Text 27143, 109 rader
Skriven 2007-02-12 19:16:29 av Gary Braswell (1:123/789.0)
  Kommentar till text 27138 av John Hull (1:123/789.0)
Ärende: Challenger disaster not related to hydrogen fuel explosion
==================================================================
John Hull -> All wrote:
 JH> You guys really ought to make sure of your facts before hand:


 JH>  From Wikipedia on the Challenger Shuttle disaster:

 JH> No "explosion"

 JH> Contrary to the flight dynamics officer's initial statement, the shuttle
 JH> and external tank did not actually "explode". Instead they rapidly
 JH> disintegrated under tremendous aerodynamic forces, since the shuttle was
 JH> near "Max Q", or maximum aerodynamic pressure. When the external tank
 JH> disintegrated, the fuel and oxidizer stored within it were released,
 JH> producing the appearance of a massive fireball. However, according to
 JH> the NASA team that analyzed imagery after the accident, there was only
 JH> "localized combustion" of propellant.[7] Instead, the visible cloud was
 JH> primarily composed of vapor and gases resulting from the release of the
 JH> shuttle's liquid oxygen and liquid hydrogen propellant. Stored in
 JH> cryogenic conditions, the liquid hydrogen could not have ignited rapidly
 JH> enough to trigger an "explosion" in the traditional sense. Had there
 JH> been a true explosion, the entire shuttle would have been instantly
 JH> destroyed, killing the crew at that moment. The more robustly
 JH> constructed crew cabin and SRBs survived the breakup of the launch
 JH> vehicle; while the SRBs were subsequently detonated remotely, the
 JH> detached cabin continued along a ballistic trajectory, and was observed
 JH> exiting the cloud of gases at T+75.237.[7] Twenty-five seconds after the
 JH> breakup of the vehicle, the trajectory of the crew compartment peaked at
 JH> a height of 65,000 feet (19.8 km); the breakup had occurred at only
 JH> 48,000 feet (14.6 km).[8]

Herein lies the confusion. This is from the Presidential Commission of the
Challenger Disaster:

Beginning at about 72 seconds, a series of events occurred extremely
rapidly that terminated the flight.  Telemetered data indicate a wide
variety of flight system actions that support the visual evidence of
the photos as the Shuttle struggled futilely against the forces that
were destroying it.

   At about 72.20 seconds the lower strut linking the Solid Rocket
Booster and the External Tank was severed or pulled away from the
weakened hydrogen tank permitting the right Solid Rocket Booster to
rotate around the upper attachment strut.  This rotation is indicated
by divergent yaw and pitch rates between the left and right Solid
Rocket Boosters.

  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.

------------------------------------------------------

"...massive, almost explosive, burning of the hydrogen..."

"...explosive burn."

With vagueness like this in the findings its not surprising the disagreements.

But its obvious the distinction is being made between explosive and explosion.
They refer to a 2.8 million pound forward thrust burn into the oxygen causing a
hypergolic ignition.

It appears John you are correct, the mixture did not explode, but burned 
mostly at once in a massive ignition.

So lets state it correctly.

A hypergolic ignition of hydrogen and oxygen, brought about by a burn through
of the o-ring of one of the SRB's broke up the orbiter.

The fact remains, without the hydrogen burn, the Shuttle still could have
survived. The o-ring burn through by itself would not have broken up the
shuttle.


-- 
"We are safe in our beds because rough men stand ready in the
night to visit violence on those who would do us harm."- George Orwell

"For those dreams taken, here are a few nightmares."
Written on a bomb dropped on Tora Bora.

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