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Rogers, William P., et al
Report of the Presidential Commission on the Space Shuttle Challenger Accident
United States Government Printing Office
June 6, 1986
The Presidential Commission on the Space Shuttle Challenger Accident, chaired by former Secretary of State William P. Rogers, investigated the circumstances surrounding the explosion of the Space Shuttle Challenger shortly after liftoff on January 28, 1986. The Commission was established in February, 1986, pursuant to Executive Order 12546, and it issued its final report in June, 1986. William Rogers was at the time a practicing attorney and senior partner in the law firm Rogers & Wells. In 1973, Rogers was awarded the Medal of Freedom. All other members of the Commission have excellent qualifications such as previous spacecraft commander, engineers, director of Space Systems and Command, Control, Communication, astronauts, and physicists.
January 28th, 1986, was the coldest day that NASA had ever attempted to launch a manned spacecraft; at 36 degrees Fahrenheit, it was 15 degrees colder than any previous launch temperature. Although lift-off time for the Challenger flight 51-L had been delayed twice that morning, all operations and systems seemed to be under control. An ice team had been sent to the launch pad at 1:30 a.m. and again at 8:45 a.m., and although there was some build-up, ice was cleared as a concern. Other weather conditions were cleared by NASA staff at Cape Canaveral through the use of weather balloons and also at the emergency landing site in Dakar, Senegal, Africa. The seven member crew arrived at the launch pad in the astronauts van shortly after 8:00 and were all strapped into their seats by 8:36 a.m. Three, two, one [stated mission control]. Roger. Go with the throttle up, shuttle commander Dick Scobee radioed. 73 seconds later, millions of people across the nation watched the awful explosion spread across their television screens and realized that something had gone wrong before they heard the voice of mission control: Obviously a major malfunction. Rather than delivering the State of the Union address that evening as scheduled, President Ronald Reagan made a brief speech. We ll continue our quest in space, he promised traumatized Americans. There will be more shuttle flights and more shuttle crews and, yes, more volunteers, more civilians, more teachers in space. There would be no shuttle flights for nearly three years. There would be no teacher in space, and for those left on the ground, for the families of seven deceased astronauts, there would be years of bitterness, grief and anger, and pain before their lives could finally heal. What went wrong? What actually happened to cause a veteran space shuttle such as Challenger to malfunction on its tenth run?
At 0.68 seconds after ignition, videotape showed black smoke coming from the bottom field joint of the right solid rocket booster (SRB). The SRB comes in four segments that are assembled. The bottom field joint is the lowest joint on the SRB. The black smoke suggested that grease, joint insulation, and rubber O-rings were being burned. The smoke continued to come from the bottom field joint facing the exterior tank in cycles of three puffs of smoke per second. The last puff of smoke was seen at 2.7 seconds. The black smoke was an indication that the bottom field joint was not sealing correctly. At 58.8 seconds into flight, on enhanced film, a flame was seen coming from the right SRB. The flame was coming from the underside of the bottom joint. It was burning gas that was escaping from the SRB. A fraction of a second later, at 59.3 seconds, the flame was well defined and could be seen without enhanced film.
As the flame increased in size, it had begun to push against the external tank due to the rushing air around the orbiter. The SRB is attached to the external tank by a series of struts that run alongside the external tank. One of these struts is located at 310 degrees of the circumference of the SRB. As the flame grew, it pushed against this strut with an intense heat of approximately 5,600 degrees Fahrenheit, making it hot and weak. The first sighting of the flame hitting the external tank was at 64.7 seconds, when the color of the flame changed. The color change indicated that the fire was being produced through mixing with another substance. This other substance was liquid hydrogen, which is stored in the bottom external tank. Pressure changes from the hydrogen tank confirmed that there was a leak.
At 72 seconds, there was a sudden chain of events that destroyed Challenger and the seven crew members on board. By now, the lower strut connecting the right SRB to the external tank was extremely hot and very weak. With the amount of force given by the SRB, the lower strut broke away from both the right SRB and the external tank, allowing the right SRB to rotate freely around the top struts. The bottom of the SRB swung around hitting, denting, and burning Challenger’s wing. There was an extreme force that shot the hydrogen tank forward into the oxygen tank causing them to burst. At 73.12 seconds into flight, a white vapor was seen from the bottom corner of the right SRB. The white vapor was the mixture of hydrogen and oxygen. Only milliseconds after the white vapor was seen, at 73.14 seconds, the glow turned into a fireball in a huge explosion. The main explosion was the hydrogen and oxygen that came from the external tank. Challenger was traveling at a speed of mach 1.92 at a height of 46,000 feet when it blew up. The last recorded transmission from Challenger was at 73.62 seconds after launch. Michael Smith was recorded as saying, Uhh oh !
