"Study of Algorithms for GNSS-based Precise Orbit Determination in space" Precise Orbit Determination (POD) of Low Earth Orbiters (LEO) includes a complicated procedure of combining GNSS observations collected by the spaceborne receivers and comprehensive dynamic models and compensating model deficiencies with stochastic accelerations. This method called the reduced-dynamic POD provides the most precise orbits which are essential in many Earth science applications such as satellite altimetry, GNSS Radio occultation, InSAR missions, etc. The thesis will address the design and optimisation of Kalman-based solutions and the performance evaluation via simulation addressing the scenario of a Lunar mission.