Algorithms for autonomous guidance of spacecraft to approach, to fly around, and to depart from a target vehicle in a circular orbit are presented. The algorithms are based on the closed-form solution of linear Clohessy-Wiltshire equations. The approach and departure algorithms are adaptations of the glideslope guidance used in the past for rendezvous and proximity operations of the space shuttle with other vehicles with astronauts in the guidance loop. The multipulse glideslope algorithms are general, capable of effecting a translation motion of spacecraft in any direction in space autonomously, decelerating while approaching a target or a nearby location, and accelerating while receding. The flyaround algorithm enables the spacecraft to circumnavigate a target spacecraft in any plane, the orbit plane and the local horizontal plane being two special cases thereof. The circumnavigation is performed in a specified period using a specified number of pulses; the larger the number of pulses, the smaller the deviation of flyaround from the specified radius of circumnavigation. The implementation of these algorithms requires estimates of position and velocity of the spacecraft relative to the target. This relative navigation is performed with an extended Kalman filter using range and angle measurements of the target relative to the spacecraft focal plane and the spacecraft attitude estimates from an inertial navigation system. The corresponding measurement models and process noise matrix are provided. Several scenarios are simulated to illustrate the guidance algorithms and relative navigation. References: 25
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