This article analyzes the decisions and technological challenges that drove the Space Shuttle’s development. The goal of the Shuttle program was to create a reusable vehicle that could reduce the cost of delivering humans and large payloads into space. Although the Shuttle was a remarkable flying machine, it never lived up to the goals of an airline-style operation with low operating costs. In January 2004, a year after the Columbia accident, President George W. Bush unveiled the “Vision for U.S. Space Exploration” to guide the U.S. space effort for the next two decades. A major component of the new vision, driven by the recommendations of the Columbia Accident Investigation Board, was to retire the Space Shuttle fleet as soon as the International Space Station assembly was completed. With cancellation of the Constellation program in 2010, the planned successor to the Shuttle, the U.S. space program is now in an era of uncertainty.
“The country needs that Shuttle mighty bad,” said Apollo 16 commander John Young as he walked on the moon on April 21, 1972. He had just been informed by mission control that the House of Representatives had approved the development of the Space Shuttle. Nine years later on April 12, 1981, Young would command the maiden flight of the Space Shuttle orbiter Columbia, as he and fellow astronaut Robert Crippen ushered in a new era for America's space program.
The Space Shuttle era is now coming to a close (with the final flight of Atlantis scheduled this month) after 30 years of operation, 135 flights, more than 1,300 days in space, almost 530 million miles traveled, and more than 3 million pounds delivered to orbit. Debates on the Shuttle program's legacy have already begun as its costs and contributions to the space program and the nation are currently being assessed. As the world's first reusable spacecraft, the Shuttle system is an engineering marvel, a testament to the ingenuity and perseverance of its designers and builders.
Yet, from an operational standpoint, the Shuttle never lived up to the dreams or expectations of its proponents and leaves a mixed result of many space firsts, great successes, and two devastating tragedies. Many consider the Shuttle program a failure and even label the Shuttle itself a flawed design. That assessment is too simple and does not account for the circumstances surrounding the Shuttle's creation, shaped by the politics and economics of the late 1960s and early 1970s.
NASA leadership at the time was looking for a worthy successor to the Apollo program, and the agency's ambitions ran directly into political and financial realities. The Nixon administration and Congress supported a human space flight program; they just wanted a far less expensive version. NASA leadership opted for a reusable space transportation system with the intent of lowering the costs of getting into space.
The Shuttle's designers would be pushing the boundaries of technology and soon found that getting to the moon was a simpler challenge. All engineering design is a compromise, but the Shuttle's creators were forced into design compromises to fit constantly shrinking budgets. The result was a design that would do the job, but it was not as good as it could have been.
As the debates have now started on the future of America's human space flight program after the Shuttle, it is a good time to look back at the decisions and technological challenges that drove the Space Shuttle's development and what lessons they might offer for our future in space.
The goal of the Shuttle program was to create a reusable vehicle that could reduce the cost of delivering humans and large payloads into space. People spoke of a craft that could voyage beyond the Earth's atmosphere perhaps more than once a week. Of course, that never happened. Even today, three decades later, the state of space technology makes that an unrealistic expectation for missions on the scale of the Shuttle's.
A Way Back In
During the late 1950s, the U.S. was focused on the development of ballistic missiles for its Cold War arsenal. These ballistic rockets would form the foundation for the human space flight program of the 1960s.
There was also research in areas that later would contribute to the Shuttle's development. In 1952, H. Julian Allen, a researcher at the Ames Aeronautical Laboratory of the National Advisory Committee for Aeronautics, made a critical discovery. He found that a high angle of attack during re-entry produced a shockwave ahead of the vehicle that deflected heat away. This theory was called the “blunt body” principle and would eventually be used in practice.
The X-15, which made use of the blunt body principle, was designed in the late 1950s by NACA and manufactured by North American Aviation to conduct flight tests in the hypersonic regime. With its reusable and throttleable rocket engine, the X-15 was able to reach altitudes above 260,000 feet, the boundary of space.
It flew at speeds greater than Mach 5, and during re-entry saw surface temperatures exceeding 1,200 °F. The flight profile of the X-15, from hypersonic to transonic to subsonic would mirror the Space Shuttle's, and the research data in these regimes would benefit the Shuttle's designers.
