Why Objects Burn Up Upon Entering Earth's Atmosphere

  • Thread starter Kronos5253
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In summary, objects burn up when entering the Earth's atmosphere from space due to the extreme speeds they are traveling at, causing severe heating due to friction and compression of the air. This can be exploited for aerocapture, but can also result in burn up if the object is not properly designed to handle the heat. Orbital speeds are much faster than the speed of the Earth's rotation, and at these speeds, traditional ideas of aerodynamics and reentry do not apply. A blunt, non-aerodynamic shape has been found to be more effective in dealing with the heat and air pressure during reentry.
  • #1
Kronos5253
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Okay, this is kind of a dumb question, but I did some searching online and still couldn't come up with an answer, although I think I many know it anyway.. BUT! Here it goes:

Why do objects only burn up entering the atmosphere from space, and not vise versa?
 
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  • #2
I think its density gradient but not sure;]
 
  • #3
When objects are in space orbiting Earth they are moving very fast, a lot faster than when they take off. When they re-enter the atmosphere they are moving so fast the friction with the air makes them "burn up". Eventually, the object will slow down due to air resistance and reach a terminal velocity.

This is just what I always assumed happened based on my common sense so I could be wrong.
 
  • #4
Kronos5253 said:
Why do objects only burn up entering the atmosphere from space, and not vise versa?

Because when you are going down you are moving faster than when you are moving up. By the time a spacecraft is moving very fast, it's already outside of the Earth's atmosphere.
 
  • #5
tmyer2107 said:
When objects are in space orbiting Earth they are moving very fast, a lot faster than when they take off. When they re-enter the atmosphere they are moving so fast the friction with the air makes them "burn up". Eventually, the object will slow down due to air resistance and reach a terminal velocity.

This is just what I always assumed happened based on my common sense so I could be wrong.

That is correct. Orbital velocities are on the order of km per second.
Entering the atmosphere causes severe heating due primarily to friction with gasses in the atmosphere.
This can be exploited in what is known as aerocapture. Where a spacecraft traveling to a planet such as Mars enters its atmosphere (sometimes multiple times) at an angle that allows it to slow down and attain orbit. If it hits too shallow it will simply skip off and keep going, and if it hits too steep it will burn up and/or crash into the planet surface.
 
  • #6
Of course, if the intent is to establish an orbit, you want it to skip.
 
  • #7
By the way, it's not the fact that you're entering the atmosphere that causes things to burn up, it's the fact that the things entering the atmosphere are usually going VERY fast.

For example, this Spaceship2 that is supposed to take tourists to space soon, does not need heat shields. This is because despite going to space, it's going much, much slower that a satellite, and therefore does not experience the extreme heat when reentering the atmosphere.
 
  • #8
Objects, when entering the Earth's atmosphere are a lot more faster relatively due to constantly having a downward acceleration.
So, they burn up due to air resistance.
 
  • #9
So, we're saying that when a satellite or the shuttle is launched into orbit, the engines continue to burn (increasing the velocity) long after the craft has risen above the atmosphere? I'm just asking.
 
  • #10
The reason is speed. When a rocket is launched, it continues acceleration after it leaves the atmosphere to a very high speed while in space. When it re-enters the atmosphere, it's speed is much higher and the heat mostly due to extreme compression of the air (as opposed to friction) combined with no way to remove the heat results in burn up of the object isn't properly designed to handle the heat.
 
  • #11
Jeff Reid said:
mostly due to extreme compression of the air (as opposed to friction)

Yeah, one of my professors was talking about this. The idea that it is mostly due to friction seems to be a popular misconception.
 
  • #12
alexgmcm said:
Yeah, one of my professors was talking about this. The idea that it is mostly due to friction seems to be a popular misconception.

Guess so, cause that's actually what I was thinking it was haha.


Thanks everyone for your answers :) It's much appreciated!
 
  • #13
Jeff Reid said:
The reason is speed. When a rocket is launched, it continues acceleration after it leaves the atmosphere to a very high speed while in space. When it re-enters the atmosphere, it's speed is much higher and the heat mostly due to extreme compression of the air (as opposed to friction) combined with no way to remove the heat results in burn up of the object isn't properly designed to handle the heat.

Which brings me to another question...

Does that mean if there's no compression of the air, there's no heat, therefore no danger? For example, if you had a solid, pointy piece of metal that was in orbit, moving the same speed that the Earth is rotating, and shot it through the atmosphere toward the Earth, there'd be no compression of the air correct? Depending on size of course.
 
