Copyright © 2018 Albuquerque Journal
It’s been more than 50 years since NASA has created a nuclear fission reactor fit for space.
In 1965, the SNAP-10a program, a pump system designed to create electricity for a year, was launched into orbit for tests. It lasted only 43 days.
New concepts for nuclear reactors that would have the ability to generate power for long-term space missions stalled in the 1970s, according to David Poston, a scientist at Los Alamos National Laboratory. Designs hit roadblocks due to high costs or complicated mechanics.
In the most advanced testing any model has reached in four decades, scientists from LANL and NASA recently put their Kilopower reactor – a small system they say opens doors for astronaut outposts on the moon or Mars, as well as quicker, more efficient scientific missions into deep space – through its paces.
“Now that we’ve shown we can build reactors, test them and potentially fly them, a lot more exploration is coming back on the table,” said Poston, the project’s chief reactor designer.
He described Kilopower as a “huge” breakthrough for space exploration.
In May, LANL announced the success of a test run known as Kilopower Reactor Using Stirling Technology, or KRUSTY, that was conducted at the Nevada National Security Site from November to March.
The Kilopower reactor itself has been in the works for about five years, Poston said. LANL scientists have been working with NASA employees at its Glenn Research Center in Cleveland.
Kilopower generates electricity by using heat produced in the reactor’s uranium core. That heat is conducted to several pipes, or sealed tubes, full of liquid sodium. That liquid turns into vapor, which is transferred to the cold end of the heat pipes, condensed and transferred to Stirling engines that act as “power conversion systems.” The heat pressurizes gas to drive a piston coupled to a motor that generates electricity.
The team is confident Kilopower reactors could last 15 years in space.
Unlike designs such as SNAP from decades ago, which used pumps to transfer the liquid and exchange heat – taking up extra energy – Kilopower is physics-controlled, meaning the pipes transfer the heat on their own.
“The less moving parts you have, the longer it should last,” said Marc Gibson, the lead Kilopower engineer at the Glenn center. He said this and the reactor’s “simplified” system is what attracted NASA.
Kilopower can produce one kilowatt of electricity – just about enough for a toaster – with the prototype that LANL and NASA tested, and would generate up to 10 kilowatts when made to scale. Four of those large reactors would match NASA’s estimated 40 kilowatts needed to sustain a four-person outpost on Mars or the moon. Smaller-scale reactors could be used for missions to Jupiter or Pluto, where solar power wouldn’t be as effective.
According to Gibson, an energy system independent from the sun could also enable missions to permanently shadowed craters on the lunar surface. Poston said there are areas at the moon’s equator where one night is equal to 14 Earth days.
The KRUSTY tests were intended to show whether the prototype could produce electricity, but also to test Kilopower’s “dynamic performance,” or how it would perform when faced with various challenges, according to Poston. He said the team threw all sorts of tests at the reactor, including reducing or doubling its power output and simulated failures with one of its engines or heat pipes.
In all the tests, he said, Kilopower was able to self-adjust and stay at a stable temperature to prevent the core from overheating or melting.
“The dynamic performance of the reactor was better than we dreamed of,” said Poston. “The testing showed the heat pipe reactors offered predictable and robust performance.”
The one-kilowatt reactor in the KRUSTY tests was about one meter tall and half a meter in diameter, according to Gibson, who estimated a 10-kilowatt model would be three meters tall and one meter in diameter. Artist renderings of Kilopower include umbrella-like heat radiators atop the reactors.
The idea for Kilopower came from 2012 tests at LANL called Demonstration Using Flattop Fissions, or DUFF, a simpler system that used then-new heat pipe technology.
Kilopower was also designed with parts and technology that the scientists had easy access to, said Poston. He said this is why it was able to be produced and tested, unlike many predecessors.
He used a “Ferrari versus Model-T” analogy to describe the difference between NASA’s other proposed models compared with the less complicated Kilopower.
Gibson acknowledged NASA has seen “several failures” in reactor development since its SNAP reactor was sent into orbit in 1965, and much of it came down to thinking too big.
“People who were within NASA (were) trying to build really sporty, big expensive power systems on the reactor side and ultimately failed to keep a budget in the time needed to develop that and physically get it into space,” he said. “That’s probably the biggest point of why several decades of reactor development never got anywhere.”
The KRUSTY experiment cost $18 million over the past three-and-a-half years, while other nuclear power projects have reached hundreds of millions.
As for the safety of the small uranium core – about the size of a paper towel roll – Patrick McClure, LANL’s Kilopower project lead, said that before the reactor is turned on, which occurs in space, there is only a small amount of naturally occurring radioactivity coming from it.
“Until you turn it on, you can go up and touch it. You can stand right up next to it, you can be there, you can handle it. It doesn’t really hurt anyone.” Final designs of the reactor will include radiation shields to protect astronauts and electronics, Poston said.
The next steps for Kilopower are to adapt the model for space flight. Gibson said it could be sent out with a space mission within the next few years, depending on NASA’s plans.
Gibson said outside factors, such as funding and NASA officials agreeing on what missions to undertake, make it difficult to predict how far away NASA is from groundbreaking missions like long-term travel to the moon or Mars with the help of reactors like Kilopower. But he added that “technology-wise, I think we’re within this decade of being able to see that.”
Poston said he is also excited about what a successful reactor like this one could do for the larger future of humanity.
“I’m a big fan of expanding the presence of humanity in space,” Poston said. “Not only for the knowledge and the inspiration, but also as an insurance policy for the long-term survival of the human race. If you think really big-picture, this is a step toward that, because we’re going to need nuclear power if we’re going to do any sort of serious exploration or expansion into space.”