Spacecraft Design Archive










Talia Jurgens




General Archive

The University of Texas at Austin
Studies in Ethics, Safety, and Liability for Engineers
Kurt Hoover and Wallace T. Fowler

Doomed from the Beginning:The Solid Rocket Boosters for the Space Shuttle

When the Space Shuttle Challenger blew up on January 28, 1986, the nation was stunned. However, the accident did not come as a major surprise to many people associated with the Shuttle program, because these people were aware of the program's history of grandiose promises, funding shortfalls, political handicaps, and technical compromises. Many of the components on the Shuttle were not as good as they could have been because of choices made during the design process. Choices of second-best technologies and components, driven by lack of timely funding, were made at many points in the design and development process. The history of the Solid Rocket Boosters (SRBs), the component that failed catastrophically, destroying the Space Shuttle Challenger, provides an excellent illustration of many of the problems and difficulties encountered in bringing the Space Shuttle from idea to operational reality.


A Reusable Spacecraft:
The original purpose of the Space Shuttle was to provide the United States with cheaper access to space than was possible using expendable rockets. By reusing most of the vehicle, hardware costs would be greatly decreased. Theoretically, if the entire Shuttle could be made reusable , costs for each flight could be reduced to no more than fuel, launching, and routine maintenance costs. It was an attractive idea. Unfortunately, no one had ever reused a piece of hardware which had been subjected to the rigors of space travel. Technically, sending a manned spacecraft to the moon was far simpler than developing a truly reusable space vehicle.

The early 1970s were very difficult for NASA. Following the successes of the early Apollo flights, the agency¹s budget was drastically reduced. Funds for research, development, and operations were cut, just as planning for the Space Shuttle got underway. Several times it appeared that the Shuttle program might be cancelled entirely. Money was in short supply, not just for the space program, but for all federally funded activities. Many Senators and Representatives saw cutting the budget for space programs as a politically harmless activity, and a method of saving money for their politically "more necessary" programs.

As design decisions on various components were made, the interfaces between components had to be developed. Often, a "cheaper" system in one area wouldn't perform well (or at all) with a "cheaper" system in another area, and considerable costly rework was necessary. The Space Shuttle provides an example of how trying to cut corners in design and development can lead to much higher overall systems costs. It has been estimated that a Space Shuttle system could have been built which was much more reliable, much safer, and much cheaper to operate with no extra design and development costs if the funding had been provided on an orderly schedule which matched the needs of the design and development process. The way that the Space Shuttle design and development program was funded is clearly an example of the Fram oil filter TV commercial "You can pay me now or you can pay me (a LOT more) later".

Compromises in the Design:
In this atmosphere, many NASA administrators felt as though they were fighting for their agency¹s life. As the largest and most visible program, the Space Shuttle, was extremely important to NASA. In the early days of development, there were many different designs competing to be the final Space Shuttle design. There were numerous and conflicting design objectives. The Space Shuttle was supposed to be extremely versatile, yet had to do everything well. It was supposed to provide easy access to space, but do it economically. A low technology Shuttle would be cheaper to develop and build, but would be more costly to operate. It was impossible to satisfy all the objectives. Each Shuttle design satisfied some of objectives at the price of others. For a long time, many different designs were considered simultaneously. The fortunes of the various designs rose and fell with such speed that a standing joke around NASA referred to the "Shuttle of the Day".

To ensure Congressional and Presidential support, NASA began making concessions. To ensure a steady supply of DOD (Department of Defense) payloads, NASA made several concessions to the USAF (United States Air Force). On-board air breathing engines were sacrificed to increase the payload mass capabilities. The required cross range capabilities with no air breathing engines further compromised the design.

The various shuttle designs options ranged from completely reusable to almost completely single-use spacecraft. Since no one had ever attempted to reuse components subjected to the rigors of spaceflight, a large amount of research and development was necessary to produce truly reusable Shuttle components. As a way of limiting the amount of research and development money needed, the decision was taken to make the external tank expendable while making the other portions of the Shuttle system reusable. In the long run this would cost more money, but it made the politically sensitive up-front development costs more palatable to Congress. Not only was Congress reluctant to fund the Shuttle, but the Nixon administration had taken the original NASA Space Shuttle budget and reduced it by twenty percent. This forced NASA to make many decisions purely on the basis of immediate costs.

