NERVA

Nerva ( ; born Marcus Cocceius Nerva; 8 November 30 – 27 January 98) was a Roman emperor from AD 96 to 98. Nerva became emperor when aged almost 66, after a lifetime of imperial service under Nero and the succeeding rulers of the Flavian dynasty. Under Nero, he was a member of the imperial entourage and played a vital part in exposing the Pisonian conspiracy of 65. Later, as a loyalist to the Flavians, he attained consulships in 71 and 90 during the reigns of Vespasian and Domitian, respectively. After Domitian was assassinated in a palace conspiracy involving members of the Praetorian Guard and several of his freedmen on 18 September 96, Nerva was declared emperor by the Roman Senate. During his reign, he vowed to restore liberties which had been curtailed during the autocratic government of Domitian. Nerva's brief reign was marred by financial difficulties and his inability to assert his authority over the Roman army. A revolt by the Praetorian Guard in October 97 essentially forced him to adopt an heir. After some deliberation Nerva adopted Trajan, a young and popular general, as his successor. After barely fifteen months in office, Nerva died of natural causes on 27 January 98. Upon his death he was succeeded and deified by Trajan. Although much of his life remains obscure, Nerva was considered a wise and moderate emperor by ancient historians.…

The Nuclear Engine for Rocket Vehicle Application (NERVA; ) was an American nuclear thermal rocket engine development program that ran for roughly two decades. 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". It was a joint effort of the Atomic Energy Commission (AEC) and the National Aeronautics and Space Administration (NASA), and was managed by the Space Nuclear Propulsion Office (SNPO) until the program ended in January 1973. SNPO was led by NASA's Harold Finger and AEC's Milton Klein. NERVA had its origins in Project Rover, an AEC research project at the Los Alamos Scientific Laboratory (LASL) with the initial aim of providing a nuclear-powered upper stage for the United States Air Force intercontinental ballistic missiles. Nuclear thermal rocket engines promised to be more efficient than chemical ones. After the formation of NASA in 1958, Project Rover was continued as a civilian project and was reoriented to producing a nuclear powered upper stage for NASA's Saturn V Moon rocket. Reactors were tested at very low power before being shipped to Jackass Flats in the Nevada Test Site. While LASL concentrated on reactor development, NASA built and tested complete rocket engines. The AEC, SNPO, and NASA considered NERVA a highly successful program in that it met or exceeded its program goals. It demonstrated that nuclear thermal rocket engines were a feasible and reliable tool for space exploration, and at the end of 1968 SNPO deemed that the latest NERVA engine, the XE, met the requirements for a human mission to Mars. The program had strong political support from Senators Clinton P. Anderson and Margaret Chase Smith but was cancelled by President Richard Nixon in 1973. 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, they never flew in space. ==Project Rover== ===Underlying concepts=== Rocket engines create thrust by accelerating a working mass in a direction opposite to their desired trajectory. In conventional designs, this is accomplished by heating a fluid and allowing it to escape through a rocket nozzle. The energy needed to produce the heat is provided by a chemical reaction in the fuel, which may be mixed together as in the case of most solid fuel rockets, or separate tanks as in most liquid fuel rockets. Selecting the fuels to use is a complex task that has to consider the reaction energy, the mass of the fuel, the mass of the resulting working fluid, and other practical concerns like density and its ability to be easily pumped. Nuclear rocket engines use a nuclear reactor to provide the energy to heat the fuel instead of a chemical reaction. Because nuclear reactions are much more powerful than chemical ones, a large volume of chemicals can be replaced by a small reactor. As the heat source is independent of the working mass, the working fluid can be selected for maximum performance for a given task, not its underlying reaction energy. Due to its low molecular mass, hydrogen is normally used. This combination of features allows a nuclear engine to outperform a chemical one; they generally aim to have at least twice the specific impulse of a chemical engine. ===NERVA XE=== With the success of the A6 test, SNPO cancelled planned follow-on tests A7 and A8 and concentrated on completing ETS-1. All previous tests had the engine firing upwards; ETS-1 would permit an engine to be reoriented to fire downward into a reduced-pressure compartment to partly simulate firing in the vacuum of space. The test stand provided a reduced atmospheric pressure of about – equivalent to being at an altitude of . This was done by injecting water into the exhaust, which created superheated steam that surged out at high speeds, creating a vacuum. ETS-1 took longer for Aerojet to complete than expected, partly due to shrinking budgets, but