Nuclear thermal rocket

A nuclear thermal rocket (NTR) is a type of <a href="/facts/Thermal_rocket/lm2Gl5ND">thermal rocket</a> where the heat from a <a href="/facts/Nuclear_reaction/202yClUr">nuclear reaction</a> replaces the chemical energy of the <a href="/facts/Rocket_propellant/IyFhQEA2">propellants</a> in a <a href="/facts/Chemical_rocket/XT5gaFAb">chemical rocket</a>. In an NTR, a <a href="/facts/Working_fluid/GvHk1AMq">working fluid</a>, usually <a href="/facts/Liquid_hydrogen/Vpk3Gb8P">liquid hydrogen</a>, is heated to a high temperature in a <a href="/facts/Nuclear_reactor/8xqjIbge">nuclear reactor</a> and then expands through a <a href="/facts/Rocket_engine_nozzle/K4kHCmFX">rocket nozzle</a> to create <a href="/facts/Thrust/EM04CqV7">thrust</a>. The external nuclear heat source theoretically allows a higher <a href="/facts/Effective_exhaust_velocity/JKGgw2I4">effective exhaust velocity</a> and is expected to double or triple payload capacity compared to chemical propellants that store energy internally.
NTRs have been proposed as a <a href="/facts/Spacecraft_propulsion/KmpMGU9u">spacecraft propulsion</a> technology, with the earliest ground tests occurring in 1955. The United States maintained an NTR development program through 1973 when it was shut down for various reasons, including to focus on <a href="/facts/Space_Shuttle/7BoyetEv">Space Shuttle</a> development. Although more than ten reactors of varying power output have been built and tested, as of 2025<a href="https://en.wikipedia.org/w/index.php?title=Nuclear_thermal_rocket&action=edit">[update]</a>, no nuclear thermal rocket has flown.
Whereas all early applications for nuclear thermal rocket propulsion used <a href="/facts/Nuclear_fission/LfkIylvm">fission</a> processes, research in the 2010s has moved to <a href="/facts/Nuclear_fusion/hP0gLDqj">fusion</a> approaches. The <a href="/facts/Direct_Fusion_Drive/LFhk8AMY">Direct Fusion Drive</a> project at the <a href="/facts/Princeton_Plasma_Physics_Laboratory/YEBMkkow">Princeton Plasma Physics Laboratory</a> is one such example, although "energy-positive fusion has remained elusive". In 2019, the <a href="/facts/United_States_Congress/mJlU46K7">U.S. Congress</a> approved US$125 million in development funding for nuclear thermal propulsion rockets.
In May 2022 <a href="/facts/DARPA/Uf9sarhT">DARPA</a> issued an RFP for the next phase of their <a href="/facts/Demonstration_Rocket_for_Agile_Cislunar_Operations_(DRACO)/Fo40J4AN">Demonstration Rocket for Agile Cislunar Operations (DRACO)</a> nuclear thermal engine program. This follows on their selection, in 2021, of an early engine design by <a href="/facts/General_Atomics/u8jAsX9y">General Atomics</a> and two spacecraft concepts from <a href="/facts/Blue_Origin/CxFvEmDr">Blue Origin</a> and <a href="/facts/Lockheed_Martin/URp9BQpA">Lockheed Martin</a>. The next phases of the program will focus on the design, development, fabrication, and assembly of a nuclear thermal rocket engine.
In July 2023, <a href="/facts/Lockheed_Martin/URp9BQpA">Lockheed Martin</a> was awarded the contract to build the spacecraft and BWX Technologies (<a href="/facts/BWXT/tBvvT5D7">BWXT</a>) will develop the nuclear reactor. A launch is expected in 2027.

Nuclear thermal rocket open-in-new

Nuclear thermal rocket