Brit startup would like to beam 5G connectivity down at you from hydrogen-fuelled drones

And Deutsche Telekom's happy with this airborne base station plan

A British startup is hoping to strap 5G antennas to liquid-hydrogen-powered high-altitude pseudo-satellites in the hope of replacing mobile base stations on the ground.

Stratospheric Platforms made a test flight over Germany last Monday (19 October) using a Grob 520 high-altitude "optionally manned" aircraft, and the firm is said to be looking at developing its own hydrogen-powered high-altitude pseudo-satellite (HAPS) for flinging 5G connectivity into the world's skies.

The trial 45,000ft over Bavaria reportedly saw a single 4G LTE smartphone enjoy "download speeds of 70Mbps and upload speeds of 23Mbps over a 10MHz bandwidth".

Deutsche Telekom (DT), an investor in Stratospheric Platforms, praised the trial. Bruno Jacobfeuerborn, chief exec of DT's mobile mast subsidiary, said in a canned statement: "We are thrilled to be working with Stratospheric Platforms to realise our vision of connectivity from the sky. SPL's unique technology will enable us to deliver to all our customers, wherever they are located, a true broadband experience. We welcome other investors to join us on this journey to cost-effectively address the challenges of broadband roll-out."

The system is intended to be integrated into ground-based mobile phone networks, in much the same way as the EU Aviation Network (another pie in which DT has a finger) is intended to serve airline passengers with seamless ground-to-air connectivity backhauled through an actual satellite, though airline uptake of it was said, during a legal challenge to part of the system, to be slow.

If the concept sounds familiar, that's because Google has already been there and done it: its Loon balloons are flown across large areas of the world that don't have ground-based mobile base stations – when, that is, they're not going out of area and crashing in countries with no idea of what's going on. Like the SPL concept, these HAPSes carry an LTE base station and antenna payload plus solar panels for power.

Where SPL differs radically from Google Loon is in its proposal to develop a hydrogen fuel cell with which to power both the payload and the HAPS aircraft itself. Richard Deakin, chief exec of SPL, told the Royal Aeronautical Society's Aerospace magazine: "The problem with literally all the existing HAPS is they are all without exception powered by solar power. That just doesn't deliver anywhere near the sort of power that you need for a serious telecoms application."

The aircraft SPL proposed for lofting 5G base stations up to altitudes of about 65,000ft are said to have a wingspan of 60m – almost that of a Boeing 747 – with which it will carry a 3m x 3m antenna. At the planned operational altitude each HAPS's electronically steerable antenna will cover an area of "140km in diameter". Onboard hydrogen fuel cells are intended to deliver up to 20kW "just for the antenna" while carrying a payload of 140kg. The power supply alone, if it matches its claimed specs, is eye-catching: last year a researcher opined to industry news site Light Reading that a 5G base station would need around 10-15kW to run a 64T64R MIMO array, compared to 6kW for a typical 4G LTE setup using a 4T4R array.

Aerospace magazine went on to describe the SPL concept of operations, consisting of "virtual giant steerable data relay footprints" created through what sounds like a mesh network of hydrogen 5G HAPSes: "This patented concept, of using a synthetic inverse aperture array to do telecoms work or cooperative aerial inter-antenna beamforming (CAIB) provides 'massive amounts more data' than a single antenna on its own and allows the creation of individual cells for each user."

Where the SPL concept may run into problems is its endurance compared with other HAPSes. Google Loon's balloons, for example, have a claimed endurance of 100-120 days. Back in late 2019, Airbus was testing its Zephyr HAPS for a month at a time (until Mother Nature intervened anyway), and Aerospace reckoned the SPL craft's endurance would be shorter than that. On the far end of the scale, BAE Systems boasted in 2018 of developing a HAPS called Phasa-35 with an endurance of a full 12 months.

Endurance (or lack thereof) is not a problem until one wants to deploy a HAPS or land one; the delicate lightweight structures which give them such long endurance are very poorly suited for coping with winds and turbulence below their ~65,000ft operating height, where the atmosphere is relatively calm. All major HAPS operators have had crashes as a result of turbulence damaging their craft.

SCL's HAPS is scheduled to be test flown in 2022. ®