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  • Writer's pictureMatt Russell

#242 - Paolo Venneri - Nuclear Space Tech

This week Matt talks to Paolo Venneri of USNC-Tech about Space Nuclear Technologies. George joins at the last minute to talk about Nerva.

All of physics is either impossible or trivial. It is impossible until you understand it, and then it becomes trivial.
Sir Ernest Rutherford


Paolo Venneri

Earned a PhD from the Korea Advanced Institute of Science and Technology in Nuclear and Quantum Engineering with the thesis of determining the feasibility of low enriched uranium for nuclear thermal propulsion.

  • In his previous position at USNC, he founded and lead the Advanced Projects Division of USNC in design efforts to support the NASA LEU-NTP program

  • He led and managed a team of engineers and scientists in building a self-supporting R&D division, growing from 2 people and $100,000 yearly budget to 10 people and yearly revenue of over $2 million.

  • He was the first to propose and computationally demonstrate the feasibility of HALEU fuel in nuclear thermal propulsion and has been a driver for the continued technical development of commercially viable space nuclear systems.

  • He has been a key player with his team in spearheading the development of ultra-high temperature fuels and the Versatile NTP system as well as the development of high-performance moderators supported by ARPA-E.

  • In January 2019, he led the splitting of USNC-Tech as a separate and independently managed subsidiary of USNC to focus on developing advanced nuclear technology and space nuclear systems.

A quick point about trip to mars.

We reported a while back that the UK government were partnering with Rolls-Royce to look at nuclear propulsion in space. So just like the Europa clipper mission to get anywhere you need massive rockets like SLS. However, it's still very very slow getting to places like Mars and that's bad news for humans. So we need to look at other things other than chemical propulsion and a new report from NASA basically says that they really need to start looking at nuclear thermal and nuclear electric propulsion for human missions to Mars

  • nuclear thermal propulsion (NTP) system designed to produce a specific impulse of at least 900 s

  • a nuclear electric propulsion (NEP) system with at least 1 megawatt of electric (MWe) power >2000s

In the paper in shows that to do the mission you need 1000-4000 tons of propellant for chemical propulsion to do the mission. SLS carries about 100 ...isn’t this just dead in the water then for Mars?

NTP look more viable than NEP.

Problems for NEP

  • scale up the operating power of each NEP subsystem and to develop an integrated NEP system suitable for the baseline mission

  • scaling power and thermal management systems to power levels orders of magnitude higher than have been achieved to date

  • no integrated system testing has ever been performed on MWe-class NEP systems

  • operational reliability over a period of years

  • parallel development of a compatible large-scale chemical propulsion system to provide the primary thrust when departing Earth orbit and when entering and departing

Problems for NTP

  • The system that can heat its propellant to approximately 2700 K at the reactor exit for the duration of each burn.

  • long-term storage of liquid hydrogen in space with minimal loss

  • lack of adequate ground-based test facilities

  • rapidly bring an NTP system to full operating temperature (preferably in 1 min or less).

  • Ground tests have been done, but this was over 50 years ago, and nothing in space of course

Also what type of Nuclear fuel needs to be reviewed.

NEP and NTP systems show great potential to facilitate the human exploration of Mars.

Using either system to execute the baseline mission by 2039, however, will require an aggressive research and development program. Such a program would need to begin with NASA making a significant set of architecture and investments decisions in the coming year. In particular, NASA should develop consistent figures of merit and technical expertise to allow for an objective comparison of the ability of NEP and NTP systems to meet requirements for a 2039 launch of the baseline mission.

An authour of the report was ROBERT D. BRAUN, NAE,1 Jet Propulsion Laboratory, Co-Chair, Any relation to Werner Von?

Modern Example

Patent for a Nuclear thermal propulsion rocket engine Application filed by Richard Hardy, Jonathan Hardy 2015

A fission based nuclear thermal propulsion rocket engine. An embodiment provides a source of fissionable material such as plutonium in a carrier gas such as deuterium. A neutron source is provided, such as from a neutron beam generator. By way of engine design geometry, various embodiments may provide for the intersection of neutrons with the fissionable material injected by way of the carrier gas, while in a reactor provided in the form of a reaction chamber. The impact of neutrons on fissionable material results in nuclear fission in sub-critical mass reaction conditions in the reactor, resulting in the release of heat energy to the materials within the reactor. The reactor is sized and shaped to receive the reactants and an expandable fluid such as hydrogen, and to confine heated and pressurized gases for discharge out through a throat, into a rocket engine expansion nozzle for propulsive discharge.

