This Wednesday, magician David Blaine hopes to ascend 18,000 feet or 5,500 metres into the sky, using 52 helium-filled weather balloons.
The event, which was already postponed due to the weather, will be live-streamed on YouTube.
The specially-made rig had to be classified as an experimental aircraft by the Federal Aviation Administration (FAA). It is set to take-off at 8:55 a.m. EDT in Arizona.
"The FAA is working closely with David Blaine and his team to ensure that the proposed flight meets all regulatory requirements," the agency said in a statement to The Arizona Republic.
"Once the requirements are met, the FAA will closely monitor the flight and will provide air traffic services as needed."
Blaine will be equipped with a parachute but will have to put it on in mid-air. If there is a balloon failure partway up, he could die.
The stunt was originally scheduled to take place on August 31 from the Hudson River from New Jersey to New York City, but due to logistical challenges, Blaine and his team moved it to Arizona.
'YEARS IN THE MAKING'
In an Instagram video Blaine says the project took years to coordinate.
"[It] is beyond anything that I could’ve imagined," he says of the event.
"It’s also really complex."
He was required to obtain a hot air balloon pilot certificate and a skydiving license. He also had to learn how to read the wind, he said in a YouTube video.
HOW WILL THE WEATHER HELP OR HINDER THE ASCENSION?
Wind will play a large role in the success of the event, with the entire project being "entirely wind-dependent."
So how do winds change from the ground to 18,000 feet? And do wind gusts strengthen and take unexpected directions?
"As a general rule, wind speed increases with height above the surface," explains Weather Network meteorologist Michael Carter.
"Around 5,500 metres above sea level, winds over 80 knots (150 km/h) would not be uncommon. However, in this particular situation, a strong ridge of high pressure is building in over the southwestern U.S. With this ridge in place, winds will be much calmer than normal and will probably not exceed around 15 knots (30 km/h) between the surface and 5,500 metres above sea level on Wednesday morning."
High altitudes can cause a person to suffer from hypoxia, a dangerous condition where the body, or a region of the body, is deprived of adequate oxygen supply. Without oxygen, organs can be damaged within minutes of symptoms presenting.
Air pressure decreases as height increases, Carter explains, so an elevation of 1,500 metres above seal level decreases the amount of air pressure to about 85 per cent of what would be observed at sea level.
"As you rise above 5000 metres, atmospheric pressure is down to about 50 per cent of sea level normal," he says.
"The summit of Mount Everest is almost 9000 metres above sea level, where air pressure is only about a third of sea level normal."
Hypothermia -- a condition that occurs when the body's temperature drops to around 35°C, causing organs to shut down to preserve the brain -- is also possible at extreme heights.
"Temperature generally decreases with height, but very often the lowest few kilometers of the atmosphere will contain a region called an “inversion” where temperatures rise as you go up," Carter explains.
"Hikers in mountainous areas may be familiar with this phenomenon, where it’s not uncommon to start a hike in cool and cloudy conditions near the base of a mountain and break out into clearer skies and warmer temperatures as you climb."
This is likely to occur Wednesday morning, where surface temperatures are expected to be in the mid-teens and reach near 20°C a few hundred metres above sea level.
Above that, things start to get chilly.
"From that point, temperatures will fall to near freezing by about 4000 meters above the surface, and into the negative teens above 5500 metres," Carter says.
Thumbnail image courtesy: Pexels/Padli Pradana