In retrospect, it was an unlikely set of conditions that came together to produce the Space Age. Not just the postwar blend of prosperity and paranoia, but a series of scientific breakthroughs, both pure and applied, that happened in such close succession that we nearly had a surplus, one that had to be invested in something.

We had to know our world well enough to be able to escape it, but not so well that we couldn’t ignore the price we were paying. And now that window may be closing.

Here are two stories that have me in an elegiac mood. “This Used To Be the Future” is a photoessay by Rachel Sussman that looks at NASA’s Ames Research Center in Silicon Valley. Most stories about Ames focus on the cutting edge stuff, the public/private partnerships; Sussman focuses on the old stuff, the military leftovers, the junk.

Next is a piece in Scientific American on plutonium-238. NASA uses the slow-burning plutonium to power its long-range probes and interplanetary craft.

Over the past half-century, NASA has used a total of 140 kilograms of Pu-238 to push the frontiers of exploration. Coupled to one of the agency’s “thermoelectric” generators that convert heat into electricity, four kilograms of the stuff can power a spacecraft for decades. Pu-238 was used in Apollo-era science experiments on the Moon, in the Galileo mission to Jupiter and in the Pioneer and Voyager space probes now exiting our solar system. Hefty hunks of Pu-238 power the Mars Curiosity rover, the Cassini orbiter at Saturn and the New Horizons spacecraft now roaming beyond Pluto. In the future, Pu-238 could power robotic probes to burrow beneath the ice of ocean-bearing moons, planes to fly in the alien atmospheres of other worlds, ships to sail the liquid ethane seas of Saturn’s moon Titan and much, much more. Those future missions can only occur if there’s enough plutonium to go around. Practically all of NASA’s Pu-238 stockpile was made as a byproduct of building nuclear weapons during the Cold War. As the Cold War wound down, so too did the Department of Energy’s Pu-238 production; it made its last batch in 1988, shutting off NASA’s supply save for occasional deliveries of small, lower-quality batches from Russia that ceased in 2010. At present, only about 35 kilograms of Pu-238 are left for the space agency, and radioactive decay has rendered all but 17 kilograms too weak to be readily used in NASA’s thermoelectric generators. NASA and DOE officials estimate there is only enough for four more generators, one of which is already committed to NASA’s upcoming Mars 2020 rover.

The plutonium shortfall makes it impossible for NASA to plan future missions that would require it, but in the absence of specific mission needs, nobody wants to make any more. Solar-powered craft could eventually fill in the gap, but the technology’s not there yet.

So the stars get further and further away.

Jonathan Hickman is currently writing Secret Wars for Marvel, but the roots of that story go back to his earlier run on Fantastic Four. There’s a great scene where Reed Richards, Mister Fantastic, resigns from the Singularity Conference (think TED/O’Reilly/Davos on steroids), a group of scientists he founded, as they argue for increasingly limited approaches to exploration.

The other scientists are basically correct. It is irresponsible to fund manned space missions in a global recession. Our global population may be impossible to sustain on our planet going forward. But Mister Fantastic, being a superhero, rejects the premise. “The future of man is not one billion of us fighting over limited resources on a soon-to-be-dead planet, but one trillion human beings spanning an entire galaxy,” he says. “The future of man is not here. It is out there. Because it’s our new horizon. Because it’s what’s next.”

It’s a corny, Sorkin-esque speech…. but I love it. It thrills me. And it makes me afraid.

I would like to think that that time isn’t over yet, that there is a way to reconcile what we know now with what we were willing to risk for the sake of knowledge then — that if not in outer space, then in medicine or genetics or some other field. But part of me wonders if the time for us to come together to do big things — that space age, that Marvel Age, that time of the Fantastic Four — is over. And all that’s left is how we manage our decline.