The Report of the Presidential Commission on the Space Shuttle Challenger Accident - The Tragedy of Mission 51-L in 1986 - Volume One of the Rogers Commission Report
National Aeronautics and Space Administration (NASA), World Spaceflight News
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Report of the Presidential Commission on the Space Shuttle Challenger Accident
June 6th, 1986
Washington, D.C.
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IN MEMORIAM
"The future is not free: the story of all human progress is one of a struggle against all odds. We learned again that this America, which Abraham Lincoln called the last, best hope of man on Earth, was built on heroism and noble sacrifice. It was built by men and women like our seven star voyagers, who answered a call beyond duty, who gave more than was expected or required and who gave it little thought of worldly reward."
President Ronald Reagan * January 31, 1986
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Francis R. (Dick) Scobee - Commander
Michael John Smith - Pilot
Ellison S. Onizuka - Mission Specialist One
Judith Arlene Resnik - Mission Specialist Two
Ronald Erwin McNair - Mission Specialist Three
S. Christa McAuliffe - Payload Specialist One
Gregory Bruce Jarvis - Payload Specialist Two
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Volume I
Chapter II * Events Leading Up to the Challenger Mission
Chapter IV * The Cause of the Accident
Chapter V * The Contributing Cause of the Accident
Chapter VI * An Accident Rooted in History
Chapter VII * The Silent Safety Program
Chapter VIII * Pressures on the System
Chapter IX * Other Safety Considerations
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Preface
The accident of Space Shuttle Challenger, mission 51-L, interrupting for a time one of the most productive engineering, scientific and exploratory programs in history, evoked a wide range of deeply felt public responses. There was grief and sadness for the loss of seven brave members of the crew; firm national resolve that those men and women be forever enshrined in the annals of American heroes, and a determination, based on that resolve and in their memory, to strengthen the Space Shuttle program so that this tragic event will become a milestone on the way to achieving the full potential that space offers to mankind.
The President, who was moved and troubled by this accident in a very personal way, appointed an independent Commission made up of persons not connected with the mission to investigate it. The mandate of the Commission was to:
1. Review the circumstances surrounding the accident to establish the probable cause or causes of the accident; and
2. Develop recommendations for corrective or other action based upon the Commission's findings and determinations.
Immediately after being appointed, the Commission moved forward with its investigation and, with the full support of the White House, held public hearings dealing with the facts leading up to the accident. In a closed society other options are available; in an open society - unless classified matters are involved - other options are not, either as matter of law or as a practical matter.
In this case a vigorous investigation and full disclosure of the facts were necessary. The way to deal with a failure of this magnitude is to disclose all the facts fully and openly; to take immediate steps to correct mistakes that led to the failure; and to continue the program with renewed confidence and determination.
The Commission construed its mandate somewhat broadly to include recommendations on safety matters not necessarily involved in this accident but which require attention to make future flights safer. Careful attention was given to concerns expressed by astronauts because the Space Shuttle program will only succeed if the highly qualified men and women who fly the Shuttle have confidence in the system.
However, the Commission did not construe its mandate to require a detailed investigation of all aspects of the Space Shuttle program; to review budgetary matters; or to interfere with or supersede Congress in any way in the performance of its duties. Rather, the Commission focused its attention on the safety aspects of future flights based on the lessons learned from the investigation with the objective being to return to safe flight.
Congress recognized the desirability, in the first instance, of having a single investigation of this national tragedy. It very responsibly agreed to await the Commission's findings before deciding what further action might be necessary to carry out its responsibilities.
For the first several days after the accident- possibly because of the trauma resulting from the accident-NASA appeared to be withholding information about the accident from the public. After the Commission began its work, and at its suggestion, NASA began releasing a great deal of information that helped to reassure the public that all aspects of the accident were being investigated and that the full story was being told in an orderly and thorough manner.
Following the suggestion of the Commission, NASA established several teams of persons not involved in the mission 51-L launch process to support the Commission and its panels. These NASA teams have cooperated with the Commission in every aspect of its work. The result has been a comprehensive and complete investigation.
