Editor’s Note: Today is the 30 th anniversary of the loss of the space shuttle Challenger, which was destroyed 73 seconds in its flight, killing all onboard. To mark the anniversary, IEEE Spectrum is republishing this seminal article which first appeared in June 1989 as part of a special report on risk. The article has been widely cited in both histories of the space program and in analyses of engineering risk management. Items that did not meet certain design, reliability and safety requirements specified by NASA’s top management and whose failure could threaten the toss of crew, vehicle, or mis­sion, made up a critical i tems list (CIL). Grey estimated that spares of the crucial modules might add another 10 percent to the space station’s cost. “But NASA is not willing to go to bat for that extra because they ’re unwilling to take the political risk,” he said— a replay, he fears, of NASA’s response to the political negativism over the shuttle in the 1970s. I added the wheels for a purely demonstrational purpose, not intending for them to be able to support the weight of the model. Two designs emerged as front-runners. One was designed by engineers at the Manned Spaceflight Center, and championed especially by George Mueller. This was a two-stage system with delta-winged spacecraft, and generally complex. An attempt to re-simplify was made in the form of the DC-3, designed by Maxime Faget, who had designed the Mercury capsule among other vehicles. Numerous offerings from a variety of commercial companies were also offered but generally fell by the wayside as each NASA lab pushed for its own version.

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During the early shuttle studies, there was a debate over the optimal shuttle design that best-balanced capability, development cost, and operational cost. Initially, a fully reusable design was preferred. This involved a very large winged crewed booster which would carry a smaller winged crewed orbiter. The booster vehicle would lift the orbiter to a certain altitude and speed, then separate. The booster would return and land horizontally, while the orbiter continued into low Earth orbit. After completing its mission, the winged orbiter would re-enter and land horizontally on a runway. The idea was that full reusability would promote lower operating costs. Before the Apollo 11 Moon landing in 1969, NASA began studies of Space Shuttle designs as early as October 1968. The early studies were denoted "Phase A", and in June 1970, "Phase B", which were more detailed and specific. The primary intended use of the Space Shuttle was supporting the future space station, ferrying a minimum crew of four and about 20,000 pounds (9,100kg) of cargo, and being able to be rapidly turned around for future flights.One reason NASA has so strongly resisted probabilistic risk analysis may be the fact that “PRA runs against all traditions of engineering, where you handle reliability by safety factors,” said Elisabeth Paté-Cornell, associate professor in the department of industrial engineering and engineering management at Stanford University in California, who is now studying organizational factors and risk assessment in NASA. In addition, with NASA’s strong pride in design, PRA may be “perceived as an insult to their capabilities, that the system they ’ve designed is not 100 percent perfect and absolutely safe,” she added. Thus, the character of an organization influences the reliability and failure of the systems it builds because its structure, policy, and culture determine the priorities, incentives, and communication paths for the engineers and managers doing the work, she said. a b "Columbia Accident Investigation Board Public Hearing". Columbia Accident Investigaion Board Report (PDF) (Technical report). Vol.VI. Houston, Texas (published October 2003). April 23, 2003. pp.219–245. Archived (PDF) from the original on May 11, 2023.

Shuttle (High Res) | 3D Resources - NASA Shuttle (High Res) | 3D Resources - NASA

All of this was taking place in the midst of other NASA teams proposing a wide variety of post-Apollo missions, a number of which would cost as much as Apollo or more [ citation needed]. As each of these projects fought for funding, the NASA budget was at the same time being severely constrained. Three were eventually presented to Vice President Agnew in 1969. The shuttle project rose to the top, largely due to tireless campaigning by its supporters [ citation needed]. By 1970 the shuttle had been selected as the one major project for the short-term post-Apollo time frame. Making the wheels can be quite hard. Although it may be hard, the rewards of someone telling you how cool they are when you have them retract are worth more than the work it takes to make it. I started off watching a few videos of the space shuttle landing to get and idea of how the landing gears work. Although my design is inaccurate (the sheer resistance on the flaps at high speed would rip them off their hinges), I chose to do it that way since it was easier to have the wheels perpendicular to the part that holds up the wheels (suspension?) vs it being parallel. The real value of probabilistic risk analysis is in understanding the system and its vulnerabilities,” said Benjamin Buchbinder, manager of NASA’s two-year-old risk management program. He maintains that probabilistic risk analysis can go beyond design-oriented qualitative techniques in looking at the interactions of subsystems, ascertaining the effects of human activity and environmental conditions, and detecting common-cause failures.