An Air Force project called Dyna-Soar, shortened from “Dynamic Soaring,” also contributed to the reusable spacecraft knowledge base. Launched from an expendable rocket, this delta-wing vehicle would use hypersonic lift to bounce off the atmosphere to lose speed before re-entry and its glide to a landing. Canceled in 1963 before flying, it provided a wealth of research that would inform the Shuttle.
A few years later, Max Hunter at the Lockheed Missile and Space Co., who was an expert in aircraft performance and airline economics, developed a concept for a reusable piloted spacecraft, dubbed the Star Clipper.
Hunter called it a stage-and-a-half concept. It consisted of a single “integrated launch and re-entry vehicle” that carried all critical flight components and an external fuel tank for liquid hydrogen and oxygen. The fuel tank would drop off and the main vehicle would continue into orbit. While going no further than conceptual design, Hunter's external tank influenced the system configuration of the Space Shuttle.
Efforts at NASA toward a reusable space-plane began with George Mueller, the associate administrator for manned space flight. Looking at options for a post-Apollo NASA, Mueller envisioned orbital space stations to support a Mars mission. But that vision needed a low-cost method to reach space.
“No law says space must be expensive,” Mueller said. In December 1967, Mueller organized a one-day industry symposium to solicit ideas for reducing the costs to orbit. The discussion would ultimately set NASA in a new direction.
Thomas Paine became the NASA administrator in late 1968, after the agency's budget had already started to decline. Undeterred, Paine advocated a robust space program: Orbiting space stations, space tugs to lift satellites to high orbit, and nuclear-powered spacecraft to carry astronauts to Mars.
Paine found support for the Mars mission from Vice President Spiro Agnew, who headed President Nixon's Space Task Group. Nixon's budget crunchers at the Office of Management and Budget, however, proposed cuts to NASA's budget of almost one-third, which would have shut down the human space flight program after the moon landings. Mars and even a space station were out of reach, and Paine realized that bringing launch costs down was paramount if there was going to be human space flight.
Concept Takes Shape
Mueller's initial efforts at developing low-cost launch options now took on greater urgency. Mueller, like Hunter, was convinced that airline economics served as a good basis for modeling a new space transportation system. Mueller conceived of a configuration that included reusable high-performance and long-life rocket engines, a reusable thermal protection system, and a sophisticated on-board computer maintenance and check system.
Maxime Faget, NASA's chief spacecraft designer, was tasked with giving shape to Mueller's concept. He proposed a fully reusable two-stage configuration that included a booster rocket that carried a winged orbiter on its back. The booster rocket would carry the orbiter to staging velocity and then would drop off and be piloted back to a runway. The orbiter, which looked like a rounded and overweight X-15, had straight and unswept wings and would continue the climb to orbit. On re-entry, the orbiter, which was protected by a thermal protection system, flew at a high angle of attack as a blunt body and then landed like a conventional aircraft.
Mueller asked McDonnell Douglas, North American Rockwell, Lockheed, Grumman, and Martin Marietta to develop workable designs for Faget's concept. The engineering challenges were enormous, but economics would shape the planning and design far more than technical needs. A fully reusable system was going to be expensive to design, with initial estimates running at $10 billion.
Was such a system worth the cost of development? In doing their budget assessment, economists would be comparing the new Shuttle system against the cost of using expendable rockets for a similar number of launches. Initial Shuttle cost estimates were about $100 per pound. The Saturn V cost $1,000 per pound of payload and $185 million to launch. The target Shuttle launch cost would be $10 million and compared favorably to $25 million for the Atlas-Centaur and $15 million for the Delta, two expendable rockets. (These costs are all in 1975 dollars.)
A reusable system would have higher development costs but the per-launch costs would be less because the flight hardware could be used again.
The number of launches that would justify the development cost, over an expected life of 15 years, ranged from 500 to 900, or a maximum of more than one flight a week. There were not enough commercial missions to justify the program, so Paine turned to the Air Force as the primary customer and said the Shuttle would be available for any of its needs.
The Air Force needed to launch heavy payloads up to 65,000 pounds to orbit and needed a payload bay of 15 x 60 feet to accommodate the largest satellites. These requirements meant that the orbiter would have to be much larger than originally planned.
