The team were unhurt yesterday after being forced to abandon their attempt to fly around the world, less than 24 hours after taking off. They ditched in the Algerian desert following a terrifying half-hour when Alex Ritchie, 51, had to climb out on top of the capsule into the freezing night air and drop two of the six 1-tonne canisters of propane attached to the capsule to halt the descent.
Mr Branson said last night that the daredevil exploit had been necessary because explosive bolts designed to release the canisters in emergency had not been enabled at take-off.
Speculation surrounded the possibility that the uncontrolled fall might have been started by a jammed helium release valve, a tear in the canopy fabric, or that the crew released too much helium to control their rapid rise after takeoff.
Don Cameron, a balloonist who is preparing to make his own attempt to cross the world by balloon, said: "It could be that everything went wrong because of a 50-franc [pounds 6] sensor."
He suggested that a piece of the thin layer of ice covering the top of the balloon in the freezing night air may have dropped into the gas valve controlling the release of helium.
"They probably tried to open the valve electronically and a piece of ice probably got in, preventing it from closing perfectly, so the balloon started descending and lost a lot of helium," he said.
Mike Kendrick, the Virgin project director, said it was clear that the system - involving releasing helium to control ascent or lose height, and dumping ballast to control descent - "did not work". But he added, "We'll look at the telemetry on Thursday morning. It wasn't a tear, and the balloon was in dry air - the possibility of icing is really remote. We're not bothering with explanations at the moment. We weren't asking them why they landed, we wanted to know where."
A potentially fatal crash was only averted by the daring of Mr Ritchie, the oldest member of the crew, who was a last-minute replacement for an ill colleague. As the balloon descended at 400ft per minute - twice as fast as an express lift - he unhitched the propane canisters, critically reducing the weight.
Eventually they landed safely in the Algerian desert near the town of Bechar at 7.29am - just 400 miles from their starting point in Marrakesh, Morocco, after flying for 20 hours and 10 minutes. It was a dismal end to the high hopes that Mr Branson had held with Per Lindstrand, the balloon's designer and a co-pilot, of circling the world non-stop in three weeks, using the jetstream at 30,000ft to blow them along. But they managed to land the capsule undamaged.
"We've had quite a lot of adventure that we would rather not have had," Mr Branson said, and added: "I'm sure that if Alex had not been on board, Per or myself would not have come back."
He admitted to having been mortally frightened as the capsule fell out of control. "I suddenly thought, What the f.... am I doing up here again? I remember saying to myself, 'If I ever get through this I am never going to do it again.'"
Without Mr Branson's backing, and perhaps participation, it is unlikely that the Challenger project will get off the ground again. His Virgin companies have been the main sponsors of the pounds 3m attempt, putting in about half of the sponsorship. Another attempt would in any case be unlikely this year as a new canopy able to hold the 1.1 million cubic feet of helium would have to be built.
However, Mr Lindstrand, asked if the trip and its equipment were too ambitious, replied "Probably"; on whether he would go on any further attempts, he answered "definitely". But Mr Branson, the guest of the British ambassador to Algeria last night, said, "I think I will need to talk to my family ... I did ring my son Sam just after landing and he asked, 'Will you try again, Dad?' I assumed he was suggesting that I shouldn't, but when I asked him what he thought he said, 'Of course you should.'
"I have to admit I was rather hoping to hear the reverse from him. But there are other elements of my family I will have to talk to about it."