| Many spacecraft have appendages, such as robotic manipulators, antennas, or solar panels, which are equipped with actuators that can cause the appendages to perform well controlled motions relative to the spacecraft in accordance with control laws. Since many motions of this type tend to give rise to changes in the attitude of a spacecraft in inertial space, there exists the theoretical possibility of employing the appendages for purposes of spacecraft attitude control, particularly when other attitude control methods cannot be used because of an equipment failure, lack of fuel, etc. In addition, the application of a blow to one of the bodies of a multi-body space system can cause the system to "tumble," that is, to acquire objectionable attitude motions. For example, this can occur during the execution of a docking maneuver of two spacecraft. Under these circumstances, it is possible, in principle, to use thrusters to modify the motion of the system, that is, to "detumble" it. However, this necessitates the expenditure of irreplaceable fuel. There does exist the theoretical possibility of detumbling a system by means of relative motions of the body parts comprising the system. What is needed for both reorientation and detumbling of multibody systems is suitable control laws which are presented.; Optimal reorientation, in an energy sense, of a planar multibody system is studied first, and comparisons are made with an alternate technique. Next, the three-dimensional reorientation problem is addressed. Both a non-optimal and an optimal technique are developed for carrying out a three-dimensional reorientation maneuver, and a practical example involving the Space Shuttle and Remote Manipulator System (RMS) is presented. Finally, it is shown how a multibody system can be detumbled by relative motions of the bodies. Optimal control theory is used here to achieve the desired result, and the Shuttle and RMS are again the subject of an example. |
