Zephyr-8 is the latest version of a highly sophisticated series of ultra-lightweight UAVs, capable of flying up to 70,000ft – twice the altitude of a commercial airliner – for up to 45 days at a time. Referred to as a High Altitude Pseudo Satellite, it performs more like a satellite than a conventional UAV.
https://ukdefencejournal.org.uk/look-zephyr-8-britains-new-surveillance-aircraft/