For Airbus and its Zephyr S, the sky really is the limit – because any higher and this "high-altitude pseudo satellite" would have to be a spacecraft.

Zephyr S, a solar-powered unmanned aircraft designed for tactical deployment to provide persistent surveillance or deliver communications to ill-served locations, is half-way through its 10-day maiden flight campaign in Arizona. And results so far point to full-term success and an endurance record for the type. The UK Ministry of Defence has ordered three, for production at a new factory just outside the Farnborough airfield fence, shown for the first time yesterday.

Jana Rosenmann, head of unmanned systems at Airbus, says the key to the flight-test campaign so far has been "fantastic results" in battery performance. The aircraft has achieved an altitude of 74,000ft in Arizona and, critically, has remained above 50,000ft at dawn, after a night's flying with no sun to charge its batteries.

Staying high is the key to Zephyr's value, she says. Solar-powered aircraft give up some altitude to conserve power at night, but if the aircraft can remain in the stratosphere for a full 24h cycle then it remains above commercial air traffic and rough weather.

Sophie Thomas, who heads up the Zephyr programme, adds that going from the 40,000ft maximum altitude achieved by an earlier prototype to 70,000ft-plus gives a "flavour" of the advances Airbus has made in battery management. In fact, she says, performance in the ongoing maiden flight campaign is so good that her team believes it can move to an even more robust design for production models.

The value of Zephyr lies in persistence, and Rosenmann says ground testing suggests that it may be possible to fly 100 day-night cycles without having to land and change batteries. "But we must do it in the air!" she says. Later this year, further testing in Australia will aim to push those limits.

Separately, Zephyr S is delivering good results from a 5kg (11lb) electro-optical payload built by Airbus. Rosenmann says the next target is to fly with a 15-20kg payload.

Airbus Defence & Space is a leading player in both satellite manufacturing for Earth observation and telecommunications, and is also a service provider in those sectors. Zephyr, says chief executive Dirk Hoke, therefore envisages selling not just an aircraft but a service based on hardware, software and solutions.

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Source: Flight Daily News