As the first person to set foot on the Moon, Neil Armstrong was a global icon who symbolized the greatest triumph of mankind’s pioneering spirit. He had all the attributes one would expect of an astronaut: bravery, professionalism, technical skill and composure. What separated him from the rest, according to those who knew or studied him, was a surreal confidence — it was with legendary aplomb that he manually guided a fuel-depleted lunar module to the surface of the Moon — and a humility that was both refreshing and inspiring.

It was partly because of these qualities that he became the world’s ambassador to the heavens. Luck also played pivotal a role: Many things had to fall into place for Mr. Armstrong to earn his place in history, including a series of precursor missions that, had any of them gone differently, would have handed someone else the opportunity. He also had a large and immensely capable supporting cast at NASA and in industry, engineers and scientists armed with tools that were utterly primitive by today’s standards. Underlying it all was a bold presidential mandate, issued in the heat of a Cold War competition with the Soviet Union.

Mr. Armstrong’s aversion, or at least indifference, to the spotlight was well documented over the years — he never sought to leverage his fame, be it for financial gain, ego gratification or influence. So it was a bit surprising when, in April 2010, he joined the chorus of voices against the direction U.S. President Barack Obama had chosen for the nation’s human spaceflight program. The president’s plan, unveiled just two months before, entailed canceling the Moon-bound Constellation program, outsourcing crew transport to and from the international space station, and investing in technologies that might someday make deep-space exploration easier.

It’s not hard to see why the Mr. Armstrong signed, along with fellow Apollo astronauts James Lovell and Eugene Cernan, an open letter of protest to President Obama: He clearly felt strongly about America’s spaceflight future, and the letter cast the Obama plan as a step backwards with no credible path to new frontiers. These concerns were not unreasonable, even if the letter overlooked the fact that Constellation in all likelihood would have required far more funding than NASA could reasonably expect and as a result would have severely eroded budgets for other agency programs.

Recent developments have fueled hopes that independent U.S. crew access to space will be restored in five or so years, but the nation’s post-space station future in human spaceflight is murky at best. President Obama has targeted an unspecified asteroid as the next destination for human space explorers, while Congress has directed NASA to develop vehicles capable of taking astronauts beyond low Earth orbit. But there’s no cohesive strategy, and given the current political and budgetary environment, it is difficult to envision a realistic plan for meaningful exploration emerging anytime soon.

Things aren’t looking much brighter in robotic exploration, the realm in which NASA has arguably done the most to expand humankind’s frontiers in the decades since Apollo. NASA recently showcased its unparalleled technical chops by landing a 1-ton, nuclear-powered rover on the surface of Mars, but has shelved all future plans for planetary missions of that scale.

NASA is willing and able, as the Curiosity Mars rover landing proved, but the appetite for risk among the agency’s political masters has dwindled amid a grim fiscal forecast and the absence of a compelling political rationale.

It is understandable — indeed inevitable — that many will view Neil Armstrong’s passing as another reminder that the nation has yet to match, let alone surpass, its Apollo-era achievements, and of the self-imposed paralysis that has quashed any hopes of doing so in the next two decades. But such an observation also speaks eloquently to the magnitude of the accomplishment and, in turn, to the immense power of political and national will. If the reaction to Mr. Armstrong’s death — and to Curiosity’s landing just a few weeks earlier — is any indication, the urge to explore is still very much a part of the human psyche. The challenge is finding a way to harness that impulse.