Acquisition, tracking, and pointing using Earth thermal images for deep space optical communications

The feasibility of using long wavelength Earth thermal (infrared) images for telescope tracking/pointing applications for both deep space free-space optical communications has been investigated and is reported here. The advantage of this technology rests on using full Earth images in this band, which yield more accurate estimates of geometric centroids than that of Earth images in the visible band. Another major advantage is that these images are nearly independent of Earth phase angle. The results of the study show that at a Mars range, with currently available sensors, a noise equivalent angle of 10 to 150 nanoradians and a bias error of better than 80 nanoradians can be obtained. This enables precise pointing of the optical communications beam for high data rate links.