The Challenger Shuttle Challenge

1
The Challenger Shuttle Challenge

• An Ethical Scenario
• Engineering Concepts
• Dr. Ron Eaglin

2
The facts

• On January 28, 1986 Seven astronauts were killed
  when the space shuttle Challenger exploded 72
  seconds after liftoff from the Cape Canaveral Air
  Force Station.
• Official cause of the accident was failure of
  O-Rings on the Solid Rocket Boosters and
  subsequent leakage of hot gasses which ignited
  the propellant causing an explosion.

3
Background

• Competition from the European Space Agency
  required NASA to demonstrate that the shuttle
  could fly a dependable, yet aggressive schedule
  to prove its viability for commercialization.
• The previous Shuttle mission was delayed a record
  number of times due to mechanical problems and
  poor weather.

4
Background

• Launch pad refurbishment was required before the
  next mission which was to carry a probe to study
  Halleys comet, the schedule was tight on this
  mission as a similar Russian probe was schedule
  to arrive in the comet vicinity shortly after the
  American probe.

5
Background

• NASA officials desired to have the Shuttle in
  space with Astronaut/Teacher Christa McAuliffe
  for the State of the Union Address Ronald
  Reagans main topic was to be Education and this
  was to be important to the speech.

6
Solid Rocket Boosters

• The Solid Rocket Boosters are the primary thrust
  for the Shuttle allowing it to achieve orbit.
• Each booster is 149 feet long and 12 feet in
  diameter.
• Each booster weighs 2 million pounds
• Solid rocket fuel (unlike liquid) cannot be
  turned off once ignited.

7
Solid Rocket Boosters

• Morton Thiokol received the contract to build the
  SRB in 1974.
• The SRB design is essentially a scaled version of
  the Titan Missile.
• The booster is comprised of 7 hollow metal
  cylinders
• The Solid rocket fuel is cast in the cylinders at
  the M-T plant in Utah and transported to KSC

8
Solid Rocket Boosters

• The SRB field joints consist of a tang and clevis
  joint held together by 177 clevis pins.
• Each joint is sealed by 2 O-rings and a heat
  resistant putty is applied to the inner section
  of the joint assembly.
• To minimize gap and squeeze the O-Rings, shims
  are inserted between the tang and outside leg of
  the clevis.

9
The Event

• The first launch delay occurred because an
  expected weather front. The launch was scrubbed
  before the front moved into the area.
• The reason to scrub the launch was to prevent the
  Vice-President from needlessly traveling to KSC
  as he was expected for launch.

10
The Event

• The weather front stalled and the weather
  conditions were ideal for the scrubbed first
  launch.
• The second launch was delayed due to a defective
  micro-switch in the hatch locking mechanisms. By
  the time the problem was solved wind conditions
  were too high for launch.

11
The Event

• The stalled weather system had started moving
  again by the 3rd scheduled launch and was
  expected to bring record low temperatures to the
  area.
• NASA contacted all shuttle contractors to
  determine if there were concerns with a cold
  weather launch.

12
The night before

• Alan McDonald (of M-T) was convinced there might
  be cold weather problems with the SRB design and
  contacted 2 project engineers, Robert Ebeling and
  Roger Boisjoly.

13
More background

• M-T knew of a design problem with the SRB in 1977
  and had initiated a redesign effort in 1985.
• NASA level I management were briefed on the issue
  in August 1985.
• Half of all shuttle flights had experienced
  O-Ring erosion in the booster joints.

14
More background

• Ebeling and Boisjoly had both complained that
  management was not supporting the redesign task
  force.
• In July 1985 new steel billets had been ordered
  for a redesigned case field joint, these would
  not be ready for months.

15
January 27, 1986

• Morning temperatures were predicted to be in the
  low 20s.
• A teleconference was scheduled between
  engineering and management at KSC, Marshall Space
  Flight Center, and M-T Engineers and management
  in Utah.

16
January 27, 1986

• M-T Roger Boisjoly and Arne Thompson were given a
  very short time to prepare a presentation for the
  conference.
• They gave a 1 hour long presentation and a
  convincing argument that cold-weather would
  exaggerate problems of joint rotation and delayed
  O-Ring seating.

17
January 27, 1986

• Previous lowest temperature launch was 53 F on
  January 24, 1985.
• O-Ring temperature at launch was expected to be
  29 F (ambient temp as expected to be 26 F)
• M-T VP Bob Lund presented conclusion the 53F was
  lowest temp that data existed for operational
  boosters. The boosters had experienced erosion at
  this temperature.

18
January 27, 1986

• Because engineers had no low temperature data
  below 53F, they could not prove it was unsafe to
  launch at lower temperatures.
• Booster specification called for booster
  operation at 31F (later it was found this was for
  booster storage, not launch)

19
January 27, 1986

• Larry Mulloy (Marshalls SRB Project Manager)
  commented the data was inconclusive and
  challenged the engineers logic.
• Mulloy called for a decision by Joe Kilminster
  (M-T middle level management) who supported the
  M-T engineers.
• Several other Marshall managers expressed doubts
  about the recommendation.

20
January 27, 1986

• The teleconference ended so M-T could review its
  data. Boisjoly and Thompson tried to convince M-T
  senior management to support decision to not
  launch.
• Senior exec Jerald Mason at M-T told Bob Lund
  Take off your engineering hat and put on your
  management hat

21
January 27, 1986

• Joe Kilminster wrote a new recommendation
  recommending launch and went back into the
  teleconference.
• The engineers refused to work on or sign the
  recommendation.
• Alan McDonald (M-T) was in KSC with NASA, he was
  surprised to see the recommendation to launch.

22
January 27, 1986

• Alan McDonald refused to sign the launch
  recommendation and appealed to NASA management
  not to launch.
• NASA management approved the recommendation to
  launch.

23
January 28, 1986

• Overnight temperature dipped as low as 8F.
• Safety showers and fire hoses were deployed to
  prevent pipes from freezing, but caused ice to
  form on the platform.
• The ice inspection team was alarmed, but the
  launch director continued with countdown.

24
January 28, 1986

• Low temperature launch limits were waived by
  several key personnel during countdown.
• 8/100 second after ignition engineering cameras
  focused on the right hand booster record 9 smoke
  puffs originating in the booster aft field joint.
• Oxides from burnt propellant temporarily seal the
  field joint preventing flames from escaping.

25
January 28, 1986

• 59 seconds into flight telemetry records most
  violent wind shear recorded in a shuttle flight.
• The glassy oxide film that is sealing the joint
  is shattered by the wind shear, flames burn
  through the external field tank within 2 seconds.

26
January 28, 1986

• 72 seconds into flight the external fuel tank
  ignites through hole causing an explosion that
  tears the SRB apart and causes extensive damage
  to the shuttle.
• 100 seconds into flight all telemetry data
  ceases.

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