Artist concept of Demonstration for Rocket to Agile Cislunar Operations (DRACO) spacecraft, which will demonstrate a nuclear thermal rocket engine. Nuclear thermal propulsion technology could be used for future NASA crewed missions to Mars. (DARPA)
WASHINGTON — NASA will fund the development of an experimental nuclear thermal engine under a new cooperative effort with the Pentagon’s far-future research agency to test the technology’s viability for powering spacecraft to the Moon, Mars and beyond, according to officials at the Defense Advanced Research Projects Agency.
Tabitha Dodson, DARPA’s program manager for the Demonstration Rocket for Agile Cislunar Operations (DRACO) initiative, told Breaking Defense on Jan. 27 that as well as funding the nuclear thermal rocket (NTR) engine, NASA also will be managing the contractor team responsible for developing it.
“They will make sure that the performers are building everything exactly to the specs that we set out for the kind of performance that we mutually agree that we both want,” she said.
This includes things like making sure the materials can withstand the high temperatures, up to 5,000 degrees Fahrenheit, generated and building a turbo-pump for the engine, she explained.
“We haven’t built a turbo pump for a nuclear thermal rocket in a very long time,” Dodson said. “Although NASA does have incredible rocket engine expertise.”
While NASA is providing the funds for the engine and ensuring the parts meet spec, DARPA will serve as the contracting agent and the work will be performed by a prime contractor, who Dodson explained has been selected but has yet to be formally put on contract — a process that she said would take about a month or two.
An NTR uses fission, the splitting of atoms, for power just like terrestrial nuclear reactors for generating electricity. Thus, nuclear propulsion “offers a high thrust-to-weight ratio around 10,000 [times] greater than electric propulsion and with two-to-five times greater efficiency than in-space chemical propulsion,” DARPA explained in its Jan. 24 announcement of the deal with NASA.
In the 1960s, rocket pioneer Wernher von Braun served as NASA’s Marshall Space Flight Center director and blueprinted use of Nuclear Thermal Propulsion to send astronauts to Mars by the early 1980s. (NASA/Marshall Space Flight Center)
Despite some uneasiness with nuclear power among the general populace, US space scientists long have understood the potential of nuclear propulsion to significantly chop time off of deep space missions, Dodson said, going all the way back to the “father of space travel” Wernher von Braun. As early as the 1960s, von Braun had created blueprints for nuclear rockets for taking humans to Mars by the 1980s.
“When people like to question the validity or usefulness of this engine, I point them to Wernher von Braun,” she said, “because this was more or less his idea. … If you don’t believe me, at least believe him.”
DARPA also is interested in NTR for its potential to allow “agile, responsive maneuverability (potentially across vast distances) within the cislunar domain for a variety of missions.”
DARPA awarded contracts to General Atomics, Blue Origin and Lockheed Martin in April 2021 for Phase 1 of the DRACO program, and in May 2022 put out a solicitation for Phases 2 and 3 to develop and test the engine and perform a flight demonstration. NASA up to now had also been pursuing NTR tech, contracting in July 2021 with three teams led by BWX Technologies, General Atomics and Ultra Safe Nuclear Technologies to design the nuclear reactor at the core of a such a rocket engine.
Under the new NASA-DARPA agreement, DARPA also will lead development of the space vehicle, called the X-NTRV, to house the engine, Dodson said, and manage the overall program, including systems integration. Building that vehicle will be no small task, because of the fact that NTR engines themselves are, well, rocket engines, rather than the small electric propulsion engines often used to maneuver satellites.
“The size of this vehicle is the size of an upper stage. So think like the Centaur,” Dodson said.
The liquid-fueled (oxygen and hydrogen) Centaur, which has long served as the upper stage of ULA’s Atlas V and has launched many a NASA probe into the far reaches of the solar system, stands at 12.7 m (41.6 ft).
While the agency originally envisioned using DRACO to also demonstrate a payload for keeping tabs on satellites and potentially dangerous meteorites in the vast volume of cislunar space between the orbits of the Earth and the Moon, the focus of the program has shifted, Dodson said.
“DRACO’s design reference mission has shifted away from space domain awareness and is now more focused on upper stage maneuver and logistics missions,” she explained.
The change was made in part because the NTR is too big to make sense for powering for a space monitoring satellite, but also because of a change in Space Force focus away from cislunar domain awareness and towards how DRACO might demonstrate high-speed maneuvering, Dodson explained.
Last August, Space Command Deputy Commander Lt. Gen. John Shaw told a DARPA Forward forum that “space maneuver and logistics” — that is, the capability to rapidly maneuver satellites and the space-based infrastructure, such as orbiting re-fueling stations, necessary to support that capability — is among the command’s top priorities for technological innovation.
Dodson said the Space Force has signed a “letter of commitment” to seek funding in the next five-year budget cycle (beginning with fiscal 2024) to pay for DRACO’s launch vehicle. DARPA hopes to be able to launch during the last quarter of fiscal year 2027, in other words in late calendar year 2026, she added.
As for the public fears about safety that often are raised about the use of nuclear fuel in rockets, Dodson explained that NASA been using radioisotope thermoelectric generators (essentially, small nuclear batteries) “that are constantly emitting high levels of radiation” on spacecraft for years with “no mishaps.”
And unlike those devices, she added, DRACO’s NTR can be powered off and on — and will only be turned on once the space vehicle is already far away from Earth so that “there will be absolutely no radioactive hazard associated with this this reactor.”
Finally, Dodson explained, even if there was an issue with an NTR on the ground, it wouldn’t explode like a nuclear bomb. Instead, she said, if a fission engine core were to overheat, it would simply “turn itself off.”