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Gas core reactor rockets are a conceptual type of rocket that is propelled by the exhausted coolant of a gaseous fission reactor. The nuclear fission reactor core may be either a vapor, gas, or plasma. They may ba capable of creating specific impulses of 3 000–5 000 s (30 to 50 N·s/kg) and thrust which is enough for relatively fast interplanetary travel. Heat transfer to the working fluid (propellant) is by thermal radiation, mostly in the ultraviolet, given off by the fission gas at a working temperature of around 25 000°C. Gaseous fission reactors are a hypothetical type of nuclear reactor proposed for use in space travel. ...
Vapor (US English) or vapour (British English) is the gaseous state of matter. ...
Jump to: navigation, search A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. ...
The word plasma has a Greek root which means to be formed or molded (the word plastic shares this root). ...
The specific impulse (commonly abbreviated Isp) of a propulsion system is the impulse (change in momentum) per unit of propellant. ...
Thrust is a reaction force described quantitatively by Newtons Second and Third Law. ...
Existing or occurring between planets. ...
This article is in the process of being merged into Heat, and may be outdated. ...
Working mass is a mass against which a system operates in order to produce acceleration. ...
A propellant is a material that is used to move an object by applying a motive force. ...
Jump to: navigation, search Thermal radiation, or radiant heat, is electromagnetic radiation from an object that is simply caused by its temperature. ...
Jump to: navigation, search Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than that of soft X-rays. ...
In general fission is a splitting or breaking up into parts. ...
Theory of operation
Nuclear gas core reactor rockets can provide much higher specific impulse than solid core nuclear rockets because their temperature limitations are in the nozzle and core wall structural temperatures, which are distanced from the hottest regions of the gas core. Consequently, nuclear gas core reactors can provide much higher temperatures to the propellant. Solid core nuclear thermal rockets can develop higher specific impulse than conventional chemical rockets due to the extreme power density of the reactor core, but their operating temperatures are limited by the maximum temperature of the solid core because the reactors temperatures cannot rise above its component’s lowest melting temperature. Rocket Nozzle A nozzle is a mechanical device designed to control the characteristics of a fluid flow as it exits from an enclosed chamber into some medium. ...
A propellant is a material that is used to move an object by applying a motive force. ...
In engineering, specific power (sometimes also power per unit mass or power density) refers to the amount of power delivered by an energy source, divided by some measure of the sources size or mass. ...
The melting point of a solid is the temperature at which it changes state from solid to liquid. ...
Due to the much higher temperatures achievable by the gaseous core design, it can deliver higher specific impulse and thrust than most other conventional nuclear designs. This translates into either shorter mission transit times for future astronauts or larger payload fractions. It may also be possible to use partially ionized plasma from the gas core to magnetohydrodynamically generate electricity, subsequently negating the need for an additional power supply.
General features of the nuclear reactor All gas core reactor rocket designs share several properties in their nuclear reactor cores, and most designs share the same materials. The closest terestrial design is the gaseous fission reactor. Gaseous fission reactors are a hypothetical type of nuclear reactor proposed for use in space travel. ...
Nuclear fuel The fissile fuel is usually highly enriched uranium pellets or a uranium containing gas (U-235 or U-233). Sometimes uranium tetrafluoride is required due to its chemical stability; the propellant is almost always hydrogen. This article or section should include material from Fissile material In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. ...
Jump to: navigation, search Enriched uranium is uranium whose uranium-235 content has been increased through the process of isotope separation. ...
Jump to: navigation, search General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...
Neutron Moderator Most gas core reactors are surrounded by a radial first wall capable of taking the brunt of the extreme environment present inside the core, a pressure shell to hold everything together, and a radial neutron moderator usually made up of beryllium oxide. The propellant also provides moderation. A radial is a line drawn along a vector. ...
In nuclear engineering, a neutron moderator is a medium which reduces the velocity of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction. ...
Beryllium oxide (BeO) is a white crystalline oxide. ...
Reactor coolant / Rocket propellant The hydrogen propellant cools the reactor and its various structural parts. Hydrogen is first pumped through the nozzle, then through the walls and back down through the core region. Once it passes through the core region the hydrogen is exhausted. If cooling from the propellant is not enough, external radiators are required. The internal gas core temperatures in most designs vary, but the designs with the highest specific impulses generally have fissioning gas plasmas heating a low mass propellant. This heating occurs primarily through radiation. A radiator is any device that emits a form of radiation. ...
Control Control can be accomplished by either changing the relative or overall densities of the fissile fuel and the propellant or by having outside control drives moving neutron absorbing drums or the radial moderator. Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ...
