Thirty years after first blasting into space, NASA’s space shuttle came to the end of the road in 2011.
A final launch of Atlantis in July saw the retirement of America’s only manned space fleet, and with it, for the moment, any US capability to put humans into orbit.
Together the Shuttles had flown a combined distance of around half a billion miles - equivalent to five return trips to Mars when at its closest!
Crewed missions to the International Space Station now depend on a deal with Russian Soyuz craft. NASA, in financial crisis, has no replacement of its own ready and seems instead to be relying on private enterprise eventually coming to the rescue, for example the Dragon manned capsule being developed by Space X.
Since 1981, when Columbia first flew in space, the Shuttle has been the world’s only reusable spaceship. It has proved a trusty workhorse, used as an orbiting laboratory, to build the space station, launch probes to other planets and to repair satellites.
Five Shuttles were built for space - Columbia, Challenger, Discovery, Atlantis and Endeavour - plus a prototype Enterprise. Sadly two - Challenger and Columbia - were lost in disasters that left America reeling.
The Shuttle was introduced as a replacement for a previous series of single-flight spacecraft which had culminated with the Apollo capsules that carried men to the Moon. What made it different, of course, was its concept as a reusable fleet of spaceships that could fly into orbit, return to Earth, and then be prepared for a new mission. The original optimistic hope was that a mission would eventually fly every week.
This was closer to spaceflight as portrayed in science fiction, though the sheer amount of rocket power needed to lift a Shuttle into orbit means we have still not reached a stage where spaceports can operate with anything like the efficiency of airports.
The project to build the space shuttle was agreed by President Richard Nixon while Apollo missions were still visiting the Moon in 1972 but the idea of reusable spacecraft was conceived in the 1950s if not even earlier.
US plans for experimental spaceplanes including the delightfully named X-20 Dyna-Soar became quite advanced, though this design never actually flew.
There was much competition to design and build the Shuttle once the concept was announced. Practical considerations led to accepted mix of a reusable spaceship plus conventional rocket launchers, though two solid boosters are retrieved from the sea after each launch to be dismantled and reused. The main, giant orange external tank is jettisoned much higher in flight and burns up. Earlier designs which would have seen this piloted back to Earth for reuse were abandoned.
After typically spending two weeks in orbit, the Shuttle itself returns to Earth, insulation tiles on its underside protecting craft and crew against the searing heat of re-entry, before it glides to a steep landing on a runway, much like a conventional aircraft, ready to be prepared for its next mission.
Before any Shuttle flew in space, a prototype was built and named Enterprise by popular demand from fans of Star Trek. Flight tests were carried out at subsonic speeds in the atmosphere with the Enterprise being released from a piggyback position on a NASA Boeing 747 jumbo jet.
The first real test came with the first launch of Columbia into space on April 12, 1981. Piloted by a two-man crew, it returned two days later to land at the Edwards Air Force Base in California. Three further test flights were carried out by Columbia before she flew her first proper mission to deploy two commercial satellites.
Since then it has carried its own European-built laboratory module, Spacelab, deployed and repaired satellites and delivered into orbit, and subsequently repaired and maintained in a series of daring missions the Hubble Space Telescope which has been such a vital ambassador for astronomy.
Unmanned spaceprobes launched into the solar system from the Shuttle include Magellan to Venus, Ulysses to study the Sun, and Galileo to a highly successful rendezvous with Jupiter, allowing us to explore that giant planet and its fascinating system of moons.
Early on, shuttles paid regular visits to a Russian orbiting outpost called Mir. More recently and most famously it has been essential in building the International Space Station, regularly adding modules like a giant Lego kit. That work is virtually complete.
As already mentioned, the Shuttle program was marred by two tragic disasters - the losses of Challenger and Columbia which killed a total of 14 astronauts.
The first came in January 1986 when Challenger exploded just 73 seconds after launch. Seven astronauts including a schoolteacher Christa McAuliffe perished. The accident was blamed on a rubber seal failing on a fuel tank after a rare icy night in Florida.
America suffered its second Shuttle disaster in February 2003 when Columbia broke up on re-entry, killing seven astronauts and showering fragments over Texas. This catastrophe was blamed on damage caused to the leading edge of a wing when insulating foam fell from a fuel tank during launch.
Inquiries revealed that both accidents had been entirely preventable and symptoms of a complacency that appeared to have pervaded NASA. But they were also a reminder of the risks that all brave men and women run as they cross the final frontier.
As the 135th and final Shuttle mission approaches, with the number of astronauts carried topping 350, the cost of the programme is reckoned to be approaching $200 billion.
Under President George W Bush, NASA had plans to follow up with a return to the Moon to build a permanent manned colony before moving on to Mars. However, his Constellation program, with its development of Apollo-style Ares rockets, an Orion capsule and lunar lander called Altair, seemed effectively cancelled by President Obama.
Under new leadership, NASA handed over the business of delivering astronauts and servicing the space station to private enterprise - new spacecraft and launch vehicles are currently being designed and tested for low Earth orbit by Blue Origin, the Sierra Nevada Corporation, Space X and Boeing.
NASA itself will focus on building spacecraft and technologies to fly humans first to an asteroid and then to Mars. The agency revealed on May 25 that the spacecraft chosen to carry these brave pioneers will be based on the Orion spacecraft showing that development of that by Lockheed Martin had not been wasted or abandoned.
Some argue that the Shuttle period and accompanying focus on the International Space Station has been something of a distraction for the US, keeping mankind moored to Earth when we could have been exploring more of the Moon or venturing out to Red Planet Mars.
But supporters point to the experience we have gained in long-duration spaceflight and its effects on humans, plus technological and medical advances that benefit the folks back on Earth.
The one thing everyone is left wondering is just when astronauts will lift off from US soil again.
Last updated 3 January 2012