Orbit Determination Analysis for SSAPurposes

Sammanfattning: Space Situational Awareness (SSA) is the characterization of the space environmentand of space activities. The fundament of SSA is the access to information about theorbit of space objects. There exist several techniques to determine the orbit of objects inspace, both from space-based and from ground-based observations. This Master's Thesisproject aims at investigating orbit determinations from ground-based radar observations.In particular, the use of the EISCAT Ultra-High-Frequency (UHF) incoherent scatterradar for orbit determination purposes is investigated. The radar data necessary forthis work were acquired during the \EISCAT Prisma Odin Experiments" (EPO-1 and2) in July 2014 and March 2015. During the experiments, the Swedish satellites Odinand Mango were tracked with the EISCAT system and their known GPS data wereused to validate the radar accuracy. The results of the analysis show that the EISCATUHF radar is aected by systematic errors in the range calculation: a constant osetand an error that increases when the target moves west from the radar. There is noevidence of systematic errors in the range rate calculation. However, the analysis showsthat between two dierent calculation methods, one seems to be more accurate. Thesecond part of this project analyzes the initial orbit determination problem (OD) basedon synthetic EISCAT data. The tool for this part of the thesis is the software SystemsTool Kit (STK). STK is used to simulate the observation of a satellite with EISCATand to propagate the orbit of the radar target from an initial state. The initial state(r,v) is derived via Lambert's initial orbit determination method based on the syntheticEISCAT observation of the satellite. The computed initial state from Lambert's methoddiers by several kilometers from the true initial state. This is a consequence of the factthat the method relies on the analytical solution of the Two-Body problem and can notbe expected to be more precise. Furthermore, the sensitivity of the Lambert's solverto perturbations of the initial radar observations is investigated. Based on expectederrors of the EISCAT radar observations, it is shown that the in-track range dierencequickly approaches several thousands of kilometers and several hundreds of kilometersin cross-track range dierence between the estimated orbit and the true orbit. Thus,the EISCAT UHF radar is not suitable for precise orbit determination but can only beused for initial orbit determination purposes of a previously known object to providecrude estimates of its initial state. Multiple target position and velocity measurementsare needed to improve the initial orbit determination.