Preliminary results of optical downlink between QUBE satellite to the upgraded Optical Ground Station Oberpfaffenhofen - experiments towardsquantum key distribution

The DLR institute of Communication and Navigation hosts an optical ground station with an 80cm primary mirror and as well a running Coudé path with optical bench, adaptive optics system, fiber coupling and a single photon detector. The station already performed successful downlinks from LEO (Flying Laptop, CubeL and others) and GEO stationary platforms (Alphasat, Project BayernQSat), as well as Aircrafts (Project QuNET). In the last year the Ground Station was upgraded from its basic configuration to adapt multi-mission support and QKD experiments. Several features were integrated and upgraded at the telescope, the Coudé path and on the optical bench. A focus on the upgrades were to connect between OGSOP (Optical Ground Station Oberpfaffenhofen) and the satellite QUBE. The target of compatibility could be achieved and improved from OGS side. Knowledge from Ground-to-Ground-Tests were considered to rebuild the receiving setups in a proper and more operational way. The QUBE satellite contains an optical terminal designed and developed by DLR to transmit two experimental quantum signals over the optical link. These sources were developed by the Ludwig-Maximilian University of Munich and the Friedrich-Alexander University in Erlangen. On May the 2nd 2025 the OGSOP was able to catch the first light from QUBE and establish a link between both sides. This major achievement led to the several more links for commissioning and optimizing the performance. After the successful commissioning of the Satellite, the scientific quantum payloads and the optical terminal, several link and experiment campaigns are planned for 2025 beginning already in Summer. The results from the first links as well from the campaigns will also gain experience for the upcoming follow-up satellite Mission QUBE-II.