DARPA is pursuing a nuclear thermal propulsion project called DRACO that could be ready for tests in cislunar space as soon as 2025. (credit: DARPA)

Nuclear thermal propulsion is key to keeping peace in space

by Alex Gilbert
Monday, February 14, 2022

In mid-January, the Mitchell Institute released a landmark report on the “strategic mandate for nuclear propulsion” of US satellites and space-based assets to evade the growing threat from Russia and China’s anti-satellite weapons. The report’s analysis and conclusions are sound and timely, but nuclear thermal propulsion (NTP) has broader applicability in space, including commercial and “soft power” uses. The US should pursue a concerted, sustained whole-of-government approach to it. Beyond achieving a first-mover advantage, this will allow the US to develop norms and solidify rules of the road espoused by the UN last fall, rules aimed at preventing war in the heavens.

Nuclear is not new

As DARPA’s Michael Leahy said last month, the first challenge is to “get folks comfortable with this” by reminding them we’ve gone here before.

At the dawn of the space age, the US and Soviet Union employed nuclear energy technologies as essential tools for exploration: radioisotope power sources used atomic decay to provide heat and electricity to spacecraft in Earth orbit and beyond. The major lunar exploration missions of both countries, Apollo and Lunokhod, relied on such radioisotopes for their scientific payloads. Both countries also tested nuclear thermal propulsion systems and space reactors, but space nuclear research ultimately stalled at the end of the Cold War.

That has changed.

Today, security and economic imperatives have led to a renaissance of space nuclear systems in the US and Russia, and an emergent focus in China. In an October 2021 hearing before the House Subcommittee on Space and Aeronautics, NASA Senior Advisor for Finance and Budget Bhavya Lal described the challenge: “strategic competitors including China are aggressively investing in a wide range of space technologies, including nuclear power and propulsion.”

NTP delivers soft and hard power in space

The US can achieve both soft and hard power with nuclear energy technologies, especially NTP, as the foundation of future American leadership in deep space exploration. Beyond the Apollo missions, many of NASA’s most iconic and inspiring missions were enabled by radioisotopes: Pioneer, Voyager, New Horizons, and the Mars rovers.

China knows this and has sought to emulate: in late 2020, China returned the first lunar samples in nearly 50 years from the Moon. Of note, Chinese lunar rovers used radioisotope batteries supplied by Russia, a sign of growing collaboration in space technologies the US should not ignore.

China has identified space nuclear propulsion as a key element of its plan to become the pre-eminent spacepower by mid-century, specifically identifying the technology as a way to access and exploit space resources. Russia is pursuing several concepts, including a fission reactor to power an electronic warfare satellite (see “Ekipazh: Russia’s top-secret nuclear-powered satellite”, The Space Review, October 7, 2019) and a reactor to power an ion engine to create a space tug.

There is good news, however. Unlike terrestrial nuclear power, where the US is falling behind Russia and China in global trade, America has a slight head start on space nuclear technologies. In 2018, the tiny Kilopower intended for NASA operations was tested, the first novel domestic reactor designed, built, and operated in decades. The United States is pursuing two approaches to nuclear rockets, one military through DARPA and another civil through NASA. DARPA’s project, DRACO, is focused on developing capabilities to support maneuverability and responsiveness for operations as far away as the Moon.

Ultimately, space nuclear technology development provides optionality as the contours of competition in the space domain evolve.

The capabilities bring decisive advantages but vary by technology. Nuclear rockets greatly increase spacecraft maneuverability, advantages for military spacecraft specifically in deep space. A basic nuclear rocket is feasible this decade; DARPA is targeting 2025 for a test launch. By contrast, the high efficiency but slower thrust of nuclear electric propulsion makes it ideal for slower-paced, economic logistics. However, the greater complexity of its subsystems make it a 2030s technology.

As described in a recent National Academies study, either type of nuclear propulsion may be needed for a crewed mission to Mars, exactly the type of mission that could cement US or Chinese soft power leadership. Meanwhile, fission reactors could be essential for early space mining. Focused on producing water for in-space refueling from the Moon, such mines are likely to be energy intensive but uniquely suited for fuel production for space nuclear systems.

NTP is the key to space leadership

Beyond technological advantage, the first nation to establish significant space nuclear capabilities can establish norms to guide global activities. The US is already taking leadership, avoiding the proliferation risks of highly enriched uranium by preferring high-assay low enriched uranium (HALEU). Technical and operational leadership breeds the influence to ensure future space norms reflect American nuclear energy priorities, like preventing proliferation, transparency of operations, and embracing safety as a guiding star.

To maintain space supremacy, the United States needs to build on its early leadership in space nuclear technologies to harness them for military, scientific, and economic purposes. Bipartisan congressional funding and support the last several years has provided a start and must continue. The Biden Administration should build on the critical policy steps taken by the Trump Administration, which reformed launch authority to enable commercial missions for the first time and issuing Space Policy Directive-6, and recognize the unique value propositions of space nuclear technologies for meeting its policy goals. Not least of these would be creating early demand for HALEU and rebuilding domestic supply chains, which would help meet the administration’s climate goals by supporting terrestrial nuclear energy.

Essential to any US pathway forward is a cohesive strategy that builds on America’s competitive advantages. Clear government demand for space nuclear systems can support the continued private sector investment necessary for a strong industrial base. A portfolio approach to support nuclear thermal propulsion, nuclear electric propulsion, and fission power reactors can ensure technological diversity.

The hard reality is that great power competition now permeates the space domain: Russia and China increasingly see space nuclear technologies as tools to establish strategic and economic dominance. Congress has a significant opportunity to respond by further incentivizing NTP both in government and across industry. But beyond the technical challenges is a question of human will: the US has to accelerate a bipartisan focus on developing these capabilities for them to truly take off and solidify a peaceful path for human activities in outer space.

Alex Gilbert is Director of Space & Planetary Regulation at Zeno Power, which develops radioisotope power sources for space and maritime applications. Alex is also a fellow at the Payne Institute at the Colorado School of Mines and adjunct faculty at Johns Hopkins University.

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