Abstract
<p>Spacecraft formation flying with coupled orbital-attitude dynamics is one of the most intriguing topics in the field of astronautics. Orbital-attitude coupling is induced when a non-symmetrical spacecraft in orbit is disturbed by means of active maneuvering or by external disturbances. Direct contributing factors to the coupled dynamics include the orbital radius, the gravitational parameter and the orbital angular velocity. Disturbance due to coupling is inherently weak in nature (in the order of magnitudes of 10−13 Newtons) for Earth orbit, which majority of spacecraft attitude-orbital control system (AOCS) can easily overcome or can be eliminated by means of system dynamics linearization. For very large spacecraft that have very high moment of inertia, coupled dynamics can impose strong nonlinear disturbance and can affect orbital trajectory. Numerical simulations of the coupled dynamics for a rigid-body single spacecraft system, a dumbbell spacecraft system and a multiple spacecraft formation flying system are conducted for Earth and asteroid 4 Vesta orbits. Simulation results suggest that dumbbell spacecraft systems are the most severely affected by the orbital-attitude coupling due to the connecting tether. Nonlinear coupled orbital-attitude equations of motion are fully developed and are used to formulate a nonlinear controller using feedback linearization. Feedback linearization control method is perfect for this system because the spacecraft’s nonlinear coupled dynamics is preserved and not approximated. The controller is validated by numerical simulations as well as implemented in a hardware-in-the-loop experiment using the Ryerson University’s Satellite Airbed Formation Experiment. For asteroid-related missions, orbital-attitude coupling can be several magnitudes times larger than the coupling experienced for Earth orbit depending on the properties of the asteroid and thus in turn, can severely affect the performance of the spacecraft control system. </p>
Highlights
1.1 Spacecraft Formation FlyingCoordination and cooperative control is a new and promising trend that replaces complex single units with several simpler and smaller agents that enables larger operation areas with greater complexity, flexibility, and performance
An Earth Centered Inertial (ECI) frame, denoted by, Fi − XY Z, has its origin located at the center of the Earth with the Z-axis passing through the celestial north pole, the X-axis directed towards the vernal equinox and the Y -axis completes the right-handed triad
Feedback linearization cancels out the nonlinearities in the nonlinear system dynamics so that the closed-loop dynamic is of a linear form
Summary
Coordination and cooperative control is a new and promising trend that replaces complex single units with several simpler and smaller agents that enables larger operation areas with greater complexity, flexibility, and performance. The new concept makes a way for new and better applications, such as Earth monitoring and its surrounding atmosphere, geodesy studies, deep-space imaging and terrestrial exploration, and in-orbit maintenance of spacecraft or space structures
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