WASHINGTON » The measure of what humanity can accomplish is a size 9 1/2 boot print.

It belongs to Neil Armstrong, the first man on the moon. It will stay on the moon for millions of years with nothing to wipe it away, serving as an almost eternal testament to a can-do mankind.

Apollo 11 is the glimmering success that failures of society are contrasted against: “;If we can send a man to the moon, why can't we ...”;

What put man on the moon 40 years ago was an audacious and public effort the world has not seen before or since. It required rocketry that had not been built, or even designed, in 1961 when President John F. Kennedy declared the challenge. It needed an advance in computerization that had not happened yet. NASA would have to learn how to dock separate spaceships, how to teach astronauts to walk in space, even how to keep them alive in space—all tasks so difficult experts were not sure they were possible.

Forty years later the moon landing is talked about as a generic human achievement, not an American one. But Apollo at the time was more about U.S. commitment and ingenuity.

Historian Douglas Brinkley called the Apollo program “;the exemplary moment of America's we-can-do-anything attitude.”; After that, America got soft, he said, looking for the quick payoff in a lottery instead of the sweat equity of buckling down and doing something hard.

In years since, when America faces a challenge, leaders often look to the Apollo program for inspiration. In 1971, when President Richard Nixon declared a war on cancer, his staffers called it “;a moon shot for cancer.”; Last year, then-candidate Barack Obama and former Vice President Al Gore proposed a massive effort to fight global warming, comparing it to Apollo 11.

Those still-unfinished efforts recall May 25, 1961, when Kennedy, fresh from a disastrous Bay of Pigs invasion of Cuba, announced America would land a man on the moon by the end of the decade and return him safely home.

“;I thought he was crazy,”; said Chris Kraft, when he heard Kennedy's speech. Kraft was head of Mission Control, the man responsible for guiding astronauts to orbit (which had not been done yet) and eventually to the moon.

“;We saw that as Buck Rogers stuff, rather than reality that would be carried out in any time period that we were dealing with,”; he said recently in Houston.

Less than three months later, Kraft was in the White House explaining to the president just how landing on the moon would be done, though he still did not believe it would work.

It was the Cold War, and Russian Yuri Gagarin had just become the first man in space. Kennedy chose landing a man on the moon because experts told him it was the one space goal so distant and complicated at the time that the U.S. could catch up and pass the Soviet Union, Kennedy adviser Ted Sorensen said.

The idea in a world where American capitalism was pitted against Soviet communism on a daily basis was “;to prove to the world which system was best, which one was the future,”; Sorensen said.

Kennedy said America would go to the moon and try other tasks “;not because they were easy, but because they were hard. Because that goal will serve to organize and measure the best of our energies and skills.”;

They were not just skills with rockets and slide rules. Bringing together aerospace companies, engineers, scientists, technicians and several NASA centers around the nation was a management challenge even more impressive than building the right type of rockets, said Smithsonian Institution space scholar Roger Launius.

And it cost money. The U.S. spent $25.4 billion on the Apollo program, which translates to nearly $150 billion in current dollars.

Yet, in the view of those heavily involved in the challenge, what made Apollo work was two tragedies: the assassination of Kennedy in 1963 and the fatal Apollo 1 fire in 1967.

The assassination made the program and its budget nearly untouchable. The moon-landing goal became a symbol of the president. The fire, which occurred in ground testing, killed three astronauts.

Kraft said he is convinced NASA could not have reached Kennedy's target were it not for the Apollo 1 fire and the way it made the space agency rethink everything. “;You really learn from failure.”;

So NASA drilled astronauts and flight controllers ceaselessly with simulations. Failures kept being thrown at the astronauts and the controllers, some just plain unsolvable.

One of the last failures simulated before Apollo 11's launch was an alarm on the lunar lander that signaled the computer was overloaded. During the simulation, Mission Control aborted the landing. But controllers were later told it was just an “;indication”; signal and that if they had thought about it, the computer was working fine.

During the real mission, as the Eagle lunar lander approached the moon, that computer signal appeared. This time controllers knew everything was OK. They didn't abort the landing.

Still, there were more hurdles to come. In another example, experience and nerves paid off. As Eagle neared the landing area in the spot called Sea of Tranquility, Armstrong saw too many boulders and craters to come down safely. So he kept flying horizontally, scouring the moonscape for a smooth place.

Eagle's fuel tank neared empty. Alarms went off.

“;We still needed to get down,”; recalled Edwin “;Buzz”; Aldrin. “;I'm not telling Neil, 'Hey Neil, hurry up, get on the ground.' I'm sort of conveying this with body English.”;

There were only 17 seconds' worth of fuel left.

Finally, the radio at Mission Control crackled with Armstrong's voice: “;Houston, Tranquility Base here. The Eagle has landed.”;

Two hours later, humans walked on a place other than Earth. The world watched on TV as the first men walked on the moon.

Decades later, Armstrong called his first words on the moon “;a pretty simple statement, talking about stepping off something.”;

But Armstrong was not merely talking about that small step of his. What came next was the big deal. It was, as he said on the moon 40 years ago, “;a giant leap for mankind.”;

It still is.