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Thread: spacecraft reentry

  1. #1 spacecraft reentry 
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    Hi everybody, Iím new here and thanks for having me.
    I have question related to the atmospheric reentry of a spacecraft. Why space shuttle for example enters atmosphere exposing its belly as a blunt body object instead of just going nose forward and piercing thru the thickest layers of the atmosphere first and then bleeding off excess speed in less dense layers.


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  3. #2  
    Forum Cosmic Wizard
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    1) That's backwards - the densest layers of atmosphere are lower, not higher. They DO bleed off speed in the higher, less dense layers; indeed, their attitude and trajectory are chosen to keep them at higher altitudes for as long as possible to minimize instantaneous heating. If they didn't do that, they'd either burn up almost instantly in the lower atmosphere or experience non-survivable decelerations. Likely both.

    2) You can't "pierce" through the atmosphere with a sharp point. It's not like a layer of plastic you are punching through.


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  4. #3  
    Forum Professor jrmonroe's Avatar
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    Whether a spacecraft is launched toward space or returning from space, it passes through a section of its trajectory involving a condition called "max q", where q refers to the dynamic pressure, that is, the pressure on the object due to its speed and the density of the ambient atmosphere. It doesn't occur where the atmosphere is densest or where the speed is greatest, but somewhere in between. Designers of the craft want to minimize the max q that the craft will experience; however, this is not always possible due to other mission requirements and physical constraints.

    q = ĹρV≤

    This graph shows various parameters representative of a typical space shuttle launch: atmospheric density (blue), velocity (red), q (black) and altitude (green). You can see that q peaks at about 1 minute into flight at about 35,000 feet (~7 miles) altitude. Both speed and dynamic pressure are well below their maximum values.

    A graph of a typical shuttle re-entry would show different profiles for the various parameters and the calculated q parameter. (You could probably find such a graph on the Internet.)



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