Like everything else about Apollo 11, the moon landing 45 years ago today was a calculated risk. Neil Armstrong would later say he thought the crew had a 90 percent chance of getting home safely from the moon, but only a 50 percent chance of landing safely on it.
Coming in from 50,000 feet with no atmosphere to support a parachute, Armstrong and Buzz Aldrin had to rely on thrusters to slow the Eagle lander to a safe touchdown. It was a "controlled fall" in the words of writer Andrew Chaikin, and the NASA team's foreboding was justified. The onboard computer in charge of thrust and direction overloaded shortly after the descent began. The Eagle was heading toward a field of boulders, and Armstrong had to take control and manually fly in search of a new landing site.
Would there be enough fuel to get to a safe place? And considering that thrust to one side of Eagle or the other was the only way to change direction, could Armstrong guide the tiny craft without tipping it over? Buzz Aldrin counted down the altitude as Eagle approached the lunar surface and then, silence.
After a few heart-stopping seconds, Armstrong radioed back the first of his iconic statements that day: "Houston, Tranquility Base here. The Eagle has landed."
A Houston mission controller replied, "You got a bunch of guys about to turn blue, we're breathing again." On television, Walter Cronkite took off his glasses, shook his head, looked at his desk and smiled.
The landing came July 20, 1969 at 3:17 a.m. CDT with 30 seconds of fuel left in Eagle's tank. It was just that close. Armstrong would leave the landing module seven hours later to become the first human to step onto another celestial body.
Armstrong would later insist that he meant to say - and thought he did say - "That's one small step for a man, one giant leap for mankind" - but what the world heard was "That's one small step for man, one giant leap for mankind." The missing "a" bothered English majors, but the larger point was clear. In a brilliant, expansive sentence not approved by NASA in advance, Armstrong claimed the moon for "mankind," not for America. The world claimed the event right back as a great step for humanity.
How big a day?
How big was that day 45 years ago today? Maybe the answer lies in another question. What event is bigger? Speaking on the occasion of Armstrong's death in 2012, Smithsonian Institution space curator Roger Launius told the Associated Press that two events from the 20th century will be remembered as long as there is human history: the invention of the atomic bomb and Armstrong's step on the moon.
"There is no way to overestimate that significance in human history and he is forever linked to that," Launius said of Armstrong.
"We may be living in the age of Armstrong," said historian Douglas Brinkley in the same article. Brinkley is an expert in 20th century history.
Believers in Apollo 11's unique significance point first to the time it happened. It was 1969, the end of one of the most tumultuous decades in American history. The nation was locked in a Cold War with the Soviet Union and a hot war in Vietnam. People took their grievances to the streets. The president who sent America to the moon, John F. Kennedy, had been assassinated, and so had Dr. Martin Luther King, the man who tried to lead the country to peaceful integration. It sometimes seemed nothing was going right, but here was something going spectacularly right.
Kennedy's funeral notwithstanding, the moon landing was the first global media event. An estimated 600 million people, one out of 5 on the planet, watched it, according to the Associated Press. We were for one day one planet.
Apollo 11 also proved that the impossible could be made possible, historians say, and it created a phrase still heard in America today: "If we can send a man to the moon, why can't we ...?"
What happens next
Why did the sense of triumph so quickly give way to the near-collapse of the space program? Why were the last three Apollo missions canceled, and why isn't America traveling routinely to the moon today?
Those are harder questions to answer, and to NASA they aren't the important questions. Here's NASA manager Jay Greene speaking on the 20th anniversary of Apollo 11 in 1989. "It's something we did that was really wonderful. It's not sad,'' Greene said. "I guess what's sad is the fact that there's nothing like Apollo in the future to look forward to. That's sad.''
A big mission is what makes NASA work and young people want to join it, and NASA says it has a mission like that today. The agency is building a new rocket - the Space Launch System - to go back into deep space. The rocket passed a critical design review this summer.
"I understand what happened in Apollo, and I got to see what happened on the (space) shuttle," NASA manager John Honeycutt said last week. "I got to experience the highs and lows, and there is nothing like the thrill of all your hard work coming to fruition when that rocket lifts off the stand. Then you go do it again."
Honeycutt is deputy program manager of the Space Launch System, and he says his job is not only building the new rocket. It's also to "set the foundation" for the next generation of rocketeers.
Honeycutt appreciates what the Apollo generation did. "Cheating gravity ain't easy," he said of the team at Huntsville's Marshall Space Flight Center. "The little things will get you. The devil's in the details. You've got to pay attention to what's going on in every aspect."
But like NASA today, Honeycutt's message is about the future. "We're really building this rocket," he said by telephone from the Michoud Assembly Facility at New Orleans, where it is taking shape. "This is a rocket that can take us to Mars."
(Updated July 21 to correct the landing time on the moon)