Investigation of the Challenger Accident
INTRODUCTION
INTRODUCTION
¶This section as well as Sections VII and VIII identify what hap- pened, as well as what did not happen, to cause the loss of the Challenger. This section also discusses why the accident happened in a n effort to prevent future catastrophes.
¶By the time the Rogers Commission had completed its report, it had been learned that many items investigated by the Commission did not contribute to the accident. Consequently, this section is di- rected toward a more narrow range of possible contributing causes.
¶There were human as well as technical failings that combined on the morning of January 28, 1986, to cause the Challenger accident. Most of NASA's personnel were not involved in the Solid Rocket Motor program while there were others outside of NASA, such as the media, the Congress and the Administration, who were in- volved through their influence on the Shuttle program.
¶It should also be recognized that this report has the advantage of hindsight. Our investigation indicates that the decision to launch Challenger on January 28 suffered equally from a lack of informa- tion, misinterpretation of the information that was available, and a complex interplay of personalities among the principals involved. We are equally convinced, however, that the resulting decision to launch was arrived at as a logical conclusion of faulty premises, coupled with a failure to recognize the effect of temperature on the design.
¶We hope the lessons learned from this accident will lead to design improvements in the Shuttle Program. Just a few years ago, the collapse of the Hartford Civic Center contributed to the im- provement of engineering design techniques to accommodate the unique secondary forces inherent in long-span structures. The Gothic cathedrals of the fourteenth century were constantly im- proved after their early failures were studied.
¶We hope this section, as well as Sections VII and VIII, properly identify the mistakes that led to the Challenger accident. It is the intent of the Committee to identify these mistakes so that NASA will regain its former level of excellence. The Committee has confi- dence that the men and women of the Natiooal Aeronautics and Space Administration will meet the challenge, improve the Shuttle and their management methods, and go on to explore new frontiers in space. This assumes, however, that the agency will now receive resources adequate to support the programs it is authorized to carry out by the Congress and the President.
¶(39)
40¶For the benefit of those who may not be familiar with the Space Transportation System, the Shuttle consists of a n Orbiter (51-L's Orbiter, the Challenger, was one of a four-vehicle fleet), a n Exter- nal Tank (ET), and two Solid Rocket Boosters (SRBs). (See Figure V-1.) A brief description of the Solid Rocket Booster and the Solid Rocket Motors is included to familiarize readers with these sys- tems.
41EXTERNAL TANK
- / - t/ ..::
LEFT'SOLID ROCKET BOOSTER I
¶L
¶TER
FIGURE
¶V-1
42¶The Solid Rocket Boosters operate in parallel with the main en- gines for the first two minutes of flight to provide the additional thrust needed if the Orbiter is to escape the gravitational pull of the Earth. At an altitude of approximately 144,000 feet (24 nautical miles), the SRBs separate from the Orbiter/External Tank, descend on parachutes, and land in the Atlantic Ocean. They are recovered by ships, returned to land, and refurbished for reuse.
¶The heart of the booster is the Solid Rocket Motor (Figure V-2). It is the largest solid propellant motor ever developed for space flight and the first built to be used on a manned craft. Larger solid motors have been test-fired but have never been carried through complete development to actual use in flight. The huge Solid Rocket Motor is composed of a segmented motor case loaded with solid propellant, an ignition system, a movable nozzle, and the nec- essary instrumentation and integration hardware.
