Elena Scotti/FUSION

If you believe in the visions of the transhumanists, billionaire entrepreneurs, and eccentric visionaries who make up the private space exploration fraternity, the future of humanity lies not on Earth but in the depths of outer space. It is there that asteroids will be found and mined for their abundant minerals. Humans will colonize Mars, a back-up planet for when we’re done with this one. Tiny nanosatellites will bridge the four-year void to Alpha Centauri in the search for intelligent life, sent aloft on their lonely journey by the most powerful lasers ever built.

These things, it is hoped, will all happen within the next 50 years. And that will be only the start. The future of space exploration, backed largely by private enterprise, is so ambitious that it makes the Moon landing look like a cakewalk. That we haven’t sent anyone into space above low-Earth orbit since 1972 does not deter these dreamers of a new Space Age. That only men have been sent to the Moon, meaning that no women have been into deep space, appears to matter little, even though it means we haven't studied the biological effects of a long haul trip on future women Mars colonists.

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There are thousands of problems yet to be solved before we can start packing our bags for the first Mars colony and many experiments underway to solve them—but they won't matter if we no longer have the power source that probes need to get to deep space.

We're projected to run out of current stocks of that power source, plutonium-238, within the next ten years.

Plutonium-238 is a one-inch by one-inch radioactive pellet that's a byproduct of making nuclear weapons. In 1988, as the Cold War wound down, the US government stopped making it. Now we are almost out of it, with just enough left to fulfill NASA's mission schedule until 2026.

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The long, long road to manufacturing more of it presents one of the most pressing and difficult problems facing the future of space exploration—and even if we succeed, it still might not be enough to get us into deep space.

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United States Atomic Energy Commission, Elena Scotti/FUSION

Space exploration’s Achilles heel has always been money. It is phenomenally, insanely expensive to send people into space and only slightly less to send robots that don’t need food, water, or shielding from deadly radiation and cosmic rays. When America went to the Moon, NASA was allocated four percent of the federal budget to do so. But these days NASA gets just half of a percent.

The science your tax dollars are funding
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That's opened the door for private industry. In Silicon Valley, aerospace companies like SpaceX and Blue Origin are stepping into the breach, hoping to disrupt the industry and bring down mission costs significantly. It seems to be working, with SpaceX unveiling big plans to get to Mars by 2018 off the back of increasingly successful rocket launches.

Some problems though, are bigger than money alone.

Plutonium-238 is a radioactive isotope with a half-life of almost 90 years. It makes for an incredibly stable power source—essentially a very, very long-life battery—that can keep onboard communications systems running for decades at very great distances. Every probe from Voyager to Cassini and the Mars Rover has been accompanied by pu-238 running a radioisotope power system, and any future mission requiring a stable, long-life power source will need to be supplied with it—or something even more powerful.

Russia continued to produce pu-238 until 1993, and that’s to whom the USA turned to buy its last remaining reserves. Right now there is only around 35kg, or 77 pounds, of pu-238 left in the US, only half of which is in usable condition, the rest being too old to meet industrial standards. (The old stuff can be upgraded, but it's a slow, laborious and complicated process.) That ~17kgs is all NASA has left right now. That’s enough for three or four more robotic missions.

I asked SpaceX how the limited reserves of plutonium-238 would impact their plans for future Mars missions. Its marketing and communications department did not have a substantive response. “Sounds like an interesting piece but we’re not able to offer a comment, sorry about that,” the company responded.

There isn’t currently any real viable alternative to pu-238, despite intermittent, unsuccessful proposals to develop new isotopes. There have been enormous advances made in solar power systems, but they come with their own risks, as when the Rosetta comet probe lost power and went dark—something that would be catastrophic for any manned mission.

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There’s enough raw materials on Earth to make decades worth of pu-238, but it’s a daunting process to restart full-scale industrial production of nuclear materials in a time of non-proliferation. It’s also expensive. It will cost around $125 million to get production scaled up over the next ten years.

“This has been a slow-speed train wreck that could be and was predicted for the last several decades," said a senior ex-NASA engineer with experience on nuclear power advisory committees.

Still, all might not be lost.

