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).:confused:

 

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]

...

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. :confused:

 

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]

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).:confused:

 

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]

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

 

It seems this misconception is rather common...

 

Heat Shield for Spacecraft

[Thunderbird]

 

 

The only stupid question is one not asked. :)

Btw, wikipedia is your friend. :)

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

[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]

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. :confused:

[Grains]

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 :confused:

[Turtle]

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

De nada. :)

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).

 

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 :eek_big:

 

A bit off topic, but further note on flying in the Martian atmosphere, as there is in fact a plan for a Martian plane. :eplane: To fly in thin atmosphere you need a big surface area wing, and with the lower Mars gravity the engineering is feasible.

>> http://asl.epfl.ch/aslInternalWeb/ASL/publications/uploadedFiles/Sky-Sailor-Paper-Final.pdf

[InfiniteNow]

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.

Maybe it could work like this helicopter:

 

 

YouTube - The Anti-Gravity Helicopter http://www.youtube.com/watch?v=SDJjRdSN0vc

 

 

It's a pretty cool video ultimately demonstrating the stroboscopic (wagon wheel) effect. The rotor speed and the film speed are matched (to some ratio) so there is no apparent movement of the blades for each frame of the camera. It's not on topic, but I thought it was really sweet and that this was a good opportunity to share it since the OPs questions has been answered. :eek_big:

[Moontanman]

Not sure if this is relevent but a nuclear light bulb rocket could land by slowly descending on it's own exhaust and avoid the dangerous slowing down by friction that craft like the space shuttle experiences.

 

BRUCE BEHRHORST ARTICLE LIST

 

I think they do have either plans for or a working scale model of a space craft that descends on helicopter type blades but I'm not sure if that concept would work on the almost vacuum of the mars atmosphere.

[Overdog]

Not sure if this is relevent but a nuclear light bulb rocket could land by slowly descending on it's own exhaust and avoid the dangerous slowing down by friction that craft like the space shuttle experiences.

 

BRUCE BEHRHORST ARTICLE LIST

 

Wow. A nuclear light bulb.:eplane: I want one of those.:eek_big:

[Grains]

Not sure if this is relevent but a nuclear light bulb rocket could land by slowly descending on it's own exhaust and avoid the dangerous slowing down by friction that craft like the space shuttle experiences.

 

BRUCE BEHRHORST ARTICLE LIST

 

I think they do have either plans for or a working scale model of a space craft that descends on helicopter type blades but I'm not sure if that concept would work on the almost vacuum of the mars atmosphere.

 

Would the concept work on Mars if you reversed the blades of the helicopter so they were pulling the other way. Much like the way you change a fan setting? Would that not counter-act the effect of the vacuum? :shrug:

[Grains]

Not sure if this is relevent but a nuclear light bulb rocket could land by slowly descending on it's own exhaust and avoid the dangerous slowing down by friction that craft like the space shuttle experiences.

 

BRUCE BEHRHORST ARTICLE LIST

 

I think they do have either plans for or a working scale model of a space craft that descends on helicopter type blades but I'm not sure if that concept would work on the almost vacuum of the mars atmosphere.

 

So if were to reverse the blades of a helicopter and caused a reverse effect (almost like reversing the flow of a home fan) would that counter-act the effect of the almost vacuum on the mars atmosphere?

[Moontanman]

So if were to reverse the blades of a helicopter and caused a reverse effect (almost like reversing the flow of a home fan) would that counter-act the effect of the almost vacuum on the mars atmosphere?

 

Helicopters need air to work, the thicker the air the better they work, the air on mars is so thin (it's close to what we would think is a pretty good vacuum) no matter which direction the turned they wouldn't be able to generate any lift.