I believe that it's common knowledge that Max-Q is the point in which a rocket is undergoing the maximum dynamic stress during a launch and ascent. But, how often have rockets actually been destroyed or failed at this point (or close to it) during launch due to Max-Q stresses? I've seen videos of many launches which fail with rapid disassembly before this point, but can't really recall that Max-Q is a statistically large factor in rocket launch failures. Am I mistaken, or have rocket designs evolved such that Max-Q is a known factor that's been successfully planned into rocket design and manufacture?
Both of the shuttle flights that suffered fatal accidents encountered significant wind shear events that took place very close to max q. I'm not aware that this was directly linked to the accidents but there were people involved in the STS-107 accident investigation who were very suspicious that this was a coincidence.
Max q was at 59 seconds. Max vehicle response to wind shear was at 61.724 seconds.
51-L Accident Report remarks on the max-Q / wind shear / booster leak correlation:
Additional structural loads resulted from turbulence. Flight 51-L experienced the most severe turbulence of any Shuttle flight and, although the loads were within the allowable design limits, those design limits did not consider a joint that had already failed. It is unknown how much the combined effect of wind gust loads, maneuvering loads and an increase in thrust contributed to the accident. But the combined effects of these forces could have dislodged the burned material at the previously breached section of the joint.
- Shortly after the vehicle was loaded by these turbulent forces, at T+58 seconds, a flame appeared from the same general region where the puffs of smoke had been seen. But, this time the joint was continuously breached by the burning propellant gases. In a little over two seconds, the flame had grown and acted as a blowtorch to burn through the hydrogen tank. The appearance of the flame at this time is also indicative of a damaged primary 0- ring and failure of the secondary O-ring to seal...
From INVESTIGATION OF THE CHALLENGER ACCIDENT REPORT OF THE COMMITTEE ON SCIENCE AND TECHNOLOGY HOUSE OF REPRESENTATIVES NINETY-NINTH CONGRESS SECOND SESSION
Max q was at ~58 seconds (I'm reading off a graph). The wind shear started at 57 seconds. The foam debris release was at ~82 seconds.
STS-107 experienced a wind shear during the period of maximum dynamic pressure starting at 57 seconds MET (Mach 1.27). The wind shear was due to a rapid change in the out-of-plane wind velocity of -37.7 feet per second over a 1200 foot altitude range starting at approximately 32,000 ft (as shown in Figure 3-21). Immediately after the vehicle flew through this altitude range, its side-slip angle began to increase in the negative direction, reaching a value of approximately –1.75 degrees at 60 seconds. This value of side-slip angle is a new flight experience value for MET 60 seconds (as shown in Figure 3-22). Post-flight data review indicates that the new flight experience side slip event not the result of the wind shear itself. Instead, it was the direct result of a difference in the L - 4:35 minutes balloon measurement, upon which orbiter guidance commands were updated on launch day, and the actual winds flown through by the orbiter during launch and ascent. Figure 3-21 highlights the difference in these two winds in this altitude region (a 25 foot per second increase in out-of-plane magnitude pre-launch compared to a 12 foot per second reduction in magnitude as experienced by the vehicle)
Quote from the "Working Scenario" linked above.
I just read of another incident, a Proton launch in Feb 1969, where the "newly designed" payload fairing collapsed at max q. (Soviet Robots in the Solar System, Huntress & Marov, p. 195).
Rockets usually fail early in flight, within a minute of liftoff, or in the vacuum stage since that is hard to simulate on Earth. You can see a list of rocket failures here. The structure is one of the most reliable rocket parts, the failures are mainly related to fuel pumping and bad design decisions.
The uncrewed Mercury-Atlas 1 flight suffered a catastrophic failure due to aerodynamic loads at or near max-Q, and the launcher's structure was beefed up for future flights:
[NASA's Owen Maynard] stated in an oral history interview that his post-flight calculations showed the skin of the launch vehicle just below the spacecraft would have buckled due to the combined drag, acceleration, and bending loads which exceeded the resisting tensile stress in the skin provided by internal pressure. Maynard recalled that "The problem of mating the Mercury capsule to the Atlas was far from being properly resolved at the time of MA-1." Based on that finding, the NASA specified that future Mercury-Atlas launch vehicles add doublers to the skin structure in that area, and that future launch trajectories be shallowed to reduce pitch angle rate, to reduce the bending stress on the launch vehicle.
It's not so much that the max-Q point itself is dangerous, the vehicle acceleration is managed to keep aerodynamic forces to levels that shouldn't be a problem. However, it is the most aerodynamically stressful point in the flight, and if the vehicle has some structural fault that would lead to it failing due to those forces, it would likely do so before reaching that point. By the time you've reached it, you've left most of the risk of such failures behind.