"Because our mission is flight in all its forms, in space and in the air, we think and work in our engineering and our science at the extremes -- and that's where the greatest discoveries are made," NASA administrator Michael Griffin said in a speech last year.

NASA began to conduct space missions within months of its creation on October 1, 1958.

"Over the last 50 years NASA has undertaken spectacular programs in human spaceflight, robotic spaceflight, and aeronautics research," Steve Dick, the chief historian of the US space agency, said.

NASA programs, such as the six Apollo missions which ran from 1969 to 1972 and saw a total of 12 US astronauts set foot on the moon, not only helped to promote scientific advancement but also had a huge impact on how humans see their planet.

"The effect of the Apollo program was profound, no more so than in its view of earth from the moon," Dick said.

"The photographs of 'Earthrise' and the full earth as a blue marble suspended in space, fragile and without national boundaries, changed humankind's view of earth forever," he said.

After Apollo, which was the US response to the Soviet Union's launch in 1957 of Sputnik the first artificial satellite to orbit the earth, the Americans and Russians entered into a less competitive era in space.

That era reached a high point in 1975 when Apollo and Soyuz capsules docked together in space, signalling the start of the development of the International Space Station (ISS).

In 1998, the first two modules of the ISS were launched and joined together in orbit. Other modules soon followed and the first crew arrived at the space station in 2000.

The next major era in the conquest of space began in 1981, with the inaugural flight of the space shuttle, the first spacecraft capable of launching into orbit like a rocket and then returning to earth as a glider.

With the space shuttle, NASA was able to ferry large parts into space to build the ISS, where experiments conducted in micro-gravity have helped to move mankind closer to long-duration stays in space.

The space shuttle has also been used to launch satellites and astrophysics instruments, such as the Hubble telescope, which has sent back to earth spectacular pictures of stars, planets, galaxies and nebulae.

"Collectively, NASA astronomy and astrophysics spacecraft, from the early probes of the 1970s and 1980s, to the great observatories of the 1990s and the 21st century, yielded the secrets of cosmic evolution from the big bang to the present," said Dick.

Instruments carried into space by the "Cosmic Background Explorer" or COBE (1989-1993) yielded major cosmological discoveries and helped scientists to understand how galaxies and galaxy clusters are formed.

NASA physicist John Mather shared the Nobel prize for physics in 2006 with University of California at Berkeley scientist George Smoot for work that "looks back into the infancy of the universe and attempts to gain some understanding of the origin of galaxies and stars," the Royal Swedish Academy of Sciences, which awards Nobel prizes, said.

The prize-winning work was "based on measurements made with the help of the COBE satellite launched by NASA in 1989," the academy said.

Nine of the 25 top scientific breakthroughs of the past quarter century have come from space, and eight of them directly from NASA, Griffin said.

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