Secure communications within a country the size of the UK can largely be supported by fibre-based networking. However, future international and worldwide secure communications will also require technologies in space. Demonstrations of QKD between a satellite and a ground station will therefore provide important first steps, towards practical and commercially viable global secure quantum communications.

The Quantum Communications Hub consortium is responding to this challenge by launching its own research mission, funded by the Engineering and Physical Sciences Research Council (EPSRC) under the auspices of the UK National Quantum Technologies Programme. SPOQC (Satellite Platform for Optical Quantum Communications) is the Quantum Communications Hub’s 12u CubeSat, which will be launched in 2024 to demonstrate in-orbit quantum key distribution from space to the Hub Optical Ground Station (HOGS), to be established at the Heriot-Watt campus near Edinburgh, in Scotland.

This demonstration requires direct line-of-sight optical access between the satellite and the ground station. The optical communications are supplemented with a sequence of radio-frequency (RF) data transfers. The optical signals to be communicated are produced in the quantum sources carried aboard SPOQC and sent to the ground using the Optical Transmission Alignment Module (OPTAM). The OPTAM contains an Active Tracking System (ATS) that uses a narrow-band laser beacon originating at the ground station as a target for the optical transmission. This ensures that the quantum signals are transmitted from SPOQC in the correct direction in order to be received on the ground.

SPOQC aims to demonstrate two different approaches to QKD, by carrying a dual quantum payload source developed in the Hub, with two corresponding receivers built into HOGS. These Hub quantum payloads have been developed by the R&D teams at the Universities of Bristol and York, with the Science and Technology Facilities Council’s Rutherford Appleton Laboratory (RAL Space) providing the necessary space technology expertise, and the Hub University of Strathclyde team developing the necessary optimal conditions modelling. Hub Director, Professor Tim Spiller from the University of York, has overall responsibility for the delivery of the technical work, supported by RAL Space’s Head of Disruptive Services, Andy Vick, and Senior Project Manager, Charles Whittington. Successful operation of SPOQC will enable us to establish the crucial next R&D steps, towards future commercial quantum secure services in space.

SPOQC’s essential components for space quantum communications include: the satellite itself, the quantum signal transmitters (payloads) on the satellite, and the optical ground station facility with appropriate quantum signal receivers attached, on the ground.