The blimp reborn

The residents of Akron, Ohio are very excited. As the birthplace of the blimp, the fortunes of this small town have always been inextricably linked with the airship industry and for its citizens the heady days of the airship boom must seem a long way off.

So the recent announcement that the gigantic deserted airship hangar on the outskirts of the city was to be used to build an airship again for the first time since the 1960s certainly came as welcome news.

In December last year Lockheed Martin received a $150m (£80m) contract from the US Missile Defence Agency to return to its historic home in Akron and construct a next-generation airship that could operate at extremely high altitudes. More than 25 times larger than the famous Goodyear blimp, the High Altitude Airship ( HAA) will provide the US military with overlapping radar coverage from far above the jet stream. It is estimated that just 11 of these giant airships could provide surveillance of the entire US coast and southern border crossings.

Ron Browning, business development director for persistent surveillance systems at Lockheed, is in charge of the HAA project and is overseeing the major refurbishment the old airship hangar in Akron required after 40 years out of action. The building of the HAA will begin some time in the next two years, he estimated, with its first flight pencilled in for late 2009.

‘There are a number of applications for the HAA but fundamentally it provides persistence at high altitude, so multi-missions including both surveillance and communications stand out as options,’ said Browning.

The prototype is a massive non-rigid (with no internal frame) 430ft airship with a staggering volume of 100,000m3. To put it into context, the largest previous airship, also built by Lockheed, was a mere 40,000m3. The plan is for the prototype to remain in position at around 60,000ft for 30 days but Browning believes that in the future this time could be lengthened considerably.

However, to even get to this prototype stage a number of engineering challenges that are peculiar to both flying at high altitude and airships must be overcome. ‘The key to the design is understanding the loads that the airship will have to tolerate both at altitude and on its way up to the stratosphere,’ said Browning.

At the same time, one of the most crucial aspects when building any airship is minimising its weight and so these two fundamental aspects had to be integrated into the final HAA design, according to Browning. ‘We looked for a high-strength, low-weight flexible composite, and then added further layers for strength and still more for impermeability and weather protection. We need it to be able to endure the environment at altitude and still be as light as possible.’

Lockheed engineers spent a lot of time and effort working on the flexible material for the HAA, finally plumping for a multifilament polymer composite based on Vectran, an advanced thermoplastic material that is five times stronger than steel.

One of the challenges posed by using conventional fuel in an airship that must remain stationary over long periods of time is mass-management. The more fuel that’s burned, the more it is extremely tricky to calculate the small movements necessary to keep the airship relatively stationary.

To counter this, the HAA will be an all-electric vehicle with four propulsors with electric motors that power four large propellers, each of which is highly manoeuvrable to give pitch and yaw control over the airship. To generate power a thin film of sophisticated but robust photovoltaic cells will be applied to the outside.

Browning expects that although the initial test flights will be remotely operated from the ground, the system will gradually evolve to encompass an increasing level of autonomy.

With the caveat that airships will never completely replace high-altitude unmanned aeroplanes such as Northrop Grumman’s Global Hawk, Browning outlined the advantages of airships over other aircraft: ‘Unmanned aircraft can currently last for one or two days at the most, so straightaway a high-altitude airship gives you significantly better persistence. An airship is also a great deal less expensive than planes and especially satellites,’ he said.

In Europe, while the benefits of a high-altitude airship platform are well known, things are coming along rather more slowly. Since the sad decline of the Advanced Technology Group’s plan for the Sky Cat airship (The Engineer, 8 August 2005) research has largely concentrated on the individual technologies that could operate at high altitude. Some of these, such as high-altitude broadband networks, are seen as able to provide a real alternative to satellite connections for a wide variety of applications.

To this end, a consortium of research organisations and industry including BT are working together on the Capanina project led by Prof David Grace from York University’s department of electronics.

The project team’s latest test flight took place in October in Sweden, when they flew a large 12,000m3 free-floating helium balloon into the stratosphere to trial a range of new technologies that would be needed for providing wireless communication from the stratosphere. The team worked on antennas, as well as testing video downloading capabilities with a server installed on the balloon itself.

One of the key technology demonstrators in the project was an experimental multi-directional system known as free space optics which is designed to provide a high data rate for simultaneously receiving and transmitting signals to and from a base station on the ground far below.

‘The free space technology is an important step,’ said Grace. ‘Developing the pointing, acquisition and tracking technologies will be crucial if this idea is to succeed in the future. The more directional you make your beam the further it can travel and the higher data rate it can carry, but the more difficult it becomes to point and track it.’

Grace believes there is a tremendous possibility for growth in high-altitude platforms and that a future balloon could provide wireless access on-board trains to broadband internet and also cover events like the Olympic Games.

