By Dr. Christopher Morrison
Nuclear energy has played a key supporting role in historic missions to Mars, Pluto, and across the Solar System for the last 50 years. On January 1 2019, the nuclear-powered New Horizons flew by the most distant object ever observed up close – Ultima Thule, after it having already flown by Pluto in 2015.

Nuclear energy for space applications is nothing new. The past 50 years have focused on robotic exploration and usually involved providing a few hundred watts for a computer and communication system. However, the next 50 years will involve providing power for human settlements and will require kilowatt and megawatt power systems for life support, propulsion, and industry. While solar is an alternative power source and works well in many locations, nuclear energy is a necessity for locations far from the sun or places like the moon which has long periods of darkness.
The most common type of nuclear technology used today is the Radioisotope Thermal Generator (RTG). RTGs use the heat produced by radioactive material (usually Pu-238) decaying into stable state. RTGs are often called nuclear batteries because they can be modularized almost like AA or AAA batteries. RTGs have played a vital role in robotic science missions including the Curiosity Rover, Cassini, and the Voyager probes. Voyager 1 and 2 have left the Solar System and are still communicating with Earth after over 40 years and billions of miles distance. RTGs will continue to play an important role in science missions such as the Mars 2020 Rover.
However, RTGs will are not suited to supply the kilowatt- and megawatt-scale power needs of future human spaceflight. There is a second type of nuclear energy called fission that can achieve high power density and can scale to power levels capable of supporting human operations.

Nuclear fission requires a

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