Why does the Shuttle roll during launch?

Factual Questions
21

Could you elaborate on this? I know nothing of these things but I’m sure I’ve watched a video that stated the crew cabin and the severed left wing emerged from the vapor cloud approximately 1 1/2 seconds after the combustion of propellants that leaked from the ET. This seems to suggest the force of the combustion was responsible for the break up.

Not challenging your assertion, just looking for clarification.

ETA:link

22

For the win! :smiley:

23

Eh, dumbing things down generally bugs me - maybe I’m overly optimistic, but I’d like to think that most people are actually reasonably intelligent and have the capacity to understand things - there’s no need to dumb things down. But I also acknowledge that there’s a big element of picking my battles here.

As for a potential STS-135: There’s been some talk.

One side is saying: We’re going to have the whole thing close to fully prepped anyway, and the ISS isn’t scheduled to be abandoned anytime soon, so why not use that last prepped shuttle to bring up a buttload of supplies? Which makes sense.

There’s a number of problems, though, which (IMO) make it extremely unlikely. One big concern is they’d only have a four-man crew because of the way they outfit potential rescue shuttles, and they also wouldn’t have time do a complete and total turnaround on Atlantis (and if they did they still probably wouldn’t for just one flight), so there would potentially be some significant safety issues. There’s also a little problem where Congress has pretty much decided to stop giving the shuttle program money in 2011, and STS-135 would probably run into 2012.

There’s also some damn issue with the external tank, where there’s basically two and a half-ish tanks: one really old one stuck in a closet somewhere, one fully built but damaged by a hurricane and not yet repaired, and two which are partially built and (apparently) abandoned in the factory (for what reason I cannot possibly imagine). The old one is heavier than they’d want to use, the damaged one is, well, damaged, and it would be costly to complete one of the two in-progress ones. Obviously they’ll have to figure something out for the contingency flight, but from what I’ve heard it’s a pretty good example of government “planning”.

24

I’m not a rocket scientist, and hopefully Stranger will return to elaborate, but: the large cloud that enveloped the orbiter and the boosters was due primarily to the fact that the fuels were incredibly cold (liquid oxygen & hydrogen.) Some of the hydrogen did burn, but not very much, and not with enough force to destroy the orbiter on its own. In other words, if the SRBs and the external tank had failed the way they did on while the orbiter was sitting on the ground, the orbiter probably would have survived largely structurally intact.

Instead, it was the imbalance in the aerodynamic forces that tore the orbiter apart. When the right SRB failed, the force from the rockets was pushing and torquing the orbiter in unexpected directions, and once the orbiter got out of the correct, streamlined orientation, the wind essentially caught it and tore it apart.

25

Rather than mess about - this is the critical part from the Rogers commision report. Note the word “almost” in the second paragraph.

  • At 73.124 seconds,. a circumferential white vapor pattern was
    observed blooming from the side of the External Tank bottom dome.
    This was the beginning of the structural failure of hydrogen tank that
    culminated in the entire aft dome dropping away. This released
    massive amounts of liquid hydrogen from the tank and created a sudden
    forward thrust of about 2.8 million pounds, pushing the hydrogen tank
    upward into the intertank structure. At about the same time, the
    rotating right Solid Rocket Booster impacted the intertank structure
    and the lower part of the liquid oxygen tank. These structures failed
    at 73.137 seconds as evidenced by the white vapors appearing in the
    intertank region.

Within milliseconds there was massive, almost explosive, burning of
the hydrogen streaming from the failed tank bottom and liquid oxygen
breach in the area of the intertank.

At this point in its trajectory, while traveling at a Mach number of
1.92 at an altitude of 46,000 feet, the Challenger was totally
enveloped in the explosive burn. The Challenger’s reaction control
system ruptured and a hypergolic burn of its propellants occurred as
it exited the oxygen-hydrogen flames. The reddish brown colors of the
hypergolic fuel burn are visible on the edge of the main fireball.
The Orbiter, under severe aerodynamic loads, broke into several large
sections which emerged from the fireball. Separate sections that can
be identified on film include the main engine/tail section with the
engines still burning, one wing of the Orbiter, and the forward
fuselage trailing a mass of umbilical lines pulled loose from the
payload bay.*

26

I could be totally wrong, but I’ve heard the details of Challenger summed up into three main points:

  1. The SRB leaked, came loose at the bottom strut, and rotated slightly around the top strut. Result: your two very powerful engines are no longer pointing you in the same direction, which is bad, and also…
  2. The ET, due to damage inflicted by the SRB, lost it’s internal containment, resulting in a very uncontrolled combination of liquid hydrogen and oxygen, which resulted in the entire tank simply disintegrating.
  3. The above points were bad and the crew was already doomed, but what actually caused the orbiter to break up was that the SRB and ET problems pushed it into a decidedly aerodynamic attitude (i.e., the shuttle was no longer leading with it’s nose and was roughly as aerodynamic as a brick), and doing so while traveling at upwards of a thousand miles per hour after having been severely damaged by everything else caused the orbiter to basically crumble like a cracker.
27

Tp paraphrase the events.

SRB field joint leaks - from an intial spurt of gas at liftoff the pressure inside the SRB eventually pushed enough hot gas past the joint to completely erode the O-ring - so that there was flame shooting out of the joint. So much so that the internal pressure measured inside the SRB was noticably less than it should have been.

Flame plume impinges on the ET and the aft attachment point - where the SRB is attached to the ET. As in the quote above, this flame cut though the ET at its base. The entire ET below the upper attachament points (which are on the intertank seperator between the hydrogen and oxygen tanks, is the liquid hydrogen tank. (Liquid hydrogen has very low density - this is one of its significant disadvantages.) The ET starts to leak lots of LH into the slipstream. Eventually the entire bottom of the tank simply falls off. This occurs pretty much at the same time as the aft attachment point for the SRB fails.

So, the huge amount of liquid hydrogen in the tank now blows back out of the back of the tank slamming the top of the liquid hydrogen tank up into the bottom of the liquid oxygen tank, at the same time the SRB, now only held at the top, pivots around. It hits part of the wing, but most importantly, the pointy end is pushed into the side of the liquid oxygen tank, which ruptures here too. At this point the stack is blown apart by the ferocity of the combustion of the hydrogen and oxygen in the inter-tank space. The reason it isn’t called an explosion is that it didn’t detonate. It just burnt very fast. Just like it does inside the rocket motor. There wasn’t much chance for the oxygen and hydrogen to mix. Most of the hydrogen had blown out of the back of the tank, and the oxygen was at the top of the structure. By the time any mixing and further combustion had occured the orbiter was already long broken up.

But yes, the orbiter pitches back into the hypersonic stream and the wings get instantly ripped off, and the rest of the orbiter is torn into chunks.

28

Thanks all… ignorance fought.