Montag, 24. März 2014

21 July 2013 Space reentry vehicles

Part 3: ICBMs and the cold war

Other than vehicles with a detached shock wave, all aircraft heat up more the faster they move.  From the NASA book Facing the Heat Barrier: A History of Hypersonics [1]
At Mach 3 and higher, there was the Lockheed SR-71 that cruised at 85,000 feet. The atmosphere at such altitudes, three times higher than Mount Everest, has a pressure only one-fiftieth of that at sea level. Even so, this airplane experienced aerodynamic heating that brought temperatures above [260C] over most of its surface.
The SR-71 Blackbird gets to 260C over most of its surface.  Aluminium anneals (softens) at 177C (alloys can be higher) making it unsuitable as a material for use on the outside of the Blackbird.  The Blackbird used titanium instead.
This temperature of 260C is in a vehicle moving at Mach 3.
The US Air Force's experimental rocket X-15 moved at Mach 5 and was designed to withstand temperatures of 1240F (671C) in some places.  If Mach 5 takes the temperature beyond the aluminium melting point (660C)*, how did the Apollo reentry capsule hold together at Mach 36?

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