Our Future in Space Depends on NUCLEAR FISSION

Our Future in Space Depends on NUCLEAR FISSION

It is hard to imagine a future in space without fission reactors. Almost every complex activity beyond low Earth orbit (LEO) will require more power than solar can reasonably produce, and much of what we now do in space is unnecessarily constrained and over-complicated by not having enough power. The robotic probes we send into deep space today are underpowered, prohibiting them from using modern cameras and other scientific instruments, and limiting their transmission bandwidth back to Earth at the cost of reduced science data. There istalk of building commercial space stations in LEO, however, a station with 100 or more residents would require preposterously large solar panels, significantly increasing the overall cost and number of launches

By contrast, a nuclear fission reactor could be placed in orbit with a single launch. With new advances in reactor technology, fission reactors can now generate massive amounts of power in a relatively small package, all with increased safety and simplicity in operations. More power will remove constraints from mission design, enabling cheaper and more-effective space exploration and will pave the way for lower-risk human habitation. Many private companies are seeking to launch fission reactors for their missions. This may have been an unthinkable proposition 20 years ago, but so were the private launch and satellite industries, both of which are now flourishing. In response, a recent Presidential memo revamped the launch approval process for government agencies, and for the first time, defined it for commercial actors. Is the public ready for this future?

Advances in nuclear fission

The design of most fission reactors the ground dates back to the 1960s and 70s. However, new designs being tested that are safer, smaller, and cheaper. Oklo, a California-based company with investment from DCVC, has been engaged in pre-application activities with the US Nuclear Regulatory Commission since 2016 for the Aurora design, and is preparing to submit its first license application. The reactor is self-regulating—the fission reaction slows or stops as core temperature increases. It can also consume waste from older, lower energy reactors - nasty stuff with a half-life of millions of years - reducing this waste to byproducts with only a 300 year half-life, generating power along the way. 300 years is a manageable waste problem on a human scale; we can store cognac for that long, but we have no real understanding of how to store something safely for millions of years. This alone is sufficient reason to start building these reactors in large quantities. The fuel is not weapons-grade, so there is no proliferation risk, and in Oklo’s case, Aurora fits on less than half of an acre. The design is modular and can be easily scaled up and down. In its smaller incarnation, the reactor could power a small satellite for years, and at the high end, an entire lunar colony from a single reactor.

USNC, a Seattle-based company, has been making similar progress with the Canadian regulators, seeking approval to build their Small Modular Reactor. Like Oklo, their reactor is dual-use. They can power small towns and cities at significantly lower costs than older reactor designs, and by the same virtues, the reactor is ideal for powering a small space station or base on the Moon.

In 2018 NASA’s Kilopower project achieved promising results with Krusty, a reactor designed for planetary surface use. Krusty is currently capable of producing ~1 kW, self-regulates through thermal expansion, and is designed to be safely operated within a reasonable distance from inhabitants. Kilopower uses Highly- Enriched Uranium (HEU), which is a weapons-grade, though, at launch, the radiological hazard would be limited to the naturally occurring radioactivity present in the uranium reactor core (<5 Curies).

More Power Will Remove Constraints From Mission Design, Enabling Cheaper And More-Effective Space Exploration And Will Pave The Way For Lower-Risk Human Habitation

Alternatives: solar

Solar panels have proven to be wholly adequate for most of our unmanned needs in LEO. However, for space stations, they are more problematic.The International Space Station has around 350 square meters of solar panels generating 80-120 kW, and the ISS currently only houses 6 people. For anything larger, solar panels quickly become too massive to launch and build. Exposure to radiation and atomic oxygen also degrade panels over time, reducing their efficiency and dictating that panels need to be oversized to account for end-of-mission power needs.

Of course, solar panels diminish in utility the further you go from the sun. Hayabusa 2 required 12 square meters of a solar panel to deliver 1,400 Watts when the vehicle was at 1.4 AU, the aphelion distance of the asteroid. By contrast, the radiator panels for a 1 kW system would be well under 1 square meter, which is insignificant.