The Commission believes that its investigation and report have been responsive to the request of the President and hopes that they will serve the best interests of the nation in restoring the United States space program to its preeminent position in the world.
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The Space Shuttle concept had its genesis in the 1960s, when the Apollo lunar landing spacecraft was in full development but had not yet flown. From the earliest days of the space program, it seemed logical that the goal of frequent, economical access to space might best be served by a reusable launch system. In February, 1967, the President's Science Advisory Committee lent weight to the idea of a reusable spacecraft by recommending that studies be made "of more economical ferrying systems, presumably involving partial or total recovery and use."
In September, 1969, two months after the initial lunar landing, a Space Task Group chaired by the Vice President offered a choice of three long-range plans:
A $8-$10 billion per year program involving a manned Mars expedition, a space station in lunar orbit and a 50-person Earth-orbiting station serviced by a reusable ferry, or Space Shuttle.
An intermediate program, costing less than $8 billion annually, that would include the Mars mission.
A relatively modest $4-$5.7 billion a year program that would embrace an Earth-orbiting space station and the Space Shuttle as its link to Earth. 1
In March, 1970, President Nixon made it clear that, while he favored a continuing active space program, funding on the order of Apollo was not in the cards. He opted for the shuttle-tended space base as a long-range goal but deferred going ahead with the space station pending development of the shuttle vehicle. Thus the reusable Space Shuttle, earlier considered only the transport element of a broad, multi-objective space plan, became the focus of NASA's near-term future.
The Space Shuttle Design
The embryo Shuttle program faced a number of evolutionary design changes before it would become a system in being. The first design was based on a "fly back" concept in which two stages, each manned, would fly back to a horizontal, airplane-like landing. The first stage was a huge, winged, rocket-powered vehicle that would carry the smaller second stage piggyback; the carrier would provide the thrust for liftoff and flight through the atmosphere, then release its passenger-the orbiting vehicle-and return to Earth. The Orbiter, containing the crew and payload, would continue into space under its own rocket power, complete its mission and then fly back to Earth.
The second-stage craft, conceived prior to 1970 as a space station ferry, was a vehicle considerably larger than the later Space Shuttle Orbiter. It carried its rocket propellants internally, had a flight deck sufficiently large to seat 12 space station-bound passengers and a cargo bay big enough to accommodate space station modules. The Orbiter's size put enormous weight-lifting and thrust-generating demands on the first-stage design.
This two-stage, fully reusable design represented the optimum Space Shuttle in terms of "routine, economical access to space," the catchphrase that was becoming the primary guideline for development of Earth-to-orbit systems. It was, however, less than optimum in terms of the development investment required: an estimated $10-13 billion, a figure that met with disfavor in both Congress and the Office of Management and Budget.
In 1971, NASA went back to the drawing board, aware that development cost rather than system capability would probably be the determining factor in getting a green light for Shuttle development. Government and industry studies sought developmental economies in the configuration. One proposal found acceptance: eliminate the Orbiter's internal tanks and carry the propellant in a single, disposable External Tank. It provided a smaller, cheaper Orbiter without substantial performance loss.
For the launch system, NASA examined a number of possibilities. One was a winged but unmanned recoverable liquid-fuel vehicle based on the eminently successful Saturn 5 rocket from the Apollo Program. Other plans envisioned simpler but also recoverable liquid-fuel systems, expendable solid rockets and the reusable Solid Rocket Booster. NASA had been using solid-fuel vehicles for launching some small unmanned spacecraft, but solids as boosters for manned flight was a technology new to the agency. Mercury, Gemini and Apollo astronauts had all been rocketed into space by liquid-fuel systems. Nonetheless, the recoverable Solid Rocket Booster won the nod, even though the liquid rocket offered potentially lower operating costs.
The overriding reason was that pricing estimates indicated a lower cost of development for the solid booster.
Emerging from this round of design decision making was the Space Shuttle: a three-element system composed of the Orbiter, an expendable external fuel tank carrying liquid propellants for the Orbiter's engines, and two recoverable Solid Rocket Boosters. It would cost, NASA estimated early in 1972, $6.2 billion to develop and test a five-Orbiter Space Shuttle system, about half what the two-stage "fly back" design would have cost. To achieve that reduction, NASA had to accept somewhat higher system operating costs and sacrifice full reusability. The compromise design retained recoverability and reuse of two of the three elements and still promised to trim substantially the cost of delivering payloads to orbit.