STATISTICS FOR EACH BOOSTER FRUSTRUM
¶THRUST AT LIFT-OFF (2,650,000 pounds)
I/ FORWARO SEGMENT PROPELLANT
Atomized aluminum powder ( f u e l ) ,16 After further investigation, the Commlttee has learned that some qualifying remarks are required for Dr. Feynman's characterization of the FAA engine qualification procedures to be totally accurate. The FAA does not permit cracks in what it calls 'critical" engine components. However, cracks located at, or above, the base of a turbine blade are not considered critical by the FAA because: (1) commercial jet engines possess adequate internal shielding to contain any Continued percent ,
¶'I
Ammnium p e r c h l o r a t e FORWARD CENTER ( o x i d i z e r ) , 69.83 percent
¶SREI SEGMENT I yon o x i d e powder
¶(catalyst), 0 .1 For the purpose of this report, a procedure is a formal set of instructions designed to guide and assist in the performance of a technical or management function. g8 mid., July 24, 1986, p. 11. 1 9 9 Ibid., June 25, 1986, p. 52. 7 percent ( v a r i e s )
. SRM AFT CENTER
polybutadiene a c r y l i c a c i d a c r y l o n i t r i le ( b i n d e r ) , 12 percent
WEIGHT
AFT SEGMENT ' Empty: (193.000 p o u n d s ) P r o p e I l a n t : ( 1 ,1 For the purpose of this report, a procedure is a formal set of instructions designed to guide and assist in the performance of a technical or management function. g8 mid., July 24, 1986, p. 11. 1 9 9 Ibid., June 25, 1986, p. 52. 0 7 , 0 0 0 pounds) WITH NOZZLE Gross: (1,300,000 pounds)
AFT SKIRT FIGURE
¶V-2
¶Each motor case is made of 11 individual weld-free steel seg- ments (Figure V-3). Averaging approximately 1.27 centimeters (0.5 inch) thick, the steel is a high-strength formulation. Each segment is heat-treated, hardened, and machined to the exact dimensions required. The 11 segments are held together by 177 high-strength steel pins at each case segment joint. The clevis-type joints are wrapped with reinforced fiberglass tape and sealed with a rubber seal band that is bonded to the case with adhesives.
43FORWARO SEGMENT
¶AFT
CENTER SEGMENT
¶AFT
SEGMENT FIGURE
¶V-3
¶In this report there are many references to the joint design, ero- sion and O-ring seals. There are several different joint designs used in the Solid Rocket Motor. The joint that failed on the last Chal- lenger flight, the aft field joint, was not the one that had been giving NASA the most trouble. More O-ring erosion had been expe- rienced on nozzle joints, the design of which is significantly differ- ent than the aft field joint. However, since NASA treated erosion as a problem that impacted both the nozzle and field joints, the data on erosion in this section includes that obtained from the nozzle joint.
¶Whenever a temperature is specified, it is essential that it be re- lated to a specific medium such as air (or ambient temperature), rocket propellant, or casing joints, for example. The temperature of the joints, air and propellant can all be different at the same time, just as the ocean temperature at the beach on a 90-degree day could be 75 degrees.
44¶Much of this discussion concerns heat, or the absence thereof. For example, if an O-ring had given up heat during the night, it would very likely be at a lower temperature than the temperature of the air in the morning after the sun had risen. This was the situ- ation at the time Flight 51-L was launched. The heat gained by the joint in the time after sunrise was not sufficient to raise the tem- perature of the O-ring material to a level where Thiokol engineers believed the O-ring could respond and seal the joint under ignition pressures.
¶The following chart describes the principal steps in the evolution, flight, and reconditioning of the Solid Rocket Motors (Figure V-4).
45SOLID ROCKET MOTOR PRINCIPAL STEPS I N THE EVOLUTION, FLIGHT AND RECONDITIONING OF SOLID ROCKET MOTORS
¶1 7
PROGRAH DIRECTION BY
¶..
1 DEFINE PROGRAM REQUIREMENTS AND VERIFY
¶THAT OBJECTIVES ARE CONSISTENTLY MET.
NASA CONTRACTOR DESIGN DESIGN THE MOTOR TO MEET ALL PERFORMANC REQUIREMENTS DURING ALL ANTICIPATED
¶CONDITIONS OF FLIGHT.
MORTON THIOKOL
(_' ., TESTING AND ASSURE THAT DESIGN MEETS ALL REQUlREMEh
MORTON THIOKOL NASA PROCURE MATERIALS AND COMPONENTS, PRODU AND ASSEMBLE AN OPERATIONAL MOTOR IN
¶ACCORDANCE WITH THE DESIGN.
