Flexible Reconfiguration for Formation Flying Spacecraft with Fuel Balancing

The concept of formation flying in spacecraft is increasingly becoming a key technology that facilitates the realization of complex concepts that would have been impossible with single satellite missions. Such concepts include Multiple Spacecraft Interferometry, Space aperture telescopes using formation flying etc. Some of these formation flying missions are performed in orbits around Earth and some in Deep-Space. Quite a few of these missions incorporate multiple reconfiguration manoeuvres to complete their mission requirements. Unfortunately, due to the nature of formation flying missions, the propellant utilization of each satellite is not equal. While a pre-determined reconfiguration algorithm could be utilized to equalize the fuel requirements for each individual satellite, such an algorithm necessitates a considerably rigid final formation configuration to calculate and perform the reconfiguration manoeuvres. In this paper, we present a fuel balancing algorithm for a flexible reconfiguration manoeuvre. The manoeuvre reconfigures each satellite to a position in the formation that both satisfy the mission requirements as well as utilizes an optimum amount of propellant that depends on the quantity of propellant left for each individual satellite. We need to consider the assumption that at least some of the satellites in the formation can perform identical functions. This assumption allows us to automatically assign each satellite to different positions in the configuration without compromising mission functions (this is the case for current and many future planned missions e.g. ESA’s Darwin). The proposed algorithm includes 3 steps: (1) computation of the reconfiguration’s cost for each individual satellite for a given time horizon, (2) comparison of the computed costs with respect to a ideal balanced partition among platforms, (3) if the balanced condition is not attained change time horizon and repeat step 1. Notice that in addition to the propellant balancing requimanoeuvres additional condition concerning collision avoidance should be met during the manoeuvering phase. The proposed approach, taking advantage of the flexibility intrinsic to formation flying (as an example, by modifying the sequence of maneuvers among spacecraft or by switching their targeted final positions) shows significant advantages while searching for an optimal reconfiguration strategy. A number of simulations, related to several possible cases of interest for different variable formation size and orbits, are presented to validate the approach.