CHALLENGER DISASTER : CASE STUDY Samiul A. Chowdhury [2021298272] mac151830@utdallas.edu EMSE-6361 Fall-2015 Dr. Lawrence Chung Term paper – Interim http://www.utdallas.edu/~mac151830/emse6361

Overview Space Shuttle Challenger was second reusable orbiter of NASA's space shuttle program Disaster occurred on January 28, 1986 Challenger Broke apart 73 seconds into its flight and exploded in midair Which led the deaths of its all seven crew members

Space Shuttle The Space Shuttle orbiter was the reusable spaceplane component of the Space Shuttle Orbiter is attached to the large External Tank—the middle cylinder with the sharp-pointed end shown in the figure; the external Tank contains 143,000 gallons of liquid oxygen and 383,000 gallons of liquid hydrogen for the Orbiter's engines. The two smaller cylinders on the sides of the External Tank are the Solid Rocket Boosters (SRBs).

Space Shuttle Challenger Country: United States Named after: HMS Challenger (1858) steam-assisted Royal Navy warship First flight: April 4–9, 1983 Status: Destroyed January 28, 1986 Number of missions: 10 Time spent in space 62 days 07:56:22 Number of orbits: 995 Satellites deployed: 10

Solid Rocket Boosters (SRBs). SRB was almost 150 feet, it was too large to ship as a single unit by rail from Utah to the Kennedy Space Center launch site in Florida. For this reason it was manufactured from individual cylindrical segments. SRBs fire for about two minutes after liftoff, and then, their fuel exhausted, are separated from external tank.

O-Ring Seals Field joint was sealed with two rubber O-rings O-rings designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface. Prevents pressurized hot gases and flame to leak

Organizations Involved Marshall Space Flight Center was in charge of booster rocket development Morton Thiokol - Contracted by NASA to build the Solid Rocket Booster The shuttle was built by Rockwell International's Space Transportation Systems Division

Key People Involved Roger Boisjoly The engineer who knew challenger has a problem and tried to stop the launch Larry Mulloy Marshall’s manager for SRB project. Challenged the engineers decision not to launch Alan McDonald Director of the SRB project at Morton Thiokol

The astronauts: seven crew members, which included five NASA astronauts and two Payload Specialists. One of the Payload Specialist Christa McAuliffe, who would have been the first schoolteacher in space.

What Happened? Disintegration of the vehicle began after an O-ring seal in its right SRB failed at liftoff. The O-ring failure caused a breach in the SRB joint it sealed, allowing pressurized burning gas from within the solid rocket motor to reach the outside external fuel tank. This led to the separation of the right-hand SRB's aft field joint attachment and the structural failure of the external tank.

Cont. Tank exploded and aerodynamic forces broke up the orbiter. Loss of 7 astronauts (entire crew) Loss of Challenger Where? Over the Atlantic Ocean, off the coast of Cape Canaveral, Florida

What Failed? O-rings were designated as "Criticality 1"—meaning that their failure would result in the destruction of the Orbiter Joint rotation phenomenon: O-ring joints were supposed to close more tightly due to forces generated at ignition, but due to the effects of booster combustion, the metal parts bent away from each other, opening a gap through which gases leaked First and Second(safety backup) O-ring seals both failed to prevent the leak Simplified cross section of the joints between SRB segments. Legend: A - steel wall 0.5 inches (12.7 mm) thick B - base O-ring gasket, C - backup O-ring gasket, D - Strengthening-Cover band, E - insulation, F - insulation, G - carpeting, H - sealing paste, I - fixed propellant

Why Did it Happened? SRB temperatures below their redline of 40 °F (4 °C). The temperature on the day of the launch was far lower than had been the case with previous launches: below freezing at 28 to 29 °F (−2.2 to −1.7 °C) O-rings were not tested at temperatures below 50 °F (10 °C). Causing the O-rings to harden Opening a gap through which hot gases—above 5,000 °F (2,760 °C)—leaked Right SRB producing a propulsive force that rammed the hydrogen tank into the liquid oxygen tank

Key Dates Morton Thiokol awarded contract to build SRBs 1974 1976 1977 1981 1985 Jan 27, 1986 Jan 28, 1986 Morton Thiokol awarded contract to build SRBs NASA- accepts Morton- Thiokol's booster design. Morton- Thiokol discovers joint rotation problem.  O-ring erosion discovered after second shuttle flight.  NASA Level I management briefed on booster problem.  Teleconferen ce to discuss effects of cold temperature on booster performance. Challenger explodes 73 seconds after liftoff.

Root Cause Direct cause of the explosion was technical – faulty design of the SRB, insufficient low temperature testing of the O-ring material that the O-ring sealed Indirect cause: The Rogers Commission* found NASA's decision-making processes and lack of communication between different levels of NASA management had been key contributing factors to the accident. The unrealistically optimistic launch schedule also possible contributing cause to the accident *Rogers Commission, a special commission appointed by United States President Ronald Reagan to investigate the accident.

Problem - Organizational Communication and Ethics Engineers at Morthon-Thiokol vigorously opposed the launching of Challenger(even before night before launch) , but their warning had not Been heeded by management Same O-rings engineers had been concerned about for more than eight years Even O-rings designated "Criticality 1” - no one at Marshall suggested that the shuttles be grounded until the flaw could be fixed. Top NASA decision makers(at levels I and II) told the commission that they had no knowledge that these had been the subject of intense controversy between Thiokol and Marshall Space Flight Center(level IV and III in the decision-making chain)

Cont. Although O-ring failure was the immediate cause, a flawed decision-making process was an equal, if not more important factor More than 30 people were in at least 25 communication situations during 1977 – 1982 discussing the O-ring problem, yet none reached Level I or II While NASA worked on solving the problem, it continued to fly and it defined the Criticality-1 feature as “acceptable” and “unavoidable”. Mulloy said, “My God, Thiokol, when do you want me to launch – next april?’ Boisjoly recalled that when the shuttle was destroyed a few seconds later, "we all knew exactly what happened.“ NASA officials said they would not have given the final approval to launch if they had heard the views of Thiokol engineers

Aftermath In the first minutes after the accident, recovery efforts were begun Search and rescue aircraft were also dispatched It took 3 months to recover bodies of crew members After the Challenger accident, further shuttle flights were suspended, pending the results of the Rogers Commission investigation. Two-and-a-half year grounding of the shuttle fleet; flights resumed in 1988

References Engineering Ethics: The Challenger Disaster [https://www.cedengineering.com/userfiles/ethics_challenger_disaster_2283.pdf] http://ethics.tamu.edu/Portals/3/Case%20Studies/Shuttle.pdf https://en.wikipedia.org/wiki/Space_Shuttle_Challenger https://en.wikipedia.org/wiki/Space_Shuttle_Challenger_disaster http://pirate.shu.edu/~mckenndo/pdfs/The%20Space%20Shuttle%20Challenger%20Disaster.pdf http://softwarephysics.blogspot.com/2014/07/new-introduction-to-softwarephysics.html

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