Scaling galileo leop from two spacecraft to four

Abstract

The Galileo programme is a European Union project which provides worldwide geolocation services. In the final configuration, Galileo will have a constellation of 24 operational satellites and 6 spares located on 3 orbital planes. The constellation at the time of writing has 18 satellites controlled by the routine Galileo Control Centre (GCC-D) in the Deutsche Luft-und Raumfahrtgesellschaft (DLR, Oberpfaffenhofen-Germany). The Launch and Early Orbit Phase (LEOP) of these 18 have been prepared and performed not by GCC but by a joint ESA/ESOC (Darmstadt-Germany) and CNES (Toulouse-France) Flight Control Team. This is known as the CNESOC Team. The CNESOC team has conducted two LEOPs of two IOV (In Orbit Validation) spacecraft each, five LEOPs of two FOC (Full Operations Capability) spacecraft each and, most recently, a single LEOP of four FOC spacecraft, launched together on an Ariane-5 rocket. After conducting five FOC LEOPs at an average interval of five months, the LEOP Flight Control team was experienced, and the tools and procedures were mature. So in many ways the 4-spacecraft LEOP was simply a more complex and strenuous version of the previous LEOPs. However, there were challenges (expected and unexpected) that were unique to the 4-spacecraft scenario. The team was enlarged to cope with the additional satellites, but nevertheless scheduling was more complicated than it had been for previous LEOPs. It was not straightforward to reconcile the planned operations with the available ground-station coverage, and the need to provide appropriate breaks to team members over the long (two-week) LEOP. The scheduling was further complicated by security requirements on the maximum period of non-visibility for any spacecraft, and the objective of maintaining a complete telemetry archive (including dumps from periods of non-visibility) The enlarged team consisted of four on-console shifts, each capable of conducting all planned operations (as opposed to two-and-a-half shifts for previous LEOPs). The simple matter of coordinating the activities of these shifts, and managing communication between them, proved to be less straightforward than had been expected. For the 4-spacecraft LEOP there were entirely new scenarios to rehearse in the simulations campaign, including the two shifts on-console for separation, and four spacecraft operated by a single shift. These simulations gave valuable experience in prioritisation in case of contingencies. Various unforeseen problems were detected and mitigated during the simulations campaign. This paper is about the challenges of the first Galileo Ariane-5 launch, highlighting the technical and the human hurdles related to LEOP operations preparation and execution with four spacecraft.