Book Description

Non-cooperative spacecrafts are those current or future assets in orbit which have lost their control authority in one or more degrees of freedom and cannot convey any information concerning their position, attitude or rates to facilitate Rendezvous and Docking/Berthing (RVD/B) process. A growing field of study in space research is to develop On-Orbit Servicing (OOS) technology capable of dealing with these space- crafts, called targets, which are designed without any intention to be serviced. To render services such as repair, refuel or removal of the target from orbit, the chaser spacecraft should exhibit sophisticated RVD/B technology for formation fly and final stage docking/berthing operations of the mission. Assuming that the terminal capture operations of the target are to be performed by a suitable manipulator system on-board chaser, this study relies upon proven technology and outlines guidance and control methodologies to achieve rendezvous during proximity phases. The entry gate of chaser after phasing can be defined at a distance of about 5 km in ± V-bar direction from the target in its orbit. To account for errors in modeling, navigation or actuation, proximity range operations from the entry gate are decomposed into three different subphases as far range, inspection or fly around and closer approach. From the entry gate and along the path of the chaser two hold points are defined: first to initiate an inspection and the second, which is close to the safe zone defined around the target, to initiate a capture. The chaser is assumed to perform a station keeping maneuver at the second hold point until initial conditions for the capture are met. Possible scenarios pertaining to the behavior of the target in a circular orbit are considered and guidance schemes for different subphases are presented using a combination of Hill-Clohessy-Willtshire (HCW) solution, elliptical fly around, glides- lope algorithm etc. Relative controllers both for position and attitude of the chaser are also presented. A Linear Quadratic (LQ) controller for relative position and a Proportional Integral Derivative (PID) controller for relative attitude with angular velocity constraints are chosen to track down the error to achieve rendezvous and attitude synchronization with the non-cooperative target. A comparative analysis between different guidance trajectories for important parameters such as time, fuel usage, minimum absolute distance and the maximum radial distance from the target is presented. Verification of the proposed guidance and control methods is done by applying them to two different case studies: the first study incorporating a stabilized target in Geostationary Earth Orbit (GEO) and the second, with a spinning target in Low Earth Orbit (LEO). The methods presented here are general and provide a simulator to the chaser to perform rendezvous analysis with non-cooperative targets. To achieve RVD/B, the study proposes a careful combination of guidance solutions for different phases of proximity operations, and for different scenario’s of the target encountered by the chaser.