Six days later, President Reagan, who was moved and troubled by the horrible accident of mission 51-L, appointed an independent commission made up of persons not connected with the mission to investigate it. The purpose 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. Other selected persons in addition to Chairman Rogers were Vice-Chairman, Neil Armstrong, a previous NASA astronaut and federal employee, and astronaut Sally Ride. The remainder of the commission were David Acheson, Eugene Covert, Richard Feyman (Nobel Prize physicist whose contributions would be critical), Robert Hotz, Donald Kutyna, Robert Rummel, Joseph Sutter, Arthur Walker Jr., Albert Wheelon, Charles Yeager, and Alton Keel Jr. Immediately after being appointed, the Rogers Commission moved forward in its investigation with the full support of the White House. It held public hearings dealing with the facts leading up to the accident, and felt that the way to deal with a failure of this magnitude was to disclose all the facts fully and openly. The commission took immediate steps to correct mistakes that led to the failure and helped to renew confidence and determination within NASA and in the eyes of the public. The investigation s main objective was not necessarily to point fingers but to insure confidence in NASA s system by the public and for the men and women who fly the shuttles. It focused its attention on the safety aspects of future flights based on lessons learned from the assessment, with the aim being to return to safe space flight.
At first, NASA seemed to be withholding information about the accident from the public, press, and Rogers Commission. The press was declaring it a news blackout by NASA. Approximately two weeks following the tragedy, the Rogers Commission was able to reassure the public that the full story was being told in an orderly and thorough manner. The consensus of the Rogers Commission and other participating investigative agencies was that the loss of the space shuttle Challenger was caused by a failure in a joint between the two lower segments of the right solid rocket booster.
The solid rocket booster’s segments are joined together by a tang and clevis joint. Each segment has a tang on the bottom and a clevis on top. The clevis is the female connector, while the tang is the male linking component. The bottom-mid segment connects to the bottom segment with a nozzle. Where this occurs is called the bottom field joint. There are two washers called O-rings that wrap around the clevis and seal the joint, as well as a zinc chromate putty that is stuck in the joint. The bottom field joint is the joint that failed on the right solid rocket booster. There were a few causes that could have led to the joint seal failure: 1) Damage or contamination could have occurred during the assembly. 2) The gap between the joints had grown as a result of prior use of the solid rocket motors. 3) The temperature on the day of the launch was 36 degrees; the temperature of the bottom right field joint was 28 degrees at launch time. 4) The performance of the putty that was applied to the joint. 5) Overall construction of field joints made by Morton Thiokol (the company that produced the SRBs for NASA).
The results included a combination of these possible causes. Although a serious concern, damage and/or contamination of the field joints at the time of assembly was ruled out as a contributing element of flight 51-L s malfunction by the Rogers Commission. Records showed that the segments were assembled using approved procedures. Significant out-of-round conditions existed between the two segments joined at the bottom right field joint. This caused a gap concern during assembly, but test records show that the gap was in the acceptable range of error. Temperature was a key factor involved in failure of the field joint seal.
On the morning of the launch, the coldest joints were the bottom field joints of the right SRB. The temperature of that field joint was 28 degrees F. The temperature of the opposite side was approximately 50 degrees F. When the O-rings are cold, they are very stiff and do not move as quickly as they should. Out of twenty-one launches with temperatures of 61 degrees F or greater, only four showed signs of O-ring thermal distress. Each of the launches below 61 degrees resulted in one or more O-rings showing signs of erosion of blow-by and soot. Tests were done to see how fast O-rings seal at different temperatures. At 75 degrees F the O-rings seal within 530 milliseconds. On the opposite side of the scale an O-ring at 20 degrees F takes 1.9 seconds to seal. It is this difference in time that most likely caused the explosion of the Challenger. It was Feyman s questions and analysis of data that brought this out.
