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Extreme sports or just plain crazy

19 mile high jump!

Kittinger's Jump

Fifty years ago a man called Joe Kittinger jumped out of a ballon 19 miles up in the air. This is three times the height airliners fly! The curve of the Earth was clearly visible and he could see stars in the dark, dark blue daylight sky. At this altitude only about one per cent of the atmosphere is left.

At that altitude, why didn't his blood boil?

Kittinger wore a space suit. He still holds the record for the highest parachute jump ever attempted. It is one of the oldest unbroken records in aviation.


Why did he do it?

Introducing the X-15 rocket plane

The reason behind the jump was to see if pilots could survive a fall from such an altitude if they had to eject from the newly developed X-15 rocket plane. The plane was capable of flying close to the edge of space and at speeds of over 4,500 mph. Neil Armstrong was one of the test pilots for this plane.

Normal parachute jumps take place at altitudes up to about 20,000 ft. At this altitude the air is quite dense. The maximum speed a parachutist can fall is limited by the density of the air.

Why is there a speed limit to the fall?


When a person jumps out of an aircraft, gravity immediately starts pulling them down. The gravitational force, their weight, causes them to accelerate. Remember, unbalanced forces cause acceleration and at the moment you step out of an aircraft the only force acting on you is gravity. If this was the only force acting on you for the whole of the descent, after about 10,000 ft you would be doing about 540 mph. This is the speed of a jet airliner! That can't be good for you!

Falling at the speed of sound

You would only have to freefall 19,000 ft to be falling at the speed of sound (760 mph). Parachutists regularly sky dive from such altitudes. They don't break the sound barrier. The maximum speed they usually achieve is about 140 mph.

Drag (air resistance)

As you start to fall another force acts on your body. This is the force of air resistance or drag. As you move faster and faster the upward force of drag on your body increases dramatically. One of the key things to remember about drag is that it doesn't increase steadily. If you double your speed the drag doesn't just double but it goes up by a factor of four: it quadruples! So a little increase in speed equals a big increase in drag.

Terminal velocity

This means by the time you reach about 140 mph the drag pushing up against your body cancels out your weight pulling you down. There is no unbalanced force acting on you. This doesn't mean you stop falling. It just means you stop accelerating. This is called your terminal velocity.

What happens if you jump from much higher?

Lots of things: the most obvious problem is lack of oxygen. At altitudes over 50,000 ft there is so little oxygen that you would pass out within seconds. So you must carry your own oxygen. The atmospheric pressure is so low that the boiling point of water is less than human body temperature! So, to stop your blood boiling you need to wear a pressure suit.

It is very cold at this altitude. At 100,000 feet it is -70oC. At this temperature even jet fuel freezes solid. The air is so thin that your terminal velocity will be very high. Kittsinger achieved a maximum speed of 614 mph. The cold also makes it very hard to control your fall.

We have all seen pictures of skydivers in the familiar spread eagle position. By moving their arms and legs they can control their position in the air, but not at high altitudes. Here the drag is so low that the tendency is to tumble out of control.

On an earlier jump Kitinger had tried deploying a small stabiliser chute. It become wrapped around his neck and caused him to spin at over 120 revolutions per minute. The forces on his body were extreme, around 22 times the force of gravity or 22g for short. People black out at about 9g. All that saved him was the automatic opening device on his main chute.

Sky Diving

Would anyone be crazy enough to try to break Kittinger's record?

Felix Baumgartner is an Austrian extreme sportsman. He is famous for BASE jumping. "B.A.S.E." is an acronym that stands for four categories of fixed objects from which an extreme sportserson can jump: Buildings, Antennas, Spans (bridges), and Earth (cliffs). He holds the record for the lowest ever base jump. The lower the BASE jump, the more dangerous it is because the parachute has less time to open. This jump was from the statue of Christ the Redeemer that stands above the city of Rio de Janeiro in Brazil. The fall was only 29m (95ft). Imagine how long you have to open your chute...Phew!

Rio de Janeiro

Skydiving from a balloon

The Petronas Towers

He also held the record for the world's highest BASE jump, a leap from the Petronas towers in Kuala Lumpur. This was the world's tallest structure for many years.

Felix wants to break Kittingers record by skydiving from a balloon at least 120,000 ft up, or 23 miles high (37Km). It is higher than anyone has ever flown without riding a rocket. He will need to wear what amounts to a space suit to survive. It is so high not even military spy planes can reach such altitudes.

The only people higher than Felix will be in the International Space Station (ISS). He hopes to be the first person on Earth to break the sound barrier in free fall. It should take him about 35 seconds to achieve terminal velocity.

Is it possible to maintain control? Will he tumble so rapidly that the G-forces will kill him? No one knows what will happen at these speeds. It has never been done before so it will certainly be very interesting!

Sky Diving Sam

The big questions:

Why is there a top speed for free-fall parachuting?

What slows you down when you fall?

How fast is it possible to fall?

What is terminal velocity?

Why does terminal velocity change with altitude?