also because of technical challenges. It was built from pure aluminum, which did not become radioactive when irradiated by neutrons, and there was a water spray to keep it cool. Rubber gaskets were a problem, as they tended to turn into goo in a radioactive environment; metal ones had to be used. The most challenging part was the exhaust ducts, which were required to handle much higher temperatures than their chemical rocket counterparts. The steel work was carried out by Allegheny Technologies, and the Air Preheater Company fabricated the pipes. The work required of steel, of welding wire and of welds. During a test the 234 tubes would have to carry up to of water. To save money on cabling, Aerojet moved the control room to a bunker away. ]] 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. To save time and money, components that would not affect the engine's performance were selected from what was available at Jackass Flats. A radiation shield was added to protect external components. The test objectives included testing the use of ETS-1 at Jackass Flats for flight engine qualification and acceptance. Total run time was 115 minutes, including 28 starts. NASA and SNPO felt that the test "confirmed that a nuclear rocket engine was suitable for space flight application and was able to operate at a specific impulse twice that of chemical rocket system[s]." The engine was deemed adequate for Mars missions being planned by NASA. The facility was also deemed adequate for flight qualification and acceptance of rocket engines from the two contractors. The final test of the series was XE Prime. This engine was long, in diameter, and weighed approximately . It was designed to produce a nominal thrust of with a specific impulse of . When the reactor was operating at full power, about 1,140 MW, the chamber temperature was , chamber pressure was , and the flow rate was , of which was diverted into the cooldown system. A series of experiments were carried out between 4 December 1968 and 11 September 1969, during which the reactor was started 24 times, and ran at full power for 1,680 seconds. ===Reactor and engine test summary=== Source: ==Cancellation== At the time of the NERVA NRX/EST test, NASA's plans for NERVA included a visit to Mars by 1978, a permanent lunar base by 1981, and deep space probes to Jupiter, Saturn, and the outer planets. NERVA rockets would be used for nuclear "tugs" designed to take payloads from low Earth orbit (LEO) to higher orbits as a component of the later-named Space Transportation System, resupply several space stations in orbit around the Earth and Moon, and support a permanent lunar base. The NERVA rocket could also be a nuclear-powered upper stage for the Saturn rocket, which would allow the upgraded Saturn to launch payloads of up to to LEO. Defending NERVA from its critics like Hornig, the chairman of the President's Science Advisory Committee (PSAC), required a series of bureaucratic and political battles as the rising cost of the Vietnam War put pressure on budgets. Congress defunded NERVA II in the 1967 budget, but President Johnson needed Senator Anderson's support for his Medicare legislation, so on 7 February 1967 he provided the money for NERVA II from his own contingency fund. Klein, who had succeeded Finger as head of the SNPO in 1967, faced two hours of questioning on NERVA II before the House Committee on Science and Astronautics. In the end, the committee cut NASA's budget. Defunding NERVA II saved $400 million, mainly in new facilities that would be required to test it. This time AEC and NASA acquiesced, because the NRX A6 test had demonstrated that NERVA I could perform the missions expected of NERVA II. The following year, Webb attempted to take money from NERVA I to pay for NASA overhead after Congress cut NASA's budget to $3.8 billion. Johnson restored NERVA I's funding, but not NASA's. NERVA had plenty of proposed missions. NASA considered using Saturn V and NERVA on a "Grand Tour" of the Solar System. A rare alignment of the planets that occurs every 174 years occurred between 1976 and 1980, allowing a spacecraft to visit Jupiter, Saturn, Uranus and Neptune. With NERVA, that spacecraft could weigh up to . This was assuming NERVA had a specific impulse of only ; was more likely, and with that it could place a space station the size of Skylab into orbit around the Moon. Repeat trips to the Moon could be made with NERVA powering a nuclear shuttle. There was also of course the mission to Mars, which Klein diplomatically avoided mentioning, knowing that, even in the wake of the Apollo 11 Moon landing, the idea was unpopular with Congress and the general public. Richard Nixon replaced Johnson as president on 20 January 1969, and cost cutting became the order of the day. NASA program funding was somewhat reduced by Congress for the federal budget, shutting down the Saturn V production line. On 4 January 1970, NASA Administrator Thomas O. Paine announced the cancellation of Apollo 20 to make its Saturn V available to launch Skylab. The cancellation of Apollo 18 and 19 followed in September 1970. But NERVA remained; Klein endorsed a plan whereby