Improvement of Space Debris Orbits

Cordelli, Emiliano (2017). Improvement of Space Debris Orbits. (Dissertation, Astronomisches Institut der Universität Bern, Phil. nat.)

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The increasing amount of space debris requires huge efforts for the tracking networks in order to maintain the orbits of all the objects. The precise knowledge of the positions of space debris objects is fundamental for collision avoidance maneuvers performed by satellite operators and for future active debris removal missions. It is very well known that the accuracy of an orbit determination process depends on the kind of observables used, their accuracy, the length of the observed arc, the number of observations, the observer orbit, and the observer-target geometry of the observations. In this thesis an in-depth study is carried out to understand how the mentioned parameters influence the orbit determination accuracy and how we can improve the quality of the estimated orbits. After a brief introduction on the least squares adjustment algorithm and on the way of propagating and manipulating the resulting covariance matrix, we will focus essentially on the influence of the object-observer relative geometry and of the use of different observables for the orbit determination of space debris. The object-observer relative geometry is approached as an information gain problem and it is studied using simulations and covariance analysis. The main aim of the covariance analysis is to identify the optimal follow-up strategy as a function of the object-observer geometry, the interval between follow-up observations and the shape of the orbit. This analysis is applied to every orbital regime but particular attention is dedicated to the highly-populated space debris orbits. Furthermore, several particular cases are analyzed with this method: more than two
follow-ups observations, the influence of a second observing station, and the introduction of the distance as second observable. The study on the combination of different types of observables is carried out investigating the influence of addition of the laser range measurements to the classical optical astrometric observations in terms of improved accuracy of the determined orbit. In particular, after some validation tests to prove the effectiveness of the implemented algorithm, it will be shown how different kinds of observables influence the accuracies of the estimated orbital parameters. Then, the influence of the observation geometry is analyzed and finally the improvements achieved on the orbit prediction, for different orbital regimes, will be shown. All the mentioned tests are performed using real ranges from the International Laser Ranging Service (ILRS) stations and real angular/laser measurements provided by sensors of the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald owned by the Astronomical Institute of the University of Bern (AIUB).

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