Object Image Linking of Earth Orbiting Objects in the Presence of Cosmics

In survey series of unknown Earth orbiting objects, no a priori orbital elements are available. In surveys of wide field telescopes possibly many nonresolved object images are present on the single frames of the series. Reliable methods have to be found to associate the object images stemming from the same object with each other, so-called linking. The presence of cosmic ray events, so-called Cosmics, complicates reliable linking of non-resolved images. The tracklets of object images allow to extract exact positions for a first orbit determination. A two step method is used and tested on observation frames of space debris surveys of the ESA Space Debris Telescope, located on Tenerife, Spain: In a first step a cosmic filter is applied in the single observation frames. Four different filter approaches are compared and tested in performance. In a second step, the detected object images are linked on observation series based on the assumption of a linear accelerated movement of the objects over the frame during the series, which is updated with every object image, that could be successfully linked.Comment: Accepted for Publication; Advances in Space Research, 201

Track association performance of the best hypotheses search method

Uncontrolled space objects in the geostationary orbit domain are hazardous threats for active satellites. Catalogs need to be build up, in order to protect this precious domain. The Swiss ZimSMART telescope, located in Zimmerwald, regularly scans the geostationary ring in order to provide a homogenous coverage. This surveying technique typically yields short measurement arcs, called tracklets. Each tracklet provides information about the line-of-sight and the rates of change but typically not about the full state of the observed object. Computationally intensive multi-hypothesis filter methods have been developed to associate tracklets with each other. An effective implementation to this approach is presented that uses an optimization algorithm to reduce the number of initial hypotheses. The method is tested with a set of real measurements of the aforementioned telescope

Optical surveys for space debris

Space debris—man-made non-functional objects of all sizes in near-Earth space—has been recognized as an increasing threat for current and future space operations. The debris population in near-Earth space has therefore been extensively studied during the last decade. Information on objects at altitudes higher than about 2,000km is, however, still comparatively sparse. Debris in this region is best detected by surveys utilizing optical telescopes. Moreover, the instruments and the applied observation techniques, as well as the processing methods, have many similarities with those used in optical surveys for ‘astronomical' objects like near-Earth objects (NEOs). The present article gives a general introduction to the problem of space debris, presents the used observation and processing techniques emphasizing the similarities and differences compared to optical surveys for NEOs, and reviews the results from optical surveys for space debris in high-altitude Earth orbits. Predictions on the influence of space debris on the future of space research and space astronomy in particular are reported as wel

Daylight Measurement Acquisition of Defunct Resident Space Objects Combining Active and Passive Electro-Optical Systems.

The uncontrolled growing number of resident space objects (RSOs) threatens the safe operation of space-related activities. Since the beginning of the Space Age, outer space is getting populated by objects emerging after breakup events; spare components through launching, orbiting, and aging of satellite missions; collisions between functional or defunct RSOs; or by missions that either completed or began their life cycle. One potential measure toward the sustainable use of outer space may start by preventing collisions between existing RSOs. Collisions between existing RSOs will only exacerbate the current situation, which could lead to a cascade effect known as the Kessler syndrome. In the context of such collisions, the enabling of optical daylight tracking has the potential to reduce the uncertainty of the estimated state vector for each RSO, thus aiding the planning and execution of efficient avoidance maneuvers when a collision is foreseeable, as well as benefiting just-in-time collision avoidance strategies in the future. This study starts by analyzing the impact of optical daylight observations, within the domain of defunct RSOs, with respect to the currently restricted nighttime observation windows, the type of observable acquired by the observing station, and the relative geometry between the Sun,the RSO, and the ground station. We highlight the role of key hardware components on each observing system deemed critical for current observing optical ground stations to enable daylight measurement acquisition. Once we have inspected all factors deemed crucial for daylight observations in our system, we present successful daylight observations, from which we derived angular observables, ranges, and apparent brightness. We additionally provide an example where the combination of measurements acquired by the different systems, operating in the optical regime only, contributed to partial disambiguation of the tumbling motion of a selected rocket body. All observations were conducted using a scientific complementary-metal-oxide-semiconductor (CMOS) sensor and a geodetic laser ranging system. Both systems make use of the 1-m Zimmerwald laser and astrometry telescope (ZIMLAT) for measurement acquisition and target RSO tracking at the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald (SwissOGS), operated by the Astronomical Institute of the University of Bern, Switzerland