Open cycle versus closed cycle There are two main variations of the nuclear gas core rocket (GCR). The open cycle concept and the closed cycle design. In order to be competitive with other nuclear rocket systems, GCRs must keep the loss of the fissile fuel as low as possible with respect to the hydrogen propellant, perhaps keeping fuel loss as low as 1% of total flow. By increasing the residence time of the fissile fuel in the gaseous core, higher burn-up of the fuel is possible. This increase translates into higher specific impulse since less nuclear fuel would need to be brought aboard. In order to address the loss of fuel, the closed cycle concept was introduced. The closed cycle relies on the fuel being surrounded by a material which is transparent to the majority of radiation emitted from the fuel. This radiation is then transmitted through the transparent medium into the hydrogen propellant. This closed cycle is often referred to as the “nuclear light bulb”. The difficulty in this design is finding a transparent medium which does not absorb a wide range of gamma ray energies but can withstand the radiation environment present in the reactor. This article is about electromagnetic radiation. ...
The disadvantage of the open cycle is that the fuel can escape through the nozzle before it reaches significant burn-up levels. On the other hand, the open cycle can attain much higher temperatures than the closed cycle design without as much materials development since finding a transparent medium to separate the fuel from the propellant is not required. The closed cycle is advantageous because its design virtually eliminates loss of fuel, but the necessity of a physical wall between the fuel and the propellant leads to the obstacle of finding a material with extremely optimized characteristics. One must find a medium which is transparent to a wide range of gamma energies, but can withstand the radiation environment present in the reactor, specifically particle bombardment from the nearby fission reactions. This barrage of particles can lead to sputtering and eventual wall erosion. Jump to: navigation, search Radiation has a variety of different meanings. ...
Sputtering is a physical process whereby atoms in a solid target material are ejected into the gas phase due to bombardment of the material by energetic ions. ...
One closed cycle gas core rocket design (often called the nuclear lightbulb) contains the fissioning gas in a quartz enclosure that is separate from the propellant. First, the hydrogen coolant runs through the nozzle and inside the walls of the quartz enclosure for cooling. Next, the coolant is run along the outside of the quartz fuel enclosure. Since the fissile gas would be directly in contact with the walls, the operating temperature is not as great as other designs because the walls would eventually ablate away. A nuclear lightbulb is a specific type of gas core nuclear reactor that is operated at such high temperature (aprox. ...
Quartz is the most abundant mineral in the Earths continental crust. ...
The open cycle designs appear to be the most advantageous since there would be no additional structure in the gas core/ hydrogen interface. However, this structure reduction leads to the necessity of finding a different way to limit the loss of fuel. Unless an outside force is relied upon (i.e. magnetic forces, rocket acceleration, etc...), the only way to contain the fuel in a specific region, thereby limiting fuel-propellant mixing, is through fuel and propellant flow hydrodynamics. Hydrodynamics is fluid dynamics applied to liquids, such as water, alcohol, oil, and blood. ...
The shape of the fissile gas core can be either cylindrical, toroidal or counter flow toroidal. Since there are issues regarding the loss of fissile fuel with the cylindrical and toroidal designs, the counter-flow toroidal gas core geometry is the primary source of research. The counter flow toroid is the most promising because it has the best stability and theoretically prevents mixing of the fissile fuel and propellant more effectively than the aforementioned concepts. In this design, the fissile fuel is kept mostly in a base injection stabilized recirculation bubble by hydrodynamic confinement. Most designs utilize a cylindrical gas core wall for ease of modeling. However, previous cold flow tests have shown that hydrodynamic containment is more easily achieved with a spherical internal wall geometry design. The word cylinder has several meanings. ...
For toroids, see Toroid. ...
The formation of the fuel vortex is complex. It basically comes down to flow over a projectile shape with a blunt base. The vortex is formed by placing a semi-porous wall in front of the desired location of the fuel vortex but leaves room along its sides for hydrogen propellant. Propellant is then pumped inside the reactor cavity along an annular inlet region. A dead space then develops behind the semi-porous wall; due to viscous and shear forces, a counter toroidal rotation develops. Once the vortex develops, fissile fuel can be injected through the semi-porous plate to bring the reactor critical. The formation and location of the fuel vortex now depends on the amount of fissile fuel that bleeds into the system through the semi-porous wall. When more fuel bleeds into the system through the wall, the vortex moves farther downstream. When less bleeds through, the vortex moves farther upstream. Of course, the upstream location is constrained by the placement of the semi-porous wall. Jump to: navigation, search Vortex created by the passage of an aircraft wing, revealed by coloured smoke A vortex is a spinning turbulent flow (or any spiral whirling motion) with closed streamlines. ...
Viscosity is a measure of the resistance of a fluid to deformation under shear stress. ...
In physics and mechanics, shear refers to a deformation that causes parallel surfaces to slide past one another (as opposed to compression and tension, which cause parallel surfaces to move towards or away from one another). ...
Magnetic confinement Barring an external force, hydrodynamic containment is the only way to increase the residence time of the fuel in the reactor. However, one may ask why bar an outside force, couldn’t magnetic confinement be used since the fuel would be highly ionized (three or four times ionized) while the propellant is only partially ionized? To answer this question one must understand a little about magnetic plasma confinement. The key parameter of interest for magnetic confinement is the ratio of kinetic pressure to magnetic pressure, β. ...
