What altitude does mach# become meaningless?
#12
Gets Weekends Off
Joined APC: Jul 2017
Posts: 1,337
Max Q is probably the most import factor.
The max q condition is the point when an aerospace vehicle's atmospheric flight reaches maximum dynamic pressure. This is a significant factor in the design of such vehicles because the aerodynamic structural load on them is proportional to dynamic pressure. This may impose limits on the vehicle's flight envelope.
The max q condition is the point when an aerospace vehicle's atmospheric flight reaches maximum dynamic pressure. This is a significant factor in the design of such vehicles because the aerodynamic structural load on them is proportional to dynamic pressure. This may impose limits on the vehicle's flight envelope.
Last edited by Elevation; 06-20-2020 at 12:02 PM.
#13
Gets Weekends Off
Joined APC: Apr 2016
Position: 767
Posts: 131
It never becomes "meaningless" per se at a certain *altitude*. Once you enter LEO, you need to be at a certain speed to maintain orbit. Once you accelerate to this speed, you no longer need to add thrust - around Mach 25, or 17500 mph, and the astronauts earn their "Mach 25" patch. At this point, it doesn't really have any meaning anymore. For the astronauts who serviced Hubble, which is further from the Earth than normal LEO, they actually reach Mach 26 on their return to Earth, so they get "Mach 26" patches. To re-enter, they only need to reduce their orbital velocity by about 200mph, so I guess their exact speed technically matters at this point as well.
Last edited by PlaneS; 07-09-2020 at 07:11 PM. Reason: Clarity
#14
The flight planning and thrust reductions kept the maximum speed on ascent below 475 KEAS again to minimize the maximum structural pressure to remain below 819 psf.
On descent, the maximum airspeed (KEAS) was set at 321 knots or a maximum pressure of 350 psf. "Redline" in that context was established at 333 KEAS for the Space Shuttle.
Minimum controllable airspeed (Speed that flight controls remain effective) is 163 KEAS and less than MACH 5.0.
L/D for the Shuttle occurred around 190-220 depending on MACH at the time. They always flew faster to retain energy reserves to extend the glide if needed.
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