Most of the original designs for the Shuttle called for liquid fueled strap-on booster rockets. Liquids are preferable to solids because they can be restarted and are easier to control. Once ignited, a solid rocket burns to completion, and cannot be shut down in case of a problem. In the history of the United States manned space program before the Shuttle, solid rockets were used only for escape systems and retro-rocket systems. Many engineers considered solids too dangerous to use in any other capacity on manned spacecraft. Statistics on solid rockets indicated that about one solid rocket in fifty fails.

Engineers at NASA Marshall were particularly against the idea of using solid rocket boosters (SRBs) on the Space Shuttle. They proposed using high pressure fed liquid rocket boosters. High pressure fed liquids would not only be safer, but would provide the Shuttle with greater payload capacity. This was important because one of the primary selling points for the Shuttle was its large payload capability.

The development of large reusable liquid rocket boosters for Space Shuttle would have required a significant research and development effort. After much internal debate within NASA, a cost and politics driven decision was made to made to use solid rockets despite their inherent dangers. It is interesting to note that the Soviet Shuttle, Buran, while very similar to the American model, has air breathing engines on the orbiter and used only liquid propellant systems. In effect, the Russians built the Buran the way that NASA wanted to build the Space Shuttle.

The Contract

Competition for the SRB Contract:
Four companies bid for the contract to design and manufacture the solid rocket boosters (SRBs). Aerojet Solid bid the program at $655 million, United Technologies at $710 million, Morton Thiokol at $710 million, and Lockheed at $714 million. All the bids were relatively similar in both price and technology. Based on cost, the NASA advisory panel recommended that the contract be awarded to Aerojet; they believed that money could be saved without sacrificing technical quality by choosing the lowest bid. NASA administrator Dr. James Fletcher overruled this recommendation and awarded the contract to Morton Thiokol in Brigham City, Utah. Aerojet appealed the decision and after many allegations and counter-allegations, the GAO (General Accounting Office) was instructed by Congress to investigate the matter. The GAO found that the contract award procedure was not improper. NASA regulations clearly stated that the decision was to be made by the chief administrator, not the advisory panel. However, the GAO could find no reason for selecting Morton Thiokol over Aerojet and recommended that NASA reconsider the decision.1

Political Compromises in the Contract:
The nature of the political connections between the Space Program and prominent figures of the state of Utah has long been debated. Utah Senators Jake Garn and Frank Moss have been active supporters of the Space Program, particularly when it benefits Utah- based industries. There is nothing wrong with this; Representatives of Congress are expected to be interested in furthering the activities of their constituents. The real cloud of suspicion hung over former Morton Thiokol employees who worked for NASA at the time of the contract award, and the head of NASA itself, Dr. James Fletcher.4

Dr. Fletcher served as the President of the University of Utah from 1964 through 1971. His connections with the state and its industries were numerous and far reaching, but he denied that these connections had any influence on his decision to award the SRB contract to Morton Thiokol. However, many people who observed the contract award process remained unconvinced. Fletcher's inability to provide solid reasons for the selection of Morton Thiokol over Aerojet did nothing to ease the controversy surrounding the decision; his reasons were vague and referred to minor points in the advisory committee's study. NASA's refusal to discuss whether former Morton Thiokol employees had been part of the advisory committee simply fueled speculation of wrong-doing. Whether Morton Thiokol used political influence to secure the SRB contract has never been determined, but lack of clear answers caused many to conclude that the contract may have been awarded improperly.1

Problems with the Design and the Oversight System

Difficulties in the Design of the SRBs:
In many respects, the SRBs are the simplest part of the shuttle design, but this is only in a relative sense. In the world of solid rockets, the SRBs are quite complex. The rocket shell must contain the propellant and rocket apparatus, house guidance, control, and recovery equipment, and most importantly, the two SRBs must support the entire Space Shuttle assembly, both during transit to the launch pad and while fully fueled on the launch pad. The fully fueled Space Shuttle system weight about 4.4 million pounds. Thus, the SRBs much be able to withstand severe mechanical stresses.