At the Oak Ridge National Lab in Tennessee, Bob Wham is the project lead for an experimental program to ensure that future space missions are possible. Wham and his team, in consultation with the Department of Energy, hope to have full-scale production of pu-238 back up and running by no later than 2026.

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“What we’re doing here at Oak Ridge, along with Idaho and Los Alamos National Labs, is taking the lead to re-establish the capability to produce new amounts of plutonium 238," Wham told me. "And we’ve made a small amount.”

That small amount was 200gms, ~4.17% of the 4.8kgs needed for a single robotic mission.

It took three years.

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United States Atomic Energy Commission, Elena Scotti/FUSION

Through the atomic age up until 1988, America was producing large amounts of Plutonium 239, the primary isotope used in nuclear explosives, at the Savannah River K Reactor, the only reactor in the country with the capability to do so. When pu-239 is combined with another isotope, Neptunium-237, the result, in an extremely complex and delicate chemical reaction process, is Plutonium-238. When Savannah River went offline, it took NASA’s future stocks of the isotope with it.

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“That was shut down indefinitely,” says Ryan Bechtel of the Office of Space and Defense Power Systems at the Department of Energy, who works alongside the Oak Ridge team on the new pu-238 production program. “It was the end of the Cold War and it was no longer needed for its primary mission.”

It's one of the great ironies of the space program: to search the universe for new life, we rely on a human creation that has the power to extinguish it en masse. Before the development of the atomic bomb there was no surefire way for us to exterminate ourselves as a species. Since then we’ve created a queasy clutch of other existential threats to our survival—climate change, overpopulation, new communicable diseases—but nothing haunts our collective psyche like the specter of nuclear annihilation.

Nuclear production comes with many fraught downsides. Though we survived the Cold War threat of mutually assured destruction, peacetime nuclear accidents rank high among the most environmentally catastrophic events in history. Beyond this, how to safely dispose of nuclear waste that will remain radioactive for thousands of years remains a work in progress and a political nightmare: not too many people are comfortable with the idea of nuclear waste being moved through their local streets.

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At Oak Ridge, the team working to make new fuel for the space program aren't making weapons, but they are creating nuclear waste, which must be transported to the Waste Isolation Pilot Plant in New Mexico.

“It’s [moved there] with trucks,” Bechtel explains. “Specialized, very large shipping containers placed on specially marked, big trucks.”

The trucks, managed by the National Nuclear Security Administration, are just one part of a complex infrastructure that exists for the safe production, transportation and use of nuclear materials for space programs. It involves multiple state and federal regulatory bodies, international peace treaties, and the United Nations' Principles Relevant to the Use of Nuclear Power Sources in Outer Space.

Then there was the matter of who would pay for restarting the pu-238 program.

“There was a tug of war between NASA and the Department of Energy, and Congress, about who would pay for it, and Congress decided that NASA would fund the process,” Bob Wham told me. The cost is $15 million a year over ten years, which seems like a reasonable way to spend a small portion of NASA’s $19.3 billion in funding. Pu-238 is, after all, integral to the future of space exploration.

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Oak Ridge was chosen as the site to restart pu-238 production because it already contained the most complete infrastructure left over from nuclear programs that were once run there. Though it still requires some further building of reactor elements in order to be capable of full scale production:

“The hot cells at Oak Ridge we can use, they were empty and we’re moving new equipment into those hot cells,” Ryan Bechtel says. Hot cells are the sealed containment chambers inside reactors that allow workers to safely manipulate “hot”, or radioactive, materials.

“What we’re doing right now is that we’re building the equipment to place into those hot cells, and that will take several years.”

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United States Atomic Energy Commission, Elena Scotti/FUSION

Sending people into deep space will need a lot more power than sending robots. This is a major sticking point for getting people to Mars—a heavier payload being far more difficult and costly to send over vast distances. How to increase the power output of an onboard generator that will keep everyone alive, while keeping down the mass of the spacecraft carrying it, is what many plans for long haul manned missions are focussed on solving.

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“Manned missions require larger amounts of power," Bechtel explains. "A multi-mission isotope thermoelectric generator, which was the power source on the Curiosity rover, uses 4.4kgs of pu-238, outputting 110 watts of power. 110 watts is great for robots that can power cycle and tightly budget when they do certain kinds of activities, but it is not enough for a human being.”

