Nuclear Propulsion for Spacecraft: A Quick Review

Nuclear propulsion, once confined to the realm of science fiction, is becoming a real possibility for future space missions. Capable of providing a continuous and efficient source of propulsion over long periods, this technology could potentially revolutionize interplanetary and interstellar travel.

What is Nuclear Propulsion?

Nuclear propulsion is a method of propulsion for spacecraft that uses nuclear reactions to generate thrust. It comes in two primary forms – nuclear thermal propulsion (NTP) and nuclear electric propulsion (NEP).

Nuclear Thermal Propulsion (NTP)

Nuclear thermal propulsion uses nuclear reactors to heat a propellant (like hydrogen) to high temperatures. The hot propellant is then expelled from the spacecraft’s engine, providing the thrust that propels the spacecraft forward. This technology offers far greater fuel efficiency compared to conventional chemical rockets, thus providing a higher effective exhaust velocity, or ‘specific impulse’.

NTP systems were heavily researched during the Cold War, most notably in NASA’s Project Rover and the Nuclear Engine for Rocket Vehicle Application (NERVA) program. The research concluded in 1972 with a successful ground test of a NTP engine, though no such engine has ever been used in a space mission.

Nuclear Electric Propulsion (NEP)

Unlike NTP, which uses the heat from a nuclear reactor directly to generate thrust, nuclear electric propulsion systems use the reactor to generate electricity, which then powers an electric propulsion system. NEP spacecraft use ion drives or Hall thrusters, where ions are expelled out to create a reaction force.

Though less efficient in terms of thrust-to-weight ratio compared to NTP, NEP systems have higher specific impulse and are better suited for missions requiring long-duration, low-thrust burns, such as deep-space missions.

Advantages of Nuclear Propulsion

Nuclear propulsion offers several significant advantages over traditional chemical rockets.

Increased Efficiency

The main advantage is the ability to achieve higher specific impulses, or the change in momentum per unit mass of propellant consumed. This efficiency translates into a greater ability to carry payload mass, increase mission speed, or extend the mission range.

Extended Mission Duration

Nuclear propulsion can provide continuous thrust for years, if necessary. This makes it an ideal technology for long-duration missions, such as those to the outer planets or even to other star systems.

Reduced Travel Time

By providing a constant thrust, nuclear propulsion can significantly reduce travel time to distant locations in the solar system. For example, a nuclear-powered mission to Mars could potentially cut the travel time in half compared to traditional chemical propulsion.

Challenges and Concerns

Despite the potential advantages, there are several significant challenges and concerns that must be addressed.


A nuclear propulsion system produces significant amounts of radiation, posing risks to both crew and instrumentation. Shielding to protect against this radiation adds mass and complexity to the spacecraft.

Waste Heat

Nuclear reactors produce a large amount of waste heat that must be managed. This is a particular challenge in space, where the vacuum environment makes it difficult to dissipate heat.

Launch Safety

The launch of a nuclear-powered spacecraft poses potential risks. In the event of a launch failure, there could be a release of radioactive material.

Political and Regulatory Challenges

The use of nuclear power in space is subject to a variety of national and international regulations and treaties. Overcoming these regulatory hurdles is a significant challenge.


Year/Period Event
1940s-1950s: Initial Conceptualization Early discussions and conceptual work on nuclear propulsion began, with physicists and engineers exploring the potential uses of nuclear power for propulsion.
1955: Project Rover Begins The U.S. starts Project Rover, aiming to develop nuclear thermal rocket engines.
1959: First Nuclear Power Satellite Launched The U.S. launches the first nuclear-powered satellite, the Transit IV-A, using a small radioisotope thermoelectric generator (RTG).
1961: NERVA Program Initiated The Nuclear Engine for Rocket Vehicle Application (NERVA) program starts as a joint effort between NASA and the Atomic Energy Commission to develop nuclear thermal propulsion for long-range space missions.
1972: Final Test of NERVA The final ground test of a NERVA engine is conducted successfully, but the program is cancelled later due to budget constraints and the end of the space race.
1980s: Work on Nuclear Electric Propulsion Studies and experimental work on nuclear electric propulsion (NEP) technologies ramp up during the 1980s.
2003: Project Prometheus NASA launches Project Prometheus to develop nuclear power and propulsion technologies for long-duration space missions. The project is cancelled in 2005 due to budget cuts.
2010s: Advancements in Nuclear Propulsion There are advancements in both NTP and NEP technologies, with several countries and private companies showing interest in these technologies for future space missions.
2018: NASA’s KRUSTY Experiment NASA’s Kilopower Reactor Using Stirling Technology (KRUSTY) experiment successfully demonstrates the use of a small nuclear reactor for power generation in space.
2020: U.S. Legislation The U.S. passes legislation to support the development of nuclear propulsion technologies for space travel.
2020: NASA’s Fission Surface Power Project A project is launched which is tasked with developing and demonstrating a fission power system which can generate at least 40 kW. A demonstration on the Moon is planned by 2030.
2023: Project DRACO NASA and DARPA announce collaboration to develop and demonstrate a NTP in space.
Project DRACO
Illustration of the DRACO spacecraft
Source: NASA

NASA and DARPA are currently partnering on the Demonstration Rocket for Agile Cislunar Operations, or DRACO, program. NASA’s Space Technology Mission Directorate (STMD) is leading technical development of a nuclear thermal engine to be integrated with DARPA’s experimental spacecraft. DARPA is acting as the contracting authority for the development of the entire stage and the engine, which includes the reactor. DARPA is leading the overall program including rocket systems integration and procurement, approvals, scheduling, and security, cover safety and liability, and ensure overall assembly and integration of the engine with the spacecraft. Over the course of the development, NASA and DARPA will collaborate on assembly of the engine before the in-space demonstration as early as 2027.

Future Prospects

Nuclear propulsion presents a transformative approach to space travel, promising increased efficiency, extended mission duration, and reduced travel time. However, several challenges and concerns remain, ranging from technical and safety issues to political and regulatory hurdles. As we continue to explore the final frontier, the development and eventual deployment of nuclear propulsion systems will be a critical area of focus and investment in the years to come.

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