The SRBs are constructed in sections, which stacked on top of each other to form the completed booster rocket. The Morton Thiokol design consists of four fuel sections stacked on top of the nozzle and topped by the nose cap. In the pre-Challenger design, each intersection was connected by a field joint held with 77 steel pins. The field joint was sealed by a simple synthetic rubber O-ring protected from the internal combustion products and high temperatures of the booster's interior by a layer of putty. Supposedly, the simplicity of the design made it less likely to experience problems than alternative, more complicated designs.

No one had ever tried to design or build a solid rocket like the SRB. Part of the rationale for choosing solids over liquids was that more was known about how to build the required solids. The large solid rocket boosters on the Titan III were touted as evidence that the SRBs could be built cheaply and effectively, but there were major differences between the solid boosters of the Titan and the Space Shuttle SRBs. The Shuttle SRBs were much bigger and were to be reusable. It was true that the Titan boosters did drop off into the ocean after use, but no one had ever tried to recover the boosters. In addition, little of the applicable experience that was gained on the Titans could applied to the SRBs, because different companies developed the two rockets. United Technologies had the most experience in the area of large solid rockets, but they had not won the contract.

In addition to the problems of inexperience and lack of experience transfer, there was an early indicator of problems to come. As early as 1972, problems began to develop in solid rocket field joints on other boosters similar to those proposed for the SRBs. Under some circumstances, the putty and O-rings did not function properly and the O-rings were subjected to hot combustion products which rapidly eroded the O-rings. In defense of the design, Morton Thiokol pointed to the successful use of similar field joints on the Titan booster as proof that the concept was sound. The putty on the Titan joints, however, was hand packed and the O-rings secured by technicians.1

The design proposed by Aerojet had included a capture field joint which would prevent burn-through of the O-rings. It was burn-through that ultimately caused the Challenger's external tank to explode. Morton Thiokol had conducted tests which it claimed verified that the field joints were sound, but these tests were always done with the SRB in a horizontal position and with the ambient temperature always 53o F or above. Morton Thiokol had no data on how the field joint functioned in cold conditions.5

A Lack of Oversight:
NASA Marshall had always been very strongly against the idea of using solids on manned spacecraft. Despite this, the responsibility for developing the SRBs was given to the Marshall center. Marshall had little or no experience in the area of solid rockets and, in the opinion of many, never acquired sufficient experience in the area to competently oversee the development of the SRBs. On top of this Marshall¹s management style did not encourage free discussion of problems. When problems did develop with the SRBs, they were hushed up.1

Despite Marshall's apparent attempts to hide any signs of difficulties with the SRBs on early Shuttle launches, some information did leak out. Top NASA officials became aware that some of the field joints on early Space Shuttle flights had shown considerable erosion. Why this occurred only on some flights was not known. However, some engineers at both NASA and Morton Thiokol suspected that the ambient temperature at launch was a factor. Months prior to the fatal Challenger flight, NASA Deputy Director Hans Mark issued a memo strongly suggesting that the Space Shuttle not be allowed to fly again until the SRB field joint problem had been adequately addressed. Unfortunately, Mark resigned from NASA soon after writing the memo, and the memo itself simply fell through the cracks.4

The Inevitable Happens: The Challenger Accident

The weather at KSC on Tuesday morning, January 28, 1986, was clear and cold. Because the overnight low was forecast at 23o F, there was doubt that Challenger would be much above freezing at launch time. The Launch Commit Criteria included very specific temperature limits for most systems on the shuttle. Morton Thiokol engineers were sure that Challenger should not be launched in such conditions as those expected for Tuesday morning. O-rings from Flight 51-C which had been launched under cold conditions the previous year showed very significant erosion. This was the only data available on the effects of cold, but all the Thiokol engineers agreed that the cold weather would decrease the elasticity of the synthetic rubber O-rings, which in turn might cause them to seal slowly and allow hot combustion gas to surge through the joint. Based on the these results, the engineers at Morton Thiokol recommend to NASA Marshall that Challenger not be launched until the O-rings reached a temperature of 53o F. The management of Marshall was flabbergasted, and demanded that Thiokol prove that launching was unsafe. This was a complete reversal of normal procedure. Normally, NASA required its subcontractors to prove that something was safe. Now they were requiring their subcontractors to prove that something was unsafe. Faced with this extreme pressure, Morton Thiokol management asked its engineers to reconsider their position. When the engineers stuck to their original recommendations not to fly, Morton Thiokol management overruled them and gave NASA its approval to launch.