The Air Force's requirement for a one-orbit polar mission also drove the need for improved “cross-range” ability, which is the distance the orbiter would need to fly from the point of re-entry using its lifting properties. Launched from Vandenberg Air Force Base in California for this mission, the Shuttle would return to the same latitude during re-entry, and because of the Earth's west-to-east rotation, the landing site would have moved more than 1,000 miles to the east. The Shuttle would need the ability to fly about 1,200 miles cross-range to its landing site after such a mission and Faget's straight-wing configuration would only provide a range of 230 miles. A delta wing would do the job, but that meant much more surface area would have to be covered by the thermal protection system.
Leroy Day, an Apollo manager who in April 1969 took a lead role in Shuttle development, offered several possible missions to support the Shuttle program. Tasks including satellite repair and checkout, retrieval of disabled satellites, and carrying a temporary laboratory into space were important selling points. That the Shuttle would eventually accomplish all of these tasks is a testament to Day's engineering foresight.
The Cost Countdown
Ten billion dollars to develop a fully reusable system was too much for the Nixon administration. Over the next two years NASA and aerospace contractors conducted hundreds of feasibility studies to determine the most practical configurations. At the same time economists at the OMB evaluated the cost estimates and kept insisting that NASA do it for less.
In a search for cost reductions NASA decided to use an external tank, like Hunter's Star Clipper, for the liquid hydrogen and oxygen. This also helped shrink the orbiter since it would not need its own internal tanks. These modifications still left the price around $8 billion, and the OMB was pushing for a $5 billion cap.
One of the most expensive components of the Shuttle system was the booster rocket. Proposed to be fully reusable, the booster rocket was the size of a 747. Configured with wings, it had rocket engines for liftoff, and jet engines for the return to its landing site. Using a conventional booster instead seemed the best opportunity to reduce development costs.
Klaus Heiss, an economist working for Mathematica, the consulting firm hired by Paine to conduct NASA's own financial analyses, pushed a concept called Thrust Assisted Orbiter Shuttle, or TAOS. At first rejected because it was not fully reusable, TAOS used a standard orbiter with an external tank and was paired with two booster rockets. At liftoff the orbiter's engines would ignite at the same time as the booster rockets. After burning all their fuel, the booster rockets would drop off and be recovered, refurbished, and reused. The estimated cost for TAOS was around $5.5 billion.
James Fletcher, who replaced Paine as NASA administrator in 1971, made the final decision with the help of OMB director George Shultz, who kept the $5.5 billion budget intact and recommended that President Nixon approve the TAOS Shuttle. On Jan. 5, 1972, the president announced the start of the Shuttle and said, “It will revolutionize transportation in near space by routinizing it.... It will take the astronomical costs out of astronautics.”
Finally, on March 5, 1972, after hundreds of design concepts and economic assessments, NASA announced the final Shuttle configuration. It consisted of a reusable delta-wing orbiter about the size of a DC-9 with a 15- x 60-foot payload bay, partly reusable solid rocket boosters, and an expendable external tank—basically the Shuttle we know today. After almost four years of studies, it was time to start doing detailed design work and build the Shuttle. NASA selected its contractors and they went to work, but two critical components of this reusable system— the Space Shuttle main engines (SSME) and a thermal protection system—would perplex and challenge engineers and ultimately delay the program beyond the target launch date in 1979.
The SSME would generate 375,000 pounds of thrust at sea level and there would be a cluster of three SSMEs in the orbiter. Designed to fire for 27,000 seconds they would have an operational life of 55 flights. Rocketdyne, the contractor, had developed the liquid-fueled F-1 and J-2 engines that powered the Saturn V, but the SSMEs would be a major leap forward in engine design. In order to get the performance NASA required, the engines would be operating at temperatures and pressures well beyond any liquid-fueled rocket engines in existence.
Splintered Bearings and Lost Tiles
The super-cold liquid hydrogen and oxygen would be fed at -400 °F and then combust at 6,000 °F. The turbo-pumps, which produced 75,000 horsepower and fed the fuel and oxidizer, were only the size of outboard motors, yet they rotated at 23,700 rpm and operated at pressures more than four times that seen in the F-1 and J-2 engines. The extremes of temperature, pressure, and rotational speed resulted in many failures during the development and testing phase— blown valves, faulty welds, split fuel lines, cracked turbine blades, and splintered ball bearings—that caused multiple fires and explosions.
