Endeavour is delivered to the Kennedy Space Center, May 2, 1991 This dramatic view looking directly down on the shuttle atop the Mobile Launcher Platform and crawler-transporter was taken from about 160 meters above the ground.
The retirement of the space shuttle - the final launch is set for Friday, weather permitting - may turn out to be a larger turning point in the history of human space flight than appears on the surface. The problem is not that the shuttle was so bad, but that it was so good.
When the shuttle first flew in 1981, it was the most sophisticated launch vehicle ever built. It overcame much of the waste of conventional rockets, which shed their lower stages as they ascended through the atmosphere. The shuttle's orbiter could return to Earth, land and fly again.
It also had an innovative heat shield; the most powerful engine ever built; a network of integrated computers capable of flying the shuttle from liftoff to touchdown; and the ability to deliver, retrieve and maintain the component parts of a space station.
But the shuttle failed to provide safe, reliable, economical access to low-Earth orbit. If this technological tour de force couldn't open up the potential of space, what could?
The shuttle is still the envy of space-faring nations. But as former NASA administrator Michael Griffin has observed, it was also "an inherently flawed vehicle." Its design was constrained by budget limitations and by U.S. Air Force insistence that it accommodate spy satellites and the mission profiles to support them. It was only partially reusable, jettisoning its main fuel tank and rocket boosters on its way to orbit. The wear and tear of flying in and out of the atmosphere drove refurbishing costs to budget-busting levels.
Far from reducing launch costs by an order of magnitude, the shuttle actually cost more to fly than the Saturn launch vehicle it replaced. On average, each of the shuttle's 135 flights will have cost U.S. taxpayers $1.5-billion.
Cost remains the bane of chemical-fuelled launch vehicles. The Russians probably have the best record, using boosters of a simple but reliable design; their real costs for human launches, however, appear not to have achieved NASA's criterion of reducing launch costs by 90 per cent. The Chinese, Indians, Japanese and Europeans have all forecast manned space-flight programs, but so far only the Chinese have joined the U.S. and the Russians in human spacefaring. And they haven't flown a taikonaut in three years.
Two physical realities constrain progress. First, manned spacecraft are heavy. Humans venturing into space must take food, water, life-support equipment, medical and safety equipment, and fuel and hardware to return them to Earth. Also, any launch vehicle carrying people into space has to be subjected to sky-high quality controls.
The second constraint is the fuel ratio. When the shuttle lifts off, 94 per cent of its weight is fuel, tankage and solid-fuelled rocket boosters. Another 5 per cent is the empty shuttle orbiter. Only 1 per cent is payload. This is the Achilles heel of all chemical-fuelled launch vehicles.
After 50 years of manned space flight, with no significant initiatives on the horizon, a new paradigm appears to be in order. One commercial company flies its prototype manned spacecraft aloft before igniting its rockets at high altitude, where it has less distance to travel to orbit and less gravity pull to overcome. Other options abound, ranging from slingshots and ski jumps to space elevators.
The shuttle, said Mr. Griffin, the former NASA administrator, was a "mistake." If NASA is to learn from that mistake, it will need to do some daring research and planning, not just recycle the chemical-fuelled rockets of the past 50 years.
Alex Roland, a former NASA historian, is professor emeritus of history at Duke University.