SPAR Institute Begins Latest Effort to Develop Nuclear Propulsion for Space 

Maneuver Without Regret, In-Space Assembly and Manufacturing Among Potential Use Cases 

In late 2024, the United States Space Force established the Space Power & Propulsion for Agility, Responsiveness & Resilience (SPAR) Institute with $35 million to develop nuclear-powered systems for spacecraft propulsion. The initiative demonstrates the latest effort by the Space Force, in partnership with the Air Force Reserarch Laboratory (AFRL), eight universities and 14 industry partners, to explore nuclear fission as an energy source in space. If successfully developed and deployed, nuclear-powered systems can unlock a broad range of capabilities: from ”maneuvering without regret” and in-space assembly and manufacturing (ISAM), to orbital clean-up and natural resource extraction. 

“Retired Lieutenant General John Shaw’s catchphrase ‘maneuver without regret,’ means we need to operate and maneuver satellites without compromising the satellite’s lifetime energy supply,” said Tom Cooley, PhD, partner at Elara Nova: The Space Consultancy and former Chief Scientist at AFRL. “The current energy consumption costs of maneuvering space assets adversely affect the Space Force’s long-term capabilities. Nuclear energy has long been considered a potential solution, and the SPAR Institute will explore its viability.” 

Traditionally, maneuvering in space has been generated through electric or chemical propulsion. But both approaches have their respective limitations. 

“While electric propulsion is extremely efficient, it can’t generate enough power to change an orbit quickly, so it tends to be used for lower impulse per unit time activities like station-keeping,” said Brad Tousley, PhD, partner at Elara Nova and former director for the Tactical Technology Office at the Defense Advanced Research Projects Agency (DARPA). “Meanwhile, chemical propulsion rockets have greater impulse per unit time, but fuel is volume and weight-constrained by the spacecraft. So chemical propulsion requires the Space Force to address on-orbit refueling and logistical challenges.” 

Alternatively, nuclear fission carries both high-impulse thrust and low-consumption rate qualities. Nuclear fission works by splitting an atom’s nucleus within a controlled reactor to generate energy in a way that could revolutionize dynamic space operations.   

“Nuclear fission’s latent energy is simply far more per unit volume compared to electric or chemical power sources,” Dr. Tousley said. “Regulatory and safety issues still exist that can inhibit nuclear development and deployment. But from a physics and energy density perspective, nuclear power can change how we approach building resilient architectures and systems in space.” 

Therefore, nuclear-powered spacecraft are an attractive endeavor for both national security and civil space applications. 

“The Space Force is interested in nuclear energy because maneuvering to change orbits requires a lot of energy,” Dr. Cooley said. “Maneuverability can also enable in-space logistics, like on-orbit refueling or conducting maintenance repairs on a spacecraft. Then for NASA, human habitation on the moon requires a reliable source of energy, especially during the two-week lunar ‘night.’” 

Nuclear-Powered Systems vs. Nuclear Weapons 

Nuclear-powered systems are not nuclear weapons. Whereas a nuclear weapon splits an uranium or plutonium atom in an uncontrolled manner to maximize energy consumption, a nuclear reactor can house this same atom-splitting process in a way that generates a low-carbon, long-term energy source.  

It’s the same technological process leveraged by nuclear power plants and even the United States Navy. 

“There’s no better analogy for using nuclear power in space than how it changed the U.S. Navy’s global operations,” Dr. Tousley said. “The Navy went to nuclear-powered aircraft carriers because the infrastructure to supply carriers with conventional fossil fuels was burdened by long-distance deployments. So today’s Navy depends on nuclear energy for their global power projection.” 

To this end, developing and deploying similar nuclear reactor technology for space is legally within the bounds of the 1967 Outer Space Treaty.  

“The 1967 Outer Space Treaty is clear that we must not put nuclear weapons in space,” Dr. Cooley said. “But a nuclear reactor simply uses nuclear technology to generate electricity. Some of the most successful NASA programs used radioisotope thermoelectric generators (RTGs), which similarly leveraged nuclear technology for deep space or interplanetary exploration.” 

Nuclear Thermal Propulsion Programs 

Historically, the United States has embarked on a series of research and development programs for nuclear energy in space. Nuclear-powered systems can be delineated in two ways, the first of which is nuclear thermal propulsion (NTP). In an NTP system, hydrogen fuel is used to split a uranium atom within a nuclear reactor to generate heat, which can create thrust. 

One of the earliest NTP efforts was the Nuclear Engine for Rocket Vehicle Application (NERVA) program, overseen by the National Aeronautics and Space Administration (NASA) and the Atomic Energy Commission (AEC). 

“NERVA aimed to develop an upper-stage rocket engine using nuclear thermal propulsion, because the heat generated by a nuclear reactor is much greater than the heat you get from a chemical reaction,” Donna Dickey, Elara Nova partner and aerospace engineer, formerly of AFRL and now supporting DARPA. “The NTP process generates twice the efficiency, while maintaining the thrust levels of a traditional chemical rocket – so it’s the best of both worlds. The NERVA program developed several nuclear reactors to be integrated into a rocket engine, and even started testing before the program ended in 1973.” 