This is another giant problem in itself.

While pu-238 is very stable—which is what makes it so appropriate for powering onboard instruments—it also has some drawbacks, one of which is that it is unlikely to ever be suitably powerful for manned missions. To manufacture a nuclear fuel source more powerful than plutonium means having to navigate the same departmental, environmental and political hoops as any other nuclear program in the search for an alternative.

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"Human missions would require a lot of power, and pu-238-powered systems, with their lower power output, would not be of much use,” Bechtel says. “Fission systems could be more useful for some of those applications.”

Testing a fission reactor as an alternative to pu-238 was demonstrated in an experiment at the Nevada Test Site in 2012: using highly enriched uranium (HEU)—what was in the bomb that destroyed Hiroshima—in a chain reaction that would produce a far more efficient, and powerful energy source. It would create a reactor that would itself go into space, perhaps to join the long dead one currently circling Earth at an altitude of 1300km—the first and only time the US sent a reactor into orbit, SNAP 10-A, in 1965. A system failure sent it dark after only 43 days in orbit, where it is now stuck, for at least 3000 more years.

While there is no shortage of highly enriched uranium stores,  broader public resistance to utilizing them for any purpose is intense, as it is for any nuclear production program that traffics in highly radioactive materials. As far as NASA and the Department of Energy are concerned, the focus currently is pu-238. Any more advanced programs involving uranium reactors are a long way in the future.

A NASA rep said further:

“NASA has a technology development project it is pursuing in partnership with the DoE to mature fission (uranium fuelled) power generation technology. These efforts are currently at the stage where research is being conducted to demonstrate the feasibility of the technology, through ground-based demonstrations of system components. Planned work will then demonstrate technology readiness of integrated fission power subsystems.

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More work would be necessary to prove the technology viable for a flight system.”

Then this is a bind. Even after making great headway in solving the pu-238 problem, there's an even bigger one looming after it: that we need something more powerful than plutonium to get people safely into deep space. And as of today, that is not a program that is yet in active production.

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United States Atomic Energy Commission, Elena Scotti/FUSION

For now, the only nuclear science program with permission to produce nuclear materials for civil space use is at Oak Ridge.

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On paper this doesn’t look super great. The plan at Oak Ridge to have production up to scale by 2026 will mean manufacturing 1.5kg per year—which means 3 years to generate enough pu-238 for a single robotic mission.

This might not be the amount of pu-238 being churned out with the giddy, unchecked optimism of decades past, but it is taking concrete, measurable steps towards addressing a big, big problem that has been stalking space missions for almost thirty years. If it succeeds in its aims, at least robotic missions of the future will still be possible.

Despite the impending crunch and tight deadline, NASA remains hopeful:

"Broadly speaking, the current U.S. inventory of plutonium-238 can support Mars 2020 and one to two additional future missions to be determined, such as potentially the next NASA New Frontiers mission. Meanwhile, the Department of Energy is making excellent progress in re-starting U.S. production of radioisotope fuel, while also producing the new pu-238 fuel pellets needed for Mars 2020."

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The byzantine hurdles presented by the pu-238 problem offer one of the clearest explanations for why getting off this planet is so difficult: there are hard physical limits to what can be done, and surmounting them can’t be achieved by sheer force of will or money alone, some things—like safely producing radioactive materials—take years to realize, which is why roadmaps for Mars and elsewhere in deep space are plotted in decades at a time.

Visions for a manned mission to Mars were first lodged in the public imagination in Collier’s magazine in the 1952. There, in the special issue, Man Will Conquer Space, Soon!, Werhner von Braun, chief rocket scientist on the Apollo missions (and repatriated ex-Nazi engineer) wrote,

What curious information will these first explorers carry back from Mars? Nobody knows—and it’s extremely doubtful that anyone now living will ever know. All that can be said with certainly today is this: the trip can be made, and will be made … someday.

With dreams of a manned-mission to Mars seemingly closer to reality than they have been at any time in the history of space exploration, it’s possible that people alive now who read this will see for themselves what those first explorers find when they do eventually get there. The byproducts of the most terrifying technology human beings ever created may fuel the moonshot visions of those among us who refuse to stay bound by the gravity of Earth.

Elmo is a writer with Real Future.