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Shuttles are the highest, fastest airplanes, but they
By Brian Welch
There were a quarter of a million people on the dry lake bed that morning of April 14, 1981, awash in a sea of Winnebagos, blue bunting, American flags and network anchormen. But most of the half-million eyes were trained on the sky.
Although they couldn't see the spacecraft just yet–Columbia was still far out over the Pacific Ocean–the onlookers had been able to hear the exchanges between the mission control center and the two pilot-astronauts, thanks to loudspeakers positioned out on the high desert floor of Edwards Air Force Base.
"OK, understand, go for the deorbit burn," Commander John Young had said when the time came to fall out of orbit. "Thank you, now."
Clad in bright orange pressure suits, sitting atop ejection seats, Young and pilot Robert Crippen were about to exercise the one capability that made their spacecraft truly revolutionary: they were going to bring it back in one piece. All of it. And then they were going to land it on a runway. But first, there was entry interface to get past, the point at which the spacecraft began to plunge through denser and denser layers of the atmosphere, trailing heat and a plasma sheath as it went. Because this descent had never before been done with such a machine, because the avionics were new and highly challenged by what was to come, because of fragile heat-shield tiles and predictions of a "zipper effect" that could rip a number of those tiles away from the airframe, millions of people on the planet below were watching and waiting. It was an edge-of-the-seat moment.
"Nice and easy does it, John," astronaut Joe Allen radioed from mission control. "We're all riding with you. We'll see you about Mach 12." And then the crackling transmissions receded, the airwaves grew quiet, and many of the spectators on the lake bed talked about how this must be the radio blackout from re-entry. They were about to witness an event unique in history, and part of its allure was that no one knew what to expect next.
Still out over the ocean, Columbia was tripping down through the high Mach numbers now, nose high, in a state of equipoise amid the fireball, while the avionics bays hummed with automatic flight controls at work, firing off thruster pulses and steering through regimes of flight never before navigated by a vessel with wings. Until now, it had all been theory, this business of balancing opposing forces along a sliding scale of altitudes, velocities and pressures, where every one-tenth of a Mach number was a distinct and separate place, a different aerodynamic address.
But in those moments of apprehension while exploring new concepts, the technical heritage of American high-speed flight research and the practical experience of sending men to the moon somehow came through to help create the granddaddy of all plane rides. Author Tom Wolfe observed in 1981 that the flight of Columbia closed a circle, bridging the aeronautics programs of the 1950s and '60s with the space program of the '80s. Wolfe contended that sending people into space atop expendable ballistic missiles was an anomaly, "the human cannonball approach," an expedient in the drive for prestige and dominance in the Cold War, and not the result of any long-range aeronautical vision. The first shuttle mission, he wrote, returned the American space program "to where it started–which was not Cape Canaveral but the throwback landscape of Edwards Air Force Base, a terrain that evolution left behind, a desert decorated with the arthritic limbs of Joshua trees and memories of Chuck Yeager, Scott Crossfield, Joe Walker, Iven Kincheloe and other pioneers of manned rocket flight."
Indeed, the original name for Project Mercury, the nation's first manned space-flight enterprise, was "Man in Space Soonest," and the fastest way to get an American into space was on top of a rocket. At the time, the U.S. Air Force was moving ahead with the X-20 Dyna Soar project, a reusable winged orbiter, but development would take too long under the circumstances. Even Wernher von Braun, who supervised the crescendo of American rocketry with development of the Saturn V, originally envisioned in a Collier's Magazine series of the early 1950s that astronauts would ride to orbit and back on winged, reusable vehicles. A generation later, when the moment finally came to Edwards with Columbia, the people who built the shuttle could only watch and wait, like everybody else.
Henry Pohl was one of them, and he still marvels at how rocketry and aeronautics came together that day in the shuttle program. "Most people can't appreciate that the shuttle, when it's in orbit up there, is going eight times faster than a bullet when it leaves the muzzle of a .30-06," said Pohl, who is director of engineering at the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) in Houston. "It's an airplane. But we launch it like a rocket. We kick it out of orbit half way around the world, dead stick, no engines. It flies like a rock, yet we set it down on the runway, and we do it time and time again."
There have been almost 50 flights to date, as a matter of fact, and the shuttle program will surpass that milestone later this year. Since 1981, the orbiters of NASA's space shuttle fleet have carried more passengers, traveled almost as many miles and hauled more cargo than all previous U.S. manned spacecraft combined. It has now been 20 years since President Richard M. Nixon approved the development of this remarkable space plane, and in that time the orbiters have come to offer the most impressive form of conveyance humans have managed to achieve in more than 50 centuries of trying. Yet for all of that, the space shuttle has become one of the most hotly debated forms of transportation in history, the fulcrum upon which a perennial battle for the heart and soul of the space program has seesawed back and forth, year after year, for nearly two-thirds of the time that NASA has existed. Understanding why this is so takes a little perspective.
