Neil Armstrong's moon landing was surely one of the 20th century's most iconic events. None of us who watched those grainy images on our television screens will ever forget the moment.
The space program was full of promise in those days. It was widely believed that Armstrong's "giant leap for mankind" was merely the first step in our voyage to the stars.
The sky was truly the limit. Or so it seemed to be. Yet that was 43 years ago, and no significant progress has been made. Is it possible that Armstrong, who died on Saturday at 82, took not a first step, but a last?
Yes, a handful of astronauts re-enacted his feat. The youngest one still living was born in 1935.
The assumption that a new frontier awaits us has not proved out. The enthusiasm of that earlier era is gone.
Indeed, if anyone is going to begin colonizing other worlds, it seems more likely to be a robot than one of us. A new fact-finding visitor touched down on Mars three weeks ago.
But the Curiosity rover is a machine. The nearest human being was 250 million kilometres away at the NASA control centre in Pasadena, California.
Part of the problem, of course, is the sheer immensity of our solar system. It takes an automated probe five years to reach Jupiter, twice that long to visit Pluto. And that's just one way.
A return trip to Mars requires at least two years with current technology, time on the surface included. And even then, huge obstacles remain, cosmic radiation and the debilitating effects of prolonged weightlessness among them.
But the real challenge, perhaps, has more to do with psychology than physics. Our tolerance of danger is diminishing.
In the early stages of the space program, risks were taken that would never be accepted now. The computers used in the Apollo 11 moon landing were less powerful than a modern cellphone.
As the lunar module descended toward the surface, its navigation program crashed. Armstrong had to fly the ungainly vehicle manually, setting it down with less than 30 seconds of fuel remaining.
A recent assessment of the space shuttle program concluded that the early missions ran a one-in-nine chance of catastrophic failure. Two of the craft were ultimately lost, along with 14 crew members.
And in earlier times still, explorers willingly faced staggering odds.
Amelia Earhart attempted to fly around the globe with a guidance system that amounted to little more than looking out the window.
No government today would accept such risks, nor survive the condemnation if it did. Perhaps we know too much.
Some of the most famous voyages of discovery were carried out in ignorance. Columbus found the new world by mistake. He thought India lay on the western shores of the Atlantic.
John Franklin perished with all his crew trying to find a northwest passage that, practically speaking, wasn't navigable with wooden sailing ships.
By comparison, we understand all too well what the wider exploration of space entails. Over the last 50 years, there have been 39 attempts by various nations to send automated vehicles to Mars. Of these, 24 failed.
Some missed their target and flew on into space. Several crashed on the surface. A few didn't even make it out of Earth orbit.
There are, in short, a lot of routes to disaster. If our nerve has failed us, perhaps we have good cause.
Only time will tell, of course. Roll the clock forward another 43 years, and who knows where we'll stand?
But one thing seems clear. Armstrong's passing marks the end of an extraordinary period in our history.
He really did boldly go where no one had gone before.
