The National Aeronautics and Space Administration (NASA) is developing a new generation of modular nuclear reactors that will power manned outposts on the moon and Mars, providing a simple, yet inexpensive way to power a space mission.
Reliable power sources have always been a problem in with any space mission. The first satellites used batteries that supplied electricity, but they only lasted for a few days. Solar panels were then added, extending a mission’s life from days to years. With manned missions, fuel cells are necessary to provide power, drinking water and hydrogen mixed with oxygen to create electricity and a potable waste product.
All of these power sources are limited, at best. Solar power is probably the best of the three, but even solar has its limits because it only works when sunlight of sufficient brightness shines on the panels. This makes the use of solar panels confined to the inner solar system.
SNAP-10: The first nuclear reactor to operate in space
Nuclear power for space travel was first suggested 75 years ago when the first nuclear reactor came online. Actually, it has been used as a basic source of power since 1965, when the U.S. launched the SNAP-10 experimental fission nuclear reactor into orbit. It was the only fission power system launched into space by the U.S.
SNAP-10 stopped working after just 43 days due to an electrical problem. The Systems Nuclear Auxiliary Power Program (SNAP) reactor was specifically developed for satellite use in the 1950s and early 1960s under the supervision of the U.S. Atomic Energy Commission.
Since 2010, over 30 small fission power nuclear reactors have been sent into space in Soviet RORSAT satellites; also, over 40 radioisotope thermoelectric generators have been used globally (principally U.S. and USSR) on space missions.
Main power source of U.S. space missions today
Just about all U.S. space missions today use the Radioisotopic Thermoelectric Generator (RTG). The RTG is a solid-state device that uses heat from plugs of plutonium-238 as either a way to keep electronics warm or to generate electricity using thermocouples.
The RTG’s use has largely been restricted deep space missions for political as well as engineering reasons, but the list of missions is long, and includes the Apollo mission lunar experiment packages, the Viking and Curiosity Mars landers, and the Pioneer, Voyager, Galileo, Cassini, Ulysses and New Horizons deep space missions.
The big problem with using RTG’s that they don’t supply much more than 300 Watts of electricity. This is alright if longevity is the only need, but for use on a planet’s surface, an RTG couldn’t handle anything much larger than the Curiosity rover.
Another problem is with the plutonium -238. It’s a by-product of our Cold War weapons program and is now in short supply. To get more would require the reopening of production lines that have been closed for many years. Safe use of RTGs requires containment of the radioisotopes long after the productive life of the unit.
The Kilopower nuclear reactor
Using well-established physics, NASA’s Kilopower reactor represents a small and simple approach for long-duration, sun-independent electric power for space or extraterrestrial surfaces. The reactor will need almost no control system and will safely generate 10 Kilowatts of power for 10 years or more. (The average U.S. household runs on about five kilowatts of power).
NASA’s Marshall Space Flight Center in Huntsville, Alabama, along with the Department of Energy’s (DOE) Nevada National Security Site and Los Alamos National Laboratory, began testing the Kilopower reactor in November this year. It is currently being tested against analytical models for hardware verification.
The Kilopower project test reactor prototype was finished in September and is small. It is designed to produce up to 1 kilowatt of electric power and is about 6.5 feet tall (1.9 meters).
“The reactor technology we are testing could be applicable to multiple NASA missions, and we ultimately hope that this is the first step for fission reactors to create a new paradigm of truly ambitious and inspiring space exploration,” adds David Poston, Los Alamos’ chief reactor designer.
“Simplicity is essential to any first-of-a-kind engineering project – not necessarily the simplest design, but finding the simplest path through design, development, fabrication, safety, and testing.”
The prototype power system uses a solid, cast uranium-235 reactor core, about the size of a paper towel roll. Reactor heat is transferred via passive sodium heat pipes, with that heat then converted to electricity by high-efficiency Stirling engines. Stirling engines use heat to create pressure forces that move a piston, which is coupled to an alternator to produce electricity, sort of like an automobile engine.
Robert Stirling was a Scottish minister who invented the first practical example of a closed cycle air engine in 1816 as a challenge to the steam engine. Over the years, all closed-cycle air engines became known as “Stirling” engines.
“What we are striving to do is give space missions an option beyond RTGs, which generally provide a couple hundred watts or so,” says Lee Mason, STMD’s principal technologist for Power and Energy Storage at NASA Headquarters. “The big difference between all the great things we’ve done on Mars, and what we would need to do for a human mission to that planet, is power.
This new technology could provide kilowatts and can eventually be evolved to provide hundreds of kilowatts or even megawatts of power. We call it the Kilopower project because it gives us a near-term option to provide kilowatts for missions that previously were constrained to use less. But first things first, and our test program is the way to get started.”
