Guidance algorithms for near distance rendezvous of on-orbit-servicing spacecraft under constraints

The algorithms for near distance rendezvous of on-orbit-servicing spacecraft to approach and depart from a target vehicle in a circular orbit are presented. These algorithms are based on the closed-form solution of linear Clohessy-Wiltshire equations. And they are adapted from the conventional glideslope guidance for rendezvous and proximity operations of the space shuttle. By using the relationship of the power functions or piecewise linear functions between distance and speed, the algorithms can be applied to any specified transfer time. In order to reduce the number of pulses, a method for the maximum permitted transfer interval between one pulse and the next one is presented. The important constraints such as safety limit velocity and guidance limit error are also considered. With the multipulse glideslope algorithms a spacecraft can make a translation motion at any time and in any direction in space autonomously, decelerating while approaching a target or a nearby location and accelerating while retracting. Simulation results illustrate the validity of the guidance algorithms.