Max Q
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- For other uses, see Max Q (disambiguation).
Max Q is an aeronautical engineering term that refers to the point of maximum dynamic pressure, the point at which aerodynamic stress on a spacecraft in atmospheric flight is maximized. The dynamic pressure <math>q</math> is defined by:
<math>q = \frac1{2}\rho v^2</math>
where <math>\rho</math> is the air density as a function of altitude and <math>v</math> is the spacecraft's speed. Aerodynamic stresses are proportional to <math>q</math>. During a normal space shuttle launch, this occurs at an altitude around 11 km (35,000 feet).<ref name="aeroweb">Jackson, Doug (6 May 2001). "Space Shuttle Max-Q". Aerodynamics Questions. AerospaceWeb.org. Retrieved on 2006-09-09.</ref> During the Apollo Moon missions, this occurred at an altitude of 13.7 km (44,900 feet).<ref name="apollojour">Woods, W. David; Frank O'Brien, transcribers (2005-10-04). "Apollo 15: Launch and Reaching Earth Orbit". Apollo Flight Journal. NASA. Retrieved on 2006-09-09.</ref>
During ascent, the spacecraft's speed is increasing as its altitude increases; however, air pressure, and with it air density, decreases with altitude until it eventually falls to zero when the spacecraft reaches orbit. Below the Max Q point, the spacecraft acceleration is faster than the rate of density change. Above the Max Q point, the opposite is true.
The chain of events leading to the Challenger disaster occurred shortly after the spacecraft passed Max Q.
Max Q can be defined similarly for a spacecraft re-entry. However, heating due to aerodynamic drag is more important than the aerodynamic drag itself, so one does not usually discuss Max Q during re-entry. The Columbia disaster occurred shortly after the point of maximum heating.
[edit] References
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[edit] See also
[edit] External links
- "STS-113 Ascent Timeline". Spaceflight Now (November 22, 2002). Retrieved on 2006-09-09. Shows Space Shuttle Max-Q at T+01:01, shortly after main engine throttle down and up.