A space shuttle flight begins with sheer spectacle. At the moment of controlled detonation–also known as liftoff–a shuttle is both creating and harnessing 6.5 million pounds of thrust. Its three main engines alone, diminutive in comparison to the raw power of the twin solid-rocket boosters, are themselves generating the output equivalent of 23 Hoover Dams.
Leaving the launch pad, a space shuttle is all rocket, its wings of little practical consequence except as impediments to airflow patterns. Reaching 100 mph as it clears the tower, the shuttle is a study in thunderous vibration, and this only builds in intensity for the first two minutes until the solid boosters tail off and drop away with a pyrotechnic clatter. But what the experience lacks in subtlety during liftoff is more than counterbalanced by the effortless grace with which a space shuttle uses all that energy to navigate once it has reached the seas of low Earth orbit. Once there, the deep-throated rumbling and bucking of ascent gives way to the more placid environment of life in orbit, answerable only to the laws of orbital mechanics and the flight rules of mission control.
But if the shuttle is such a wondrous vehicle, "the world's greatest, all-electric flying machine," as four-time flier Robert Crippen put it, then why has it also inspired such descriptions as "untouchable folly," "space lemon" and "flying brickyard"? Morton Dean, who has covered the space shuttle for two television networks, said the shuttle's public relations problems go all the way back to what he calls original sin at the beginning of the program. There were too many fantastic promises made, he said, for it to be otherwise, from a launch a week to freight cargoes well below $1,000 per pound (the current rate is variously calculated between $5,000 and $6,000 per pound).
But during its first decade of operation it became painfully obvious that the shuttle–contending with the realities of launch scrubs, schedule slips, remanifested payloads, upset and very critical customers and, ultimately, the cauterizing spectacle of the Challenger explosion–was not going to meet its advance billing. "There was an aura of expectation," said Joe Loftus, assistant director for plans at JSC, "and the failure to meet some of those expectations has totally obfuscated anybody's actually looking at what's been accomplished."
The technical heritage of the space shuttle goes back at least to the 1950s, but one could argue that the space plane's roots stretch all the way to the earliest days of flight. The agency that made the shuttle possible in the first place was not NASA but its predecessor, the National Advisory Committee for Aeronautics, commonly referred to as NACA. Created in 1915, the organization was charged to "supervise and direct the scientific study of the problems of flight, with a view to their practical solution."
There are many ties between NACA and the space shuttle. In the 1950s, for example, the work of the Pilotless Aircraft Research Division (PARD) of the old Langley Memorial Aeronautical Laboratory in Hampton, Va., was launching instrumented scale models on top of sounding rockets and telemetering data back to the ground. Although difficult and primitive by today's standards, the research was both viable and fundamental. It gave engineers valuable insights into the problems of high-speed flight, beyond Mach 2 or 3 and into the hypersonic regime.
The head of PARD was Robert Gilruth, who had been with NACA since the 1940s and was destined to direct Project Mercury. Gilruth was later the director of the Manned Spacecraft Center in Houston when the first serious feasibility studies for the shuttle were conducted. His deputy at PARD was a young man from Virginia Polytechnic Institute named Chris Kraft, who went on to become the first flight director in the first mission control center and who, as Gilruth's successor in Houston, helped bring the space shuttle into being. Another member of the PARD team was a brilliant engineer from deep in Louisiana by the name of Maxime Faget. He went on to supervise the designs that became Mercury capsules, Apollo command and service modules and space shuttles. In fact, many of the engineers in PARD joined the Space Task Group in 1959 to create Project Mercury, as did many others from the Langley laboratory.
The experience of these seasoned experts stretched far back into the corporate memory of NACA, for corporate memory was one of the many things in which the NACA excelled, and they left an indelible mark on the space program.
To understand why proponents were so optimistic about the space shuttle in the 1970s, one has to return to the heady days of Project Apollo. "You could not have built the shuttle without the Apollo heritage," Loftus said. "You couldn't have done it with another team." Pohl agreed. "A lot of people who worked on the orbiter worked on the X-15," he said. "Then they worked on Apollo. So they had the knowledge of how to build airplanes, they had the knowledge of how to build rockets and the kinds of things that you had to be concerned about when operating in the space environment."
The designers of the shuttle thought in terms of a rough-and-ready, rugged and robust wheel-drive kind of spacecraft, capable of bouncing around the back roads of space with a vast array of redundant systems, four deep in many cases, to provide defense in-depth against hardware problems and ground processing headaches.