As the SRBs ignited, the cold conditions did not allow the O-rings to properly seat. Within the first 300 milliseconds of ignition, both the primary and secondary O-rings on the lowest section of the right SRB were vaporized across 70o of arc by the hot combustion gases. Puffs of smoke with the same frequency as the vibrating booster are clearly present in pictures of the launch. However, soon after clearing the tower, a temporary seal of glassy aluminum-oxides from the propellent formed in place of the burned O-rings and Challenger continued skyward. Unfortunately, at the time of greatest dynamic pressure, the shuttle encountered wind shear. As the Challenger's guidance control lurched the Shuttle to compensate for the wind shear, the fragile aluminum-oxide seal shattered. Flame arched out of the joint, struck the external tank and quickly burned through the insulation and the the aluminum structure. Liquid Hydrogen fuel streamed out and was ignited. The Challenger exploded.

Safety and Ethics Issues

There are many questions involving safety and/or ethics which are raised when we examine the history of the development of the Solid Rocket Boosters. The ethics questions are complex. If high standards of ethical conduct are to be maintained, then each person must differentiate between right and wrong, and must follow the course which is determined to be the right or ethical course. Frequently, the determination of right or wrong is not simple, and good arguments can be made on both sides of the question. Some of the issues raised by examining the history of the SRBs are listed below.

  1. Are solid rocket boosters inherently too dangerous to use on manned spacecraft? If so, why are they a part of the design of the Space Shuttle System?

  2. Was safety traded for political acceptability in the design of the Space Shuttle?

  3. Did the pressure to succeed cause too many things to be promised to too many people during the design of the Space Shuttle?

  4. Did the need to maintain the keep costs low force decision makers to compromise safety in the decision to use SRBs with manned vehicles?

  5. In awarding the SRB contract to Morton Thiokol, NASA did not violate any laws, but did it violate ethical standards?


  1. Challenger: A Major Malfunction. Malcolm McConnell. Doubleday & Company, Inc. Garden City, NY. 1987

  2. ³Mixed Mode Propulsion for the Space Shuttle.² Robert Salkeld. Aerospace America. American Institute of Aeronautics and Astronautics, New York, NY. August 1971, Vol. 9, No. 8. pp 52-61.

  3. "Our Next Steps in Space.² J. Preston Layton. Aerospace America. American Institute of Aeronautics and Astronautics, New York, NY. May 1972, Vol. 10, No. 5. pp 56-65.

  4. Prescription for Disaster. Joseph J. Trento. Crown Publishers Inc. New York, NY. 1987

  5. ³Report of the Presidential Commission of the Space Shuttle Challenger Accident.² The Presidential Commission of The Space Shuttle Challenger Accident. Washington, D.C. June 6, 1986.

  6. ³Space Shuttle Safety--A Hybrid Vehicle Breeds New Problems.² Irving Pinkel. Aerospace America. American Institute of Aeronautics and Astronautics, New York, NY. December 1971, Vol. 9, No. 12. pp 28-35.

  7. ³Space Shuttle--The New Baseline.² M. S. Malkin. Aerospace America. American Institute of Aeronautics and Astronautics, New York, NY. January 1974, Vol. 12, No. 1. pp 62-78.

Shuttle SRB Design Decision Assignments

The problems faced the parties involved in the development ant construction of the Space Shuttle fleet were large and complex. Many times there were no obvious answers. Decisions had to be made in the face of many conflicting demands. Sometimes it appears that the wrong demands were satisfied. However, hindsight is always better than foresight.

In a any project, compromise is always necessary. The larger the project, the larger the compromises. Usually, people know a great deal about their particular part of the project and consider it the most important. However, it is necessary to see more than just part if the correct compromises are going to be made. Unfortunately, this perspective is often difficult, if not impossible, to achieve. Still, decisions must be made.

When considering alternatives, it is important to prioritize the needs. However, this also can be difficult. In the case of the SRBs, it was determined that the lower cost and greater risk or solids was a better choice that the higher cost and lesser risk of liquids. In retrospect, this appears to have been a bad decision, but what if the design had been different. Was it possible for NASA administrators to know that SRBs would cause problems. Similar questions could be asked about other incidents in the history of the Shuttle boosters.

