Image copyright Getty Images Image caption Fedor Konyukhov already holds the record for the fastest round-the-world balloon flight

Serial adventurer Fedor Konyukhov is preparing for one of his greatest challenges yet, flying a hot-air balloon up to the stratosphere.

The 67-year-old Russian Orthodox priest has conquered the North and South Poles, scaled Mount Everest twice, rowed across the Atlantic and Pacific Oceans, and sailed solo around the world four times.

But his latest adventure is special, even by his standards.

In the spring, Mr Konyukhov will attempt a world high-altitude record for a hot-air balloon.

He will be using equipment designed and built by Bristol-based Cameron Balloons - the same company which propelled him around the world in a balloon in record time in 2016.

Taking off from a site in Western Australia, Mr Konyukhov will try to reach 25km (82,000ft) - more than twice the height at which commercial airliners typically fly.

If all goes according to plan, he will be up and down within a day.

Image copyright Getty Images

Who is Fedor Konyukhov?

Mr Konyukhov was born in 1951 on the coast of the Sea of Azov in Ukraine.

He was ordained as a priest in the Ukrainian Orthodox Church of the Moscow Patriarchy in 2010.

He has completed the Adventurers Grand Slam - reaching the North and South Poles and conquering the highest mountain peaks on all seven continents.

Mr Konyukhov is an honorary member of the Russian Arts Academy and has produced more than 3,000 paintings.

Mr Konyukhov, whose flight sponsors include Russian energy giant Gazprom, says he wants to "fly high enough to see the curvature of the earth and to look out at the inky-blackness of the cosmos".

The current record was set in 2005 by Indian Vijaypat Singhania, who soared past 21km (69,000ft) in another Cameron-made balloon.

If you would like to see a video simulation of the high-altitude flight, click here.

The Russian had to postpone his record attempt earlier this year after he took longer than planned to complete the 7,000-mile first leg of a solo journey around the southern hemisphere in a rowing boat.

The balloon required for the latest high-altitude record attempt is the biggest that has ever been constructed.

The Z-3,500's envelope is made of about 9km (5.6 miles) of special lightweight fabric and - together with the gondola, or capsule - will stand 68m (223ft) tall, once inflated.

A typical envelope for a sport balloon is about 2,500 cubic metres in volume. This one is a staggering 100,000 cubic metres.

'Edge of space'

Cameron Balloons chief executive Don Cameron, who co-built Britain's first modern hot-air balloon - the Bristol Belle - in 1967, says its vast size presents big technical challenges.

The 80-year-old, who is from Glasgow, says: "The balloon has to be extraordinarily big because he's going to really the edge of space, where there's only about 2% of the atmosphere left. That means that the lifting force is very weak and we can only counteract that by making the balloon enormous.

Image copyright Cameron Balloons Image caption The Z-3,500 has been constructed using 5.6 miles of special lightweight fabric

"We've had great difficulty even inspecting and testing it because if we inflate it in the sunshine, just the warmth of the sun heating it a few degrees at the surface would give it an uncontrollable amount of lift.

"We took it to a big aircraft hangar in Bristol where I used to work years ago and inspected it thoroughly, but we couldn't fully inflate it. Its first full inflation will be on the day it flies."

Mr Konyukhov and his tiny Z-3,500 capsule will be fitted with special parachutes in case there is a mishap during the record attempt.

Image copyright Fedor Image caption Mr Konyukhov is seen sitting in the Z-3,500 capsule during its early stages of construction

But the adventurer, who says he undertakes his record attempts in order to "push the limits of human endurance", acknowledges that it is still "a risky flight".

"When I was flying around the world in 2016 my flight altitude was between 8km and 10km," he says.

"The cabin was not pressurised. I could open the hatch and climb on top of the capsule, clean ice from the burners and check the hoses for the fuel tank using an oxygen mask, so I had much more control of the situation.

"This time, flying to 25km, I will be using a pressurised capsule. It is like a small spaceship. This capsule gives more comfort and sense of security but I will have only buttons to control the burners and envelope."

Image copyright Cameron Balloons Image caption Don Cameron checks out the capsule in readiness for the world record bid

Mr Konyukhov may take comfort from Mr Cameron's track record with world record attempts.

His company made the only three balloons to have successfully circumnavigated the world non-stop - the Breitling Orbiter 3 in 1999, Steve Fossett's The Spirit Of Freedom in 2002 and Mr Konyukhov's Morton in 2016.

The Russian adventurer seems relaxed about his prospects for his latest mission.

"I am confident that the capsule will survive the flight and save me during the flight and landing, but this project cannot guarantee 100% success," he says.