Optical Communications, 2nd Edition

10

POINTING, ACQUISITION, AND TRACKING IN SPACE OPTICS

Before any data transmission can occur in a space communication system, it is necessary that the transmitter field power actually reach the receiver detector. This means that the transmitted field, in addition to having to overcome the effects of the propagation path, must also be properly aimed toward the receiver. Likewise, the receiver detector must be aligned with the angle of arrival of the transmitted field. The operation of aiming a transmitter in the proper direction is referred to as pointing. The receiver operation of determining the direction of arrival of an impinging beam is called spatial acquisition. The subsequent operation of maintaining the pointing and acquisition throughout the communication time period is called spatial tracking.

The problems of pointing, acquisition, and tracking become particularly acute when dealing with fields having narrow beamwidths and long propagation distances. Because both these properties characterize long-range optical space systems, such as intersatellite links and Earth–space links, these operations become an important aspect of the overall communication design problem. In this chapter, we discuss pointing, acquisition, and tracking in optical space links and present several procedures for system implementation. The effect of these subsystems on communication performance will also be considered.