To date, no nuclear thermal rocket has flown, although the NERVA NRX / EST and NRX / XE were built and tested with flight design components.

The NERVA NRX / XE, judged by SNPO to be the last " technology development " reactor necessary before proceeding to flight prototypes, accumulated over 2 hours of run time, including 28 minutes at full power.

The United States tested twenty different sizes and designs during Project Rover and NASA's NERVA program from 1959 through 1972 at the Nevada Test Site, designated Kiwi, Phoebus, NRX / EST, NRX / XE, Pewee, Pewee 2 and the Nuclear Furnace, with progressively higher power densities culminating in the Pewee ( 1970 ) and Pewee 2.

Although the Kiwi / Phoebus / NERVA designs were the only ones to be tested in any substantial program, a number of other solid-core engines were also studied to some degree.

Dumbo was similar to KIWI / NERVA in concept, but used more advanced construction techniques to lower the weight of the reactor.

While the NERVA engine was projected to weigh about 6, 803 kg, the final STNP offered just over 1 / 3 the thrust from an engine of only 1, 650 kg by improving the I < small >< sub > sp </ sub ></ small > to between 930 and 1000 seconds.

SNPO fired NERVA NRX / XE twenty-eight times in March 1968.

NERVA NRX / XE produced the baseline 75, 000 lbf ( 334 kN ) thrust that Marshall required in Mars mission plans.

For the NERVA replacement considered above, this would be 121 kg / s.

One of the reasons for the cancellation of the NERVA project was the risk of radioactive particles being released in the rocket exhaust, so Hergé's chemical / nuclear combination makes sense.

NERVA demonstrated that nuclear thermal rocket engines were a feasible and reliable tool for space exploration, and at the end of 1968 SNPO certified that the latest NERVA engine, the NRX / XE, met the requirements for a manned Mars mission.

Although Los Alamos tested several KIWI and Phoebus engines during the 1960s, testing of NASA's NERVA NRX / EST ( Engine System Test ) contractor engine didn't begin until February 1966.

The NERVA NRX / EST engine test objectives now included:

The Rover / NERVA program accumulated 17 hours of operating time with 6 hours above 2000 K. Although the engine, turbine and liquid hydrogen tank were never physically assembled together, the NERVA was deemed ready to design into a working vehicle by NASA, creating a small political crisis in Congress because of the danger a Mars exploration program presented to the national budget.

SNPO would depend on what was then known as Los Alamos Scientific Laboratory to supply technology for NERVA rocket engines as part of Project Rover.

Phase 2 of Project Rover became called Phoebus, and Phase 3 was known as Pewee, demonstrating much higher power ( 4000 MW ), power density and long-lived fuels, but these programs did not make their way to NERVA.

Without the Saturn S-N rocket to carry the NERVA to orbit, Los Alamos continued the Rover Program for a few more years with Pewee and the Nuclear Furnace, but it was disbanded by 1972.

The name was a play on the larger systems being developed under Project Rover, which led to NERVA.

Hergé's rocket most closely resembles a nuclear thermal rocket, such as the design tested in the United States NERVA project.

This was NASA's first serious foray into nuclear spacecraft propulsion since the cancellation of the NERVA project in 1972.

* In Stephen Baxter ’ s 1996 alternate timeline novel Voyage the NERVA project is not canceled but development goes on throughout the 70s producing a test article Apollo-N in 1980.

NASA director of the Mars project and a big supporter of NERVA, and former Nazi rocket scientist.

In 1961, the NERVA program ( Nuclear Engine for Rocket Vehicle Applications ) was created.

Marshall Space Flight Center had been increasingly using KIWI for mission planning, and NERVA was formed to formalize the entry of nuclear thermal rocket engines into space exploration.

A 75, 000 lbf ( 334 kN ) thrust baseline NERVA design was based on the KIWI B4 series, and was considered for some time as the upper stages for the Saturn V, in place of the J-2s that were actually flown.

Although NERVA engines were built and tested as much as possible with flight-certified components and the engine was deemed ready for integration into a spacecraft, much of the U. S. space program was cancelled by the Nixon Administration before a manned visit to Mars could take place.

NERVA was considered by the AEC, SNPO and NASA to be a highly successful program ; it met or exceeded its program goals.

Almost all of the NERVA research, design and fabrication was done at Los Alamos Scientific Laboratory.

The second NERVA engine, the NERVA XE, was designed to come as close as possible to a complete flight system, even to the point of using a flight-design turbopump.

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, and the KIWI gradually gave way at Los Alamos to the smaller Pewee and Pewee 2 as funding was cut to lower and lower levels by Congress and the Nixon administration.

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.

Each year the RIFT was delayed and the goals for NERVA were set higher.

Ultimately, RIFT was never authorized, and although NERVA had many successful tests and powerful Congressional backing, it never left the ground.

NERVA is an acronym for Nuclear Engine for Rocket Vehicle Application, a joint program of the U. S. Atomic Energy Commission and NASA managed by the Space Nuclear Propulsion Office ( SNPO ) until both the program and the office ended at the end of 1972.

* In the 1968 short story " Wait It Out ", by Larry Niven, an ill-fated exploration mission to Pluto uses a landing craft with a NERVA engine.

* The 1970 novel The Throne of Saturn by Allen Drury describes a fictional Project Argosy, a mission to Mars consisting of three Saturn V vehicles, each with a NERVA upper stage.

A disaster occurs, the NERVA technology is abandoned as unsafe, and a mission to Mars is launched using chemical rocket engines with a slingshot gravity assist via Venus allowing an expedition to arrive on Mars in 1986.

This leads to a crash program with Russia and the United States partnering to re-engine a partly complete manned Mars spacecraft with a NERVA rocket motor to send a team to inspect the device.

At the same time, the NERVA program is revived to become the chosen Mars spacecraft development, with larger tests in Nevada, but without containment and plagued with engineering problems.

The book centers around chronicling the lives of the future Mars mission astronauts, NASA and contractor personnel all involved helping in making the mission become a reality, and the shifts within NASA's astronaut and management hierarchy throughout the mission's preparations, including female geologist Natalie York's quest to become an astronaut, and her stormy relationships between fellow astronaut Ben Priest and with NERVA engineer Mike Conlig.

NASA plans for NERVA included a visit to Mars by 1978 and a permanent lunar base by 1981.

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.