The final configuration was selected in March, 1972.
Artist's drawing depicts Space Shuttle stacked for launch in view from dorsal side of Orbiter (left) and from the left side of the stack.
The Space Shuttle Development
In August, 1972, NASA awarded a contract to Rockwell International Corporation's Space Transportation Systems Division for design and development of the Space Shuttle Orbiter. Martin Marietta Denver Aerospace was assigned development and fabrication of the External Tank, Morton Thiokol Corporation was awarded the contract for the Solid Rocket Boosters, and Rocketdyne, a division of Rockwell, was selected to develop the Orbiter main engines.
NASA divided managerial responsibility for the program among three of its field centers. Johnson Space Center, Houston, Texas, was assigned management of the Orbiter. Marshall Space Flight Center, Huntsville, Alabama, was made responsible for the Orbiter's main engines, the External Tank and the Solid Rocket Boosters. Kennedy Space Center, Merritt Island, Florida, was given the job of assembling the Space Shuttle components, checking them out and conducting launches. Because these three centers will be mentioned repeatedly in this report, they will hereafter be identified simply as Johnson, Marshall and Kennedy.
It was in an increasingly austere fiscal environment that NASA struggled through the Shuttle development years of the 1970s. The planned five-Orbiter fleet was reduced to four. Budgetary difficulties were compounded by engineering problems and, inevitably in a major new system whose development pushes the frontiers of technology, there was cost growth. This combination of factors induced schedule slippage. The initial orbital test flights were delayed by more than two years.
The first Shuttle test flights were conducted at Dryden Flight Research Facility, California, in 1977. The test craft was the Orbiter Enterprise, a full-size vehicle that lacked engines and other systems needed for orbital flight. The purpose of these tests was to check out the aerodynamic and flight control characteristics of the Orbiter in atmospheric flight. Mounted piggyback atop a modified Boeing 747, the Enterprise was carried to altitude and released for a gliding approach and landing at the Mojave Desert test center. Five such flights were made. They served to validate the Orbiter's computers and other systems. They also demonstrated the craft's subsonic handling qualities, in particular its performance in the precise unpowered landings that would be required on all Shuttle flights.
The Enterprise test flights were followed - in 1977-80 - by extensive ground tests of Shuttle systems, including vibration tests of the entire assembly-Orbiter, External Tank and Solid Rocket Boosters-at Marshall. Main engine test firings were conducted at National Space Technology Laboratories at Bay St. Louis, Mississippi, and on the launch pad at Kennedy.
By early 1981, the Space Shuttle was ready for an orbital flight test program. This was carefully crafted to include more than 1,000 tests and data collection procedures. All flights were to be launched from Kennedy and terminate at Edwards Air Force Base, where the Dryden Flight Research Facility is located (actually the third flight landed at White Sands Test Facility, New Mexico, because the normally dry lakebed at Edwards was flooded). Originally intended as a six-mission program, the orbital test series was reduced to four flights:
STS-1 (Space Transportation System-1), April 12-14, 1981, Orbiter Columbia, was a two-day demonstration of the Orbiter's ability to go into orbit and return safely. Its main payload was a flight instrumentation pallet containing equipment for recording temperatures, pressures and acceleration levels at various points around the Orbiter. In addition, there were checkouts of the cargo bay doors, attitude control system and orbital maneuvering system.
STS-2, November 12-14, 1981, Orbiter Columbia, marked the first test of the Remote Manipulator System and carried a payload of Earth survey instruments. This was the first time any spacecraft had flown twice. Failure of a fuel cell shortened the flight by about three days.
STS-3, March 22-30, 1982, Orbiter Columbia, was the longest of the initial test series, staying aloft eight days. Activities included a special test of the manipulator in which the robot arm removed a package of instruments from the payload bay but did not release it into space. The flight included experiments in materials processing.
