SCIENCE: HOT AIR AND HIGH HOPES

Balloonists can glide thousands of miles through the sky and stay aloft for days. So what's so challenging about circumnavigating the world? Norman Miller reports

SOME START in Missouri and get as far as Russia. Others kick off in Switzerland but end up sinking into the Med. Another goes to North Africa but doesn't even get going. Who'd be a round-the-world balloonist, eh? Hot air and high hopes are the common link between the various teams of adventurers seeking to achieve what British challenger Richard Branson calls "the last great aviation record left on earth". While aircraft have been breaking distance records almost from the moment they first flew, the great endurance records have eluded balloonists until relatively recently, despite their much longer history of flight.

The balloons used by today's would-be circumnavigator might impress Jules Verne with their size but the basic principles would be nothing new. Napoleon was just another ambitious teenager when, in 1785 (two years after the Montgolfier's first manned balloon flight), French physicist Jean Francois de Rozier came up with the idea of building a balloon with two envelopes: an inner one filled with lighter than air gas to provide the main lift (nowadays, helium), and an outer hot air envelope which, using something like a propane burner, could be heated to maintain the temperature of the internal helium sphere whatever the temperature outside. This allows altitude to be controlled with minimum use of ballast. By contrast, conventional balloons have no mechanism for controlling gas temperature, causing everything to go up as the gas warms during the day and then come down as it cool at night.

Four teams have hogged the headlines over the past month - Global Hilton, Global Challenger, Solo Spirit and the Breitling Orbiter - though the sudden rush to get airborne at New Year has more to do with the weather several miles up than a flood of resolutions to travel more in 1998.

Winter in the northern hemisphere means ideal jetstream conditions in the upper atmosphere, where winds at speeds of between 110 and 400kmph (70-250mph) whistle along at an altitude of between 5.5 and 8 miles in currents shaped like flattened tubes. These sky-roads can be from 500 to 2,500m (1,600-8,300ft)in height and range from B-roads a few kilometres across to 1,000km (625m) wide motorways, used by passenger jets as well as by Jules Vernes types. While a balloonist counts on helium to do the lifting, jetstreams provide speed, direction and distance - in particular, the Polar and Subtropical streams, stretching thousands of miles around the globe.

If you want to drift your way around the earth, you have to face up to challenges in three areas - technology, meteorology and politics. While problems with a recalcitrant jetstream or a nasty bit of weather can stymie your journey, the political outlook on the ground can make the skies just as risky.

Air space is as jealously guarded today as land or sea. This was made tragically clear in 1995, when two US balloonists drifted into airspace over Belarus and were shot down by a military not keen on Americans hanging around over their country. Both were killed.

Nature can be unfriendly, too, with air temperatures down to -70C, precious little atmospheric pressure and not much in the way of oxygen. It's more challenging if you hope to be hanging around up there for the couple of weeks it would take to do the planetary round trip. With this in mind, all but Steve Fossett in Solo Spirit have opted for a hi-tech living chamber. In a pressurised aluminium capsule about 10ft high and the same around, two or three people share a space with global positioning satellite (GPS) navigation gear, communications equipment, food and drink, a pilot desk with controls, ventilation system, sleeping bay and a loo. Cramped perhaps, but luxury compared with Fossett's high-rise home.

Forsaking comfort for weight-saving, Fossett's recent journey (his third attempt) took place in an unsealed gondola, where heaters and an oxygen supply provided little real comfort. Being open to the elements also limited how high (below 6,000m/ 20,000ft) he could fly, denying Fossett access to the jetstreams. A failed heater which meant temperatures dropped to well below freezing, trouble with a propane burner and bad weather finally cut short his flight. After four and a half days and 11,600km (7,300m), he came down to earth in a southern Russian field, greeted by puzzled farmers rather than a press corp.

While none doubted Fossett's bravery and achievement - he still holds the world endurance record for a balloon flight, just over six days and 16,000km (10,000m) from Missouri to India in January 1997 - some doubted his wisdom. "It's not possible to fly around the world unpressurised and solo," says Swiss balloonist Bertrand Piccard.

Hi-tech doesn't guarantee anything, though. Piccard's previous effort ended up in the Mediterranean after a fuel leak, while Americans Dick Rutan and Dave Melton came a cropper in Global Hilton this month when a deteriorating jetstream over the Atlantic deflated their hopes.