Assignment A:

Read the General Information provided on the Space Shuttle Solid Rocket Boosters. Consider each of the following questions carefully in light of that information and write a complete and grammatically correct paragraph answering each.

  1. Could NASA have resisted political pressures and developed the kind of Shuttle which would have been truly reusable?

  2. How safe is safe enough? Was the decision to use solid rocket boosters sound?

  3. Should Aerojet Solid or United Technologies, instead of Morton Thiokol, have been awarded the SRB contract?

  4. Was there a possible breach of ethics in awarding Morton Thiokol the SRB contract? In a similar case, what would constitute a breach of ethics?

  5. If you were on a jury attempting to place liability for the Challenger accident, whom would you say was responsible for the deaths of the Challenger astronauts? Are several groups responsibility?

  6. Considering an explosion like the the Challenger accident as an almost unavoidable ramification of the SRB design decision, do you think that there are legal liability questions here? If so, how far back does the liability go (to Morton Thiokol, to the NASA administrator, to Congress)?

  7. In light of the Challenger accident and its roots in the funding driven design choices made early in the Shuttle program, comment on the conflicts among the following points of view. A national design project such as the Space Shuttle should be:

    A. Funded year by year by Congress, just like everything else.

    B. Given multi-year funding and be insulated from Congressional political tampering - once Congress has decided that it is in the best interest of the nation to proceed with the project.

Assignment B:

Choose one of the following statements, research the topic, and write a two page paper in which you explore the topic.

  1. Following Apollo, the manned space program suffered from lack of funding and direction. Should a Space Shuttle type program be started in this environment?

  2. The design for the space shuttle was a series of compromises driven by poorly timed allocations of funds from congress. Identify and describe at least five design features which would have been different if the funding had been more timely.

  3. Solid rocket boosters are inherently less safe than liquid rocket boosters. Many engineers, including Werner Von Braun, believe that solids should never be used with manned spacecraft. However, to minimize R & D costs, solid boosters were used on the Space Shuttle. Locate and review a pertinent article written at the time which discusses the liquid vs. solid decision.

  4. Morton Thiokol won the contract to build the SRBs despite the lower bid by Aerojet Solid. In awarding the contract to Morton Thiokol, Dr. Fletcher overruled the recommendation of the NASA advisory panel. After investigating the contract award, the GAO recommended that NASA reevaluate the decision. NASA took no further action. Propose an alternate decision making process for such situations and contrast the ethical questions inherent in the proposed process against those present in the situation as it happened.

Assignment C:

Divide the class into small groups, no more than three to a group. Each group is to choose one of the four roles outlined below and develop statements outlining the position represented by those in your role and their part in the SRB saga. Develop two statements: (1) what you think was the position of those in your role, and (2) the position that those in your role should have taken.

  1. NASA Management: You want to develop the best Space Shuttle possible, but you must contend with the realities of limited funding, technical requirements, and politics. You are aware that you must make some compromises to ensure that the Shuttle continues to receive funding. You must attempt to balance the technically feasible with the politically feasible..

  2. Thiokol Management: Your first concern is to win the SRB contract. What will you do to win this? How do you give your company the edge over the competition? When it appears that your company's design is flawed, how do you deal with this. You must listen to your engineers, but at the same time you must please your primary customer. The last thing you want to do is admit that your product is defective.

  3. NASA Marshall Middle Management: You are in a tough position. The culture where you work does not look kindly on any kind of failure. The center director sets a style of management which pervades the entire facility, and does not encourage the free exchange of information. You are aware that there is a problem with the SRB field joints, but you don't know how serious it is. If you halt the program, for something that turns out to be minor, you will have committed professional suicide.

Assignment D:

Working in three person groups, examine some of the aspects of NASA culture present in the SRB saga. Consider that NASA is a government agency. What does this mean? Originally NASA was exempt from civil service regulations, but this is no longer true? What impact does this have? Is NASA still a technical organization, or has it been reduce to a bureaucracy content to push paper? Congress is notorious for a lack of vision and does not fund long term projects with consistency. How does this affect NASA? Is there anything NASA can do about this problem?