the Space Shuttle would lift a NERVA engine into orbit, then later return with fuel and a payload. This could be repeated, as NERVA was restartable. NERVA now needed the shuttle, but the shuttle did not need NERVA. NERVA still had the steadfast support of Anderson and Cannon in the Senate, but Anderson was aging and tiring, and now delegated many of his duties to Cannon. NERVA received $88 million in fiscal year (FY) 1970 and $85 million in FY 1971, funds coming jointly from NASA and the AEC. In December 1970, the Office of Management and Budget recommended the cancellation of NERVA and Skylab, but Nixon was reluctant to do so, as their cancellation could cost up to 20,000 jobs, mostly in California, a state that Nixon felt he needed to carry in the 1972 election. He decided to keep it alive at a low funding level, and cancel Apollo 17 instead. The concern about Apollo 17 was about the political fallout if it failed rather than the cost, and this was ultimately addressed by postponing it to December 1972, after the election. When Nixon tried to kill NERVA in 1971, Senator Anderson and Senator Margaret Chase Smith instead killed Nixon's pet project, the Boeing 2707 supersonic transport (SST). This was a stunning defeat for the president. In the budget for FY 1972, funding for the shuttle was cut, but NERVA and Apollo 17 survived. Although NERVA's budget request was only $17.4 million, Congress allocated $69 million; Nixon only spent $29 million of it. Congress supported NERVA again in 1972. A bipartisan coalition headed by Smith and Cannon appropriated $100 million for the small NERVA engine that would fit inside the shuttle's cargo bay that was estimated to cost about $250 million over a decade. They added a stipulation that there would be no more reprogramming NERVA funds to pay for other NASA activities. The Nixon administration decided to cancel NERVA anyway. On 5 January 1973, NASA announced that NERVA was terminated. Staff at LASL and SNPO were stunned; the project to build a small NERVA had been proceeding well. Layoffs began immediately, and the SNPO was abolished in June. After 17 years of research and development, Projects Nova and NERVA had spent about $1.4 billion, but NERVA had never flown. ==Post-NERVA research== In 1983, the Strategic Defense Initiative ("Star Wars") identified missions that could benefit from rockets that are more powerful than chemical rockets, and some that could only be undertaken by more powerful rockets. A nuclear propulsion project, SP-100, was created in February 1983 with the aim of developing a 100 KW nuclear rocket system. The concept incorporated a particle/pebble-bed reactor, a concept developed by James R. Powell at the Brookhaven National Laboratory, which promised a specific impulse of up to and a thrust to weight ratio of between 25 and 35 for thrust levels greater than . From 1987 to 1991 this was funded as a secret project codenamed Project Timber Wind, which spent $139 million. The proposed rocket project was transferred to the Space Nuclear Thermal Propulsion (SNTP) program at the Air Force Phillips Laboratory in October 1991. NASA conducted studies as part of its 1992 Space Exploration Initiative (SEI) but felt that SNTP offered insufficient improvement over NERVA, and was not required by any SEI missions. The SNTP program was terminated in January 1994, after $200 million was spent. In 2013, an engine for interplanetary travel from Earth orbit to Mars orbit and back was studied at the MSFC with a focus on nuclear thermal rocket (NTR) engines. Since NTRs are at least twice as efficient as the most advanced chemical engines, they allow quicker transfer times and increased cargo capacity. The shorter flight duration, estimated at 3–4 months with NTR engines, compared to 8–9 months using chemical engines, would reduce crew exposure to potentially harmful and difficult to shield cosmic rays. NTR engines were selected in the Mars Design Reference Architecture (DRA). (DRACO) spacecraft]] Congress approved $125 million in funding for the development of nuclear thermal propulsion rockets on 22 May 2019. On 19 October 2020, the Seattle-based firm Ultra Safe Nuclear Technologies delivered a NTR design concept to NASA employing high-assay low-enriched uranium (HALEU) ZrC-encapsulated fuel particles as part of a NASA-sponsored NTR study managed by Analytical Mechanics Associates (AMA). In January 2023, NASA and the Defense Advanced Research Projects Agency (DARPA) announced that they would collaborate on the development of a nuclear thermal rocket engine that would be tested in space to develop nuclear propulsion capability for use in crewed NASA missions to Mars. In 2023, DARPA announced that the Demonstration Rocket for Agile Cislunar Operations (DRACO) reactor and fuel would be supplied by BWXT. The project was canceled in 2025. ==See also== RD-0410, a Soviet nuclear thermal rocket engine SNAP-10A, an experimental nuclear reactor launched into space in 1965 Project Prometheus, NASA nuclear generation of electric power 2003–2005 ==Footnotes== ==Notes== ==References== ==External links==

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