BREMEN, Germany — Balloons, airships, unmanned planes and other so-called pseudo satellites loitering in the stratosphere are likely to enrich the global communications and Earth-observation ecosystem in the not-so-distant future.

Google, an especially deep-pocketed proponent of these satellite alternatives, demonstrated again this week that at least some high-altitude pseudo satellites have passed the purely research and development stage, when it dispatched its helium-filled balloons, developed as part of the Google Loon Project, to provide basic internet and text messaging services to a Puerto Rico still reeling from Hurricane Maria more than month ago.

Facebook, another believer in internet through high-altitude platforms, sometimes called pseudo-satellites, successfully test-flew its Aquila drone earlier this year.

At this year’s World Space Risk Forum in London, Antonio Abad, chief technology officer of Hispasat, said the Spanish telecom satellite operator is in fact looking into high-altitude platform technology and sees more potential in it than in small-satellite LEO constellations.

However, Berlin-based start-up AlphaLink, presenting at this week’s Space Tech Expo in Bremen, Germany, says that quite a few technical problems need to be solved before high-altitude platforms can fully take off.

“With high-altitude platforms, you deliver pretty much the same services as with satellites but you can do it much more cheaply,” said Daniel Cracau, general manager of AlphaLink, which has just recently spun out from the University of Berlin. “You can also be more flexible with your missions and reuse the platform for different missions.”

Time in the air

The AlphaLink team has looked at some of the major issues impeding their more-famous competitors and designed a solution, which they believe would allow high-altitude platforms to operate for much longer periods of time.

Zephyr, Airbus’s high-altitude pseudo-satellite, or HAPS, can remain in the air for up to two weeks, which Airbus says is a world record for any unrefueled aircraft.

AlphaLink believes their AlphaLink 3 model, currently in development, could remain in the air for up to 100 days using state-of-the-art battery and solar panel technology.

“After that, the platform can come down, be recharged and operated again,” said Cracau. “Our later models, we hope, will be able to operate for up to a year and potentially indefinitely as solar panel and battery technology advances.”

Wind stability

While helium-filled balloons, such as those used by Google, are difficult to steer, aircraft, or one-wing solutions such as Facebook’s Aquila drone, frequently struggle with strong stratospheric winds, said Cracau. The platforms need a very long wing to accomodate a sufficient amount of solar cells but at the same time need to be extremely lightweight. That makes them vulnerable to bending and breaking when subjected to strong wind gusts. Making the aircraft sturdier and heavier thus would reduce the amount of communications or observation payload the platform could carry, said Cracau.

AlphaLink approached the problem by designing the platform as a formation of several aircraft of smaller sizes connected at wing tips.

“By combining several smaller aircraft, we achieve a long total wing length but because the aircraft are connected via joints at their wing tips, we can control the wind influences,” Cracau explained. “Because we can handle better these aero-elastical phenomena, we can in general build the aircraft lighter, which is why we can fly longer and also carry more payload.”

If any of the aircraft in the formation experiences technical problems, it can be disconnected from the rest and send to a ground station for repairs, Cracau said, while a replacement aircraft could be send up to join the formation.

Cracau said AlphaLink estimates the platforms could provide internet connectivity and other communication services to remote areas at 10 percent of the cost of satellite technology.

From test to practical application

Earlier this year, AlphaLink tested its concept with a small-scale model flying at a lower altitude.

“We have launched three connected aircraft from a car and observed the flight performance to verify that our flight control system is able to handle such an aircraft,” said Cracau. “We are now looking into scaling the model to be able to show that the solution of connecting individual aircraft really works on the larger scale.”

AlphaLink chief engineer Alexander Kothe has been developing the technology since 2012 as part of his PhD project at the University of Berlin. The company hopes to find a commercial partner to help fund the development.

“In general, the interest and the need and the demand for high-altitude platforms really is visible,” said Cracau. “We have particular interest indicated by disaster management institutions, the Federal Office of Disaster Management and Civil Protection in Germany, as well as the International Disaster Management Association. We hope that here in Bremen, we will be able to find a particular client with a particular user case who would help us fund the development of the full-scale solution.”