MadSci Network: Engineering

Re: How are space shuttles protected from friction when they reenter the Earth's atm

Date: Tue Apr 10 13:47:57 2001
Posted By: Jeff Yap, Materials Engineer
Area of science: Engineering
ID: 986430520.Eg

Hi Maggiw!  (I think you meant to type "Maggie", but you never know...)

That's a great question.  When the Space Shuttle reenters Earth's atmosphere, 
the friction of the air can get the temperature up as high as 3000 F 
(1650C).  To keep the shuttle from burning up, it's covered with special 
materials that can stand that kind of heat.

The four main materials currently used for the skin of the shuttle are:
1) Reinforced Carbon Carbon.  No, I didn't accidentally type "Carbon" 
twice twice.  RCC is a sheet of carbon reinforced with carbon fibers.  
Then it has a layer of Silicon Carbide grown on the outside.  This black 
material coats the nose and most of the leading edges of the shuttle, 
where the temperatures get above 2300 F.
2) Fibrous Refractory Composite Insulation - High Temp Reusable Surface 
Insulation tiles.  (FRCI HRSI)  These are the black tiles that are on the 
underside of the shuttle, where re-entry temperatures range between 1200-
2300 F.  They're made from a Silica (same stuff as sand or glass) ceramic 
material interlaced with Alumina Borosilicate fibers.  These tiles are 90% 
void and 10% material.  I think that's pretty neat.  A cubic foot of this 
material only weighs 9 pounds.
3) Advanced Flexible Reusable Surface Insulation.  This is a white quilted 
silica fabric that covers the top parts of the shuttle, where the 
temperatures run around 700-1200 F.  This quilt is actually an upgrade.  
For the first few Columbia flights, the upper skin used to have the same 
kind of tiles that were on the bottom, just white colored.
4) Felt Reusable Surface Insulation.  This is a fluffy sheet of Nomex, 
which is the same synthetic stuff firefighters wear.  It's used on spots 
like doors and panels where the temperature doesn't exceed 700 F.

The tiles that make up most of the skin of the space shuttle will last 
about 100 missions, and they dissipate heat very quickly.  So quickly, 
that you can put it in an oven until it's red hot, pull it out, and in a 
few seconds, pick it up with a bare hand, even though the center is still 
glowing.  The
tiles on the bottom and nose of the shuttle are black because black 
objects radiate more heat than lighter objects, which also helps cool down 
the shuttle during reentry.  The tiles not only have to withstand the 
high heat of reentry, but also the coldness (-250 F) of space, the sonic 
stress (165 decibels) of liftoff, as well as the other stresses and 
strains that are applied to something that gets launched into space.

More Space Shuttle info:
* The five NASA shuttles are: Columbia, Challenger, Discovery, Atlantis, 
and Endeavour.
* The next generation shuttle is 
almost complete, but the project is currently on hold.  It will use a 
Titanium Aluminide skin for it's Thermal Protection System.
* Shuttle reentry is a controlled, unpowered glide that starts at 18,000 
miles per hour, and touches down at about 220 mph.  They start entering 
the atmosphere at a 40 degree angle of attack.  If it's any steeper, the 
shuttle will burn up (even with the nifty tiles), and if it's any 
shallower, the shuttle will skip off the atmosphere like a stone over 
water.  The
 shuttle won't be able to land if the winds are too strong because it's 
heavier and fatter than a plane.
* In addition to air friction, the shuttle gets heated because it 
compresses the air in front of it.  Gay-Lussac's Law shows that if you 
compress a gas, you increase the temperature.  When the shuttle starts 
pushing into the atmosphere at 24 times the speed of sound, that can 
really heat things up.

Well, I hope your question is answered, and that you think that the Space 
Shuttle and all of the engineering that goes into it is pretty cool.  (Pun 
intended...)  If you want more information, feel free to write us back or 
check out the following web sites.
NASA Space Shuttle Reference Manual 

Encyclopaedia Britannica

How Stuff Works - 
The Space Shuttle

Track Realtime Spacecraft Tracking

Jeff Yap
Mad Scientist

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