That defense in-depth, known as quad redundancy, had an odd-sounding acronym (even for NASA) to express its method of operation: FO/FO/FS. It was pronounced "Fo-Fo-Fis," and that stood for "Fail Operational/Fail Operational/Fail Safe." Safe enough to get the crew home even if three levels of systems failed, and for anything short of that, you just kept on operating–and launching.
If the influences of the Apollo era were profoundly felt in the early years of the shuttle program, there is every reason to believe that the common experience many in NASA shared from the old NACA days was equally important. The young engineers who grew up around wind tunnels and flight lines in the 1940s and '50s, and who went on to become managers in the '60s, had a strong, almost overwhelming faith in the results of their research. Their minds were focused on building the shuttle, on making it work and finding the technical breakthroughs that would allow a 100-ton vehicle to drop out of space and land safely half a world away.
"There never was a machine imagined like the shuttle before there was a shuttle," Faget said. "Embodied in that one machine you have a launch vehicle, you've got a spacecraft, and you've got a re-entry airplane–not a re-entry vehicle. Prior to the shuttle, when the Apollo came down, it just fell down."
The shuttle, on the other hand, must remain perfectly balanced on its wings throughout the long, steep drop to Earth, said Kraft, an engineer with some experience in the world of flight-control systems. "The way you balance something is with pure force," he said, "and those forces are totally known because there are no aerodynamic forces [on the orbiter] above about Mach 10. The real problem was between Mach 8 and Mach 1."
And it was that region of the entry profile that required a tool of the trade called a Monte Carlo analysis. In that procedure, Kraft explained, aerodynamic parameters were plotted against different Mach numbers in random combinations. The idea was to first fashion an aerodynamic curve along which the shuttle would fly, a corridor where the flight-control system would be designed to guide the ship through precise forces at specific velocities, compensating for changing conditions all the way down. Then they expanded that envelope above and below the curve by adding variations to the flight-control settings.
They even went so far as to break the Mach numbers down into tenths of Mach numbers, threw all the parameters back into the hopper, and then ran it again and again until they could go a thousand times without a glitch. "If we had a single failure we went back and made a correction to the system until we got 1,000 runs without a failure for every mach number," Kraft said.
Since theory alone could not account for all the complexities of a typical shuttle flight profile, the engineers used at least 50 different wind tunnels to hone and shape the vehicle. Many of those tunnels, such as the 8-foot thermal-structures tunnel at Langley, were originally conceived at NACA.
In time, the shuttle design accumulated more than 100,000 hours of wind tunnel time, four times as many as the Boeing 757 and 767 development programs, in an effort to predict what the parameters would be along the corridor of flight. The shuttle's designers also measured their ability to forecast the phenomena of flight by poring over data from high-speed research aircraft such as the X-15 and the YF-12. Not yet satisfied, they tweaked the responsiveness of the controls by adding gains to the system, damped out and tight in one place, high and loose in another. They varied the gains all through the Mach numbers they were concerned with, Kraft said, adjusting the flight path angle here, the angle of attack there, until the aerodynamic factors, the thermal constraints and the structural integrity of the vehicles were all harmoniously balanced.
What the shuttle's creators didn't realize, unfortunately, was that there is nothing harmonious about the realm in which the spacecraft flies today: that murky sphere where technology, budgets and politics all meet. Money was never a problem during the Apollo program, but by the time of the shuttle, there was never a time when money was not a problem.
"Very early in our discussions with the Office of Management and Budget [OMB]," Kraft remembers, "we found out that we couldn't build what we wanted to build. And we had to compromise greatly in order to get the program to fit into the budget that people were allowing us to have. We estimated $15 billion to build a totally reusable machine and they said, 'You can have five.' And we ended up compromising at a fixed-price contract of about six and a half, with a $1billion overrun possibility."
What this meant in practical terms was that the OMB had effectively set a spending cap, from the beginning of the program, at $1.1 billion annually in 1971 dollars. In order to stay within that cap, NASA managers accepted schedule slips in lieu of compromising the shuttle's performance, and over the next 10 years that worked out to a 50-percent hit on the program time lines. It seemed like a reasonable compromise at the time, albeit painful, but the shuttle managers got 20 years of vilification in the press. The myth arose that NASA stumbled blindly on during the 1970s, ignoring the schedule delays and making one excuse after another for the cost overruns, which have, for two decades, been characterized as "massive" despite the fact that the total design and development costs of the shuttle exceeded the original estimates by less than 5 percent.