MORTON THIOKOL ROHR INDUSTRIES PARKER SEAL COMPANY
.. LOAD, TRANSPORT, UNLOAD AND STORE MOTOR SEGMENTS.
MORTON THIOKOL
¶0 STACK I NG ASSEMBLE MOTOR SEGMENTS IN PREPARATION .
¶FOR FLIGHT.
MORTON THIOKOL
¶F ' i
REVIEW AND DECISION ON LAUNCH, IGNITE
¶MOTORS, SEPARATE AN0 RECOVER SPENT MOTOf
NASA MORTON THIOKOL REFURBISHMENT RESTORE COMPONENTS IN ACCORDANCE WITH
¶SPECIFICATIONS.
MORTON THIOKOL FIGURE
¶V-4
FIGURE
¶V-4
46¶Because of the difficulty the reader may find in understanding the NASA Flight Readiness Review for the Solid Rocket Booster for Flight 51-L and the terms used to describe the steps in the process, the following chart describes the level of review, office con- ducting the review, and the scope of the review. In addition to the following meeting chart, there were numerous other ad hoc meet- ings on the SRMs including the meeting between NASA and Thio- kol personnel during the evening before the launch of Flight 51-L.
TABLE I.-FLIGHT READINESS REVIEWS
¶[STS-5111
¶Level and date Reviewing office %ope of review
¶IV-Dee. 11, 1985 .................. Thiokol Wasatch....................... Conducted by Thiokol Solid Rocket Motor program managers in
preparation for presentations to Marshall Space Flight Center (MSFC) .
¶Ill-Dec. 17, 1985 .................. SRM Office ............................... Conducted by Larry Wear, Manager of the Solid Rocket Motor
¶Program Office, MSFC. Material presented by Thiokol personnel. Ill-Jan. 3, 1986..................... SRB Project Office .................. Conducted by Larry Mulloy, Manager of the Solid Rocket Booster
Project Office. This is a combined briefing on the SRM and the elements making up the booster assembly, which, when integrated make up the Shuttle Solid Rocket Bwsters. Shuttle Projects........................ Conducted by Stanley Reinartz, Manager, Space Shuttle Projects Office, MSFC. This review discusses all elements of the Shuttle managed by Marshall.
¶Ill-Jan. 13, 1986................... Center Board ............................ Conducted by Dr. William Lucas, MSFC Director. Final discussion
of Marshall hardware in preparation for review by the Space Transportation System Program Manager.
¶Il-Jan. 14, 1986.................... STS Program ............................ Conducted by Arnold Aldrich, Space Transportation System Pro-
gram Manager. First review dealing with the flight vehicle and associated ground support in its entirety.
¶I-Jan 15, 1986...................... Space Flight ............................. Conducted by Jesse Moore, Associated Administrator for Space
Flight. Remaining items that impact launch are discussed and assigned for disposition. Certificate of Flight Readiness is signed.
¶I-Jan. 25, 1986..................... 1-1 Review .............................. Meeting of the Mission Management Team to receive reports on
action items remaining from the Flight Readiness Review. All action items should be closed by this time.
¶Considerable reference will be made to the "joint design" throughout this section of the report. Consequently, the following description of the joint is provided. (See Figures V-5 thru V-7.)
47OPELLANT INSULAT
¶<
- TPPER STEEL ASING STEEL
¶'INS
FIGURE
¶V-5
48A, JOINT I M MORYAL ALIGNMENT (NO GAPS BETYEEN O-RINGS AND TAME) TANG P PRESSURE POINT LOCKING
¶/ PIN
¶CLEV I s
49B . JO I NT POTATED (OUT OF ALIGNFENTI
- \
7 PROPELLPNT PRESSUPE
¶l- TY
FIGURE
¶V-7
50