MadSci Network: Astronomy

Re: Why do space shuttles go through a heat changes?

Date: Mon Aug 15 11:13:18 2005
Posted By: John Haberman, Space Scientist, NASA Goddard Space Center, Greenbelt MD
Area of science: Astronomy
ID: 1122952857.As

Hello Jessica,

The shuttle does experience heating during both launch and when returning.
The heating is much less, for several reasons, during the launch phase. 
This heating results from friction between the air molecules and the
shuttle.  The amount of friction is strongly dependent on velocity.  The
heat load is dependent on the length of time of the heating.


The launch phase of a mission is much faster so less heat builds up because
the shuttle rises almost vertically.  The shuttle launch starts from zero
velocity (no friction) and quickly increases and this generates heat. 
However, as this is occurring the friction is decreasing because the
density of the atmosphere (number of gas molecules per cubic centimeter) is
decreasing.  Also the temperature in the atmosphere is falling and this
helps carry away the heat from the thermal tiles.


The re-entry starts with the shuttle moving very fast in the upper
atmosphere.  As the shuttle's altitude decreases the atmosphere's density
is increasing and the result is more friction.  If the re-entry angle is
too steep (fast) the shuttle will penetrate the atmosphere too quickly with
the result that the temperature build-up will exceed the limits of the heat
shield tiles.  If the re-entry angle is too shallow (slow) then the thermal
tiles will experience high heat loads due to the long re-entry time and the
heat conduction through the tiles will cause failure because of the
temperatures in excess of the structure's design limits.  Only a small
range of re-entry conditions is acceptable and this still requires thermal
protection to protect the shuttle from the atmospheric friction heat load
generated during the re-entry.

More information can be found at:

Shuttle Thermal Protection System 

Why do
reentering bodies experience extreme heating? 

With your search engine look for the 1979 paper presented at 14th AIAA
Thermophysics Conference titled "Effects of Aerodynamic Heating and TPS
Thermal Performance Uncertainties on the Shuttle Orbiter" by Goodrich,
Derry and Maraia

John Haberman
NASA/Goddard Space Flight Center

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