The stare and chase observation strategy at the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald: From concept to implementation

A sustainable use of the outer space becomes imperative for preserving current operational missions and enabling the placement of new space-based technology in the outer space safely. The uncontrolled growing number of resident space objects (RSO) increases the likelihood of close conjunctions and therefore collisions that will populate the space environment even more. To prevent such situations, orbit catalogues of RSO are built and maintained, which are used to assess the collision risk between RSO. In order to keep the catalogues up-to-date, a worldwide ground-based infrastructure is used to collect observations coming from different observation techniques. The current study focuses on the so-called stare and chase observation strategy using an active and passive- optical system. The final aim is to correct the pointing of the telescope so that the target will be within the field of view of the laser beam, thus enabling the acquisition of laser ranges. By doing so, objects with poor ephemerides, available e.g. from Two Line Elements (TLE), will not pose a problem anymore for the rather small field of view of the laser beam. The system gathers both angular and range measurements, which can be used for an immediate orbit determination, or improvement, that will enhance the accuracy of the predictions helping other stations to acquire the target faster and permitting the station to repeat the procedure once more. The development of the observation strategy is particularized for the Zimmerwald Laser and Astrometry Telescope (ZIMLAT), located at the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald (SwissOGS), Switzerland. Likewise, all the implemented algorithms were tested using real measurements from ZIMLAT and the tracking camera

Application of attributables to the correlation of surveillance radar measurements.

Space surveillance by radar is especially used for the low Earth orbit to maintain a database, also calledcatalogue, of objects on orbit. Among others, surveillance radars which are constantly scanning a region ofinterest in the sky are used for this purpose. The detections from such a radar which cannot be assigned toan already known catalogue object might not contain enough information to obtain a reliable initial orbitfor a new catalogue entry from a single measured pass, also called tracklet. Instead, two tracklets can becombined to improve the quality of the initial orbit which leads to the correlation problem. This means thatit has to be tested whether two tracklets belong to the same object and an initial orbit has to be derivedby combining the tracklets. A common approach to condense the information in the tracklet is fitting themwith so-called attributables. Because radar observations include different types of observables, the fitting ofthese attributables has to be considered as an important part of the entire correlation process. This paperanalyses the effect of the attributable fitting considering the achieved accuracy and influence on the trackletcorrelation. A new singularity-free coordinate system is introduced, which improves the results of the fittingand correlation. Finally, a test on a simulated survey scenario introduces two additional filters to remove falsepositive correlations. It is shown that the attributable-based approach can be applied successfully to trackletsof up to three minutes length with different detection frequencie

Reflectance spectroscopy characterization of space debris

When characterizing the space debris environment one important point is the identification of the physical properties of the space debris objects. Reflectance spectroscopy is a possible technique to study the surface material of these objects with observations from the ground. In this work the results collected from spectroscopy observations of space debris in orbit are presented. The observations were performed at the 1-m ESA Space Debris Telescope (ESASDT) in Tenerife equipped with a spectrograph in the 450–960 nm wavelength range. A preliminary classification using three different categories purely based on the shape and appearance of the spectra was proposed. Two debris objects with high AMR could be successfully associated with materials analyzed in the laboratory. The results show that the two debris objects are probably pieces of Kapton MLI with ‘gold’ and ‘silver’ coating, respectively. Color indices were extracted from the spectroscopic measurements. For high AMR objects the colors seem to be consistent with the proposed classification in three categories. The B-R and R-I laboratory measurements of ‘gold’ and ‘silver’ MLI taken from the literature are comparable with the obtained results

Covariance study to evaluate the influence of optical follow-up strategies on estimated orbital parameters

An in-depth study, using simulations and covariance analysis, is performed to identify the optimal sequence of observations to obtain the most accurate orbit propagation. The accuracy of the results of an orbit determination/improvement process depends on: tracklet length, number of observations, type of orbit, astrometric error, time interval between tracklets and observation geometry. The latter depends on the position of the object along its orbit and the location of the observing station. This covariance analysis aims to optimize the observation strategy taking into account the in fluence of the orbit shape, of the relative object-observer geometry and the interval between observations