The disclosed embodiments generally relate to optical communication links and laser optical ranging, and in particular, to optical communication links and laser optical ranging between extraterrestrial bodies.
In space based optical communication and ranging, pointing, or attitude precision is critical as it directly affects the communication link power budget, communication link power fluctuations and the size, weight, and power of the communication or ranging instrumentation. In most examples, the communication link and communication and ranging instrumentation may use optical beams, in particular, lasers. Because of the distances between a space craft and a target, for example, Earth, and the coherence of the optical beam, pointing errors in the micro-radian range may result in missing the target.
A star tracker may be used to determine the attitude of the space craft with respect to the stars. Because the positions of many stars have been accurately measured over the years, a camera may be used with a database of star locations and patterns to determine and adjust the orientation of the spacecraft. The accuracy of the control systems used for attitude adjustment may limit the pointing accuracy. For example, present reaction wheel attitude control systems may limit pointing accuracy to approximately 50 micro-radians. Attitude dynamics, atmospheric drag, magnetic fields, solar radiation pressure, gravity gradients, vibration, and heating and cooling effects may also affect the ability of a space craft attitude control system to maintain a particular attitude in order to accurately direct a communication or ranging beam toward a target.
It would be advantageous to improve provide a system that improves laser beam pointing accuracy to the level of that of the start tracker pointing knowledge so the overall pointing accuracy will not be limited by the accuracy of the control systems used for attitude adjustment.