Satellites may be very useful for communications, navigation and other applications, but they're awfully expensive to build and launch, and once they're in orbit ... well, there's no reusing them. That's why a consortium led by Thales Alenia Space is developing the StratoBus. It's a planned autonomous airship that can be launched like a regular blimp, but that will be able to hover at an altitude of 20 km (12 miles) – that's up in the stratosphere, hence the name.
According to the company, the StratoBus will be 70 to 100 meters long (230 to 328 ft), and 20 to 30 meters (66 to 98 ft) in width. Its envelope will be made mainly of UV-resistant woven carbon fiber, and its two fuel cell-powered prop motors will allow it to maintain its position, even when subjected to winds blowing at up to 90 km/h (56 mph).
The fuel cell will be located in its nacelle (the bottom part, that sits where the gondola would be on a manned airship), along with an electrolyzer for obtaining hydrogen from an onboard water supply, plus its communications and other electronics. Different nacelles will be swapped on and off of one airship body between missions, as each one will be specially outfitted for its intended purpose. Payloads of up to 200 lb (91 kg) will be possible.
The electrolyzer will be solar-powered. Sunlight will stream into the airship's "balloon" through a transparent section of the envelope, then reflect off an internal concentrating mirror, and onto a row of solar panels. That section will be able to stay aligned with the sun, as the balloon will rotate relative to the rest of the vehicle.
Suggested applications for the StratoBus are much the same as those currently served by satellites, including observation, security, telecommunications, broadcasting and navigation. It is estimated that each airship should have a lifespan of about five years, which is also the amount of time that Thales Alenia Space believes it will take to build the first prototype. The company is collaborating on the project with Airbus Defence & Space, Zodiac Marine and CEA-Liten.
The whole thing sounds not unlike Google's Project Loon, which is aimed at getting high-speed internet to underserved parts of the world via radio-equipped balloons. According to Thales Alenia, though, "The advantage of StratoBus is that it offers long endurance and complete autonomy from a fixed position, while the high-altitude balloons in Loon move around the Earth and will offer only limited autonomy."
It also, however, brings to mind Lockheed Martin’s HALE-D airship, and Titan Aerospace's fixed-wing Solara "atmospheric satellite."
Source: Thales Alenia Space via Phys.org
Going down to 55kft / 17km gives 63% more lift, and is still well above air traffic - but getting down to 36kft/11km would give 4x the lift at 20km. Airships work much, much better at lower altitudes.
Any system intended to operate here also has to be able to fairly tightly stabilize altitude against daytime heating and nighttime cooling of the lift gas.