Alessandro Vananti

Associating optical observations of space debris in GEO with an Elitist Genetic Algorithm

This research aims to provide a method that can treat the association and initial orbit determination problems simultaneously. This problem is also known as the Multiple Target Tracking (MTT) problem. The complexity of the MTT problem is defined by its dimension S. The S>3 MTT problem is an NP-hard combinatorial optimization problem. In previous work an Elitist Genetic Algorithm (EGA) was proposed as a method to approximately solve this problem. It was shown that the EGA is able to find a good approximate solution in a reasonable computation time. In this work the algorithm is applied to observations taken at the Zimmerwald observatory.

Orbit improvement merging angular and laser range measurements

The increasing amount of space debris requires huge efforts for the tracking networks to maintain their orbits. The precise knowledge of their positions is fundamental for the planning of collision avoidance maneuvers and future active debris removal missions. The accuracy of an orbit determination process depends on the observables used, their accuracy, the length of the observed arc, and the observer-target geometry. To improve orbits and reduce the needed observation time, the combination of different type of observables is a possible solution. An in-depth study is carried out to investigate the influence of laser range measurements in the orbit determination process based on the classical astrometric observations. After the validation of the algorithm, the influence of the different observables on the estimated orbital parameters is studied. Then, the effects of the observation geometry and the achievable accuracy in the orbit determination process for high altitude bjects are shown. All tests are performed using real measurements provided by the International Laser Ranging Service (ILRS) stations and the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald owned by the Astronomical Institute of the University of Bern (AIUB).

Associating optical measurements of geocentric objects with a Genetic Algorithm: application to experimental data

Currently several thousands of objects are being tracked in the MEO and GEO regions through optical means. This research aims to provide a method that can treat the association and orbit determination problems simultaneously, and is able to efficiently process large data sets with minimal manual intervention. This problem is also known as the Multiple Target Tracking (MTT) problem. The complexity of the MTT problem is defined by its dimension S. The number S corresponds to the number of fences involved in t he problem. Each fence consists of a set of observations where each observation belongs to a different object. The S≥3 MTT problem is an NP-hard combinatorial optimization problem. In previous work an Elitist Genetic Algorithm (EGA) was proposed as a method to approximately solve this problem. It was shown that the EGA is able to consistently find a good approximate solution when applied to simulated data. In this work the algorithm is applied to observations taken by the ZimSMART telescope of the Zimmerwald observatory.

Relative estimate of accuracy in orbit determination from a short tracklet

The Astronomical Institute of the University of Bern (AIUB) is conducting several search campaigns for orbital debris. The debris objects are discovered during systematic survey observations. In general only a short observation arc, or tracklet, is available for most of these objects. From this discovery tracklet a first orbit determination is computed in order to be able to find the object again in subsequent follow-up observations. The additional observations are used in the orbit improvement process to obtain accurate orbits to be included in a catalogue. In this paper, the accuracy of the initial orbit determination is analyzed. This depends on a number of factors: tracklet length, number of observations, type of orbit, astrometric error, and observation geometry. The latter is characterized by both the position of the object along its orbit and the location of the observing station. Different positions involve different distances from the target object and a different observing angle with respect to its orbital plane and trajectory. The present analysis aims at optimizing the geometry of the discovery observation is depending on the considered orbit.

Optimization of Optical Follow-up Strategies Based on Covariance Analysis

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 influence of the orbit shape, of the relative object-observer geometry and the interval between observations.

Dependence of Orbit Determination Accuracy on the Observer Position

The Astronomical Institute of the University of Bern (AIUB) is conducting several search campaigns for space debris in Geostationary (GEO) and Medium Earth Orbits (MEO). Usually, to improve the quality of the determined orbits for newly discovered objects, followup observations are conducted. The latter take place at different times during the discovery night or in subsequent nights. The time interval between the observations plays an important role in the accuracy of the calculated orbits. Another essential parameter to consider is the position of the observer at the observation time. In this paper, the accuracy of the orbit determination with respect to the position of the observer is analyzed. The same observing site at varying epochs or multiple site locations involve different distances from the target object and a different observing angle with respect to its orbital plane and trajectory. The formal error in the orbit determination process is, among other dependencies, a function of the latter parameters. The analysis of this dependence is important to choose the appropriate observation strategy. One of the main questions that arises is e.g. whether observing the same object from different stations results in better determined orbits and, if yes, how big is the improvement. Another question is e.g. whether the observation from multiple sites needs to be simultaneous or not for a better orbit accuracy.