US military planning to develop nuclear rockets for future Moon missions

The US military is planning to develop a nuclear rocket to help monitor the area between Earth and the moon, a space that it considers a strategic priority for “modern commerce, scientific discovery, and national defense”.

On 4 May, the US military’s Defense Advanced Research Projects Agency (Darpa) announced it is seeking proposals for the second and third phases of a project to design and demonstrate a nuclear thermal rocket engine operation in orbit by 2026.

“The United States employs maneuver to maintain advantages in the land, sea, and air domains. However, maneuver is more challenging in space due to propulsion system limitations,” Major Nathan Greiner, program manager in Darpa’s Tactical Technology Office, said in a statement.

“To maintain technological superiority in space, the United States requires leap-ahead propulsion technology that the Draco program will provide,” Mr Greiner added.

Darpa believes maintaining domain awareness in the space between Earth and the moon would require a “leap-ahead in propulsion technology”.

The new proposals for phase 2 of the project will support the agency’s Demonstration Rocket for Agile Cislunar Operations (Draco) program for developing a nuclear thermal propulsion (NTP) system for use in the Earth-moon space.

NTP uses a nuclear reactor to heat rocket propellant to extreme temperatures before expelling it through a nozzle to produce thrust.

Compared to conventional technologies used for propulsion in space, Darpa says NTP can offer a high thrust-to-weight ratio around 10,000 times greater than electric propulsion and two-to-five times greater efficiency than chemical propulsion.

“These propulsive capabilities will enable the US to enhance its interests in space and to expand possibilities for Nasa’s long-duration human spaceflight missions,” the defence agency noted.

Phase 1 of the Draco program involved two parallel risk reduction activities, which included awards for General Atomics, Blue Origin, and Lockheed Martin in April 2021.

These activities included Track A, for General Atomics, which was focused on developing a preliminary design for the rocket engine reactor.

Track B, pursued by Blue Origin and Lockheed Martin independently, concentrated on developing a conceptual design for the in-orbit demonstration system.

“The objectives of Phase 2 are to complete the preliminary and detailed design of a Demonstration System (DS) and to construct and experimentally validate the NTR flight engine to the extent possible,” Darpa officials said.

Nasa has also expressed interest in nuclear space propulsion, and its 2023 budget request, which is yet to be approved by the US Congress, includes $15m to support this technology.

In 2022, the US Congress provided “steady funding” of $110m for nuclear thermal propulsion efforts, rejecting the Biden administration’s proposal to refocus Nasa’s efforts on developing a nuclear reactor to power crewed bases on the Moon.