|Fig. 1: Orion crew module (Source: Wikimedia Commons)|
The colonization of Mars has long been a goal of national space programs worldwide, also occupying a prominent space in science fiction and pop culture. The recent emergence of private space companies like SpaceX and Mars One has only intensified global interest in fulfilling this goal. This is understandable as the Red Planet offers one of the best chances of establishing a permanent extraterrestrial colony within the foreseeable future, due to, amongst other factors, its relative proximity to Earth, mostly carbon dioxide atmosphere, and presence of water.  This paper will discuss the potential role of nuclear energy in two important fields essential to the establishment of a Martian colony: rocket engines and the colonys on-site generation of energy.
The most common form of rocket engine relies on chemical propulsion technology, in which a fuel and oxidizer are combusted to produce thrust. One major issue with this form of engine is that they are simply far too slow, with manned missions to Mars utilizing such technology projected to take approximately two years to complete. [2,3] Thus, scientists have long searched for potential nuclear alternatives to chemical rocket engines. Perhaps the most famous historical foray into nuclear-powered spacecraft is NASAs Project Orion, which sought to develop a nuclear-pulse rocket that used a series of contained nuclear explosions to provide thrust, shown in Fig. 1.  Although the project was eventually shelved, due to a combination of cost, safety, and political issues, nuclear technology continues to offer viable potential alternatives to traditional chemical rockets.  The development of fusion rockets is one such technology. Based on the principle of nuclear fusion, which releases energy by fusing together atoms at extreme temperatures and pressures, companies like Princeton Satellite Systems have conceptualized a small engine that may allow crewed missions to reach Mars in only 310 days.  Envisioned to be no larger than a few refrigerators, these engines are designed to be much cheaper and lighter than their terrestrial counterparts. On top of this, they should be able to provide much more energy for the operation of scientific instruments and communications devices than traditional chemical rocket engines. 
Another possible application of nuclear technology is as a power source for colonies. NASAs Kilopower project is perhaps the most feasible effort to develop near-term technology that could be used in a hypothetical Martian colony.  Unlike fusion reactors, Kilopower concepts are based on the more conventional principle of nuclear fission, which derives energy from the splitting of atoms. Instead of innovating the means of energy release, the Kilopower initiative is an attempt by NASA to decrease the size and maintenance requirements of traditional fission reactors. Conceptually, Kilopwer reactors are simple, using the heat from a uranium core to carry heated liquid to a Stirling engine, whereupon the heat energy pressurizes a gas to drive a piston attached to an electric motor.  The result is a source of electricity that is compact and contains few moving parts, ideal for transportation and reliable operation on a Martian colony.
In conclusion, nuclear energy has the potential to play an important role in our quest to establish a human colony on Mars. Whether these be in the form of cutting edge fusion applications in rocket engines, or in refining existing fission technologies to power colonies on the Red Planet, such advancements may allow our species to permanently break free from our terrestrial bounds and usher in an exciting new age of space exploration.
© Paco Litonjua. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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