28 November 2017
Recent advances in key technologies are poised to make high-flying uncrewed aircraft a useful supplement to satellites for Earth observation, communications, navigation and emergency response. And, says the European Space Agency, so-called High Altitude Pseudo-Satellites – or HAPS – should also be a way to accelerate development of space technologies through early, high-altitude flight testing.
Says Thorsten Fehr, of the Earth observation programmes directorate at ESA’s European Space Research and Technology Centre (ESTEC), “We’ve been looking into the concept for the last 20 years but now finally it’s becoming reality.
“That’s come about through the maturing of key technologies: miniaturised avionics, high-performance solar cells, lightweight batteries and harness, miniaturisation of Earth observation sensors and high-bandwidth communication links that can deliver competitively priced services.”
Fehr’s remarks followed ESA’s inaugural HAPS workshop, held in October at ESTEC in Noordwijk, Netherlands. The event attracted some 200 HAPS experts and potential customers including Europe’s Copernicus Earth monitoring service and Frontex, the EU agency tasked with border management.
HAPS, which ESA describes as a “missing link” between drones and satellites, would float or fly at high altitude like conventional aircraft but operate more like satellites – except that rather than working from space they can remain in position inside the atmosphere for weeks or even months, offering continuous coverage of the territory below.
The best working altitude is about 20km, above the clouds and jet streams, and 10km above commercial airliners, where wind speeds are low enough for them to hold position for long periods.
From such a height they can survey the ground to the horizon 500km away, variously enabling precise monitoring and surveillance, high-bandwidth communications or back up to existing satellite navigation services.
For Earth observation, says ESA future-systems specialist Antonio Ciccolella, “they could provide prolonged high-resolution coverage for priority regions, while for navigation and telecoms they could shrink blind spots in coverage and combine wide bandwidth with negligible signal delay.”
Because they can be quickly deployed or repositioned, such systems have clear potential to aid in disaster response. Or, being on station semi-permanently, could extend satnav or other communications services to deep, narrow valleys and cities.
Says Ciccolella, “ESA is looking into how these various domains can be best brought together.”
At least one HAPS platform is available today. Airbus Defence & Space’s solar-powered Zephyr in 2010 set a world endurance record, staying aloft for 14 days without refuelling. The improved Zephyr S version has a 25m wingspan and flies at 65,000′, weighing 30% less than its predecessor but carrying 50% more batteries. The UK ministry of defence intends to buy at least three for unspecified uses. But, says Airbus, in addition to military use Zephyr “can be used for humanitarian missions, precision farming, environmental and security monitoring and to provide internet coverage to regions of poor or zero connectivity.”
However, high-altitude drone operation is clearly challenging. Both Facebook and Google have worked on drone programmes to provide internet access to remote locations. Facebook’s Aquila, designed to fly at 60,000-90,000′ – commercial airliners fly at about 35,000′ – suffered a crash on landing in 2016 after what the company says was an otherwise successful flight. Earlier this year it emerged that Google abandoned a drone development project, but it has had some success with a high-altitude balloon programme called Loon.
Thales Alenia Space is working on a cross between aircraft and balloons; it describes its StratoBus autonomous airship as a “surprising vehicle halfway between a drone and a satellite”. Compared to balloons like Loon which move with the wind, TAS says its airships – with electric motors for positioning and station-keeping – promise “long endurance and complete autonomy from a fixed position”. The airship, adds TAS, will fly in the “lower reaches of the stratosphere” and carry payloads of up to 250kg.
According to ESA, first flight of StratoBus is expected in 2021.