Cluster flight for fractionated spacecraft

Fractionated spacecraft constitutes a satellite design methodology wherein the functional capabilities of a single monolithic satellite are distributed among multiple free-flying, wirelessly-communicating modules. One of the main challenges of a fractionated spacecraft system is cluster flight, i.e. keeping the various modules within a bounded distance, typically less than 100 km, for the entire mission lifetime. This paper presents a methodological development of cluster flight algorithms for fractionated spacecraft systems. To obtain distance- bounded relative motion, a new constraint on the initial conditions of the modules is developed. A concomitant analytical bound on the relative distance between the modules is proven based on a design model assuming timeinvariance of the environmental perturbations. It is then shown that if the actual astrodynamical model includes other, possibly time-varying effects, mild drifts between the modules are obtained. Furthermore, this paper presents a cluster establishment algorithm for tracking a given nominal orbit, whose characteristics satisfy the previously-develop no-drift constraint. This algorithm provides fuel balancing among the maneuvering modules as well as minimization of the total fuel consumption. Numerical simulations using realistic astrodynamical models are used to validate the analysis.