A quantum network1–3 provides an infrastructure that connects quantum devices with revolutionary computing, sensing and communication capabilities. A quantum satellite constellation offers a solution to facilitate the quantum network on a global scale4,5. The Micius satellite has verified the feasibility of satellite quantum communications6–9; however, scaling up quantum satellite constellations is challenging, requiring small lightweight satellites, portable ground stations and real-time secure key exchange. Here we tackle these challenges and report the development of a quantum microsatellite capable of performing space-to-ground quantum key distribution using portable ground stations. The microsatellite payload weighs approximately 23 kilograms, and the portable ground station weighs about 100 kilograms, representing reductions by more than 1 and 2 orders of magnitude, respectively. Using this set-up, we demonstrate satellite-based quantum key distribution with multiple ground stations and achieve the sharing of up to 1.07 million bits of secure keys during a single satellite pass. In addition, we multiplex bidirectional satellite–ground optical communication with quantum communication, enabling key distillation and secure communication in real time. Also, a secret key, enabling one-time pad encryption of images, is created between China and South Africa at locations separated by over 12,900 kilometres on Earth. The compact quantum payload can be readily assembled on existing space stations10,11 or small satellites12, paving the way for a satellite-constellation-based quantum and classical network for widespread real-life applications.