The performance of the putty was another probable cause of the joint seal failure. The zinc chromate putty is placed on the inside of the joints and also forced between the gap of the tang and clevis during assembly. It is there to stop hot gas from reaching the O-rings. The hot gases can make holes in the putty, thus letting gas go through to the O-rings which could cause damage. Prior to the tenth launch of the Challenger, the company that had been producing the putty for the SRB joints went out of business. Putty had to be obtained from a new source, and post-testing showed that it was more susceptible to environmental effects; moisture made it tackier. Due to the launch temperature being very significant, the Rogers Commission took this finding into account as a contributing factor.
The Rogers Commission found that the failure was due to a faulty design unacceptably sensitive to a number of factors (reusability, putty and O-ring performance in adverse temperatures). It concluded that the company producing the O-rings, Morton Thiokol, and NASA were guilty of allowing an avoidable accident to occur. This accident was deemed avoidable through research done by both companies engineers, prior memoranda sent between the companies and department heads, and events that took place on the eve of flight 51-L.
On July 31st, 1985, Roger Boisjoly, Staff Engineer in applied mechanics at Morton Thiokol, sent a memo to Robert Lund, Thiokol s Vice President of Engineering, urging that Thiokol s unofficial task force originally said to be assigned to the field joint problem officially be pulled from its regular duties and actually assigned to the problem. Prior to this request, NASA and Morton Thiokol both knew that the solid rocket boosters were poorly designed. In that period of time, nearly every launch had been recorded as having some type of erosion with the infamous O-rings. When Roger Boisjoly voiced his concern, nearly a year and a half before the launch of the Challenger, the department heads nonchalantly assured him that it was being worked on. A message sent in August, 1985, from the project engineer recognized the problem, stated that long term solutions looked good, and simple short term measures should be taken to reduce flight risks . The long term solutions were projected to require several years. Shuttles had already been at risk, and for the time being would remain at risk. The night before the fatal launch, a number of engineers voiced their concerns. Roger Boisjoly and others advised that a launch temperature of 53 degrees Fahrenheit was crucial for proper functioning of the field joints O-rings.
The Rogers Commission later found that executives of Morton Thiokol were in agreement with the lower level research engineers until they found out that NASA was considering other companies to build the rocket boosters. Not wanting to lose their biggest client, Thiokol heads changed their minds a few days before the 28th to act in the best interests of the firm–to go a head with the launch. This provided an even tougher challenge for Boisjoly and company to change anyone s mind on the launch eve. He later stated, This was a meeting where the determination was to launch, and it was up to us to prove beyond a shadow of a doubt that it was not safe to do so. This is in total reverse to what the position usually is in a preflight conversation or a flight readiness review. The engineers were ignored. No one went to the press or a member of Congress. No one tried to reach the astronauts and inform them of the risks they were taking if they launched the following morning. High-level engineers told NASA what it wanted to hear, and low-level engineers held their breath and went back to work.
These were the reasons the Rogers Commission found NASA and Thiokol guilty of an avoidable accident. NASA s rush to launch despite engineering objections is typical of American corporate behavior. Although NASA is a government agency, not a business, by trying to make the shuttle commercially practical, NASA subjected its operations to business considerations almost from the beginning. Furthermore, the agency is essentially a coordinator of the work of a large number of private corporations, where most of the engineers and technicians that were at question were employed. The profit motive for the companies seemed to be overriding engineering concerns at exactly the time when the engineer s views were crucially important. What happened at NASA and Morton Thiokol is a useful lesson for corporations: not only were the engineers overruled by the management, they were so afraid of retaliation that they did not go outside the chain of command. Other than honest ethical practices, they had a reason to be. Thiokol s first reaction to the disaster was to punish Roger Boisjoly and Allan McDonald, Director of Solid Rocket Motors. These two were the main culprits of presenting the contradicting launch evidence on the night before the launch and also the engineers who testified exclusively before the Presidential Commission.
The Report of the Presidential Commission on the Space Shuttle Challenger Accident was a thorough and complete investigation into the space shuttle accident. The members of the commission did a excellent job of methodically going through each possible scenario and showing how it could or could not have affect the final result of the space shuttle accident. Upon finding the root of the problem, they were able to present a history of prior problems with the O-rings, and show a lack of steps in assuring the complete solution to this problem. The commission completed its assigned task of finding the problem and proposing a solution to assure that a national tragedy of this magnitude would not occur in the future and did an excellent job of presenting it in the Report of the Presidential Commission on the Space Shuttle Challenger Accident.
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