Solar-powered pseudo-satellite breaks airborne endurance record

Zephyr S Arizona flight test campaign (Airbus)

25 July 2018

An Airbus-built solar-powered “high-altitude pseudo-satellite” (HAPS) has set the world record for flight endurance without refuelling, reaching 14 days 22 mins 8 sec during a test flight in Arizona; Zephyr S, having surpassed the record set in 2010 by its predecessor, Zephyr, remains aloft. This is the uncrewed aircraft’s first flight, begun on 11 July.

Ultra-light with a 25m wingspan, Zephyr S is understood to be operating at around 70,000ft during the day and, critically, has remained above 50,000ft at dawn. Solar-powered aircraft necessarily lose altitude at night, when they cannot charge their batteries. According to Airbus, battery management for extended operation is the key to HAPS success.

Such aircraft promise to provide much of the benefit of a satellite, for ground observation or to provide a communications relay to ill-served areas, while being tactically deployable in response to a disaster or security event. But such an aircraft must sustain enough altitude to avoid interference with commercial airline traffic. The UK defence ministry has purchased three Zephyr S aircraft for unspecified purposes; they are being built at a new facility in Farnborough, shown for the first time during this month’s international air show.

Farnborough is a focal point for HAPS development. The Zephyr programme was originated by British defence technology company Qinetiq, which saw it through its 2010 endurance record before selling it to Airbus in 2013. Several Qinetiq and Zephry veterans went on to form a company called Prismatic, based in Farnborough, which developed a concept called PHASA-35 – Persistent High Altitude Solar Aircraft – which features a 35m wingspan but mass of just 150kg. Designed for remote sensing, surveillance, communications or environmental science, a quarter-scale version flew last year, to replicate at sea level the behaviour of flight at 65,000ft. Earlier this year Prismatic and BAE Systems teamed up to develop the full-size craft and expect to begin flight trials next year. According to Prismatic, PHASA-35 should be able to operate year-round at latitudes up to 35°, or at the poles in summer.

Also eyeing the high-altitude market is Thales Alenia Space, which describes its StratoBus airship concept as a cross between an aircraft and a balloon – and “halfway between a drone and a satellite”. California unmanned air systems maker AeroVironment has teamed up with Japanese telecommunications group SoftBank to develop a solar-powered HAPS; performance and applications have not been specified, but the project has a $65 million budget.