The Defense Innovation Unit (DIU), a Department of Defense organization focused on swiftly putting commercial technology to use in the U.S. military, has awarded contracts for two nuclear technologies—compact fusion and radioisotope heat—for spacecraft that could carry a high-power payload and freely maneuver in cislunar space. The objective is to accelerate ground and flight testing and launch a successful orbital prototype demonstration of each approach in 2027.

The Department of Defense wants to deploy spacecraft in cislunar space—the area between Earth and the moon’s orbit—with thrust and agility that only nuclear thermal propulsion (NTP) can provide. The Defense Advanced Research Projects Agency (DARPA), through its Demonstration Rocket for Agile Cislunar Operations (DRACO) program, is looking to private industry for the design, development, fabrication, assembly, and testing of a nuclear thermal rocket engine fueled with high-assay low-enriched uranium fuel to heat a liquid hydrogen propellant.

With three commercial teams under contract to produce reactor designs for nuclear thermal propulsion rockets that would use solid high-assay low-enriched uranium fuel to heat hydrogen propellant, NASA’s investment in nuclear thermal propulsion (NTP) has increased in recent years. But just as there is more than one way to fuel a terrestrial reactor, other fuels are under consideration for future NTP rocket engines.

Nuclear thermal propulsion (NTP) is one technology that could propel a spacecraft to Mars and back, using thermal energy from a reactor to heat an onboard hydrogen propellant. While NTP is not a new concept, fuels and reactor concepts that can withstand the extremely high temperatures and corrosive conditions experienced in the engine during spaceflight are being designed now.

BWX Technologies announced on December 13 that it has delivered coated reactor fuels to NASA for testing in support of the Space Technology Mission Directorate’s NTP project. BWXT is developing two fuel forms that could support a reactor ground demonstration by the late 2020s, as well as a third, more advanced and energy-dense fuel for potential future evaluation. BWXT has produced a videoof workers processing fuel kernels in a glovebox.

The U.S. Department of Defense is aiming to demonstrate a novel nuclear thermal propulsion (NTP) system above low Earth orbit by 2025. The Defense Advanced Research Projects Agency (DARPA) announced on April 12 that following a competitive solicitation process, it has awarded a contract to General Atomics Electromagnetic Systems (GA-EMS) for the design of the nuclear reactor that will power the Demonstration Rocket for Agile Cislunar Operations (DRACO). Blue Origin and Lockheed Martin will work on a parallel track to design a spacecraft tailor-made to demonstrate the NTP system.

An artist's concept of a fission power system on the lunar surface. Image: NASA

A national strategy for the responsible and effective use of space nuclear power and propulsion (SNPP)—Space Policy Directive-6 (SPD-6)—was released by the White House on December 16 as a presidential memorandum.

Space nuclear systems include radioisotope power systems and nuclear reactors used for power, heating, or propulsion. Nuclear energy can produce more power at lower mass and volume compared to other energy sources and can shorten transit times for crewed and robotic spacecraft, thereby reducing radiation exposure in harsh space environments. SPD-6 establishes a road map for getting space nuclear systems into service and sets up high-level goals, principles, and federal agencies’ roles and responsibilities.

Illustration of a Mars transit habitat and nuclear electric propulsion system. Image: NASA

NASA aims to develop nuclear technologies for two space applications: propulsion and surface power. Both can make planned NASA missions to the moon more agile and more ambitious, and both are being developed with future crewed missions to Mars in mind. Like advanced reactors here on Earth, space nuclear technologies have an accelerated timeline for deployment in this decade.

Space nuclear propulsion and extraterrestrial surface power are getting funding and attention. New industry solicitations are expected this month, and a range of proposed reactor technologies could meet NASA’s specifications for nuclear thermal propulsion (NTP). Nuclear electric propulsion could increase the feasibility of crewed missions to Mars with a shorter transit time, a broader launch window and more flexibility to abort missions, reduced astronaut exposure to space radiation and other hazards, expanded payload mass capabilities, and reduced cost.

The United States is pursuing the objective to land humans more than 100 million miles away on Mars, and nuclear power has the potential to be a key technology in getting to the Red Planet and providing power while there. Specifically, nuclear thermal propulsion (NTP) is a promising approach that could enable astronauts to travel from Earth’s orbit to Mars and back in a fraction of the time, and with greater safety, than is available with other options.