It never got any easier after that. A slowdown hit the aerospace industry in the early 1970s, thousands of engineers lost their jobs, reductions in force (known as RIFs) swept NASA, and the agency lost almost a third of its employees, down from 33,000 during the peak Apollo years to around 24,000, the number NASA still employs today. The civil service complement at the space center in Houston was reduced from 4,800 to 3,200 employees. All this occurred while trying to bring a revolutionary space vehicle on line.
For the person running the orbiter project at the time, the budget situation was "very severe and very hard." But Aaron Cohen, who today runs JSC, is just as quick to point out that when the budget ax had to fall, it generally fell on the schedule, not quality and not on safety. "I don't think we made any shortcuts in that sense," he recalls, "but when I had a problem, I couldn't solve it as rapidly because I couldn't go with parallel approaches. I had to pick an approach and then hope it was right, rather than go down two or three paths at the same time, as we did in the Apollo program."
In the end, neither the engineers nor the technical managers nor the people who ran things in Washington could make the shuttle all things to all people and somehow also manage to achieve every one of the enormous promises that were made. As late as 1979, NASA Administor Robert Frosch was still talking in public about the shuttle making regular Monday morning runs into space.
But although this sounds like fantasy today, it is illuminating to consider just some of the elements that were a part of the list of things on which NASA planned to enable 60 shuttle flights to be made a year. That list included a baseline of seven orbiters, three launch pads, two orbiter-processing facilities, adequate spare parts, regular Florida landings and a large percentage of highly standardized, commercial satellite deployment missions. It also included a space station and a fleet of space tugs to ply satellites back and forth from geosynchronous Earth orbit. In one way or another, for one reason or another, not one of those fundamental assumptions was ever met; yet the expectations placed on the shuttle scarcely lessened.
Despite all the impediments, work on the shuttle program continued, and now the fleet is flying. Was it a good choice for the nation to make? Was it a good thing? History will need a long time to work out those questions. But there are some observations that can be made based on the statistics and the performance of the system.
Notwithstanding its bad press, the shuttle has become one of the most reliable launch vehicles in history, with a success-to-failure ration of .978-to-1, with 1 being perfect. Over the course of the program, the fleet has logged more than 100 million miles, more than equivalent to an astronomical unit (AU)–the distance to the sun–with one accident. That figure is made more impressive by the fact that launch vehicles usually experience a higher rate of failure in the early years of operation, before hitting a stride of design maturity after 100 or more flights. But the shuttle has a higher reliability rating than any other U.S. launch vehicle, and most other types of launch vehicles that have been in operation for more than 30 years. Europe's Ariane booster, the only other vehicle designed in the 1970s and operated in the '80s, had five failures in its first 40 flights.
In its first decade of operation, the shuttle did not fly to orbit every week, but it did launch almost half of all the mass the United States has ever deployed to space. "For all intents and purposes," Loftus said, "we've launched 1,200 tons of payload every decade. It took us 215 launches in the 1960s, 152 launches in the '70s and 102 launches in the '80s. The shuttle, with 4 percent of all U.S. launches, has carried 41 percent of all the mass. Not including the orbiter."
There are other, more technical ways in which the shuttle has weathered well over time. Its 1970s design is still state of the art in many areas, including computerized flight control, airframe design, the electrical power system, the thermal protection system and the main propulsion system. The shuttle main engines are the world's most efficient chemical rockets, and they remain the only rockets that can be throttled. The shuttle flight software is the most sophisticated aerospace code on the planet, even after more than a decade of flight. It is also the one vehicle flying that offers any sort of meaningful capability to return cargo from space to Earth. Additionally, it is the only human-rated vehicle type now being emulated by all of the other major space-faring powers.
How will history judge the shuttle? Max Faget, one of this century's most renowned aerospace designers, offered an insider's perspective: "When we first broke the speed of sound, we did this in a research airplane. After we flew that airplane a dozen times, we discarded it, put it into a museum, and then got to work on designing airplanes based on the knowledge we gained from it. The shuttle is the first one that…flew this tremendous Mach number range, but it also did the job of a launch vehicle and a spacecraft that could stay in orbit for days or weeks at a time. If it is a little bit wanting in some of its operational features, I think it's excusable. Maybe the second and third generation shuttles could be really good, but I don't know how you can make the third generation shuttle without have the first and second generation shuttle. We are still learning."
For the people who pioneered American high-speed flight, then worked on Apollo and then turned to the space shuttle, that was the goal all along.
Brian Welch, a writer and spokesman for the space agency since 1979, has worked at both the Langley Research Center and the Johnson Space Center. For further reading: Entering Space: An Astronaut's Odyssey, by Joseph P. Allen; and Liftoff: The Story of America's Adventure in Space, by Michael Collins.
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