Transmitter alignment with clouds

US Naval Research Laboratory has been developing a lasercom facility for communications to satellites in low earth orbit. The system uses four transmitters mounted evenly around a central receive aperture. This transmitter configuration has advantages in spatial diversity and maintaining eyesafe levels at smaller apertures with increased total power at the spacecraft. One challenge of the system is aligning the transmitters. With tight beam divergence, using a camera to define an aimpoint in the laboratory and then aligning all transmitters and the receive telescope to the same star was insufficient. Instead, NRL developed a method to use transmitter reflections from a cloud deck to perform in situ alignment and motion calibration. This paper describes the alignment procedure and results.