when something enters the atmosphere it burns up, even the space shuttle has heat sheilds for re-entry, so how is it that a space shuttle leaving the earth dosn't burn up ?
2006-07-01 08:16:30 · 20 answers · asked by Byds 2 in Science & Mathematics ➔ Astronomy & Space
relative airspeed and friction. You can come down alot faster than you can go up.
As an example, the SR71 aircraft reaches airspeeds that heat the aircrafts structure to extreme levels. It never leaves the earth's atmosphere (although it is often high enough that the sky is no longer blue) and encounters enough friction from the air that pilots must be cooled!
For an orbital vehicle, its not the speed going up. Why? Because it takes quite a while, even after the vehicle has left the atmosphere for it to attain the speeds necessary for orbiting the earth. How do you slow down from those speeds? Simply use the friction from the air so that you can slow down in a predictable controlled manner.
Actually this was a very good question! For more details, search the Internet for orbital speeds (orbital mechanics). My space facts are rust, but I thought the shuttle moved at something like 18000 mph. The SR71's top speed is obviously top secret, but pretty commonly believed to be well over Mach 3 (roughly 2100 mph!) I don't think the space shuttle attains that speed until after it has left the atmosphere.
2006-07-01 08:28:34 · answer #1 · answered by Mack Man 5 · 2⤊ 0⤋
The simple fact is that heat build up is caused by the increased resistance from the extra 'thickening' of the atmosphere. As an object leaves space (where there is a vacuum and no or very little resistance against an object) the object hits air resistance, which increases the friction as the object enters the denser layers of air and comes down.
The other way, to give you an example, up to 12000 ft oxygen is freely available, after that the proportion of oxygen goes down as you go higher. That's why aircraft are pressurised. The air gets thinner the higher up you are until it becomes a vacuum and you're in space. So going up the air gets thinner - less resistance - less friction - no heat build up.
As Mack Man says the speed at which the shuttle is going up is a slow increase so that when it goes into space it isnt going fast enough to generate large amounts of heat.
Look at this site for the complete answer
http://www.ksc.nasa.gov/nasadirect/archives/KSCDirect/archives/launch/sts110/shuttle-qa.htm
Dave B
2006-07-01 15:35:10 · answer #2 · answered by Dave B 2 · 0⤊ 0⤋
Leaving Earth's atmosphere doesn't require nearly as much speed as an object entering the atmosphere builds up because of gravity. That's why reentry has to be handled very carefully, or the Space Shuttle will burn up. The Shuttle has to reenter at just the right angle or it will either glance off the atmosphere and back out into space, or ( if it reenters at too steep and angle ) will burn up due to friction with the atmosphere.
2006-07-01 15:27:53 · answer #3 · answered by fhornsr 5 · 0⤊ 0⤋
We do 'burn up' as we leave the earth, passing through the earths atmosphere. It doesn't usually happen because anything leaving the earth is always checked, e.g. NASA check spacecraft before they exit. Another factor is the speed. When we exit, we fight against gravity, meaning we are slower, we also have the friction to contest with, however when a spacecraft enters earths atmosphere it has been in a vacuum meaning it is travelling much faster. Some spacecraft enter upto and over 24000mph. This coupled with the fact that earths gravity is pulling the craft towards it i.e. accelerating it, causes more friction thus more heat.
2006-07-05 14:33:22 · answer #4 · answered by shaun_ready 2 · 0⤊ 0⤋
Because we gradually attain speed as a rocket is launched and put into orbit. When the speed gets to where air friction would be a problem, then the rocket is way high where there is no atmospheric friction. The heat that is generated is from the energy source putting it up in orbit aka the rocket!
Now contrast that to hitting the air moving at about 17,500mph! Big difference and a lot of heat is generated quickly as the air friction tries to slow the object down. Most of that kinetic energy in the 17,500mph is used up to heat up the tiles or burn away at a heat shield (old Apollo, Gemini, Mercury spacecraft).
2006-07-01 15:51:07 · answer #5 · answered by cat_lover 4 · 0⤊ 0⤋
Well actually LEAVING and ENTERING does effect you. Going down you get static as well as the Therm-ion-sphere would just burn you up from the collected sun heat and energy. Falling in would force you in via gravity and you plunge into the Thermosphere then into the Thermo-ion-sphere and then into the Ion-sphere. The 3 layers have collected up the sun's microwave heat and infra-red energy and this makes the layers hot with static and non-fluorescent matter. It would burn up here and then plunge into the air layers and as it it enters the stratosphere it will then lapse into the tropopause and then the winds would cause static making the final process like a shooting star does, if it passes this and the object is inanimate and very large expect a massive thud and an explosion.
Going up is harder and you would go through the same process but slower and with more ease. but more shuddery. Spacecraft receive the same brace and force but they have special material in tiles, so that it is has protection from the force. As so for coming back in, on both shuttles and rockets.
2006-07-03 15:51:39 · answer #6 · answered by Anonymous · 0⤊ 0⤋
Cat_lover is basically right. The shuttle undergoes much of the acceleration needed to reach orbital velocity in what we would consider 'space'. The shuttle follows a trajectory that takes it out of the atmosphere quickly and then "downrange" for much of the boost phase.
The leading surfaces do heat significantly during the trip to orbit. For example, the foam coating on the nose cone of the external fuel tank does suffer some ablation during the the boost phase.
In contrast, the orbiter approaches the atmosphere at very close to orbital velocity. Aside from the de-orbit burn, there's little to slow the craft before it plows into gas of significant density (our atmosphere).
One misconception...
Due to it's tremendous speed, the orbiter shock-heats air at it's leading surfaces during reentry. The temperatures of the thermal protective surfaces rise primarily in response to thermal radiation from the incandescent shockwave. NOT FROM FRICTION.
2006-07-01 18:12:19 · answer #7 · answered by Ethan 3 · 0⤊ 0⤋
I think it's all about the force of gravity and the lack of air pressure. The thing is that leaving the earth is done at "escape velocity", which is pretty slow compared to reentry velocity, which is extremely fast. I think what happens is that a reentry has to be done basically by guided freefalling, but since there's no air pressure, you pick up speed quick. All a spacecraft can do is enter at a certain angle so that you don't get completely destroyed by the atmosphere.
2006-07-01 15:27:38 · answer #8 · answered by SkyRaider 4 · 0⤊ 0⤋
The heating occurs due to friction with the air. Re-entry happens at much higher speeds due to gravity. An object leaving the atmosphere is travelling relatively much slower, so the friction is less, so the object doesn't get hot.
2006-07-01 15:20:56 · answer #9 · answered by Anonymous · 0⤊ 0⤋
The difference is speed. You can reach fantastic speeds in space because there's no air resistance, and in fact you always do reach such speeds because, well, that's how you orbit. You don't feel it when you're up there of course. Anyway, once at that incredible speed, if you then shove your vehicle into the atmosphere, the friction between atmosphere and vehicle is enormous, so you get very hot.
If you start your acceleration within the atmosphere, you're not going to be going terribly fast until you get outside it. So you don't get so hot.
2006-07-01 15:22:35 · answer #10 · answered by wild_eep 6 · 0⤊ 0⤋