Position and Attitude Determination of Orbiting Manipulators Using GNSS

Manipulator GNC problem calls for an effective, robust control, which can actually provide good performance only up to the level the kinematic state (i.e. the position, velocity and attitude) is well known. The present paper is devoted to the sensors, which should provide such a state. Besides the request for accuracy, a special attention, as for the other components of the GNC loop, should be paid to the extreme-operational environment they will face onboard. A typical solution for manipulators’ kinematic sensing is represented by encoders, located at the joints and able to provide the rotation between the following arm members. The location of the end effector is therefore computed by simple geometry due to the knowledge of the arms’ length (Figure 1). Different technical solutions do exist, for the observables nature (analog or digital), for the working principle (optical, electromagnetic) and for the measurements (incremental or absolute). In order to provide a different, possibly better solution, and also looking for a back-up sensing technique, the chance to use GNSS is suggested. The idea is to locate receiving antennas at the joints, and even along the arms to define the end effector’s relative position.