The December winds which scuppered Richard Branson's latest attempt when they ripped his Global Challenger from its mooring in Morocco and blew it into Algeria highlights another hurdle Nature can put in the way. Just when the weather up high is at its best for jetstreams, conditions on the ground can be at their worst.

At least Rutan and Melton got into the sky, before losing out in what Andy Yeatman of the Met Office compared to "an airborne game of chess" in which the players are not only worrying about the weather where they are but also looking ahead several hundred miles to try and catch the right jetstream. Get it wrong and it's like missing your turning on the motorway, only much worse. You might end up a few miles out of your way, they could end up over the wrong continent.

In the end, though, it will be done - there is no reason why it can't be. Things just need to click. With no technical hitches and jetstreams at their back, someone somewhere will lift off from a field and drift across the longitudes to achieve the last great aviation record. Anyone fancy a couple of weeks getting high? !

THE TECHNICALS

If big numbers impress, then check the spec on these babies. Size is important in a balloon envelope that has to carry a life-support capsule weighing up to four tons. Global Challenger, Global Hilton and the Breitling Orbiter have envelopes between 45-55m (150-180ft) high and 35-45m (110- 150ft wide, with volumes between 15,000-31,000 cubic metres (150,000-310,000 cubic feet) and weights of around two tons. These aerial juggernauts can reach a top speed of around 400kmph (250mph) and do 0-9,000m (0-30,000ft) in, well, who's in a hurry?

IT'S ALL IN THE JETSTREAMS

Unknown before the Second World War, these high-altitude winds extend thousands of kilometres under the tropopause at altitudes of between 9,000-14,000m (30,000-46,000ft). Jetstream currents are instrumental in large-scale exchanges of air to and from ground level and the upper atmosphere, and are occasionally visible by the cirrus clouds which are one of their features.

They can reach speeds of 400kmph (250mph), especially along the Eastern Seaboard of the USA and over Asia.The two main jetstream currents are the Polar, generally located between the N30th and N60th parallels at about 9,000m (30,000ft), and the more southerly subtropical current generally blowing between the N20th and N30th parallels (though it can extend almost to the equator) at a height of 12,000m (40,000ft).

Though the strength and direction of jetstreams vary, they are strongest during January and early February. During the summer, jetstreams are less consistent over land, where winds take on a more north-south orientation - "Not a lot of use when you want to fly west to east," says Andy Yeatman of the Met Office. Balloonists find the jetstreams using accurate high level wind forecasts, calculated on super-computers at two major world centres (one in Washington, the other at the Met Office HQ in Bracknell).

Balloons will not always travel in a jetstream. Sometimes they will sacrifice speed and height to steer beneath a particular jetstream in order to pick up a wind that will steer them towards another jetstream going in a different direction. There are only four main jetstreams of any significance, the Polar and Subtropical ones in each hemisphere. The southern hemisphere jetstreams are at their best in their winter (ie our summer). It seems that no-one is trying to do the circumnavigation round the southern hemisphere because there is much less land around if anything goes wrong.

BALLOONING RECORDS/ATTEMPTS

11981-82 Maxie Anderson and Don Ida make three attempts to fly around the world

11992-94 Larry Newman makes four attempts

11997 Steve Fossett sets current record from Missouri to northern India (16,000km/10,000m) - about half the 32,000km (20,000m) a circumnavigation would take

OTHER DISTANCE LANDMARKS

11987 Richard Branson - first hot-air balloon crossing of the Atlantic

11991 Branson first to cross Pacific

ROUND THE WORLD IN 18 DAYS - A BRIEF HISTORY

Ever since American John Wise attempted the first global balloon flight in 1850 - and wrote about it in his book Through the Air - balloonists have been vying to circumnavigate the globe in what National Geographic labelled "the last great aeronautical adventure".

Per Lindstrand and Richard Branson became the first to cross the Atlantic in the 1980s (Lindstrand went on to cross the Pacific), and the race was on for the world title. The first abortive attempts to make the 18 to 20 day trip were made in the early Eighties by Maxie Anderson and Don Ida, followed by four attempts in the early Nineties by pilot Larry Newman.

Costing anywhere from $350,000 (pounds 220,000) to launch, a round-the-world balloon is enormous and takes between six and 10 hours to inflate, containing around 120,000 cubic metres (400,000 cubic feet) of inert helium gas. The Virgin balloon stood at one and a half times the height of Nelson's Column. Hollow spaces are good for take-off, but in the States, sports stadia are popular.

