NTP Engines Nuclear Thermal Propulsion


Nuclear thermal propulsion (NTP) systems work by heating up a gas, usually hydrogen or ammonia, with a nuclear fission reactor and expanding that gas through a nozzle to produce efficient thrust. Nuclear engines will be used exclusively in space, not inside Earth’s atmosphere.

USNC's nuclear thermal propulsion (NTP) system


Deceptively Powerful

Ultra Safe Nuclear is developing a class of NTP engines with variants for technology demonstrations, Mars missions, and commercial applications. NTP engines are just a little larger than a trash can but can offer high specific impulse, enabling 2x ∆V (change in velocity) and 3-10x greater payloads than chemical propulsion engines. NTP engines will be cheap, fast, and carry lots of payload.


NTP engines will use a remarkably low quantity of uranium fuel in roughly 3-ton or smaller engines. The ZrC cercer-fueled, beryllium-moderated reactor core achieves all DOE and NASA goals with sufficient flexibility for commercial variants.


<50 kg


Use of monopropellants like H2 means fewer tanks and pumps compared to chemical bipropellants. Commercial variants will use non-cryogenic NH3 propellant.

Full Fission Product Retention

NTP engines will use nuclear fuels derived from FCM Fuel that allow for high temperature operation in hot hydrogen and ammonia environments.


With in-space refueling, NTP engines have the potential for extensive reuse, performing multiple startups and shutdowns with margin.


NTP engines can also be used for power-intensive applications such as cryocoolers, life support, electric propulsion/bimodal operation, and other applications.



Get there Faster and Carry More Payload

NTP engines will offer step change capabilities for commercial missions including space tugs and deep space missions.


Lunar Gateway
NTP system with space background.
NTP system with space background.

Commercial Capability

Unparalleled Orbital Maneuverability

Commercial NTP engines can produce more impulsive Δv than any current impulsive propulsion system.

Storable Propellant

Pressurized ammonia is storable at room temperatures and enables long duration missions.

5X+ Payload Capacity On High Δv Missions

Spacecraft equipped with commercial NTP engines can move more than five times the payload on high Δv missions compared to existing impulsive propulsion technology.

Lunar Round Trip Capable

Spacecraft equipped with commercial NTP engines enable travel from Earth orbit to Lunar orbit and back to Earth orbit.

55°+ Inclination Change Capable

The Δv enabled by commercial NTP can enable large inclination changes for spacecraft.

Falcon 9 Launchable

Dense ammonia propellant and a compact reactor design leaves ample room for payload even in a standard Falcon 9 fairing.

Refuellable On-orbit

Commercial NTP engines can be refilled with ammonia propellant and operate for multiple missions.

Mars Capability

Enabling Opposition-Class Mars Missions

The voyage to Mars is long and perilous, filled with cosmic and solar radiation. To protect astronauts from a high dose of space radiation, transit time must be significantly reduced. NTP engines will be able to complete opposition-class crewed Mars missions significantly faster than chemical propulsion.

12.5–25 klbf

250 MWth
Thermal Power


651 days

  • Day 0: Earth Departure 8/30/2037
  • Day 217: Mars Arrival 4/4/2038
  • Day 247: Mars Departure 5/4/2038
  • Day 465: Venus Swing-By 12/8/2038
  • Day 651: Earth Return 6/11/2039

The Human Mars Mission Done Fast

NTP enables an opposition-class mission trajectory for human Mars exploration. The lower Δv conjunction class mission requires astronauts to be away from Earth for approximately 2.5 years. The opposition-class mission can be completed in approximately 1.5 years. The shorter opposition-class mission limits the astronauts’ exposure to the dangers of space travel but requires approximately 3 times the Δv – made possible by nuclear thermal propulsion.

Back to the Future

We Stand on the Shoulders of Giants

Nuclear thermal propulsion is a proven concept first demonstrated in the Rover and NERVA programs in the US from 1955 to 1973. These programs designed, built, and tested 22 engines before ending without attempting space launch.

Kiwi A Rendering Kiwi B Rendering Phoebus I/NRX Rendering Phoebus 2 Rendering Padme Rendering
Kiwi A Kiwi B Phoebus I/NRX Phoebus 2
1958 1961 1965 1967
100 MW 1000 MW 1500 MW 5000 MW
5 klb Thrust 50 klb Thrust 50 klb Thrust 250 klb Thrust


Launch Failures

Launch failures do not pose an excess risk for NTP engines. The core is designed to withstand water submersion without activation. This means explosive launch failures or water submersion scenarios do not lead to nuclear accidents and pose no additional risk compared to ordinary launch failures.


Ultra Safe Nuclear first pioneered the new paradigm for low enriched uranium nuclear rocket cores in 2015. Ever since, USNC-Tech has developed fuels, moderators, and core designs to enable the first NTP demonstration systems for NASA and DARPA NTP programs.


NASA Selects USNC Advanced Technologies for Ultra-High Temperature Component Testing Facility

USNC-Tech has been selected for a Phase II SBIR to develop an ultra-high temperature facility for testing materials planned for use in NTP systems.

USNC-Tech Team Wins Contract to Develop Nuclear Thermal Propulsion System For NASA

Idaho National Laboratory has selected USNC-Tech and its partners to develop a nuclear thermal propulsion (NTP) reactor concept design for space exploration: the Power-Adjusted Demonstration Mars Engine (PADME) NTP engine.

USNC supports two DARPA Awards to Design Cislunar Nuclear Thermal Propulsion System

SEATTLE, WASHINGTON, June 10, 2021— The U.S. Defense Advanced Research Projects Agency (DARPA) recently awarded contracts to General Atomics (Track A, $22M) and Blue