Orbital Re-Entry into Atmosphere

[Grains]

I had a quick question and I apologize in advance if I use incorrect terminology/reasoning/etc.

I recently watched a video that was a simulation of Phoenix entering Mars's atmosphere. It got me thinking and I was curious about this process.

I understand that when an object is entering the atmosphere from space there is some type of friction that causes they heat (I am guessing).

My question is that if an object (like a spacecraft) were able to hover down through the atmosphere would that heat still be generated? For example: say we had a space helicopter. A helicopter can move up and down without varying horizontally. If a "space helicopter" were to enter the atmosphere just by moving downward would the friction (heat) still be created? I hope that makes since I can't think of another way to explain it.

Sorry if its a stupid question. I was just curious and could not find an answer on the net.

Thanks,
Grains

[Turtle]

Originally Posted by Grains

...
My question is that if an object (like a spacecraft) were able to hover down through the atmosphere would that heat still be generated? For example: say we had a space helicopter. A helicopter can move up and down without varying horizontally. If a "space helicopter" were to enter the atmosphere just by moving downward would the friction (heat) still be created? I hope that makes since I can't think of another way to explain it.

Sorry if its a stupid question. I was just curious and could not find an answer on the net.

Thanks,
Grains

Yes, 'hovering' down eliminates the heat. The problem is, a re-entry vehicle would need to carry fuel to slow down enough to hover down, rather than slow down using the atmosphere as a brake.

Check some of the X-Planes. >> NASA X-38 - Wikipedia, the free encyclopedia

[freeztar]

Originally Posted by Grains

I understand that when an object is entering the atmosphere from space there is some type of friction that causes they heat (I am guessing).

It's actually not friction, though that is a common misconception.
The heat is generated from pressure from the front of the craft on the atmosphere. This is actually a simplification though. For a full description, see here.

My question is that if an object (like a spacecraft) were able to hover down through the atmosphere would that heat still be generated? For example: say we had a space helicopter. A helicopter can move up and down without varying horizontally. If a "space helicopter" were to enter the atmosphere just by moving downward would the friction (heat) still be created? I hope that makes since I can't think of another way to explain it.

It depends on the speed it is descending. Greater speed would mean greater heat. Two important things though. The atmosphere on Mars is very thin compared to Earth. This means that there is less heat, but also less slowing down. Another thing to consider is that helicopters use air to creat lift. I don't think the Martian atmosphere is thick enough to allow this type of flight (and obviously not in outer space).

Sorry if its a stupid question. I was just curious and could not find an answer on the net.

The only stupid question is one not asked.
Btw, wikipedia is your friend.

[Overdog]

Yes, I believe it would. When the spacecraft first enters the atmosphere, the atmosphere is too thin for the helicopter blades to work, so there would be nothing to slow down the space craft except the resistance of the atmosphere itself. It is this resistance, called friction, which produces the heat.

[Overdog]

Originally Posted by freeztar

It's actually not friction, though that is a common misconception.

It seems this misconception is rather common...

Heat Shield for Spacecraft

[Thunderbird]

Originally Posted by freeztar

The only stupid question is one not asked.
Btw, wikipedia is your friend.

Why do men have nipples?...opps, sorry.. wrong thread.

[freeztar]

I found a different link on re-entry heating. This one says that the heat comes from compression and friction, but more so compression than friction.

Heat Shield Heating: Friction or Compression

[Overdog]

Excellent link, much better explanation than the wiki...thanks, I learned something new today!

[Grains]

Originally Posted by Turtle

Yes, 'hovering' down eliminates the heat. The problem is, a re-entry vehicle would need to carry fuel to slow down enough to hover down, rather than slow down using the atmosphere as a brake.

Check some of the X-Planes. >> NASA X-38 - Wikipedia, the free encyclopedia

Thanks Turtle!!! That is exactly what I was curious about.

[Grains]

[quote=freeztar;223460]Another thing to consider is that helicopters use air to creat lift. I don't think the Martian atmosphere is thick enough to allow this type of flight (and obviously not in outer space).
QUOTE]

I like the other link you sent that was very helpful. I didn't mean an actual helicopter I was just trying to describe the movement I was thinking about (up-down).....bad example on my part