The implementation of the cluster II constellation

This paper highlights the challenging aspects of the Cluster II mission from both the operations and flight dynamics point of view. The first new aspect of the mission was the double dual launch using two Russian Soyuz rockets, especially upgraded with a Fregat upper stage, and each carrying a pair of spacecraft. This choice led to some important consequences: a launch scenario with highly elliptical and inclined separation orbits, operational support of two launches in 4 weeks; and setting up new interfaces with the launch authority and the Russian Lavotchkin industrial complex. The Launch and Early Orbit Phase was one the most demanding phases of the mission, where intense operations were executed under high time pressure. Each spacecraft was then manoeuvred separately through various intermediate orbits, and finally the four spacecraft were brought together. The paper discusses the manoeuvre strategy required to place the two pairs in the operational orbit and to achieve the initial constellation. It describes the operational constraints and problems that had to be examined in the definition of the mission sequence of events, and the major operations and flight dynamics activities.