Article kindly provided by Casey Heigl (casey@heigltech.com).


Introduction


Since 1981, the space shuttle has hauled more cargo, carried more passengers, and traveled practically as many miles as all other U.S. manned spacecraft’s combined. Astoundingly, it’s now been almost 50 years since President Nixon signed off on the development of the space shuttle. Since that time, the shuttle has offered the most ambitious method of transporting humans into space in over five thousand years of effort.

Although most of us are familiar with the spectacle of manned space flight, those who are younger among us may not be. At the moment of liftoff, the shuttle both created and harnessed about 6.5 million pounds of raw thrust. Its three main engines, tiny in comparison to the unleashed power of twin solid-rocket boosters, generated the equivalent output of the Hoover Dam 23 times over.

Departing the launch pad, the space shuttle was all rocket. When it cleared the tower at a relatively slow 100 miles per hour, the shuttle was a study in thunderous vibration that grew in intensity over the initial few minutes of flight until the tail-off and drop of the solid rocket boosters.


Shuttle Safety in Space


 

Those who designed the shuttle envisioned a rough and tumble four-wheel-drive type of spacecraft that can handle the rugged back roads of space. It would come equipped with a standard array of overtly redundant systems—as many as four deep, in some cases—to heartily defend against any possible hardware or software problems. The systems onboard were meant to be nimble enough to return the crew home safely even if up to three levels failed.

The space shuttle’s thermal protection system or TPS was comprised of thousands of thermal tiles that served as a barrier to protect the vehicle during the scalding 3,000-degree heat of reentry into the Earth’s atmosphere. The TPS also protected the vehicle from the extreme cold and heat of outer space while in orbit.

The shuttle, in contrast with other vehicles, such as the Apollo, was designed to stay perfectly balanced on its own wings for the duration of the long, steep return to Earth. This balance was achieved through pure force. Scientists knew there were no aerodynamic forces on the shuttle above Mach 10. However, the real problem existed between Machs 8 and 1.

Scientists even broke down the Mach numbers into tenths, throwing all of the possible parameters back into a hopper, running and rerunning scenarios over and over until they could run a thousand times or more without a problem. If there was a single failure, they went back and made corrections to the system until 1,000 runs without failure were achieved for every possible Mach number.

Engineers used 50 or more wind tunnels of various speeds to shape and hone the vehicle since theory alone could not possibly account for every complexity of a typical shuttle flight.

Over time, the design of the shuttle accumulated over 100,000 hours of time in wind tunnels, which amounted to four times the testing of both the Boeing 757 and Boeing 767 developmental programs.


Tiles


The Challenger disaster came about in part due to a weakness in the tiles used to guard against the extreme heat of reentry. Later space shuttles used tiles made of ceramic fibers and a special silicone glue that bonded the tiles directly to the aluminum frame of the shuttle.


Plans Versus Budget Cuts


What the creators failed to realize, however, was that politics affects technology, which affects budgets. In practical terms, it meant there was a spending cap, and, to stay under that cap, compromises in the shuttle’s performance had to be made. Over the subsequent ten years, those budget cuts resulted in a painful hit to the program. Although painful, the compromises seemed somewhat reasonable at the time.

Although it might seem unheard of today, it’s interesting to consider even some of the elements that were included on the list of items NASA planned to include with their proposed 60 shuttle flights per year. The list included seven shuttles, three dedicated launch pads, a space station, and a fleet of “space tugboats” to pluck and place satellites in and out of Earth orbit. For some reason, not one of those “wish list” items was totally fulfilled, yet there was no change in the performance expectations of the shuttle program.


It’s a Go for Launch


In spite of all they had to go through, work on the space shuttle program continued and, eventually, the fleet began flying. Other than a couple of catastrophic events, the shuttle went on to become one of NASA’s most reliable vehicles for space launch and exploration. Indeed, its success-to-failure ratio indicated a much higher reliability than any other launch vehicle in the United States among space launch vehicles that have been in operation for more than 30 years. In comparison, Europe’s Ariane booster rocket had five failures within its initial 40 flights.

In its first ten years of operation, the space shuttle flew every week, yet it managed to launch nearly half of the entire mass of everything the United States has ever deployed into space.


The Space Shuttle Legacy


There are still other ways in which the space shuttle has stood the test of time. Its seemingly retro 1970s design template is still standard and state-of-the-art in many areas, including airframe design, automated flight control, thermal protection systems, electrical power systems, and the main propulsion system. The space shuttle’s main engines proved to be the world’s best chemical rockets, and they remain the only ones to date that can actually be throttled.

The space shuttle’s flight software is among the most advanced aerospace code on Earth, even years after the shuttle’s been retired. The space shuttle was also the only space vehicle that offered any kind of practical capability to return space cargo back to Earth. Additionally, it remains the only human-carrying vehicle type to be emulated by all other major space-faring nations.


The Future of NASA Space Travel


Who knows how history will ultimately judge the space shuttle? When the speed of sound was first broken, it was done with a research airplane. After flying a dozen times, the plane was discarded, donated to a museum, and work was initiated to create the next model with intelligence gained from that experience. The space shuttle did a tremendous job of serving both as a launch vehicle and a spacecraft which was capable of remaining in space for days or even weeks at a time. Perhaps the next generation of manned space vehicles will improve upon some of the space shuttle’s shortcomings. We are all still learning.

For the early American astronauts who pioneered high-speed flight, who worked on missions like the Apollo, and who helped turn that experience into the space shuttle, this was their goal all along.