We mark NASA's 50th anniversary with a look at the organisation's new main challenge - another manned flight to the moon.
No engineering enterprise since the construction of the Hoover Dam in the 1930s better exemplified America's hopes for the future than NASA at the dawn of the Space Age.
Signed into law on 29 July, 1958 as a response to Russia's launch of Sputnik ten months earlier, it symbolised the 20th century technological dream at its most self-assured: spending vast sums of taxpayers' money on engineering and science in order to improve education, stimulate flagging industries and redefine the management structures and beliefs of large-scale organisations across the country.
NASA's vision for its crowning achievement, the 1960s Apollo lunar landing project, was not just directed at winning triumphs in space. The genuinely innovative techniques in systems engineering, personnel management and information control pioneered by the Agency were supposed to serve as a model for social change on the ground too.
According to the Smithsonian Institution's chief space historian Roger Launius: "NASA thought it was possible to create the perfect organisation. They talked about the application of their techniques to other sorts of activities such as homelessness and poverty, welfare and education."
One of the reasons we feel so nostalgic for the days of Apollo is our sense that "they could do things better in those days".
However, in January 1986, space shuttle Challenger exploded in mid-air shortly after launch, denting forever our acceptance that NASA knows how to run "the perfect organisation".
The loss of a second shuttle, Columbia, during re-entry in February 2003 highlighted that the entire US space programme needed to renew its sense of purpose after years of post-Apollo neglect.
The White House responded with surprising vigour to Columbia's loss. On 14 January 2004, President George W Bush made a televised speech during a special visit to NASA headquarters in Washington. The priority, he said, was to return the shuttle system to flight status and finish construction of the International Space Station. No surprises there, but as his speech continued, a radical alternative vision emerged for America's future in space.
From now on, NASA's principal task is to "undertake extended human missions to the Moon, with the goal of living and working there. With the experience and knowledge gained on the Moon, we will then be ready to take the next steps of space exploration: human missions to Mars and to worlds beyond". The ageing space shuttle system will be retired from flight in the year 2010, and a new spacecraft, the Crew Exploration Vehicle (CEV), known as Orion, will take centre stage.
In terms of manned space flight at least, Orion is a reversal of everything that NASA has worked towards over the last 25 years. The dream of an all-purpose winged space shuttle, flying cheaply and reliably like a commercial cargo plane, never quite came to fruition.
Whenever a shuttle carries a satellite or a space station module in its cargo bay, the costs of launching those payloads are exaggerated because astronauts always come along for the ride. Quite apart from the massive additional complications of life support, the launch weight given up to the crew cabin - and the shuttle's heavy wings - has to be subtracted from the cargo capacity.
It is more efficient, say Orion's designers at the Lockheed Martin company, to lift cargo in unmanned rockets, and launch astronauts separately in a small module that carries people and nothing else. There is no need for the shuttle unless the intention is to return large payloads to Earth. So, with the Orion concept, all that remains is the human-carrying element: a small conical crew cabin at the front of the launch stack.
Despite the unwelcome evidence of two disasters, there has never been anything uniquely hazardous about the shuttle. Dr John Logsdon, director of George Washington University's Space Policy Institute, served on the Columbia Accident Investigation Board (CAIB).
"Naturally we had an emphasis on investigating the specific problems that doomed Columbia, but space vehicles are risky across the board, and they need constant vigilance to be flown successfully." That said, NASA is eliminating certain risks identified by the CAIB.
At launch, the shuttle is attached to the flank of its huge external fuel tank, in what is known as a 'parallel' stack. Columbia was destroyed because a suitcase-sized piece of thermal insulation foam peeled off the external fuel tank shortly after launch and hit the left wing's leading edge, making a small but ultimately catastrophic hole.
During Columbia's re-entry two weeks later, hot gases rushed into that hole, destroying internal controls and melting the underlying metal airframe. Orion will revert to the 1960s paradigm, with the capsule at the very top of the launch vehicle: an 'in-line' arrangement that prevents stray debris, such as loose insulation foam or ice peeling away from the cold flanks of the liquid oxygen and liquid hydrogen fuel tanks, from endangering the crew.
Many kinds of failure can occur during a rocket launch. Orion's crew compartment will be a discreet cone-shaped capsule at the tip of the stack that can serve as an escape pod in the event of mid-flight explosions or control problems in the main booster assembly.
The shuttle has no such distinction between its crew compartment and the rest of the launch vehicle. The winged orbiter has three liquid-fuelled engines that share the thrust load with the rest of the launch stack, drawing fuel from the external tank.
This has always been a concern to Apollo veterans, used to the idea of a complete structural separation between the crew capsule and the tankage and propulsion systems. The CAIB noted that when the Moon-bound Apollo 13 spacecraft suffered an oxygen tank explosion in April 1970, the 'command module' at the front of the vehicle, though drained of power, was undamaged and eventually made a safe return to Earth.
Back to the future
Robert Seamans, NASA's deputy administrator in the Apollo era, was one of a dozen ageing veterans called upon to advise Orion's designers. "I served on what they called the 'Greybeard Committee,' all these old hands who knew how we'd reached the Moon first time around.
"Astronaut John Young was there and he'd flown in Gemini, plus two Apollo missions, and he'd commanded the first shuttle flight. We didn't fool around. They put us in a room from eight until five. They brought in food because there was no break for lunch. What we came up with is amazingly similar to what we did with the Apollo."
The Orion capsule and its upper stage will be launched on top of a solid rocket booster, as currently employed by the space shuttle. A lunar landing spacecraft, the Altair, will be carried to orbit, unmanned, aboard a heavy-lift rocket. Then the Orion and its crew will locate it in Earth orbit, make a docking and head to the moon.
On arrival, Altair will detach and drop down to the lunar surface. At the end of its surface mission the lower part of the Altair will stay behind while the upper crew module blasts back into lunar orbit, makes a rendezvous with Orion and transfers its crew. Then Orion heads back to Earth for an Apollo-style re-entry and recovery by parachute.
Is this forward progress, or a weird leap back in time? Robert Zubrin, formerly a senior engineer at Lockheed Martin and now a respected full-time lobbyist for human Mars missions, is not sure. "In the 1970s, when President Nixon closed down the Apollo program and ended lunar exploration, NASA said we would do all that again one day, after we had developed cheaper transportation to orbit using a winged shuttle.
"We've spent 30 years trying that, with mixed results. The shuttle costs more to fly than the Saturn V boosters that we had for the Moon missions. Now the shuttle is going to be replaced with a capsule just like Apollo."
The 'back to the future' technology for Orion is shaping up fast, but there is no guarantee that it won't be cancelled before it reaches the Moon.
NASA marks its many astonishing achievements over the last half-century with budgetary doubts clouding its future. John Logsdon warns that everything could change next year, when the Bush presidency comes to an end. "If the current proposals for human space exploration fail politically, then major programmes that depend on government spending could lose momentum.
"It's far from certain that we're going back to the Moon, let alone on to Mars. I think we are still struggling to answer the most basic question: why is the government in the business of sending people into space?"