In December 1998 the European Space Agency (ESA) awarded LBL a design study contract for a geostationery stratospheric unmanned airship.  In this venture LBL is in a 50/50 partnership with DASA Bremen (now Daimler-Chrysler Aerospace).  This contract had its final presentation at the end of September 1999.  If the study is deemed successful ESA will issue a build contract in 2000.  DASA was the natural partner because of its expertise in fuel cell technology which is crucial to the success of the HALE (High Altitude Long Endurance) programme

The airship is unmanned and will fly in the stratosphere at 70,000 feet and is geostationary, i.e. it will use its propulsive power to motor into the wind and will therefore remain stationary over its intended position on earth

At this altitude the airship will have a tremendous coverage reaching 400 miles in every direction.  This means that if the airship is used as a mobile telephone relay station two airships flying over the UK can instantly create complete mobile phone coverage of the entire country.

The airship is closer to a satellite than an aircraft as it is intended to leave it on station for up to five years.  Unlike a satellite the airship can be brought back to earth for repair and service, although that is a secondary option.
This very idea was first voiced in the mid 70s by the US Navy in what was called the HASPA programme.  The HASPA concept was almost identical to the ESA HALE study in that it used solar cells for daytime power, fuel cells for night-time power and an electric motor with propeller for propulsion.  However, the solar cell technology at that time was not sufficiently advanced to achieve the required electrical power for the available weight and the project was shelved.  

The solar power available at 70,000 feet is over 1kW/m² and with an 8% efficiency this will translate to 80-watt electricity per m².  The airship’s total surface area is 30,000m² , so only a small percentage needs to be covered by solar cells to achieve the required daytime power extraction of 400kW.  The amorphous silicone solar cells are very flexible and will be integrated as an extra layer in the airship’s skin fabric.
The nighttime power is delivered by a fuel cell almost identical to those used in today’s spacecraft where H₂ and O₂  produce water and electricity.  During daylight hours an electrolyser will split the water into H₂ and O_2.  This regenerative fuel cell is a totally enclosed system and the three gases, i.e. H₂ O₂ and water vapour, are stored in what is called nurse balloons inside the main airship envelope.  This is a unique feature available to an airship due to its vast envelope volume there are probably no other vehicles that could house such vast quantities of gas without compressing it.

The propulsion is by a brushless DC motor configurated to run at the speed where the propeller is most efficient (500rpm) and thus eliminating the need for a gear box.  As the atmosphere at 70,000 feet is very benign, i.e. no weather, almost no humidity, and no pollution the propeller will need virtually no maintenance.  
The flight guidance system will be built by DASA and is very similar to what you would find on today’s airliners.  There are essentially two flight modes, geostationary and free flight.  The airship could be launched from almost anywhere since it has the capabilities to motor itself to its intended location.

The size of the airship is similar to the pre-war Zeppelins but there the similarity stops.  The airship envelope is entirely made from fabric and maintains its shape by slight super-pressure.  The lifting gas is helium, which is totally inert.
The 70,000 feet flight level is selected as it is above 99.9% of all other air traffic (controlled air space stops at 65,000 feet), it is above all weather and the winds at 70,000 feet are the lowest in the stratosphere.
The payload is one ton and could be just about anything.  The most obvious is mobile phone exchange platform but it can also be a radar or a sensor package.  In the current configuration the HALE airship has allocated 15 kW for the payload power consumption.