A high-altitude platform, as well as fulfilling obvious military applications as the HAA does, could also be used in disaster relief efforts. Eventually it could carry multicast technology that may include high-definition television, he said.

But there is one major hurdle severely hampering the development of stratospheric communications technologies in Europe: we have got nothing to carry it up there yet.

Until this rather considerable problem is solved, Europe’s ambitions will remain resolutely stuck on the ground. For its recent tests the Capanina team had to use a balloon that it borrowed from the Swedish Space Agency, which had only limited station-keeping capabilities and no on-board motor.

‘The lack of a platform remains a massive problem. The communications technology is coming along very nicely but we are all desperate for a platform and we need the aeronautical industry to take this seriously. While Lockheed is getting nearly $150m (£80m) to fund its HAA there is sadly nothing of the sort happening in Europe,’ said Grace.

There is no easy answer to this problem either, suggested Grace, as he foresaw a number of technical challenges that will cause problems in the development of a high-altitude platform. The main one is likely to be developing materials and systems that are robust enough to survive at that altitude for long stretches of time, particularly the damaging impact of solar radiation.

Back across the Atlantic it is possible that a US firm, Sanswire, could have the answer as it prepares to launch its own version of a high-altitude airship: the Stratellite, designed to be stationed at 65,000ft. Stratellite’s developer hopes that it will then remain in place to an accuracy of one GPS co-ordinate, providing seamless wireless coverage over approximately 300,000 square miles.

With the first Stratellite technology demonstrator due to be launched from Edwards Air Force Base next month Sanswire is currently well ahead of Lockheed in its development of a high-altitude platform. At 126ft, the Stratellite is considerably shorter than the HAA but the major difference between the two is that the Stratellite is a rigid airship, rather than the more balloon-like HAA.

Sanswire’s president, Bob Jones, questioned Lockheed’s decision to base the HAA on a non-rigid design. He pointed to potential problems that occur when helium leaks through material because of the small size of the individual gas molecules.

‘The traditional non-rigid design is a mistake because it means that the envelope itself has to be extremely thick to retain the helium,’ claimed Jones. ‘The Japanese in their work on airships have found that already. Those types of non-rigid balloon-type airships are fine at low altitude but even then the helium has to be reconditioned regularly. Lockheed will find the same.’

The Stratellite demonstrator will test Sanswire’s photovoltaic solar cells as well as the batteries that will store the generated energy and a variety of different electric motors. The Stratellite is equipped with a sophisticated on-board computer that runs the airship’s guidance and navigation system, allowing it to run autonomously or be remote controlled from a control centre on the ground. This computer system also automatically monitors the level of power that has been generated and distributes that power to the Stratellite’s different subsystems as required.

Proving Grace’s earlier assertion that the weather conditions at high altitude pose the biggest challenge to stratospheric platforms, Sanswire used CFD analysis and wind tunnel testing to aid in the airship’s design as well as developing a specialised composite fibre to coat the airship, specifically designed to minimise helium loss.

‘Our airship is an advanced rigid design, using an extremely lightweight envelope and very lightweight materials such as carbon composite rods in the structure to give a strong but light vehicle,’ said Jones. ‘One of the biggest challenges is getting the airship through the jet stream safely so it must be strong.’

Inside the Stratellite the difference with the HAA becomes clear. A network of criss-crossing carbon composite frame beams effectively compartmentalise the individual bags that contain the helium. According to Jones, the Stratellite is the only airship that uses this internal design and with its series of individual helium balloons the risk of gas leaking is greatly minimised.

According to Jones, the environment in the stratosphere poses a number of problems for airships, especially if they are expected to stay there for long periods of time.

‘At 65,000ft it is extremely cold which will affect the battery while at the same time the engines have to be kept cool, because they can easily overheat at that height,’ said Jones. ‘We have put a lot of developmental work into cooling the engine and particularly the photovoltaic cells because they can reach 160-180^o C.’

Sanswire has developed a unique proprietary cooling system that is built into the solar panel to keep it cool.

Many of the broadband wireless technologies that the Stratellite will use are being developed by Sanswire’s parent company Globetel at its German base, which works with the University of Stuttgart. Within the next month some of these will be tested on-board one of NASA’s high-altitude aircraft which are capable of reaching altitudes of up to 65,000ft.

Jones and his team have grand ambitions for the Stratellite and he dreams of providing a national wireless broadband network using a fleet of airships. However, possible future applications for the Stratellite also extend to areas such as border control and battlefield surveillance as well as climate research.

For those who thought the future of the airship went down with the Hindenburg, it would seem the tide is finally turning back in favour of this most graceful of vehicles, as the next generation of airship begins to take shape. Meanwhile, back in Akron, the town is still buzzing. For Don Plusquellic, the town’s mayor, this rebirth of the blimp is fantastic news. ‘The airships are back and it’s thrilling,’ he said.