Guidance and Control of a Spacecraft to Rendevous and Dock with a Non-cooperative Target

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 ¿eld 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 ¿y and ¿nal

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 de¿ned 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 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¿ned

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 di¿erent subphases are presented using a

combination of Hill-Clohessy-Willtshire (HCW) solution, elliptical ¿y 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 di¿erent guidance trajectories for important parameters such as time, fuel

usage, minimum absolute distance and the maximum radial distance from the target

is presented. Veri¿cation of the proposed guidance and control methods is done by

applying them to two di¿erent case studies: the ¿rst 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 di¿erent phases of

proximity operations, and for di¿erent scenariös of the target encountered by the

chaser.