Officials from the project discussed the system during a briefing from the National Atomic Testing Museum in Las Vegas. They said the test, which began in November 2017 and will continue through March, is showing the Kilopower project could provide safe, efficient, and plentiful energy needed for future space missions.
“With this technology, I really think we are at a breakpoint in terms of having a capability for allowing crews to survive and flourish on planetary surfaces,” said Lee Mason, the principal technologist for NASA’s Space Technology Mission Directorate. “Its innovation will have impacts on future missions and we have some serious goals that we hope to achieve as part of this project and follow-on projects.”
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A full-power test will be conducted near end of March, which is later than originally planned in order for the team to gather more data on the Kilopower project.
Mason described the system as “very small and well-suited to space applications.” It uses currently available technology, with a uranium-235 reactor core that is roughly the size of a paper towel roll. The reactor heat is transferred via passive sodium heat pipes, and the heat is converted to electricity by high-efficiency Stirling engines. The engines use heat to create pressure forces that move a piston, which is coupled to an alternator to produce electricity, similar to how a car engine works.
The reactor has the delightful acronym of KRUSTY (Kilopower Reactor Using Stirling TechnologY), and can continuously provide up to 10 kilowatts of power for at least 10 years. Its compact dimensions could enable the delivery of multiple units on a single lander that could collectively provide the 40-50 kilowatts of power that NASA expects a human mission will require.
“This system has all the right properties to make this a great reactor,” Mason said. “It would have tremendous impact on enabling missions that really aren’t achievable with what is currently available.”
One of the biggest known hurdles for sending humans to the moon or Mars for long-duration missions is having some type of energy source that is powerful enough to fuel habitats, life-support systems, and other equipment yet remains small and lightweight. One of the most expensive parts of a space mission is launching it from Earth, and lightweight payloads make space missions more feasible.
“Being able to ‘live off the land’ reduces the amount of supplies we have to send along to Mars,” said Steve Jurczyk, associate administrator of NASA‘s Space Technology Mission Directorate. “Mars is a very difficult environment for power systems, with less sunlight than Earth or the moon, very cold nighttime temperatures, and dust storms that can last weeks and months that engulf the entire planet. The compact size and robustness of this system allows us to deliver multiple units on a single lander to the surface that provides tens of kilowatts of power, to power the systems to enable crews to remain healthy on the planet.”
This isn’t the first time that nuclear power systems have been proposed for space missions. The idea has been around since the 1950’s, with several attempts to develop a power system. But none have proved to be successful enough to seriously consider for human space missions.
“Earlier attempts to develop nuclear systems primarily tried to push technology that required lots of R&D,” said Patrick McClure, the Kilopower Project lead at Los Alamos National Laboratory. “They proved to be too expensive, with too much optimism for out-of-the-box systems. In the end they were invariably canceled.”
McClure said his team took a different approach to create a system that was smaller and made out of existing technology. In a 2012 test, KRUSTY produced 24 watts. It took less than 6 months to develop the system and it cost less than $1 million.
NASA recently received a directive from the Trump administration to return to the moon and develop a Deep Space Gateway, a cislunar space station that could lead to an eventual mission to Mars.
Mason said Mars has been the main focus of their work leading up to this current experiment.
“The gap that exists for Mars and our desire to send humans there is that the power requirements are so much greater than what we’ve flown with robotic systems,” he said.
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The current Curiosity rover on Mars runs on less than 200 watts, but human missions would need the 40-50 kilowatts that KRUSTY could provide.
Jurczyk noted that the upcoming Mars 2020 rover mission includes a small experiment called the Mars Oxygen in Situ Resource Utilization Experiment (MOXIE) that will extract a small amount of pure oxygen from carbon dioxide in the Martian atmosphere. The hope is that the Kilopower project could enable equipment to extract oxygen and create rocket fuel on a scaled-up human mission.
Asked if this system could be ramped up and used as a power source for a propulsion system such as electric propulsion, Mason said that would need 100s of kilowatts of power, which is well beyond the range of the Kilopower project.
But all the participants in the briefing were extremely optimistic about the KRUSTY reactor and the Kilopower project. Jurczyk said he has the confidence that the technology is viable.
“We look forward to bringing this technology to fruition to give future explorers the power they need to succeed,” he said.