The rules for the title, worth pounds 600,000, are set by the Federation Aeronauticale Internationale: contenders must, for example, pass through one longitude line, such as the Greenwich Meridian, twice.

Crews, who survive on military food rations and use a bucket to urinate, must be prepared to parachute out if things get hairy.

One of the first groups to plot a round-the-world trip in the 1980s was sponsored by ICI, but plans faltered and the balloon never managed to get off the ground. One member, Julian Nott, went on to use a gas balloon to fly across Australia. Rachelle Thackray

AND THE CONTENDERS ARE ...

PER LINDSTRAND AND RICHARD BRANSON

Branson, 47, has spent millions attempting to win, and teamed up with Swedish-born Per Lindstrand, to create the Virgin Global Challenger, the biggest balloon on earth, with a capacity of 110,000 cubic metres (1.1m cubic feet) and a height of 60m (194ft). Lindstrand, 46, who began flying 20 years ago in the Swedish Air Force, designs and manufactures balloons commercially. Third crew member is Branson's business associate Rory McCarthy, 37, a hang-glider who flies a supersonic jet at weekends. The team took champagne and caviare on their second attempt departing from Marrakesh in December. Celebrations were thwarted after a string of disasters. Lindstrand, who founded a balloon company in 1991, has now built a second balloon and the pair plan a third attempt.

STEVE FOSSETT

Fossett, 53, an American multi-millionaire commodities dealer, has proved his track-record for toughness many times. He's swum the English Channel (twice), attempted to climb Everest (twice) and competes in husky races. He won a solo yacht race across the Pacific, and has flown solo across both the Atlantic and Pacific. Naturally, he took to ballooning alone in Solo Spirit, with a low-tech approach. His balloon is smaller too - just 10,500 cubic metres (350,000 cubic feet). In his latest attempt this month he flew at around just 6,000m (20,000ft), using portable oxygen and wearing thermal underwear to keep warm. It ended with a crash-landing.

DICK RUTAN

Sponsored by Global Hilton, Rutan and crewmate Dave Melton's recent first attempt was delayed because of bad weather; after eventually taking off from Albuquerque, things rapidly went wrong and the pair bailed out. Rutan, 59, a former air force pilot and designer from Mojave, was the first to circumnavigate the world by air 11 years ago in the long-winged plane Voyager - now in the Smithsonian Air and Space Museum in Washington DC. The pair used an air-conditioned gondola and a balloon built by Bristol- based Cameron Balloons.

BREITLING ORBITER

The three-man team in this balloon, sponsored by Breitling Watches, includes British flight engineer Andy Elson, Belgian Wim Verstraeten and Bertrand Piccard, 38, a Swiss psychiatrist and the grandson of the pioneering balloonist Auguste Piccard. They are planning a second attempt taking off from the Swiss village of Chateux d'Oex, from where the team hope to cruise across the Mediterranean and hit a jetstream above North Africa. A first attempt ended when a 69p fuel clip leaked kerosene into the gondola; a second attempt has suffered a hiccup when the cabin was accidentally dropped.

KEVIN ULIASSI

Also flying solo, with an unpressurised 2m (6ft) foam cabin, Uliassi, 34, is from Chicago. In his recent attempt he was forced to land after one of his balloon's helium containers burst. His balloon, named after his wife of one year J Renee, resembled an ice-cream cone. He launched from a gravel pit in Rockford, Illinois, a few hours after his rival, Fossett, but was airborne for less than three hours. Uliassi, who has flown balloons for 16 years, slept in a low-pressure chamber during nights before the launch. A former balloon pilot instructor, he is a trained architect and mechanical engineer, and began planning his flight 11 years ago.

BOB MARTIN AND JOHN WALLINGTON

The two Australians were due to launch the Dymocks Flyer from Alice Springs on 28 December, but the project faltered because of money problems. Nick- named "basket-in-space", the white balloon was designed to float to around 39,000m (130,000ft) (38km/24m up), to conduct experiments for Nasa. Its envelope was to be filled solely with helium, and the cabin included life-support systems, cameras, electricity and scientific data-gathering machines. The idea was to drift upwards and wait for the world to rotate. Wallington, 42, who runs Balloons Aloft, the largest commercial balloons enterprise in Australia, was named the continent's balloon cham-pion in 1988; in 1993, he and Dick Smith were the first to fly across Australia.