Flight Dynamics Experience on Galileo Station-Acquisition Operations

Kurzfassung

December 5 2021 marked the start of Galileo’s eleventh launch, L11, from the Guiana Space Centre in Kourou with a Soyuz carrying the latest two Galileo spacecraft, GSAT0223 and GSAT0224. For the first time, the Flight Dynamics operations was under the full responsibility of DLR GfR - in close cooperation with DLR German Space Operations Centre’s Flight Dynamics team - conducted from within the Galileo Control Centre in Oberpfaffenhofen, Germany. The preparation and execution of the Galileo station-acquisition operations are described, focusing on the close collaboration between both Flight Dynamics teams. The paper explains the mission analysis to define a manoeuvre strategy of three drift-start manoeuvres, three drift-stop manoeuvres and up to six fine-positioning manoeuvres after separating from the Soyuz launcher. While the target acquisition method was laid out and the Flight Dynamics teams were trained and prepared for mission execution, sources of dispersion were introduced during L11 operations, causing the operational manoeuvre strategy timeline to diverge from the nominal timeline originating from the mission analysis. By investigating the divergence between station-acquisition manoeuvre plan and manoeuvre execution, this paper shows an assessment on the robustness of the mission planning and operation procedures of the Flight Dynamics teams. Outlining the refinements that needed to be introduced during operations - in order to react to these sources of dispersion - are an important aspect of this paper. The main sources of dispersion mentioned in this paper are: (1) four launch delays, which is more than covered by the ESA-required mission analysis including two delays; (2) injection assessment and separation; (3) orbit determination and propagation; and (4) thruster activity early in the spacecraft’s life. Analysing the effect of these sources of dispersion led to valuable insights and lessons learned for upcoming launches. An example recommendation is to extend the time in between fine-positioning manoeuvres in order to improve the orbit determination process. In its turn, it allows for a better assessment in the decision-making process whether to execute an additional fine-positioning manoeuvre to reach the target slot. Ultimately, the successful L11 stems from an efficient collaboration between both Flight Dynamics teams so that GSAT0223 reached its target slot B03 after 10 manoeuvres: three drift-start, three drift-stop and four additional fine-positioning manoeuvres. GSAT0224 needed one additional fine-positioning manoeuvre to reach its target slot B15.