  • #14
Kronos5253 said:
Which brings me to another question...

Does that mean if there's no compression of the air, there's no heat, therefore no danger? For example, if you had a solid, pointy piece of metal that was in orbit, moving the same speed that the Earth is rotating, and shot it through the atmosphere toward the Earth, there'd be no compression of the air correct? Depending on size of course.

"Moving at the same speed that the Earth is rotating" is actually quite slow. The Concorde easily went faster.

The point is that orbital speed is WAY beyond that. About 17,000mph. At that speed many interesting phenomena occur which no layman would even consider. It's so fast that convention logic of what shape would work for reentry and what shape wouldn't, simply breaks down. And, at that speed no matter what you do, there will be heat, and lots of it. It's just a question of how you deal with it.

For example, a solid pointy piece of metal was actually tried, and it quickly burned up. Turned out that a blunt, highly "non-aerodynamic" shape is actually better at reentry, because the accumulation of compressed air underneath it actually serves to push the heat and horror out of the way of the vehicle.
 
  • #15
Lsos said:
"Moving at the same speed that the Earth is rotating" is actually quite slow. The Concorde easily went faster.

The point is that orbital speed is WAY beyond that. About 17,000mph. At that speed many interesting phenomena occur which no layman would even consider. It's so fast that convention logic of what shape would work for reentry and what shape wouldn't, simply breaks down. And, at that speed no matter what you do, there will be heat, and lots of it. It's just a question of how you deal with it.

For example, a solid pointy piece of metal was actually tried, and it quickly burned up. Turned out that a blunt, highly "non-aerodynamic" shape is actually better at reentry, because the accumulation of compressed air underneath it actually serves to push the heat and horror out of the way of the vehicle.

Ah okay, well thank you for the answer :)
 
  • #16
What If an astronaut who's flying perpendicular to Earth (not in orbit) starts entering the atmosphere? Will he still fry despite having a considerably lesser than orbital velocity?
 
  • #17
I mentioned above that Spaceship2, which is supposed to take tourists to space soon, does not need heat shields, since it is going considerably slower than orbital. So, simply entering the atmosphere is not enough to fry you. You also need to be going pretty fast. Keep in mind though, that even if you started from a stop, the Earth's gravity will accelerate you towards it, possibly enough that you might end up going dangerously fast (I don't know though, I haven't done the calculations).
 
  • #18
If you had enough energy (fuel)left when returning to Earth, you could hit the atmosphere at a more reasonable speed by using retro rockets (or face backwards).

I still think that, with suitable control (which is a major problem, I know) it is conceivable to 'fly' in and reduce speed slowly enough to reduce the rate of heating. It would have to involve a long spiral path.
 
  • #19
Yeah but if you really think about it, the amount of fuel that would require, and the amount of fuel it would require to bring that fuel up in the first place...it would just be a waste. It's easier, cheaper, and makes more sense to put a bunch of heat tiles instead of making rockets 2x bigger. It's not a problem that needs to be solved...
 
  • #20
I totally agree that retro rockets are far too expensive a proposition but the 'flying in' solution would remove a significant risk, I think.
Most solutions to most problems in Space revolve around the Energy situation. (Just like down here, only worse).
ps The rocket would have to me quite a bit more than 2X bigger - I think there's an exponential law involved.
 

1. Why do objects burn up when entering Earth's atmosphere?

Objects burn up when entering Earth's atmosphere due to the intense heat and friction caused by the interaction between the object and the gases in the atmosphere. This process is known as ablation.

2. How does the speed of the object affect its burning up?

The speed of the object plays a significant role in its burning up. Objects entering Earth's atmosphere at high speeds experience more friction and heat, causing them to burn up faster than objects entering at lower speeds.

3. Can the shape of the object affect its burning up?

Yes, the shape of the object can affect its burning up. Objects with a streamlined shape, such as spacecraft, are designed to minimize the effects of friction and heat while entering the atmosphere, reducing the chances of burning up.

4. What happens to the material of the object when it burns up?

When an object burns up upon entering Earth's atmosphere, its material heats up and vaporizes, turning into gas. This process is called sublimation and is responsible for the bright trail of light seen during a meteor shower.

5. Are there any objects that do not burn up upon entering Earth's atmosphere?

Yes, there are some objects, such as large spacecraft or satellites, that are designed to withstand the heat and friction of entering Earth's atmosphere and do not burn up. These objects are usually equipped with heat shields and other protective measures to prevent burning up.

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