Are manned missions to the moon and Mars something we'll see in our lifetime? If it's up to the space engineers currently tackling how to power future rockets and spaces bases, the answer is yes. One solution in the works is the use of mini nuclear reactors in space to not only power exploration crafts but to also meet the energy needs of future bases on the moon and Mars.

Nuclear power in space exploration is nothing new. Both Russian and American space agencies have tested nuclear propulsion systems in their space craft. There are currently 30 distinct types of nuclear-powered satellites in orbit today.

It began in 1976 and continued through 1988, when Russia's Roscomos sent about 40 nuclear-electric satellites into space. They were mostly powered by BES-5 reactors, but with mixed success—not all reached orbit or even became operational once there.
Meanwhile, NASA's uranium-fueled SNAP-10A went into earth's orbit in 1965, but operated for just 43 days before it stopped responding. It is now in a slow trajectory that's expected to hit earth's ground in about 3,000 years.
For more than 50 years, NASA has provided nuclear batteries for deep space missions, such as those for the Pioneer, Voyager, and New Horizons. In fact, the Mars 2020 Perseverance Rover will soon be fueled using a multi-mission radioisotope thermo-electric generator, which is essentially a battery to keep it warm and productive on its mission in search of signs of habitability on Mars. This technology depends on radioisotope power systems designed to convert heat from the natural radioactive decay of the isotope plutonium-238 into electrical power.

National space agencies such as NASA and Roscosmos are currently investigating different mini nuclear reactor designs, with Space X CEO Elon Musk making this recommendation on his Twitter feed:

A nuclear thermal propulsion rocket engine design, like the one Musk references, would make use of a small nuclear reactor to generate heat from uranium fuel. That thermal energy would then be transferred to a liquid propellant, possibly liquid hydrogen, which expands into a gas and is blast out through a jet to produce thrust.

Currently, conventional chemical-fueled rockets take between eight months and two years to reach Mars, depending on the relative position of the planets at launch. Nuclear-powered rockets could take just 100 days to make the journey, thereby transforming possibilities for human space exploration.

In addition, faster journeys use fewer resources and reduce the crews' exposure to harmful cosmic radiation.

It is estimated that to reach Mars so speedily, a large spacecraft would need just 230 grams of uranium fuel - comparable in size to a bag of sugar.

There are also plans to employ mini nuclear power plants to convert local minerals into the building materials needed to construct future bases on the Moon and Mars. Nuclear power would also provide a reliable long-term source of energy to sustain base occupants, communications, operations, and functions such as farming for food.

Nuclear power seems to be the energy of choice, since potential alternatives like oil and solar have shown significant disadvantages. Using oil as a source of fuel for a base on Mars would be too heavy and dangerous to deliver, so much so that any experts regard it as a logistical nightmare.

As for solar power, most experts feel it's a non-starter for Mars, which is known to suffer tremendous dust storms that block out the sun for months at a time. Also, because of the distances involved, the sunlight that reaches its surface is only a fraction of what the Earth receives. Even for the moon, solar power is problematic since lunar nights are equivalent to 14 days on Earth, whereas nuclear energy operates regardless of the weather or time of day.

As for specific mini nuclear power designs, NASA is working with a number of American research agencies, including the Los Alamos National Laboratory and the Nevada National Security Site, on the Kilopower project.

The Kilopower reactor generates power through active nuclear fission, in which atoms split apart to release energy. This a small and lightweight fission power reactor system can generate up to 10 kilowatts of electrical power—enough to run several average households for at least a decade. Powering a station on Mars would require about 40 kW, or four Kilopower reactors.

NASA completed a series of experimental tests during 2018 to prove the feasibility of Kilopower technology. In the first two phases, each component of the reactor was tested without power. In the next phase, power was switched on and gradually increased to heat the core. The fourth and last phase involved full-power testing over a day to simulate a virtual mission. This included a reactor start-up, then a ramp-up to full power, followed by steady operation and shutdown.

During the tests, the NASA team simulated various operational problems, including power reduction, failed engines and failed heat pipes, to successfully demonstrate that the system could work despite multiple component and operational failures.

“Kilopower gives us the ability to do much higher power missions, and to explore the shadowed craters of the moon," said Marc Gibson, lead engineer on the project. “When we start sending astronauts for lengthy stays on the Moon and to other planets, that's going to require a new class of power that we've never needed before."

Current forecasts suggest that the first small nuclear reactor should be ready for use on the moon by 2024 onwards as part of NASA's planned Artemis program. The intention is to send American astronauts to the moon, but are not necessarily in need of a nuclear reactor at the planned base.

As for a future Mars mission, it is likely that nuclear-powered rockets could be ready by 2033 when the Earth and Mars will come closer together than at any other point in the previous 18 years. It has been suggested that the first stage would use a chemical-fueled rocket to lift off the mission from Earth, but the next stage of the Mars expedition could use a nuclear rocket engine to speed up the trip.

One thing is clear—much work needs to be done to ensure nuclear technology can meet the future challenges of space flight and expeditions.

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