While the nuclear-powered rocket engine NERVA developed was never launched into space, the program has been considered a successful proof of concept for nuclear thermal propulsion.  

Today, similarly-inspired DARPA programs have emerged, like the Demonstration Rocket for Agile Cislunar Operations (DRACO) and LunA-10 programs.  

“DRACO is focused on demonstrating nuclear thermal propulsion technology on-orbit,” Dr. Tousley said. “Effectively managing the excess heat a nuclear reaction generates continues to be a technical challenge that DARPA and NASA are working through, but the program is an effective example of how we can develop nuclear technology in a way that adheres to the Outer Space Treaty. Meanwhile, LunA-10 was a capability study of the lunar economy and how shared systems could benefit everyone, including nuclear power and propulsion.” 

Nuclear Electric Propulsion 

The second way to leverage nuclear energy is known as nuclear electric propulsion (NEP), which uses nuclear fission to create electricity that generates the magnetic fields used to accelerate and expel gas propellants like xenon and krypton. The NEP process provides a lower amount of thrust compared to its NTP counterpart, but it can still efficiently propel a spacecraft for extended periods of time.  

That’s been the focus of the Joint Emergent Technology Supplying On-Orbit Nuclear High Power (JETSON) program, overseen by AFRL. JETSON emerged after the Kilopower Reactor Using Stirling Technology (KRUSTY) experiment, led by NASA and the Department of Energy’s National Nuclear Security Administration, safely demonstrated NEP capability. 

“KRUSTY created a relatively small nuclear reactor and used that to generate electricity,” Dr. Cooley said. “Now, JETSON gets back to powering an ion thruster with that electric energy, but the hard part is getting the nuclear reactor into space safely.” 

Remaining Challenges and Terrestrial-Driven Solutions 

Launch presents one of many remaining challenges needed to be overcome before the government, with its industry and academic partners, can successfully adopt nuclear-powered systems for spacecraft propulsion. 

“The biggest concern is not launching the reactor structure, but rather the nuclear material itself,” Dr. Tousley said. “But launching the reactor structure on one rocket and the nuclear material on a smaller, more reliable rocket before assembling it in space is one example of how we can creatively reduce the risk of an accident or reentry. Although we would still need mission assurance during the system’s lifetime, and a means for appropriately disposing it at end of life.” 

But similar, land-based nuclear energy efforts may in turn facilitate solutions for getting a nuclear reactor to space. For example, the Strategic Capabilities Office’s Project Pele aims to develop a mobile nuclear reactor to power remote military bases.  

“It’s difficult to get fossil fuel sources to places like Eilson Air Force Base in Alaska, where winter limits opportunities to resupply,” Dr. Tousley said. So Project Pele’s investment in  nuclear research and development for terrestrial power purposes can advance similar technologies for space.” 

Land-based applications for nuclear power systems are also drawing the attention, and investment, of technology companies and their private equity partners.  

“Companies are developing small nuclear reactor concepts to meet the growing nationwide energy demands of data centers,” Dr. Tousley said. “So nuclear developments may not start with space, but the government is still going to benefit from private capital investments in developing advanced reactors and power systems for terrestrial purposes.” 

Enabling the Future of Nuclear in Space 

If successful, these programs could enable the development of other space-based capabilities, like in-space assembly and manufacturing (ISAM), orbital clean-up, recycling and even natural resource extraction in space.  

“Nuclear energy can solve two problems at once: building the future infrastructure in space, while cleaning up the old one,” Dr. Cooley said. “Nuclear power systems can maneuver space debris into remote orbits, or recylce and manufacture debris into new material. But all of these capabilities would require tremendous amounts of energy that nuclear-powered systems can uniquely provide, and the United States needs to take that risk and invest in these capabilities now if we are going to lead that change.” 

However, the government must also make the appropriate regulatory and policy changes if it’s to overcome the risk-averse mindset triggered by nuclear accidents like Three Mile Island. 

“Japan, France and the United States led the free world in nuclear power development for electric generation purposes before the 1979 partial nuclear meltdown at Three Mile Island,” Dr. Tousley said. “That accident impacted U.S. public policy and set us back in nuclear development for decades, while Japan and France continued forward. Likewise, we need to be more risk-tolerant in order to make progress because the physics don’t lie – nuclear energy is incredibly efficient.  

The complex challenges facing the SPAR Institute and other nuclear energy programs require the type of intersecting technology, human capital, regulatory and policy-driven solutions Elara Nova partners are prepared to provide. 

“The SPAR Institute is funding graduate students to work in nuclear development, an area that is critical to the United States,” Dr. Tousley said. “These students will likely go on to work in industry or start their own companies in support of the U.S. government’s nuclear development efforts. That’s where Elara Nova can support them, by bridging the gap between policy and technical challenges to enable their company’s success.” 

Elara Nova is a global consultancy and professional services firm focused on helping businesses and government agencies maximize the strategic advantages of the space domain. Learn more at https://elaranova.com/.