Nuclear Reactor Test Requirements Put DRACO Launch Plans On Hold

A vision to accelerate U.S. access to cislunar space and the wider Solar System through a landmark demonstration of nuclear thermal propulsion technology must wait.

The 2027 launch date for the Demonstration Rocket for Agile Cislunar Operations (DRACO) is on indefinite hold. Since initiating the program’s design phase two years ago, the DARPA-NASA management team has encountered the challenges inherent in sending a nuclear reactor into space for the first time in more than 60 years.

• The demonstration rocket’s engine reactor remains in “pre-PDR” phase
• Safety requirements are critical factors in finalizing the engine’s design

The team, including BWX Technologies (BWXT) and Lockheed Martin, hit snags in designing an engine that can be ground-tested safely while adhering to the protocols necessary to test a nuclear reactor, Matthew Sambora, one of two DRACO program managers in DARPA’s Tactical Technology Office, tells Aviation Week.

“We’re bringing two things together—space mission assurance and nuclear safety—and there’s a fair amount of complexity,” he says.

DARPA and NASA awarded a contract to BWXT and Lockheed Martin in July 2023 for DRACO Phases 2 and 3. BWXT was in charge of designing and building the reactor, manufacturing the fuel and delivering the complete subsystem. Lockheed would integrate the reactor with the engine and a demonstrator space vehicle ahead of on-orbit tests, then scheduled for 2027.

That team is now focused primarily on developing and delivering the DRACO engine and associated reactor, Sambora says. As such, “2027 is not a date that we’re shooting for at this point,” he explains, stressing that an eventual on-orbit demonstration remains a primary goal of the program.

The engine would consist of a 1-m-long (3.2-ft.), ultra-high-temperature, high-assay low-enriched uranium-fueled, flow-through nuclear reactor. The fission reaction is harnessed to generate heat to energize a helium gas propellant, which is exhausted to produce thrust. A follow-on operational engine would replace helium with more energetic liquid hydrogen fuel.

The DRACO team has not signed off on a design for BWXT’s reactor, Sambora says. “We are considering ourselves still pre-completed PDR,” he adds, referring to the preliminary design review. But he asserts that DARPA and its NASA partners will get there and that DRACO’s mission is not “undoable” but rather “difficult.”

While the reactor is at a “PDR level of maturity,” DARPA says it is examining design refinements meant to improve ground processing safety and enhance on-orbit data collection.

Lockheed Martin and BWXT plan to perform a cold flow test of the reactor in 2025, Kevin Au, Lockheed Martin Space’s vice president of lunar exploration campaigns, tells Aviation Week, expressing support for DARPA’s approach to focus resources on engine development.

The U.S. has not launched a reactor since the 1960s, an era euphemistically referred to as “the time before safety was invented,” says Jim Shoemaker, DARPA’s second DRACO program manager.  Scientists in the Nuclear Engine for Rocket Vehicle Applications program conducted six ground tests of radioactive reactors in open air between 1964 and 1969, “which we could never get approved to do today,” Shoemaker notes.

A DRACO ground test would need to capture plume exhaust fully to ensure no radioactive materials are released to the environment, but the U.S. does not possess this type of engine test capability, Ramon Osorio, a spokesperson at NASA’s Marshall Space Flight Center in Huntsville, Alabama, tells Aviation Week.

While “cost-effective” approaches are being explored for a single-event, short-duration engine test comparable to what the DRACO effort would require, Osorio says that “qualifying an operational nuclear thermal propulsion engine for space transportation will require a ground-test capability that accommodates full-duration engine operations, with additional facility support to disassemble the engine for an engineering assessment of the internal hardware post-test.”

As it explores potential means of testing the engine, the DRACO team is working to maximize ground-based component and subsystem testing that can be done with existing capabilities, a subset of which will take place at Marshall Space Flight Center, Osorio says.

Even after the demonstration, DRACO’s challenges will not be behind it. Long-term storage of cryogenic hydrogen for the follow-on propulsion system remains a key challenge for the scientific community.

Meanwhile, DARPA released a request for information on Dec. 13 regarding ways the DRACO engine could be hosted more widely across a range of space vehicles—for example, by building a nonproprietary interface based on the current reactor design and development program.

“As part of any program, it’s good to understand what’s available and to be continually evaluating options and ways forward and adjusting your thinking,” Sambora says.

At this point, Lockheed Martin’s role in the DRACO project is to provide an engine and support DARPA and NASA in developing the safety requirements and launch integration protocols along with ground handling procedures, he explains, to integrate and launch a reactor safely. “We’re not set into, at this point, any one way of getting this demonstration done,” he says.

DRACO’s current spacecraft bus design is based on Lockheed Martin’s Osiris-Rex spacecraft, which visited and collected samples from the near-Earth asteroid Bennu over a seven-year mission that ended in 2023. “We have a strong baseline we can apply from that to DRACO,” Au says.

Once a DRACO demonstration proves successful, it could take another 10-15 years before the technology is used on an operational basis, says Shoemaker, who was the first program manager for DARPA’s Orbital Express mission.

That project demonstrated satellite servicing activities in 2007, such as rendezvous proximity operations, docking and fluid transfer. In 2019, Northrop Grumman launched its Mission Extension Vehicle-1, a commercial satellite designed to service aging satellites.

Nuclear propulsion is crucial to future military and civil space programs, offering the potential to reduce trip times substantially and lower the risks associated with space radiation, zero gravity, launch and orbital assembly requirements. The U.S. Space Force needs it to allow spacecraft to maneuver more nimbly on orbit, while NASA’s goal is to support deep space exploration and transport humans to Mars.

For the first time since the collapse of the Soviet Union, the U.S. and Europe are not alone in their pursuit of space nuclear propulsion. Six years ago, China launched a program to develop a “megawatt-class, ultra-small, liquid metal-cooled, space nuclear reactor,” scientists reported in the April 2024 edition of the Chinese Science academic journal. Component-level testing verified the feasibility for an experimental prototype Chinese reactor, which is based on a highly enriched uranium fuel, the report states.

The U.S. and Chinese programs share a common goal of unleashing space travel at durations and speeds impossible with chemical- or solar-based propulsion systems. The U.S. program also capitalizes on newly gained bipartisan support for nuclear power. In his first term, President-elect Donald Trump signed a policy document that kick-started the Pentagon’s space nuclear reactor testing efforts. The updated policy transfers authority for launching a nuclear reactor into space from the White House to the Pentagon, easing the political road to approval.

—With Steve Trimble in Washington

Editor’s note: This article has been updated to correct the length of the nuclear reactor.