The constantly increasing growth of the space debris population is also causing that more and more devices are looking into the sky in search of undetected objects. The process of orbit determination and further object cataloguing requires the initialisation of the object orbital state. This process is particularly complex in the cases when only angular observations from passive devices are available (e.g. topocentric right ascension and declination from a ground telescope). This paper describes the process of initial orbit determination when only a limited number of angular observations are available. Different orbital scenarios (e.g. LEO, MEO, GEO) are analysed together with the available algorithms. The analysis focuses on the suitability of the algorithm for the different orbital regimes and also in the robustness of the solution. The main objective of the analysis is to evaluate the adaptation of the algorithms and their parameterisation for the implementation in operational automated scenarios.

Results obtained using operational four-way TAR data are analyzed and compared to results obtained with both 2-station range measurements and 1-station range and angle measurements. Four-way turn around ranging (TAR) is currently in use operationally by Measat for their new satellite, M-3a (formerly M-1R). The orbital accuracies being obtained for the TAR are similar to ones obtained using classical 2-station ranging when the same two stations used for the TAR are compared. TAR does not make the satellite operations more complex however there are slightly different calibrations that need to be performed. Several cases are considered, including free space propagation and maneuver estimation, both with solar radiation pressure scale factor estimation. The test cases were analyzed using GMV's focusGEO software. The tracking scenario using the full set of tracking measurement including TAR, range, and angles yields the baseline for orbital accuracies used for comparison to the other TAR scenarios. The TAR only orbit determination produces an orbit determination that is on par with the full measurement set solution as does the TAR plus range case. Therefore the use of TAR measurements in place of more costly scenarios is a viable option for GEO satellites. The test case demonstrate focusGEO's ability to consistently mix tracking data types while estimating dynamic parameters and produce a reliable orbit determination solution from TAR measurements independent of the ground stations producing the raw measurements.

The Spacecraft Flight Dynamics Markup Language (OrbitML) is an eXtensible Markup Language (XML) implementation for the representation of information objects in the spacecraft Flight Dynamics problem domain. OrbitML encompasses all the range of space missions (scientific, telecommunications, earth observation, navigation, ...) and phases (LEOP, commissioning, routine, end of life, ...).By providing a standard definition of the involved concepts, their structure, relationships and interfaces based on an extensively used and well known underlying technology (XML), OrbitML allows easy interaction between different operators and agencies in the space field.The initial implementation aims to the operations support of a variety of satellite missions while allowing the extension of its coverage to incorporate new requirements for navigation missions, constellations, interplanetary scenarios and beyond. 12

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