Optical Wireless Links for Extra-Spacecraft Communication

Here, we successfully design and experimentally demonstrate for the first time a challenging Optical Wireless Communication (OWC) link connecting two units placed on the roof of a satellite, thus removing the electrical cable. The system design accounts for the impact of the strong sunlight and the realistic misalignment. First we precisely quantify the maximum sunlight intensity at the OWC receiver in the worst case, i.e. when the Sun is aligned with the optical axis of the link. We then experimentally realize a MIL-STD 1553 OWC system by commercially available components, in a directed line-of-sight configuration: we set a non-negligible value of beam divergence (4.) to provide both high-signal intensity at the receiver and the required tolerance to misalignment. The link is experimentally analyzed in the lab, first under normal illumination and then emulating the intensity of the (filtered) sunlight. In the experiments, the quality of the transmitted MIL-STD 1553 signal is successfully assessed by means of test-modules for industry-level qualification. Most importantly, the link margins are so high that the system effectively works even under direct sunlight. Finally, the measured tolerance to misalignment proves that our system is robust to misplacement of the transceivers (around 15 mm),e.g. due to vibrations.