Sen—Fifty years ago today, America was set an extraordinary challenge. To put a man on the Moon by the end of the decade.

The challenge came from the then President of the USA John F Kennedy in a powerful speech at Rice University in Houston, Texas.

In words that are now part of history, he said: "We choose to go to the Moon. We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard..."

The speech came 16 months after Alan Shepard had been rocketed on a sub-orbital trip to catch up on the Soviet achievement of putting the first man in space, Yuri Gagarin, in April 1961. And those events had come less than four years after the first satellite, Sputnik 1, had been put in orbit by the USSR.

Yet amazingly NASA was able to meet the President's challenge in less than seven years with the landing of Apollo 11 astronauts Neil Armstrong and Buzz Aldrin in July 1969. Another ten men were to walk on the Moon's surface before the Apollo programme was terminated abruptly in the wake of public apathy.

It had been a fantastic achievement - even including the dramatic rescue of the Apollo 13 crew following an explosion mid-flight. And who could have guessed that the giant leap for mankind would become a faltering step on the road to the stars with no further visits to the lunar surface?

J F Kennedy makes his inspiring speech at Rice University. Credit: NASA

Advances have, of course, been made with the development of the space shuttles and the construction and continued maintenance of the International Space Station, though they have kept astronauts in low Earth orbit.

Perhaps more spectacular have been the unmanned missions, with robotic probes successfully exploring the Solar System, either on tours of the planets or on specific visits to the Moon, Mercury, Venus, Mars, Jupiter, Saturn and the asteroids.

Probably all these missions were born at least in part on the inspiration from Kennedy's speech. It included the words: "Those who came before us made certain that this country rode the first waves of the industrial revolutions, the first waves of modern invention, and the first wave of nuclear power, and this generation does not intend to founder in the backwash of the coming age of space. We mean to be a part of it - we mean to lead it.

"We set sail on this new sea because there is new knowledge to be gained, and new rights to be won, and they must be won and used for the progress of all people. For space science, like nuclear science and all technology, has no conscience of its own.

"Whether it will become a force for good or ill depends on man, and only if the United States occupies a position of pre-eminence can we help decide whether this new ocean will be a sea of peace or a new terrifying theatre of war."

Tragically, Kennedy was assassinated little more than a year later in November 1963, so was never able to see his challenge achieved thanks to possibly the most focused efforts ever on achieving progress in space.

Apollo 11's Buzz Aldrin with an experiment on the lunar surface. Credit: NASA

NASA TV is marking the 50th anniversary of Kennedy's speech by broadcasting a high-quality version of the address at precisely the same time, 11.15am EDT. The NASA website will also carry a special blog from NASA Administrator Charlie Bolden plus informations about NASA's future exploration programmes.

A message about the speech from NASA astronaut Suni Williams on board the International Space Station will also be broadcast. And at 3 pm, NASA astronauts, scientists and engineers will hold a Google+ Hangout to discuss NASA's past and future plans.