On the Moon, solar panels only do half the job - lunar night survival remains a problem, where heating is required in addition to power. The projected power needs for a lunar colony are 40 kW ~100kw day/night continuous power, which could be achieved from four higher-powered Kilopower units. Nuclear power would also help us extract ice water from the permanently shadowed regions of the lunar poles.

The solar insolation on the surface of Mars is not too dissimilar to that at many places on Earth, and a human colony there could be powered by a massive sun-tracking solar farm. However, transporting the necessary solar panels from Earth would be staggeringly expensive. Even advocates of manufacturing panels in situ must admit they would be significantly aided by the presence of a ready-to-go nuclear fission reactor when they pick up the task. Another complication on Mars is dust blocking the panels, which is entirely avoided with nuclear.

Alternatives: RTGs vs Fission reactors

Radio-isotope thermal generators (RTGs) have been used to power a number of lunar and interplanetary missions. These systems convert power from the heat generated by naturally decaying plutonium-238 in the range of 200W. The most recently launched RTGs are MSL/Curiosity (2011) and Chang'e 3 and Yutu (2013, also with radioisotope heater units to aid nighttime survivability). NASA’s Mars 2020 will also carry an RTG.

One of the most stunning accomplishments for nuclear powered-spacecraft in recent history is the New Horizons mission. Launched in 2006, New Horizons was powered by an RTG that provided a measly 244 W at the time of launch. New Horizons was not without its problems at that time. It was the first nuclear-powered spacecraft launched by the US in almost a decade (Russia’s Mars 96 failed in 1996, dropping 200g of Plutonium-238 onto land), was plagued by lack of a nuclear- qualified launch vehicle, and a lack of sufficient fuel to power an RTG. Through heroic engineering, the final design was adequate to power the spacecraft through its 2015 visit to Pluto and 2019 flyby of Arrokoth, producing stunning science results that have transformed our understanding of the outer solar system. However, such a small power source - barely enough to power three incandescent light bulbs - imposes a very hard constraint on mission design. New Horizons was an exercise in making the impossible possible, but I would argue it doesn’t have to be that hard.

As we travel further into deep space, back to the orbits of Neptune and Uranus - both of which have been sorely neglected since Voyager - it can take over 8 hours to send and receive a message. Continuing to design spacecraft solely dependent on open-loop communications via Earth for their instructions will severely limit the types of activities they can accomplish. On these meagre power budgets, task planning with modern Artificial Intelligence and Machine Learning techniques can only lightly be used (self-driving cars currently need a trunk full of servers to safely navigate streets), and our spacecraft will remain forever dumb.

Perhaps, most importantly, higher-powered radio transmitters can be flown, trading off against the risk posed by large deployable antennas (Galileo’s high gain antenna failed to open, almost crippling the mission). With increased transmission strength, significantly more science data can be returned.

Nearer to home, asteroid prospecting and mining operations require large power sources. The grappling, excavating, and lifting requirements will be power-hungry, and these spacecraft in particular would benefit from the automated task planning via AI. Yes, they could be solar powered, but the proximity operations around an asteroid are made unnecessarily complex when hauling 12 square meters of solar panels along.


Fission reactors are needed to learn more about the outer solar system, and for the human race to begin accessing the resources that lie waiting beyond the Earth. Newer technologies allow us to create safer and smaller nuclear reactors, and these could enable a whole new generation of robotics and human exploration in space. Although we have made recent progress towards regulatory approval, the road to launch is still a long one. There has been a resurgence public distrust of nuclear power in the wake of Fukushima, and entirely valid concerns that need to be addressed. The need for nuclear-rated launch systems cannot be overlooked, and maintaining non-proliferation is a must. The trust of the public must be earned and guaranteed at all times. However, nuclear fission in space is worth revisiting, and we should start now.

Weekly Brief

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