STS-4, June 27-July 4, 1982, Orbiter Columbia, featured another test of the robot arm, which extended a scientific payload over the side of the payload bay, then reberthed it. Materials processing experiments were conducted, as were a number of scientific investigations. This flight carried the first Department of Defense payload.
With the landing of STS-4, the orbital flight test program came to an end with 95 percent of its objectives accomplished. The interval between flights had been trimmed from seven months to four, then three. NASA declared the Space Shuttle "operational," a term that has encountered some criticism because it erroneously suggests that the Shuttle had attained an airline-like degree of routine operation. In any event, NASA regarded all flights after STS-4 operational in the sense that payload requirements would take precedence over spacecraft testing, requiring larger crews.
After completing the orbital test in mid- 1982, NASA began the "operational phase" of the Space Shuttle program, beginning with STS-5. The STS -for Space Transportation System- sequential numbering was still in effect at that time; after STS-9 NASA changed the method of numbering missions. Thereafter each flight was designated by two numbers and a letter, such as 41-B. The first digit indicates the fiscal year of the scheduled launch (4 for 1984). The second digit identifies the launch site (1 is Kennedy, 2 Vandenberg Air Force Base, California). The letter corresponds to the alphabetical sequence for the fiscal year, B being the second mission scheduled. Here is a brief summary of the 21 missions launched from late 1982 to January, 1986:
STS-5, November 11-16, 1982, Orbiter Columbia, launched two communications satellites, which later were boosted to geosynchronous orbit by attached propulsion systems.
STS-6, April 4-9, 1983, Orbiter Challenger, was highlighted by the first Shuttle-based spacewalk, or extravehicular activity. The crew successfully deployed the 5,000-pound Tracking and Data Relay Satellite, first of three planned NASA communications satellites.
STS-7, June 18-24, 1983, Orbiter Challenger, delivered a second pair of commercial communications satellites. The mission also included additional payload release and recapture tests using the Remote Manipulator System. This flight marked the first retrieval of an object from orbit.
STS-8, August 30-September 6, 1983, Orbiter Challenger, included more robot arm tests plus deployment of a commercial/public service communications satellite. STS-9, November 28-December 8, 1983, Orbiter Columbia, carried the first Spacelab in the payload bay. The mission marked Columbia's return to service after a year's hiatus, during which it had been extensively modified.
Flight 10 (41-B), February 3-11, 1984, Orbiter Challenger, was highlighted by the introduction of the Manned Maneuvering Unit, a backpack propulsion unit that allows astronauts to maneuver in space independent of the Orbiter. The mission also launched two communications satellites, but their boosters failed to put them into geosynchronous orbit. For the first time, the Shuttle landed on the concrete runway at Kennedy Space Center.
Flight 11 (41-C), April 6-13, 1984, Orbiter Challenger, featured an important demonstration of Shuttle ability: the retrieval, repair and redeployment of the malfunctioning Solar Maximum Mission spacecraft with the help of a Manned Maneuvering Unit. Other activity included deployment of the Long Duration Exposure Facility, a large cylinder containing materials samples to be retrieved and examined after long exposure to the space environment.
Flight 12 (41-D), August 30-September 5, 1984, Orbiter Discovery, was devoted primarily to launch of three communications satellites. The mission demonstrated repeated deployment and retraction of a large, foldable solar array to investigate the practicability of using such solar wings as power sources for extended Shuttle missions, space platforms or the space station.
Flight 13 (41 -G), October 5- 13, 1984, Orbiter Challenger, launched the NASA Earth Radiation Budget Explorer. A cargo bay pallet carried instruments for Earth observations, including an advanced imaging radar.
Flight 14 (51-A), November 8-16, 1984, Orbiter Discovery, launched two communications satellites and retrieved two others that had been sent into unusable orbits after deployment on Flight 10.
Flight 15 (51-C), January 24-27, 1985, Orbiter Discovery, carried a Department of Defense payload.
Flight 16 (51-D), April 12-19, 1985, Orbiter Discovery, deployed two commercial satellites; one, Leasat-3, remained in low orbit when the upper stage booster failed to activate.
Flight 17 (51-B), April 29-May 6, 1985, Orbiter Challenger, carried a second Spacelab mission and materials processing experiments.
