Bøger af Anantha Sayanam Komanduri

Non-cooperative spacecrafts are those current or future assets in orbit which havelost their control authority in one or more degrees of freedom and cannot convey anyinformation concerning their position, attitude or rates to facilitate Rendezvous andDocking/Berthing (RVD/B) process. A growing ¿eld of study in space research is todevelop On-Orbit Servicing (OOS) technology capable of dealing with these space-crafts, called targets, which are designed without any intention to be serviced. Torender services such as repair, refuel or removal of the target from orbit, the chaserspacecraft should exhibit sophisticated RVD/B technology for formation ¿y and ¿nalstage docking/berthing operations of the mission.Assuming that the terminal capture operations of the target are to be performedby a suitable manipulator system on-board chaser, this study relies upon proventechnology and outlines guidance and control methodologies to achieve rendezvousduring proximity phases. The entry gate of chaser after phasing can be de¿ned at adistance of about 5 km in ± V-bar direction from the target in its orbit. To accountfor errors in modeling, navigation or actuation, proximity range operations from theentry gate are decomposed into three di¿erent subphases as far range, inspection or¿y around and closer approach.From the entry gate and along the path of the chaser two hold points are de¿ned:¿rst to initiate an inspection and the second, which is close to the safe zone de¿nedaround the target, to initiate a capture. The chaser is assumed to perform a stationkeeping maneuver at the second hold point until initial conditions for the capture aremet. Possible scenarios pertaining to the behavior of the target in a circular orbitare considered and guidance schemes for di¿erent subphases are presented using acombination of Hill-Clohessy-Willtshire (HCW) solution, elliptical ¿y around, glides-lope algorithm etc. Relative controllers both for position and attitude of the chaserare also presented. A Linear Quadratic (LQ) controller for relative position and aProportional Integral Derivative (PID) controller for relative attitude with angularvelocity constraints are chosen to track down the error to achieve rendezvous andattitude synchronization with the non-cooperative target. A comparative analysisbetween di¿erent guidance trajectories for important parameters such as time, fuelusage, minimum absolute distance and the maximum radial distance from the targetis presented. Veri¿cation of the proposed guidance and control methods is done byapplying them to two di¿erent case studies: the ¿rst study incorporating a stabilizedtarget in Geostationary Earth Orbit (GEO) and the second, with a spinning targetin Low Earth Orbit (LEO).The methods presented here are general and provide a simulator to the chaser toperform rendezvous analysis with non-cooperative targets. To achieve RVD/B, thestudy proposes a careful combination of guidance solutions for di¿erent phases ofproximity operations, and for di¿erent scenariös of the target encountered by thechaser.