Horizontal Link Demonstration Over 143 km With CubeISL: The World's Smallest Commercial Optical Communication Payload for Inter-Satellite Links

New developments in the field of free-space optical (FSO) communications are enabling a breakthrough in satellite miniaturization and data rates. The CubeISL laser communication terminal (LCT), developed by the German Aerospace Center (DLR), shall demonstrate in-orbit inter-satellite links (ISLs) at 100 Mbps and downlinks at 1 Gbps. When it launches in 2025, it aims to become the state-of-the-art technology for efficient CubeSat communications at high data rates and the world's smallest optical inter-satellite link terminal.\nThe performance of the CubeISL terminal was tested in a 143 km horizontal link between the islands of La Palma and Tenerife. In this setup, the transmitter from the LCT was used to characterize the atmospheric aberrations of the horizontal link using the ESA Optical Ground Station. Additionally, another LCT was used to demonstrate the tracking capabilities between two CubeISL terminals. This paper describes the current development status that allowed achieving an inter-island link. It analyzes the atmospheric aberrations encountered among the horizontal link and presents the results from the tracking performance between the two ISL terminals.\nThe focus of the paper lies specifically on the system's design which allows effortless transportation, swift assembly, and eye-safe operation. This design enables a pragmatic automatization of FSO links with CubeISL in flexible terminal–OGS configurations and campaign sites.