Flight 18 (51 -G), June 17 -24, 1985, Orbiter Discovery, delivered three communications satellites, deployed a low-cost Spartan scientific satellite and retrieved it after a period of free flight.
Flight 19 (51-F), July 29-August 6, 1985, Orbiter Challenger, carried the third Spacelab mission, which covered a broad range of experiments in plasma physics, astrophysics, solar astronomy and materials processing.
Flight 20 (51-I), August 27-September 3, 1985, Orbiter Discovery, deployed three communications satellites. The Leasat-3 satellite which failed to activate after deployment on Flight 16 was retrieved, repaired and successfully redeployed.
Flight 21 (51-J), October 3-1O, 1985, Orbiter Atlantis was devoted to another Department of Defense mission.
Flight 22 (61-A), October 30-November 6, 1985, Orbiter Challenger, carried the fourth Spacelab mission, devoted to materials processing experimentation.
Flight 23 (61-B), November 26-December 3, 1985, Orbiter Atlantis, was highlighted by an experiment in astronaut assembly of structures in orbit and attendant study of extravehicular dynamics and human factors. The mission also deployed three communications satellites.
Flight 24 (61-C), January 12-18, 1986, Orbiter Columbia, launched a commercial communications satellite, deployed a Hitchhiker secondary payload, conducted experiments in infrared imaging, acquired photos and spectral images of Comet Halley.
Flight 25 (51-L), January 28, 1986, Orbiter Challenger. The accident.
Including the initial orbital tests, the Space Shuttle flew 24 successful missions over a 57-month period. Columbia made seven trips into space, Discovery six and Atlantis two. Challenger flew most frequently-nine times prior to its fateful last flight.
In those 24 flights, the Shuttle demonstrated its ability to deliver a wide variety of payloads; its ability to serve as an orbital laboratory; its utility as a platform for erection of large structures; and its use for retrieval and repair of orbiting satellites.
Elements of the Space Shuttle
The Space Shuttle is the principal component of a national Space Transportation System designed to accommodate not only NASA's predictable needs but also those of the Department of Defense and commercial payload sponsors. Technically speaking, transportation system hardware embraces not only the Shuttle but its Spacelab laboratory component, the upper stage propulsion units, contemplated heavy lift vehicles and space tugs for moving payloads from one orbit to another. To provide for the broadest possible spectrum of civil/military missions, the Space Shuttle was designed to deliver 65,000 pounds of payload to an easterly low Earth orbit or 32,000 pounds to polar orbit. The following sections describe the main elements of the Shuttle system.
The Orbiter
The Orbiter is as large as a mid-size airline transport and has a structure like that of an aircraft: an aluminum alloy skin stiffened with stringers to form a shell over frames and bulkheads of aluminum or aluminum alloy. The major structural sections of the Orbiter are the forward fuselage, which encompasses the pressurized crew compartment; the mid fuselage, which contains the payload bay; the payload bay doors; the aft fuselage, from which the main engine nozzles project; and the vertical tail, which splits open along the trailing edge to provide a speed brake used during entry and landing.
The crew compartment is divided into two levels-the flight deck on top and the middeck below. Besides working space, the crew compartment contains the systems needed to provide a habitable environment (atmosphere, temperature, food, water, the crew sleep facilities and waste management). It also houses the electronic, guidance and navigation systems.
The Orbiter crew may include as many as eight people, although generally the limit is seven. The crew consists of the commander, the captain of the ship; the pilot, second in command; and two or more mission specialists. One or more payload specialists can also be accommodated. A mission specialist coordinates activities of the Orbiter and crew in support of a given payload objective. A payload specialist may manage specific experiments. The commander, pilot and mission specialists are career astronauts assigned to the mission by NASA. Payload specialists do not come from the Astronaut Office. They are assigned, by payload sponsors in coordination with NASA.
Cargoes up to 24 tons have been carried in the payload bay. Clamshell doors on the top of the Orbiter meet along the craft's spine to enclose the bay, which is 15 feet wide and 60 feet long.
