The Design of an Attitude Control System for a Space Vehicle

The system considered la representative of certain inertially stabilized attitude control systems for NASA Space Vehicles. Its design is presented in order to indicate how such systems may be designed using various available analytical and graphical procedures. The essential problem is to select appropriate compensating network parameters such that for a range of variations of the angles between the vehicle axes and the reference direction given from the sensors, the system stability ia acceptable. The Sil-jak parameter plane method (Refs. 1 and 2), is used for the design as it givea in evidence a system relative stability in terms of two system parameter and is applicable to multi-loop systems. For any particular compensating network considered, the effects of variations of the angles between the vehicle axes and the reference direction may be represented on a parameter plane, and their penniasible range of variations for an acceptable stability la given from relative stability contours plotted on the parameter plane. For the system design all that is required is a systematic search for the best compensating network parameter, and for each trial, the parameter plane may be used to check the effects of sensor angle variations on the stability. Approximate analytical methods (Ref. 3) are used to select some of the compensator network parameters. Graphical methods (Ref. 3) which involve the plotting of complex plane root loci having a specified branch are also used to select some of the system parameter. For the two parameter problem, the root loci may be plotted for which one branch is in fact a relative stability contour. This means that the various transfer function pole-zero configuration encountered can be examined more clearly with regard to relative stability and dominancy characteristics than if just parameter plane diagrams were used. Further, the effects of a third or fourth parameter may be efficiently examined. The problem specification and the problem solution are now presented. Relationships between the system parameters and various equation parameters are used together with the available analytical and graphical methods in order to select eight system parameters.