In 1946, Ulam and C. J. Everett wrote a paper in which they considered the use of atomic bombs as a means of rocket propulsion. This would become the basis for Project Orion

Stanisław Marcin Ulam was a Polish-American scientist in the fields of mathematics and nuclear physics. Manhattan Project, originated the Teller–Ulam design of thermonuclear weapons, discovered the concept of the cellular automaton, invented the Monte Carlo method of computation, and suggested nuclear pulse propulsion.

Project Orion was a study of a starship intended to be directly propelled by a series of explosions of atomic bombs behind the craft (nuclear pulse propulsion). But nuclear treaties ended research. later proposals have tended to modify the basic principle by envisioning equipment driving detonation of much smaller fission or fusion pellets, in contrast to Project Orion's larger nuclear pulse units (full nuclear bombs) based on less speculative technology.

Val Cleaver, the chief engineer of the rocket division at De Havilland, and Leslie Shepherd, a nuclear physicist at the University of Cambridge, independently considered the problem of nuclear rocket propulsion. They became collaborators, and in a series of papers published in the Journal of the British Interplanetary Society in 1948 and 1949, they outlined the design of a nuclear-powered rocket with a solid-core graphite heat exchanger. They reluctantly concluded that nuclear rockets were essential for deep space exploration, but not yet technically feasible

The Nuclear Engine for Rocket Vehicle Application (NERVA) was a nuclear thermal rocket engine development program that ran from ‘58-’73

  • 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".

  • NERVA 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.

  • Project Rover was a United States project to develop a nuclear-thermal rocket that ran from 1955 to 1973 at the Los Alamos Scientific Laboratory (LASL). It began as a United States Air Force project to develop a nuclear-powered upper stage for an intercontinental ballistic missile (ICBM).

  • The project was transferred to NASA in 1958 after the Sputnik crisis triggered the Space Race.

  • Project Rover became part of NASA's Nuclear Engine for Rocket Vehicle Application (NERVA) project and henceforth dealt with the research into nuclear rocket reactor design, while NERVA involved the overall development and deployment of nuclear rocket engines, and the planning for space missions.

  • 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 Los Alamos Scientific Laboratory concentrated on reactor development. NASA built and tested complete rocket engines.

  • The AEC, SNPO, and NASA considered NERVA to be a highly successful program in that it met or exceeded its program goals.

    • NERVA demonstrated that nuclear thermal rocket engines were a feasible and reliable tool for space exploration,

    • 1968 SNPO certified that the latest NERVA engine, the XE, met the requirements for a human mission to Mars.

    • 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.

      • Plans for deep space exploration generally require the power of nuclear rocket engines, and all spacecraft concepts featuring them use derivative designs from the NERVA.

In principle, the design of a nuclear thermal rocket engine is quite simple: a

  • turbopump would force hydrogen through a nuclear reactor that would heat it to very high temperatures.

  • Complicating factors

    • Controlling reactor temperature and power output.

    • Storing hydrogen in liquid form, at −253.2 °C

    • hydrogen would be heated to a temperature of around 2,500 K (2,230 °C), and materials would be required that could both withstand such temperatures and resist corrosion by hydrogen

  • Fuel

    • Plutonium as it could not reach temperatures as high as those of uranium.

    • Uranium-233, as compared to uranium-235, is slightly lighter, has a higher number of neutrons per fission event, and a has a high probability of fission, but its radioactive properties make it more difficult to handle, and in any case it was not readily available.

  • As to structural materials in the reactor, the choice came down to graphite or metals

    • Tungsten best metal was expensive, hard to fabricate, and to get around its neutronic properties, it was proposed to use tungsten-184, which does not absorb neutrons.

    • graphite was cheap, actually gets stronger at temperatures up to 3,300 K (3,030 °C), and sublimes rather than melts at 3,900 K (3,630 °C). Graphite was therefore chosen.

