Wikipedia's explanation of the sequence of events:

The O-ring failure caused a breach in the SRB joint it sealed, allowing pressurized hot gas from within the solid rocket motor to reach the outside and impinge upon the adjacent SRB attachment hardware and external fuel tank. This led to the separation of the right-hand SRB's aft attachment and the structural failure of the external tank. Aerodynamic forces broke up the orbiter.

I understand that lots of debris was being created by the SRB destruction, and the destruction of the fuel tank intuitively seems fatal. But this text doesn't go in that direction. In spite of the various debris, it is stated that aerodynamic forces tore up the orbiter itself. Maybe it's a combination of the two, but it certainly implies that aerodynamic forces were sufficient to break up the orbiter.

But this Space Shuttle was climbing, not reentering. That should put it well below orbital velocity and (I would assume) well below the velocity that the reentry vehicle sees at that altitude. If it has a heat shield which can withstand the tremendous aerodynamics of reentry, then why was this point in flight obviously destructive when the attitude changed?

up vote 3 down vote accepted

then why was this point in flight obviously destructive when the attitude changed?

The vehicle was just past maximum dynamic pressure (max Q) so the aerodynamic loads on the launch vehicle and orbiter were near maximum when the breakup began.

From what I've read, both the hydrogen and oxygen tanks were breached at approximately the same time thus, the breakup of the ET happened very quickly.

As the ET suddenly disintegrated, the attitude of the orbiter, with respect to the velocity vector changed, which, in combination with stresses from the attach points to the disintegrating ET, quickly broke the orbiter apart.

If you carefully watch a slow motion video of the initial moments of the ET breakup, you can see the nose and crew compartment rotate 'down' in a way that it couldn't possibly do if it were still attached to the payload bay.

For a contemporary example, consider the recent break-up of Spaceship 2 when its attitude (evidently) suddenly changed with respect to its velocity vector due to the tail booms prematurely feathering.

I'm reminded of a quote by Story Musgrave that the shuttle is ..."very fragile. A butterfly bolted onto a bullet, you know."

If it has a heat shield which can withstand the tremendous aerodynamics of reentry

The structural loads on the orbiter are what are relevant here. The loads during (a nominal) re-entry are quite a bit less than the loads during ascent.

From the same Wikipedia article:

Challenger veered from its correct attitude with respect to the local airflow, resulting in a load factor of up to 20 (or 20 g)

The SRB pushed the stack sideways. With the nose no longer pointing into the wind, aerodynamic load grew much larger than it would be on a normal ascent or descent.

Any high-performance aircraft will break up if abruptly turned from its direction of travel at speed.

In normal flight, the thin leading edges of the aerodynamic surfaces catch relatively little air resistance, so there's relatively little force on the wings and it's directed down the length of the craft. As the aircraft turns out of the direction of travel, the effective aerodynamic cross section of the wings and tail suddenly gets a lot bigger, and the load on the wings goes rapidly to 20g as noted in Hobbes' answer. The maximum expected load on the shuttle was about 3g (in reentry), and the airframe was rated for 5g.

Keep in mind also that the hottest, fastest part of reentry happens in very thin air at high altitude. In contrast, the Challenger explosion happened during ascent at 48,000 feet -- at 14% of sea level pressure, this is still relatively dense air compared to the beginning of reentry, and a bad place to be flying sideways at mach 2.

  • "instead of the 3g of a normal reentry" Challenger broke up during ascent, not re-entry. You may want to clarify that. It was Columbia that was destroyed during reentry. – α CVn Oct 29 '14 at 13:16
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    Reference to reentry is correct in both the question and answers: aerodynamic loadings are larger on reentry so that's what the orbiter must be designed for. – Hobbes Oct 29 '14 at 14:08
  • Right, didn't intend to imply Challenger was in reentry. :) – Russell Borogove Oct 29 '14 at 17:06

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