On a hot summer's day, two British adventurers endure Arctic temperatures inside an environmental chamber at the
Boscombe Down airfield in Wiltshire.
By Helen Briggs
BBC News Online science reporter
Clad in a spacesuit over five layers of clothing, balloon pilots Colin Prescot and Andy Elson are down to -50 Celsius.
They are midway through a dress rehearsal for a balloon flight that will take them to the fringes of space.
The two pilots were put through their paces in Boscombe Down
If they succeed with the real thing, they will break the World Balloon Altitude record for a manned flight held by the United States for 40 years.
The equipment the pair is testing is visible through a small window on the side of the chamber.
Obscured by silver panels that will reflect solar rays, the pilots sit strapped into their seats on an open flight platform just big enough for two.
Outside, a team of British and Russian engineers monitor conditions and talk to them.
The Russians have flown to Britain to supervise the final tests on the spacesuits that the men wear.
They are from the company Zvezda, which has been making spacesuits since the days of Gagarin.
The outfits are similar to the ones cosmonauts wear on space walks. They contain a life support system that will allow Prescot and Elson to breathe and carry out their duties at more than 130,000 feet (40 km).
The pilots could not survive the attempt to fly 25 miles above the Earth without them. Besides the cold, the air pressure is so low that they would rapidly lose consciousness.
"It is impossible to be in a balloon which is to rise up to an altitude of about 40 km without spacesuits and it is impossible for the spacesuits to function without life support systems," says Evgeney Albats of Zvezda through an interpreter.
The tests have gone well, he adds, and nothing unexpected has happened.
The launch date depends on the weather, but the current plan is to ascend from a ship off the north Cornwall coast some time between late July and September.
During the flight, Prescot and Elson will conduct science experiments and operate a solar plane tethered to the balloon.
The pair will also send digital stills and video footage back to the ground. From the open platform, they will have a remarkable view.
The balloon has been tested to destruction
Mission controller Brian Jones, himself an outstanding balloonist, says he would love to be up there with them.
"They will be absolutely still, not going anywhere, and just looking down at the Earth," he says. "It's a view that nobody else has seen really since the two guys did it back in 1960."
Once the tests are completed, the chamber is brought up to room temperature and the doors are pushed back to reveal the pilots on their platform.
In a few weeks' time, it should be floating above the Earth tethered beneath a balloon as tall as the Empire State Building.
Colin Prescot zips down the orange cocoon that forms an extra layer of protection over the spacesuit and blinks in the sunlight.
The tests have gone well, he says, but his hands are a little cold! After a succession of TV interviews and photographs, the men clamber out of the test chamber, looking somewhat weary. Their enthusiasm for the adventure, however, is undaunted.
"Today's tests, because we are at sea level pressure, are far harder on the life support system than the actual flight," says Andy Elson. "So we're very, very happy with it all - our confidence has gone up a big notch."
So how will he feel on the big day? "It's only 25 miles," he says, and laughs.