'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.'

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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.

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