  • To control the reactor, the core was surrounded by control drums coated with graphite or beryllium (a neutron moderator) on one side and boron (a neutron poison) on the other.

    • The reactor's power output could be controlled by rotating the drums

    • To increase thrust, it is sufficient to increase the flow of propellant. Hydrogen, whether in pure form or in a compound like ammonia, is an efficient nuclear moderator, and increasing the flow also increases the rate of reactions in the core. This increased reaction rate offsets the cooling provided by the hydrogen. Moreover, as the hydrogen heats up, it expands, so there is less in the core to remove heat, and the temperature will level off. These opposing effects stabilize the reactivity and a nuclear rocket engine is therefore naturally very stable, and the thrust is easily controlled by varying the hydrogen flow without changing the control drums.

LASL produced a series of design concepts, each with its own codename: Uncle Tom, Uncle Tung, Bloodhound and Shish. By 1955, it had settled on a 1,500 MW design called Old Black Joe. In 1956, this became the basis of a 2,700 MW design intended to be the upper stage of an ICBM.

  • The December 1959 Silverstein Committee had defined the configuration of the Saturn launch vehicle, including the use of liquid hydrogen as the fuel for the upper stages. In a 1960 paper, Schmidt proposed replacing the upper stages with nuclear NERVA stages.

    • This would deliver the same performance as Nova (big saturn V), but for half the cost.

      • pound of payload into lunar orbit as $1,600 for an all-chemical Saturn, $1,100 for Nova, and $700 for a chemical-nuclear Saturn.

      • issued a study contract for a RIFT (Reactor in-flight test) with NERVA as the upper stage of a Saturn C-3, but the C-3 was replaced soon after by the more powerful C-4 and ultimately the C-5, which became the Saturn V. Only in July 1962, after much debate, did NASA finally settle on lunar orbit rendezvous, which could be performed by Saturn V, and Nova was abandoned.

      • The RIFT vehicle would consist of an S-IC first stage, a dummy S-II middle stage filled with water, and an S-N (Saturn-Nuclear) NERVA upper stage. For an actual mission, a real S-II stage would be used.

      • The SNPO planned to build ten S-N stages, six for ground tests and four for flight tests. Launches were to take place from Cape Canaveral. NERVA engines would be transported by road in shockproof, watertight containers, with the control rods locked in place and nuclear poison wires in the core. Since it would not be radioactive, it could be safely transported and mated to the lower stages without shielding.

      • The RIFT test vehicle would be 111 meters (364 ft) tall, about the same as the Saturn V; the Saturn C-5N mission configuration would be larger still, at 120 meters (393 ft) tall, but the 160-meter (525 ft) Vehicle Assembly Building (VAB) could easily accommodate it.

      • In-flight, the poison wires would be pulled and the reactor started 121 kilometres (75 mi) above the Atlantic Ocean. The engine would fire for 1,300 seconds, boosting it to an altitude of 480 kilometres (300 mi). It would then be shut down, and the reactor cooled before impacting the Atlantic 3,200 kilometres (2,000 mi) downrange.

      • NERVA would be regarded as mission-ready after four successful tests

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 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, which would allow the upgraded Saturn to launch much larger payloads of up to 150,000 kg (340,000 lb) to LEO.

Nixon eventually canned it, Richard Nixon replaced Johnson as president 20 January 1969, and cost cutting became the order of the day. NASA program funding was somewhat reduced by Congress for the 1969 budget, shutting down the Saturn V production line and cancelling Apollo missions after Apollo 17, but NERVA remained.

One plan whereby the Space Shuttle lifted a NERVA engine into orbit, then returned fuel and a payload. This could be repeated, as NERVA was restartable. NERVA now needed the shuttle, but the shuttle did not need NERVA

On 5 January 1973, NASA announced that NERVA was terminated. Staff at LASL and SNPO were stunned; the project to build a small shuttle cargo bay 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

12 January 2021

Rolls-Royce has signed an innovative contract with the UK Space Agency for a study into future nuclear power options for space exploration.

February NASA releases the report

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Flight Clinic
Jul 06, 2021

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