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NERVA II Diagram

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Blender built NERVA model.

Nuclear rockets utilize fission energy to heat a reactor core to high temperatures. Hydrogen gas flowing through the core becomes super heated and exits the engine at very high exhaust velocities. The combination of temperature and the low molecular weight of hydrogen will produce an engine with specific impulses above 900 seconds. This is almost twice the performance of the LOX/hydrogen space shuttle engines.

See Winchell Chung’s Atomic Rockets site, Engine List page under the NTR Solid Core entry for more information.

NERVA History

NERVA is an acronym for Nuclear Engine for Rocket Vehicle Application, a U.S. nuclear thermal rocket engine development program that ran for roughly two decades. NERVA was a joint effort of the U.S. Atomic Energy Commission and NASA.

Los Alamos Scientific Laboratory began researching nuclear rockets in 1952, accelerating into Project Rover in 1955. By 1961, after unexpectedly fast-paced progress on Project Rover, NASA's Marshall Space Flight Center began to use nuclear thermal rockets in their mission plans. Marshall planned to use a nuclear-powered rocket from Los Alamos to power a RIFT (Reactor-In-Flight-Test) nuclear stage to be launched as early as 1964, and the need for planning and oversight led to the formation of the Space Nuclear Propulsion Office (SNPO).

Aerojet and Westinghouse were selected to develop the NERVA engine. Almost all of the NERVA research, design and fabrication was done at Los Alamos Scientific Laboratory. Testing was done at a large installation specially built on the Nevada Test Site.

The final engine tested used a core made of graphite rods 54 inches long, hexagonal in cross section with 0.75 inches across the flats, and with 19 holes running the full length of the rod. The rod was a mixture of uranium/zirconium/carbide in a graphite matrix. Each flow hole was independently orificed to match the heat generation levels.

NERVA was considered by the AEC, SNPO and NASA to be a highly successful program; it met or exceeded its program goals. Its principal objective was to "establish a technology base for nuclear rocket engine systems to be utilized in the design and development of propulsion systems for space mission application". Virtually all space mission plans that use nuclear thermal rockets use derivative designs from the NERVA NRX or Pewee.

NASA plans for NERVA included a visit to Mars by 1978 and a permanent lunar base by 1981. NERVA rockets would be used for nuclear "tugs" designed to take payloads from Low Earth Orbit to larger orbits as a component of the later-named Space Transportation System, resupply several space stations in various orbits around the Earth and Moon, and support a permanent lunar base. The NERVA rocket would also be a nuclear-powered upper stage for the Saturn rocket (the Saturn S-N), which would allow the upgraded Saturn to launch much larger payloads of up to 340,000 pounds to Low Earth Orbit.

NERVA rockets had progressed rapidly to the point where they could run for hours, limited in run time by the size of the liquid hydrogen propellant tanks at the Jackass Flats test site. They also climbed in power density. The larger NERVA I rocket gradually gave way to the smaller NERVA II rocket in mission plans as efficiency increased and thrust-to-weight ratios grew.

The RIFT vehicle consisted of a Saturn S-IC first stage, an SII stage and an S-N (Saturn-Nuclear) third stage. The Space Nuclear Propulsion Office planned to build ten RIFT vehicles, six for ground tests and four for flight tests, but RIFT was delayed after 1966 as NERVA became a political proxy in the debate over a Mars mission. The nuclear Saturn C-5 would carry two to three times more payload into space than the chemical version, enough to easily loft 340,000 pound space stations and replenish orbital propellant depots. Wernher von Braun also proposed a manned Mars mission using NERVA and a spinning donut-shaped spacecraft to simulate gravity. Many of the NASA plans for Mars in the 1960s and early 1970s used the NERVA rocket specifically, see list of manned Mars mission plans in the 20th century.

Although NERVA engines were built and tested and the engine was deemed ready for integration into a spacecraft, the program was cancelled at the end of 1972.

NERVA
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Special thanks to Winchell Chung for a truly impressive archive of diagrams he offered in assistance.
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menutman's avatar
Really cool, I also like the explain in the desc.,