Conference 7.286::space

147.0. "CHALLENGER 51-L Chronology" by CASTOR::MCCARTHY () Thu Feb 13 1986 01:24

Note 145 mentioned the Aviation week and Space Technology article on the
loss of flight 51-L. For those of you who haven't seen it, here's the
chronology of the flight as presented:

	   Digital engineering data transmitted by Challenger and new
	photography of the accident are building a detailed chronology
	of what occurred Jan. 28 following liftoff from pad 39B.

	   At liftoff, the two solid rocket boosters were functioning
	normally, each generating about 3.3 million pounds of thrust.
	[period above is accidental]
	in addition to the oxygen/hydrogen main engines, each operating
	at 104% thrust.

	   Twenty seconds into the flight the solid rockets each began to
	reduce their power toward 2.4 million pounds of thrust. This power
	reduction was to slow the rate of Challengers acceleration as it
	apporached the region of maximum aerodynamic pressure. The three
	liquid engines also began to throttle down at about this point.

	   At 40 sec. into the flight, Challenger flew through a wind
	shear, and data show that the solid motors and main engines
	pivoted to maintain the proper vehicle flight path. At about
	45 sec., the thrust on both solid rockets leveled off as planned
	at about 2.4 million pounds. At about 50 sec. into the flight,
	the propellant in both solid motors was to start burning in a
	way that would gradually start to build thrust back toward about
	2.7 million pounds.

	   There are three chamber pressure sensors on the motors, and
	the sensors on the left motor showed that it was beginning to
	increase thrust as planned. Sensors on the right motor, however,
	showed that it was not increasint thrust properly-indicating that
	a rupture of the case had occurred and hot, high velocity gas
	was beginning to escape from the 149 foot long stage.

	   At about 59 sec. into the flight, Kennedy tracking camera
	photography of the right booster detected the leak as a 4x8 foot
	brigth plume emerging from the attach joint between the two
	aft segments of the right motor. The photography shows this plume
	growing for about 15 seconds until it became severa feet wide anf
	[and] at least 40 feet long. Chamber pressure from the motor 
	continued to lag until at about 70 seconds it was 4% below the
	desired level, indicating that a massive leak was underway on
	the stage.

	   At about 71 seconds - 2 seconds before the explosion, several
	events began to take place as noted in the digital data. The right
	motor at this time was providing over 100,000 pounds less thrust
	than the left motor - a difference that was starting to affect the
	flight path of the vehicle.

	  The flight control system noted this difference and began moving
	both the main engine rocket nozzles and solid motor nozzles to
	steer the vehicle and compensate for the lagging booster, whcih
	[which] by then had a massive plume spraying from the ruptured
	joint. This motor nozzle gimbaling was not dramatic, and the
	vehicle was starting to compensate properly. The solid rocket
	boosters are attached to the shuttle external tank by struts on
	the boosters at both their foreward and aft ends.

	   The 5600[degree]F plume from the booster's leak was directed
	toward the booster's lower attach points with the tank. In the
	last second before all data were lost, the aft attach points for
	the right booster were either severed by the fire or broken
	structurally by the abnormal stresses created by the high velocity
	leak.

	   At the time this occurred the booster's plume or structural
	loads also severed the 17 inch diameter liquid oxygen line that
	runs down the outside of the external tank. This line carries
	liquid oxygen from the upper oxygen section of the external tank
	down to the orbiter's main engines.

	  A split second after the aft attach points for the booster
	failed, data from the rate gyro systems in that booster show that
	the bottom of the solid rocket began to flip outward, pivotting
	around its upper attach point but still secured to the portion of
	the external tank that separates the oxygen and hydrogen sections.

	   This had the effedt of driving the upper portion of the booster
	into the side of the external tank, rupturing the oxygen and hydrogen
	section and resulting in a powerful explosion that destroyed Challenger.
	Recently updated information indicates the explosion occured at 73
	seconds.

	   The two solid motors then flew off in opposite directions still
	generating over two million pounds of thrust. The right booster's
	nose was badly damaged from its collision with the tank, and recovery
	parachutes in its nose began to trail out of the motor as it flew
	off prior to thrust termination by range safety explosives detonated
	on command from Cape Cannaveral Air Force Station.

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							-Brian

Brian,

I believe you spelled that wrong.  Isn't it Aviation Leak?

Brett.

This is an afterthought, and it may be overkill, but I thought I'd include
it anyway.  I got a letter from one of the Engineers at the Cape with her
description of what happened.  It's very brief, but it captures the mood
better than Brokaw and the sensationalists.  It follows:

Things aren't quite as depressing around here as they were.  I still do not
think I could describe it to you though.  The pictures on T.V. made it pretty
clear, but watching it out here, you could not see quite as well.  There
was so much smoke, everybody just stood there watching the sky, praying that
they had separated and the bird would miraculously appear out of the clouds.
Everytime I picture it I get cold shivers.  I did not watch the news much
that week.  Seeing it over and over was a bit much.  That afternoon we had
to gather up all the code we changed in the 53 release and it was locked
up in the boxcars with the disks until someone from the investigation team
said they didn't need it.  We still can't use FR2 to test code and rumor
has it we won't be able to use FR2 anymore.

What is FR2?
    John Sauter

Sorry....

53   (1985, 3rd quarter software release)

FR2  (Firing Room 2)  There are 4. 1 and 2 are primaries and 3 and 4 are
     backups.  FR4 is the secure Firing Room.

Brett.