The Heat of Re-Entry

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therocketjohn

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<p>Why do space vehicles get so hot upon re-entry into the earth's atmosphere? In the videos I've seen, I never see flames on the sides of space vehicles when leaving the atmosphere, but always see them during re-entry. This makes me think the heat is not due to high altitude gases. One person once told me the heat was due to the friction between the vehicle and the atmosphere at high speeds. Is this true? and if this is the case, couldn't a space vehicle just open a parachute or re-enter much slower than it does to avoid subjecting itself to intense heat upon re-entry? Also, is the heat at re-entry the most extreme heat the vehicle would encounter when journying to the Moon or to Mars? Thanks for any insight. </p>
 
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lampblack

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<p><font size="2">An orbiting satellite is traveling about 17,500 mph -- and if it reenters, extreme heat is produced because a fast-moving object is interacting with the atmosphere (which is becoming more dense as the reentering satellite continues moving more deeply into it).</font></p><p><font size="2">Here's one online overview explaining the matter in somewhat more detail. Google is your friend. :) </font></p> <div class="Discussion_UserSignature"> <font color="#0000ff"><strong>Just tell the truth and let the chips fall...</strong></font> </div>
 
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oklahoman

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Why do space vehicles get so hot upon re-entry into the earth's atmosphere? In the videos I've seen, I never see flames on the sides of space vehicles when leaving the atmosphere, but always see them during re-entry.</DIV></p><p>In a launch, most of a spacecrafts speed is acquired after it leaves the atmosphere.</p><p>During reentry, most of the heat is generated by the compression of the air in front of the space vehicle. These craft reenter so fast that the air does not have time to get out of the way, and "piles up" in front of the spacecraft, resulting in extremely high pressures.</p><p>If you take a gas, and suddenly double its pressure, its temperature doubles as well.&nbsp; The gases in the high atmosphere are very tenuous and cold, but when they are suddenly compressed hundreds of times, they suddenlygain thousands of degrees, enough to melt almost anything.</p><p>&nbsp;</p><p>&nbsp;</p><p> Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>One person once told me the heat was due to the friction between the vehicle and the atmosphere at high speeds. Is this true? and if this is the case, couldn't a space vehicle just open a parachute or re-enter much slower than it does to avoid subjecting itself to intense heat upon re-entry?</DIV></p><p>Friction is a factor as well.</p><p>Slowing down would reduce the heat.&nbsp; But in space, slowing down requires lots of energy.&nbsp; Parachutes would get blown apart and burned up if deployed at high speeds. </p><p>&nbsp;</p><p> Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Also, is the heat at re-entry the most extreme heat the vehicle would encounter when journying to the Moon or to Mars? Thanks for any insight. <br /> Posted by therocketjohn</DIV></p><p>Yes. </p> <div class="Discussion_UserSignature"> </div>
 
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vogon13

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<p>&nbsp;</p><p>The Concorde aircraft (and fighter jets) are speed limited to (IIRC) less than Mach 2.2 as the friction with the air will dangerously heat and weaken the aluminum. </p><p>The Mach 3 capable XB-70 bomber had an interesting brazed honeycomb stainless steel skin that could withstand the higher temps of Mach 3 flight.</p><p>&nbsp;</p><p>SR-71/YF-12/D-21 all used titanium for a substantial (and classified) bump above Mach 3.</p><p>&nbsp;</p><p>And these materials are just for fast (and faster) high altitude flight, not re-entry from 17,000 to 25,000 MPH.</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp; </p> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Why do space vehicles get so hot upon re-entry into the earth's atmosphere? In the videos I've seen, I never see flames on the sides of space vehicles when leaving the atmosphere, but always see them during re-entry. This makes me think the heat is not due to high altitude gases. One person once told me the heat was due to the friction between the vehicle and the atmosphere at high speeds. Is this true? and if this is the case, couldn't a space vehicle just open a parachute or re-enter much slower than it does to avoid subjecting itself to intense heat upon re-entry? Also, is the heat at re-entry the most extreme heat the vehicle would encounter when journying to the Moon or to Mars? Thanks for any insight. <br />Posted by therocketjohn</DIV></p><p>When a vehicle is launched into orbit it requires energy to both lift up to the required altitude and energy to give the necessary orbital velocity.&nbsp; So, while it is in orbit it has the potential energy associated with its height above the Earth and the kinetic energy associated with its rather high speed in orbit.&nbsp; Some of the energy from the fuel burned to provide propulsion is turned into heat of friction between the orbiter and the atmosphere, but a great deal of it is&nbsp;in in the form of the potential and kinetic energy just mentioned.&nbsp; </p><p>When it comes back to earth and lands, all of the kinetic and potential energy that the orbiter had when on orbit must be given up, and given up to something.&nbsp; That something is heat.&nbsp; Some of the heat goes into the atomosphere that it flies through, where there is heat from compression of the air in front of the vehicle and some from friction with the air itself.&nbsp; But that same heat is also applied to the skin of the orbiter and it gets very hot.&nbsp; <br /></p> <div class="Discussion_UserSignature"> </div>
 
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