Why Meteorites Burn In The Atmosphere, But Skydivers Jumping Almost From Space – No?

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When an object falls from a great height, let us say from 100 km, the speed it develops is insufficient to burn from friction against the atmosphere, provided that the initial velocity of the object relative to the Earth is zero.

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Felix Baumgartner's jump
Felix Baumgartner’s jump

 

Felix Baumgartner’s jump in this sense did not fundamentally differ from the fall of the V2 rocket. He simply rose vertically above the surface of the Earth and jumped down. At the same time, at the beginning of the jump, his speed relative to the Earth was zero.

So during the fall, Felix developed a top speed of 1357.6 km/h. For comparison, a passenger aircraft flies at a speed of about 900 km/h and is capable of accelerating to 1000 km/h if necessary, and the supersonic Concord can fly almost twice as fast as Felix crashed.

Why are meteorites and satellites burnt?

Spacecraft in orbit move relative to the Earth, 10 times faster than the maximum speed achieved by Baumgartner. So, for example, the ISS orbital speed is about 27500 km/h, or about 7.6 km/s.

Why are meteorites and satellites burnt?
Why are meteorites and satellites burnt?

As for meteorites, their speed of entry into the atmosphere can be almost any: it all depends on the vector sum of the speeds of the Earth and the meteorite at the time it enters the atmosphere. For the vast majority of meteorites, this speed far exceeds the orbital speeds of spacecraft.

Entering the dense layers of the atmosphere at great speed generates very much friction against the air. Huge kinetic energy is converted into heat, which is the cause of combustion in the atmosphere.

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If the spacecraft could drop 90 percent of this speed within a few minutes, then it could fall to Earth and not burn out in the atmosphere, in which case spacecraft would not need heat shields or ablation coatings, for example, that protect descent vehicles from high temperatures.

However, for braking from orbital speeds to speeds that allow to enter the atmosphere and not burn out, the object needs a lot of fuel. Not as much as it takes to put a spaceship into orbit, but somewhat comparable to that. In order to burn, fuel needs an oxidizing agent which also has mass.

All this must be put into orbit with the ship. As a result, a spaceship that can slow down in orbit will cost fabulous money. There is no practical sense in such a project.

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