Reconfigurable ground and flight testing facility for robotic servicing, capture, and assembly

As space missions grow more complex, engineers must rely increasingly on multi-satellite operations to accomplish various mission objectives. Several concepts have emerged for autonomous robotic servicing and assembly of orbiting assets which rely on close proximity operation of independently controlled elements. These architectures are inherently associated with increased levels of mission risk. Consequently, mission architects often rely on pre-flight testing for risk mitigation. Unfortunately, this process historically has led to the development of dedicated testbeds that provide risk reduction for a limited number of mission architectures. This paper describes an extension to the Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) facility that allows for unprecedented reconfigurability. This SPHERES extension incorporates hardware and software that can enable TRL6 verification of control algorithms for classes of missions through ground, simulation, and flight testing. The SPHERES facility, consisting of two sets of three identical satellites located at both the MIT Space Systems Laboratory and on the International Space Station (ISS), is being upgraded to include six SPHERES Docking Ports (SDPs) and two SPHERES Halo multi-port expansion structures. The docking ports allow two SDP-equipped elements to dock with each other, and the Halo structures allow for a Halo-equipped satellite to operate up to six peripherals simultaneously through the inclusion of six identical electromechanical expansion ports. This hardware is available for testing on the ground with 3-DOF air carriage systems and aboard the ISS in its 6-DOF long duration microgravity environment. The SPHERES simulation environment, a high-fidelity model of the satellites in 6-DOF, is also being upgraded to include these hardware expansions. This paper describes the design of the hardware and software upgrades, and the expected testbed capabilities they will create. It details how this unique facility enables comprehensive testing to determine the behavior characteristics of future robotic servicing and assembly missions and the interactions between multiple satellites operating in close proximity. A sequence of planned, incremental test sessions aboard the ISS is also described to demonstrate the process by which ground, simulation, and flight testing can be combined constructively to reduce risks associated with these multi-satellite architectures. Results from ground, simulation, and reduced gravity aircraft environments are shown in support of the planned ISS operations.