As for actually making the wheels, I cut out a template of a diameter of 2cm and using that drew around 36 of them (9 for each wheel). Causes: inadequate original design (booster joint rotated farther open than intended); faulty judgment (managers decided to launch despite record low temperatures and ice on launch pad); possible unanticipated external events (severe wind shear may have been a contributing factor).

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NASA’s “management methodology” for collection of data and determination of risk was laid out in NASA’s 1985 safety analysis for Galileo. The Johnson space center authors explained: “Early in the program it was decided not to use reliability (or probability) numbers in the design of the Shuttle” because the magnitude of testing required to statistically verify the numerical predictions “is not considered practical.” Furthermore, they noted, “experience has shown that with the safety, reliability, and quality assurance requirements imposed on manned space­flight contractors, standard failure rate data are pessimistic.” Statistics don’t count for anything,” declared Will Willoughby, the National Aeronautics and Space Administration’s former head of reliability and safety during the Apollo moon landing program. “They have no place in engineering anywhere.” Now director of reliability management and quality assurance for the U.S. Navy, Washington, D.C., he still holds that risk is minimized not by statistical test programs, but by “attention taken in design, where it belongs.” His design-­oriented view prevailed in NASA in the 1970s, when the space shuttle was designed and built by many of the engineers who had worked on the Apollo program. Statistically an airliner is the least risky form of transportation, which implies high reliability. And in the early 1970s, when President Richard M. Nixon, Congress, and the Office of Management and Budget (OMB) were all skeptical of the shuttle, proving high reliability was crucial to the program’s continued funding. As an example of how the “mindset” in the agency is now changing in favor of “a willingness to explore other things,” Buchbinder cited the new risk management program, the workshops it has been holding to train engineers and others in quantitative risk assessment techniques, and a new management instruction policy that requires NASA to “provide disciplined and documented management of risks throughout program life cycles.”The probabilities originated in a series of quantitative risk assessments NASA was required to conduct by the Interagency Nuclear Safety Review Panel (INSRP), in anticipation of the launch of the Galileo spacecraft on its voyage to Jupiter, originally scheduled for the early 1980s. Galileo was powered by a plutonium-­fueled radioisotope thermoelectric generator, and Presidential Directive/NSC-25 ruled that either the U.S. President or the director of the office of science and technology policy must examine the safety of any launch of nuclear material before approving it. The INSRP (which consisted of representatives of NASA as the launching agency, the Department of Energy, which manages nuclear devices, and the Department of Defense, whose Air Force manages range safety at launch) was charged with ascertaining the quantitative risks of a catastrophic launch dispersing the radioactive poison into the atmosphere. There were a number of studies because the upper stage for boosting Galileo into interplanetary space was reconfigured several times.

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Initially, the orbiter was to carry its own liquid propellant. However, studies showed carrying the propellant in an external tank allowed a larger payload bay in an otherwise much smaller craft. It also meant throwing away the tank after each launch, but this was a relatively small portion of operating costs. It’s not that simple,” Buchbinder said. “A probabilistic way of thinking is not something that most people are attuned to. We don’t know what will happen precisely each time. We can only say what is likely to happen a certain percentage of the time.” Unless engineers and managers become familiar with probability theory, they don ’t know what to make of “large uncertainties that represent the state of current knowledge,” he said. “And that is no comfort to the poor decision-maker who wants a simple answer to the question, ‘Is this system safe enough? ’”The NRC space station committee warned: “It is dangerous and misleading to assume there will be no losses and thus fail to plan for such events.” Aldridge, Edward. C. "Pete" Jr. (c. 1989). Assured Access: 'The Bureaucratic Space War' (PDF) (Technical report). Archived (PDF) from the original on October 28, 2022 . Retrieved September 17, 2012.