The payload bay is designed to hold securely a wide range of objects. They may include one or more communications satellites to be launched from orbit, an autonomous Spacelab for experiments in space, or cargo disposed on special pallets. To handle cargo in orbital flight, the payload bay has the 50-foot mechanical arm that is controlled from within the crew compartment. A television camera and lights mounted near the end of the arm enable the operator to see what the "hand" is doing.
Just as important as delivering cargo to orbit is recovering a satellite and bringing it back to Earth-retrieving a satellite in need of refurbishment, for example. The Orbiter can carry 16 tons of cargo back from space.
The feasibility of a reusable Space Shuttle hinges on a particularly vital requirement: protecting the Orbiter from the searing heat generated by friction with the atmosphere when the craft returns to Earth. Temperatures during entry may rise as high as 2,750 degrees Fahrenheit on the leading edge of the wing and 600 degrees on the upper fuselage, the "coolest" area. The thermal protection system devised for the Orbiter must prevent the temperature of the aluminum skin from rising above 350 degrees during either ascent or entry.
The Orbiter has four kinds of external insulation that are applied to various parts of the structure according to the temperature each is likely to experience. The craft's nose cap and the leading edges of the wings are protected with an all-carbon composite consisting of layers of graphite cloth in a carbon matrix. The outer layers are converted chemically to silicon carbide, the same material that has long been used as an abrasive in grindstones. Areas subjected to the next greatest heat are shielded with high-temperature ceramic tiles about six inches square and varying in thickness from one to five inches, depending on the protection needed. So-called "low temperature" tiles are of the same material- nearly pure glass, of which 90 percent of the volume is "air"-for use on areas requiring less protection. (Low-temperature is relative; tiles so designated can withstand a temperature of 1,200 degrees Fahrenheit.) About 30,000 tiles, each different, are installed on each Orbiter.
Space Shuttle Main Engines
The three high-performance rocket engines in the aft section of the Orbiter fire for about the first 8 1/2 minutes of flight after liftoff. At sea level, each engine generates 375,000 pounds of thrust at 100 percent throttle.
The propellants for the engines are the fuel (liquid hydrogen) and the oxidizer (liquid oxygen) carried in the External Tank. Combustion takes place in two stages. First, the propellants are mixed and partly burned in pre-burners. Hot gases from the pre-burners drive the high-pressure turbopumps which deliver propellants to the main injector. Combustion, once initiated by electrical igniters, is self-sustaining. Before firing, the very cold liquid propellant is allowed to flow into the system as far as the pre-burners and combustion chamber to cool the pumps and ducts so that the hydrogen and oxygen in the system will remain liquid when the engine is started.
The main engines have been throttled over a range of 65 to 104 percent of the thrust at sea level. At liftoff, they are thrusting at 100 percent. Computers command engine thrust to 104 percent as soon as the Shuttle clears the tower. They throttle to 65 percent to reduce the maximum aerodynamic loads that occur at an altitude of about 34,000 feet. Thereafter, the thrust is again increased to provide an acceleration of three times that of gravity in the last minute or so of powered flight.
External Tank
The External Tank carries the propellants for the Orbiter's main engines-143,000 gallons of liquid oxygen and 383,000 gallons of liquid hydrogen, which is much lighter than a comparable volume of oxygen. Together, the propellants weigh a little more than 790 tons. Martin Marietta Denver Aerospace, Michoud, Louisiana, builds the tank, a welded aluminum alloy cylinder with an ogive nose and a hemispherical tail. It is 154 feet long and 27 1/2 feet in diameter.
Because the Orbiter and the two Solid Rocket Boosters are attached to it at liftoff, the External Tank absorbs the thrust of the combined propulsion system. It withstands complex load effects and pressures from the propellants.
The liquid oxygen tank forms the nose of the External Tank. It contains oxidizer kept liquid at a temperature of - 297 degrees Fahrenheit. A removable conical nose cap acts as an aerodynamic fairing. Inside the tank, baffles reduce sloshing and the associated control problems. The liquid hydrogen tank does not need baffles because the fuel is so light that sloshing does not induce significant forces. The liquid hydrogen tank accounts for the greater part of the External Tank. Its contents are even colder than the LOX: - 423 degrees Fahrenheit.