Richard Branson lost his balloon but will try again. Steve Fossett landed in Russia after hitting technical problems. And two other teams in the United States and Switzerland are standing by, waiting for just the right moment. Why is it so difficult to circumnavigate the earth by balloon? Sarah Griffiths of BBC Science has been investigating:

Steve Fossett is the latest hot-air ballooning casualty in what has been described as "the last great aeronautical adventure within the Earth's atmosphere."

Steve Fossett

The American millionaire chose a low-tech approach, using a small balloon with an unpressurized cabin. This meant he had to carry oxygen supplies to be able to breath at altitudes of about nine kilometres.

Unfortunately, he was forced to land in southern Russia after a series of equipment breakdowns.

"I'm a little bit discouraged, but nevertheless it was a good flight and so I have to be satisfied with having made a good flight across the Atlantic and made it one third of the way around the world."

Of the six teams involved in the competition, only three now have a chance of making the daring attempt this year, and these are larger balloons, designed to make use of the so-called jet streams, the fast winds that blow at altitudes of around 12 kilometres from West to East in the Northern hemisphere. And it is because of this that the balloonists are forced to attempt the trip during the winter months, as Britain's Richard Branson explains.

Richard Branson

"Really the only time to attempt to go around the world is in January. This is when the winds are incredibly strong and the jet streams can go up to 2 or 3 hundred miles and hour. What we are trying to do is to tuck our balloon into the core of one of those jet streams and try not to get into an eddy on the edge where you would go nowhere."

So there are two different approaches to the challenge, low-tech low altitude flights and high-tech higher altitude attempts. Cameron Balloons of Bristol, England are involved in both, having designed four of the competing vehicles. Jim Howard is their production director.

"The high-tech high level attempt, you have to produce a capsule which you can live and breath in for up to 21 days; a sealed capsule which is pressurized. The high altitude on the face of it would appear to be the best bet. The lower altitude balloon, you are more likely to encounter different types of weather and be blown off course and other things."

In fact having failed in his recent attempt, Steve Fossett now feels that any successful around-the-world voyage may have to be made in a pressurized capsule and Jim Howard agrees with this.

"If you are going to go in a pressurized balloon, it is much heavier and you can have heating. Poor Steve [Fossett] over five days has had to endure temperatures of minus twenty degrees celcius and it really saps your energy and your morale goes. So I probably agree with Steve that it's going to be very difficult to do it at low level. It can be done, but it's going to be difficult."

But there are drawbacks to using a more technical balloon, as Don Cameron of Cameron Balloons points out. He is currently with the team in Switzerland, who hope to launch their Breitling Orbiter this week.

"This can be an advantage and a disadvantage. It should have better performance, being able to go higher, but with more untried experimental equipment, there is a risk of things going wrong."

And on top of the technical problems are the dangers of severe air turbulence and lightning strikes, and the accumulation of ice which forces balloons to make regular excursions into lower and warmer altitudes to melt it. So in the face of all these difficulties, is it really likely that one of the teams will succeed? Jim Howard is convinced it is only a matter of time.

"It isn't just a stupid dream. There are many unmanned balloons that have travelled around the world and come back again. What we do know is it will be done. Within the next three years it will definately be done and we hope it's this year."
 

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