized objects was found in these surveys. For all objects a circular orbit was determined using the discovery observations. In order to test the hypothesis of circular orbits – which most likely is not valid for all detected objects – it is necessary to determine eccentricities for at least a part of the population. This in turn requires follow-up observations of the detected objects. The improved orbits resulting from follow-up observations also increase the probability for a successful recovery of the object in subsequent nights. Eventually, follow-up observations over several nights yield “secure” orbits allowing to build up a catalogue. In this paper we present the results of the determination of circular orbits and the orbit improvement process yielding elliptical orbits. The accuracy of the determined orbits is discussed, and the orbit quality is tested with follow-up observations after a few nights. The orbital elements are compared with those based on the assumption of circular orbits. [Copyright &y& Elsevier]

The space debris population in low Earth orbits (LEO) has been extensively studied during the last decade and reasonable models covering all size ranges were produced. Information on the distribution of objects in the geostationary ring (GEO), however, is still comparatively sparse. Until quite recently the population of man-made objects in GEO had to be inferred solely from the about 900 continuously tracked objects and the modeling of the two explosions known to have occurred in GEO. Optical observations from the last two years performed with ESA''s 1-m telescope at the Teide observatory in Tenerife changed the situation substantially. A hitherto unknown but significant population of small-size objects with diameters as small as ten centimeters has been detected in GEO. Objects in highly-eccentric orbits crossing the GEO region, in particular objects in geostationary transfer orbits (GTO), also contribute to the density of space debris in GEO. This family is even less well known than the GEO population, although many explosion events were reported in this orbital region. The paper will summarize recent results from the ESA GEO survey and describe the techniques and first results of a trial GTO survey. [Copyright &y& Elsevier]

Abstract: Two ESA-funded feasibility studies that aimed to develop observation strategies, to propose suitable sensor architectures, and to assess the expected performance of an independent European Space Surveillance System were carried out during the last years. The French company ONERA led two study teams comprising a number of European companies. The proposed space surveillance system consists of two subsystems, a phased-array radar system that shall be located in the South of Spain, and a network of ground-based electro-optical telescopes at four low latitude sites. This system allows to build-up and to maintain a catalogue of orbital elements of objects in space. It provides means to perform additional space surveillance tasks such as independent detection of fragmentation events, launches or manoeuvres, and allows to acquire the necessary measurements to assess the collision risk between catalogued objects. As a member of both study teams, the Astronomical Institute of the University of Bern (AIUB), Switzerland, contributed to the observation strategy definition, the system design, and the performance estimation of the optical observation part of the space surveillance system. This part of the system is intended to cover the Geostationary Orbit (GEO) and the Medium Earth Orbit (MEO) regions. This paper focuses on the development and evaluation of observation strategies for GEO and MEO within a space surveillance network. Observation requirements, possible strategies fulfilling the requirements, and the expected performance of selected strategies in terms of the coverage of a reference population are addressed. We conclude that GEO and MEO shall be covered by “stripe-scanning” approaches carried out by a network of telescopes. The simulations of the approaches using a reference population reveal that for both regions a nearly complete coverage can be guaranteed within a short time. [Copyright &y& Elsevier]