High Altitude Platforms – HAPS – are designed to operate in a stratosphere at 17 – 22km altitude, a benign band in the atmosphere that enables efficient station-keeping. Here, they are closer to the Earth than satellites, with improved link budgets, and a field of view sufficient for regional coverage. HAPS station-keeping facilitates continuous service and re-location, providing flexibility in the point of service delivery. QKD from HAPS has the potential to fulfil an increased number of requirements beyond satellites, while also playing a part in the strategic visions of a global quantum-secured network backbone based on Space and Near-Space – especially the Stratosphere. HiQ builds on a previous feasibility study at York that established the viability of QKD from HAPS. An experimental free-space testing phase is currently underway, using line-of-sight test ranges up to 20km, as well as a tethered Helikite aerial platform operating up to 400m with greater positional instability than that of the relative calm of the stratosphere at 20km. The next stage in the testing / demonstration process is a flight at high altitude on platform with an operational QKD payload. The project will build a CV-QKD payload, which will be tested in conjunction with UK industry partners who have expertise in the design, building and operation of HAPS. CV-QKD offers particular advantages for stratospheric delivery, operating with transmitters and receivers of reduced size and physical complexity, in addition to offering daylight operation.