To overcome the challenges of the engines the Rocketdyne engineers solicited the help of researchers from leading universities and laboratories and had to develop new materials and manufacturing processes. Before the first flight, these new designs were coupled with a rigorous testing program that included 726 hot fire tests totaling more than 110,000 seconds. The hard work paid off, and in operation the SSMEs have performed admirably and remain the most advanced (and only reusable) liquid-fueled rocket engines ever developed.
For protecting the orbiter from the heat of re-entry, prime contractor North American Rockwell employed a new technology developed by Lockheed Missile and Space called reusable surface insulation. It consisted of tiles made of silica fibers and could withstand temperatures up to 2,300 °F. There were more than 30,000 tiles on Columbia and no two were alike.
They bonded to the skin by hand and fit within 0.002 to 0.003 inch, but the tiles were fragile and the adhesive not as strong as expected. During Columbia's flight to the Kennedy Space Center on the top of a 747, more than 7,500 tiles were lost or damaged under pressures far less than would be seen during a spaceflight. The adhesive problem was solved by applying a DuPont coating called Ludox to the bottom of each tile and this acted like cement reinforcing the tile's strength. It took NASA 20 months of round-the-clock work to solve the adhesive problem and re-apply all 30,000 tiles to Columbia before its first flight.
It took nine years to overcome the many technical challenges and get the Shuttle launched, longer than it took to achieve the first moon landing. President Nixon in announcing the Space Shuttle program said it was going to make flying into space routine. But the reality after 50 years of human space flight, and the loss of orbiters Challenger and Columbia, is that launching humans safely into space is hard and leaves no room for error.
$1.3 Billion per Flight
In January 2004, a year after the Columbia accident, President George W. Bush unveiled the “Vision for U.S. Space Exploration” to guide the U.S. space effort for the next two decades. A major component of the new vision, driven by the recommendations of the Columbia Accident Investigation Board, was to retire the Space Shuttle fleet as soon as the International Space Station assembly was completed.
Although the Shuttle is a remarkable flying machine—rocket, spacecraft, and glider all in one—it never lived up to the goals of an airline-style operation with low operating costs. The cost estimates were based on twoweek turnarounds and the economies of scale from 55 flights per year. But in reality the Shuttle is an incredibly complex machine that requires a massive support infrastructure of facilities and people to keep it flying safely. Even in 1985, its best year, it never achieved more than nine flights. It has been estimated that the entire Shuttle program (including R & D) will have cost $174 billion, averaging almost $1.3 billion per flight.
There is no doubt the designers of the Space Shuttle oversold its capabilities and underestimated its costs. They had, however, nothing to base their estimates on except concepts. A reusable space launch system didn’t exist, and they were tasked with creating one. It was impossible to foresee the technical and operational challenges they would face. And the thousands of engineers, scientists, and technicians who designed the Shuttle and kept it flying these last 30 years were asked continually to do more with less by cost-conscious government leaders.
Through their innovation, persistence, and dedication these engineers created and sustained an incredible vehicle that has carried more than 70 percent of the 500-plus individuals who have flown into space, launched more than 100 payloads into orbit, and made possible the construction of the International Space Station.
With last year's cancellation of the Constellation program, the planned successor to the Shuttle, the U.S. space program is now in an era of uncertainty. The Obama administration has plans to get NASA out of the launch business and rely on commercially developed and operated vehicles to get astronauts and payloads to space. The true plan is still not defined, but the legacy aerospace companies along with a new brand of space entrepreneurs such as Space X, XCOR, Blue Origins, Armadillo Aerospace, Virgin Galactic, and others are exploring innovative launch approaches.
Whether it's the government or the private sector that paves the way for the future of the U.S. in space, the best tribute we can pay the Shuttle and the tens of thousands of people who contributed to the program is to make a commitment to the passengers flying on future spacecraft that we’re going to do it right. Richard Feynman, the physicist who served on the Rogers Commission investigating the Challenger disaster, said it best: “For a successful technology, reality must take precedence over public relations, because nature cannot be fooled.”