Large companies across the globe are working on the Internet of the future, which will one day be available on the ground with good coverage from airborne platforms flying continuously on solar power. The development of such autonomous solar-electric powered gliders is in full swing. Until now, only unmanned models with a very small payload have been tested for stratospheric flight, but now the SolarStratos initiative is aiming for new dimensions with the 25-metre span Elektra-2 in order to speed up commercial applications in the field. On 5 May 2017, the prototype successfully completed its first flight over Payerne in Switzerland. In future, flights and research experiments are planned at an altitude of up to 20 kilometres. No other solar-electric aircraft in the world with a comparable payload has reached this altitude. The Elektra-2 is equipped with an automatic flight control system developed at the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR) and was developed and built by the DLR spin-off Elektra-Solar.

"We are proud of what has been achieved," says Konstantin Kondak of the DLR Institute of Robotics and Mechatronics in Oberpfaffenhofen, who is also involved in the DLR spin-off Elektra Solar. "With the first flight of Elektra-2, we have taken a major step towards the application of high-altitude platforms for data transmission and remote sensing."

Lightweight for heavy loads

The extremely light Elektra-2 is the world's first solar-electric aircraft designed to take a payload of up to 100 kilograms to an altitude of about 20 kilometres in autonomous operation. The ultra-light aircraft itself weighs just 420 kilograms. This has made it possible to, for the first time, test technologies for broadband Internet supply and remote sensing for stratospheric use directly at this altitude. The next step for the solar aircraft will be to undergo extensive flight tests in 2017. The first stratospheric flights are planned in 2018, which will culminate in new record altitudes for solar-electric aircraft.

Autonomously controlled and without landing gear

For the time being, the planned flights have a pilot on board and up to 50 kilograms of payload. In these research experiments, the pilot is supported by the autonomous control unit and is only present to monitor the mission. The next version of the Elektra-2, which is already under construction, will fly longer missions in the stratosphere without a pilot. "In addition, we plan to fly a lighter version of the Elektra-2 without landing gear," says Kondak. " In 2016 we successfully tested the control technology needed for unmanned landing in flight tests carried out in the Allgau region."

Flying platforms complement satellite technology

Nowadays, global communications and remote sensing are covered to a large extent by satellites in Earth orbit. In the future, high-altitude flying platforms could extensively supplement today's satellite technology. Satellite images are produced in orbit at an altitude of several hundred kilometres, while stratospheric flyers achieve a significantly higher resolution at just 20 to 25 kilometres of altitude. In addition, the operating costs can be significantly lower than those of satellites, as there is no need for expensive rocket launches and any defects/problems can be repaired easily on the ground, which in turn increases reliability. It is clear that high-altitude flying platforms will be able to offer a significantly larger bandwidth than satellites for wide-coverage Internet from the air and its popular application perspectives. "For all applications in future, it will be necessary to have sufficiently large and resilient aircraft that can carry the sensor payloads," says Kondak. "The development of suitable ultra-light aircraft is thus becoming a key technology."

DLR spin-off on its way to the stratosphere

Elektra Solar GmbH, the company founded by the DLR Institute of Robotics and Mechatronics, has set itself the goal of building new prototypes for stratospheric flight since 2015, in order to bring the application-oriented research in this area closer to actual product development. The company has created five new high-tech work places in the Munich area, as well as expanded capabilities in the exploration of high-altitude platforms and their applications. The Elektra-2 is the first aircraft for extreme altitudes developed by the DLR spin-off. The basic control system was developed in several cooperation projects with the DLR Institute of Robotics and Mechatronics. Experience and technology from the mobile and space robotics field at the institute were used for this.

SolarStratos Initiative

The SolarStratos initiative has set itself the goal of solar-electric flight in the stratosphere and is coordinated by SolarXplorers and financed by numerous sponsors. DLR is involved in the initiative and plans to use the platform for research experiments in the stratosphere.