“I will achieve two things: the first is to provide valuable scientific data to space researchers. We’re seeking to achieve learnings and data that contribute to establishing safety protocols for astronauts and high-altitude aviators. This would be a remarkable legacy. The second: I will be the first man to jump at that altitude and the first to break the sound barrier in freefall.” This is what Felix Baumgartner told T3 when we asked him about his attempt to break the world record for the highest jump.

The record currently stands at 19.5 miles, but Baumgartner and the Red Bull Stratos team is aiming for a more ambitious 23 miles on Tuesday this week. In a test jump recorded this week in Roswell, New Mexico Felix managed 13.6 miles, but what exactly happens when you freefall for 23 miles? Here's the cold hard facts...

How will Baumgartner’s suit protect him?

A high-tech cross between a sleeping bag and a skinny-fit spacesuit, the suit is cumbersome, weighs over 100lbs, but should keep him alive. A flameretardant shell and layers of insulation and nylon keep out the fierce cold, while a bladder of gasses inside keeps the suit pressurised and instantly responds to changes in atmospheric pressure, stopping his blood and internal organs from bubbling up like a Lancashire hotpot. Any failure in these systems or the telemetry that tells the team on the ground what’s happening could be catastrophic, but the suit has undergone 36 months of testing.

What will he breathe?

100 per cent oxygen, delivered from two cylinders on his back. Felix will also breathe this for two hours before the ascent to expel nitrogen from his body, which could otherwise cause decompression sickness as the air gets thinner. When he exhales on the descent, his breath will be vented into the suit.

What’s it like, 23 miles up?

Temperature is a nippy -55ºC, and atmospheric pressure is roughly one hundredth what it is at sea level. The air is too thin to breathe and at such low pressure, bubbles begin to form in liquid. In other words, your blood boils. Baumgartner will be freefalling head-first through this less-than friendly environment. Because it’s a near vacuum, there’ll be hardly any air resistance to slow him down and the team of scientists behind Felix estimate that within 35 seconds, he will hit 690mph, faster than the speed of sound.

What will happen as he breaks the sound barrier?

That’s the big unknown of the Red Bull Stratos mission. No human being has ever gone supersonic without millions of pounds-worth of machinery around them. What is known is that as he approaches the sound barrier, the airflow around him will change. Different waves of air pressure will compress together, eventually merging into one almighty shock wave known as a sonic boom. It’s anyone’s guess what this could do to Baumgartner’s body or his high-tech suit, although it’s believed that the thin air will minimize the impact. Even so, there’s still a real risk that he’ll lose control of his trajectory and enter an uncontrollable flat spin.

That’s bad, yes?

It’s not ideal. It happened to US Air Force pilot Joe Kittinger during a similar jump in 1959. His body span around like a propeller at a terrifying 120rpm. When that happens, centrifugal forces can cause all the blood in your body to rush either to your head or your lower extremities. Kittinger experienced G-forces 22 times the force of gravity. He lost consciousness and only survived because his parachute opened automatically.

What would happen if the parachute didn’t open?

An emergency chute will deploy automatically should Baumgartner lose  consciousness. It’s designed to open if the suit clocks that he’s falling too fast at an altitude of 762m. If the reserve chute fails for any reason, he wouldn’t hurtle into the ground at the speed of sound because the air resistance would slow him down the closer he got. He’d have the same chance of survival as a regular parachutist unlucky enough to have two chutes fail. Falling at a speed of around 120mph, those are not great odds.

What about bad weather?

The Stratos team will monitor the weather at the site obsessively. If there’s even a remote chance of rain, they’ll postpone the jump because it could severely affect the balloon on ascent or Baumgartner’s parachute on the way down. Freak winds are more difficult to predict and have been known to compromise scientific balloons in

the past. If he runs into trouble on the way up, he’ll have two options: evacuate the capsule early and parachute back to Earth. Or, if that’s not feasible, detach the capsule from the balloon, deploy the capsule’s parachute and ride down in that.

…Or a bird-strike?

When Felix is travelling at the speed of sound birds won’t be an issue because they can’t fl y that high – nor can conventional aircraft. Running into any object at lower altitudes would be a mid-air collision at 120mph or more. The suit would offer limited protection, but it’s still going to be a very serious thud. We don’t fancy the bird’s chances much, either…

More: Watch the live broadacast of the Red Bull Stratos attempt

Credit: Red Bull