When β<1 magnetic confinement is possible (most fusion schemes have a β close to 0.05). However, the pressures in a gas core rocket are much higher than pressures in fusion devices, on the order of 1000 atm. For these pressures, the necessary magnetic field strength required is close to 16 tesla just to produce β=1. For a magnetic field of this magnitude, superconducting technology is necessary and the added mass of such a system would be detrimental. Also, even with a β<1, resistive diffusion will cause the fuel core to collapse almost immediately unless β<<1, which would require an even larger magnetic field. Fusion typically refers to the merging of two or more entities into a single one: In physics, nuclear fusion is the combination of two atomic nuclei into a single nucleus. ...
ATM is an initialism with the following meanings: Automatic teller machine or automated teller machine, a cash dispenser Association of Teachers of Mathematics in the UK. Adobe Type Manager, font management software from Adobe Systems Advanced Traffic Management and Arterial Traffic Management, terms used in the intelligent transportation system industry...
Tesla can refer to: Scientist and inventor Nikola Tesla The tesla, an SI unit named after Nikola Tesla. ...
In science, magnitude refers to the numerical size of something: see orders of magnitude. ...
Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect. ...
Impact of rocket acceleration Another important aspect to GCRs is the impact of the rocket acceleration on the containment of the fuel in the fuel bubble. A rocket acceleration of only 0.001 g will cause buoyancy effects to decrease core containment by 35% if all other flow-rates are held constant from a zero g startup. Ultimately, the fuel-propellant flows will have to be throttled until the rocket approaches some sort of steady state. Jump to: navigation, search In physics, buoyancy is an upward force on an object immersed in a fluid (i. ...
Neutronic considerations Since steep temperature gradients will be present in any such gas core reactor, several implications for neutronics must be considered. The open cycle gas core reactor (OCGCR) is typically a thermal/epithermal reactor. Most types of OCGCR require external moderation due to the steep temperature gradients inside the gaseous core. Neutrons born in the fuel region travel relatively unimpeded to the external moderator where some are thermalized and sent back into the gas core. Due to the high core temperatures, however, on the return trip the neutrons are up-scattered in the fuel region, which leads to a significant negative reactor worth. To achieve criticality, this reactor is operated at very high pressure and the exterior radial wall is made up of a moderator of some sort, generally barium oxide. Moderation can also come from introducing moderating particles into either the fuel or propellant streams, but by doing so, the benefits in neutronics is canceled by loss of rocket performance.
Technology summary and outlook The open cycle gas core rocket has many unique design attributes that make it a serious challenger to other proposed propulsion for interplanetary missions. Due to the necessity of having a transparent wall inside the reactor for a closed cycle concept, the benefit of moving to a gas core from a solid core are nearly negated. The high specific impulse and large thrust possible for the OCGCR correspond to shorter mission times and higher payload fractions. However, the technical challenges and unknowns inherent in its design are many. Additionally, any test of the system performed on earth would be under a gravity field of 1 g, which would bring buoyancy effects into play inside the gaseous core. See: transparency (optics) alpha compositing GIF#Transparency transparency (overhead projector) market transparency transparency (telecommunication) transparency (computing) For X11 pseudo-transparency, see pseudo-transparency. ...
Due to the inability to perform live testing on earth, research is focused primarily on computational modeling of such a system. It was previously mentioned that the specific impulse can be as high as or higher than 3000 s. However, results of computational modeling point towards this number being somewhat optimistic. When thermal hydraulics were modeled more completely for a typical base injection stabilized recirculation bubble gas core rocket by D. Poston, the specific impulse dropped from >3000 s to <1500 s. In the base injection stabilized recirculation bubble gas core rocket concept, it is thought that some additional method of fuel confinement will be beneficial. As mentioned earlier, relying completely on magnetic containment of the fuel bubble is not yet practical. However, a magnetic field may be able to assist in containment or help suppress turbulence which would lead to fuel-propellant mixing.
The primary areas of future research for such an OCGCR would therefore be centered on keeping the fuel and propellant from mixing as much as possible. Although this article has focused on enriched uranium for the fuel and hydrogen for the propellant, this may not be the optimal choice for either. Other fuels, such as plutonium, and other propellants, including helium or even helium-3, have also been considered and in certain situations provide advantages.
References 1: Thode, L., Cline, M., Howe, S. (July-August, 1998). Vortex formation and stability in a scaled gas-core nuclear rocket configuration. Journal of Propulsion and Power. Pg. 530-536.
2: Poston, D., Kammash, T. (January, 1996). A computational model for an open-cycle gas core nuclear rocket. Nuclear Science and Engineering. Pg. 32-54.
3: Sforza, P. M., Cresci, R.J. (May 31, 1997). Fuel Efficient Hydrodynamic Containment for Gas Core Fission Reactor Rocket Propulsion. DOE/75786-3.
4: Innovative Nuclear Space Power and Propulsion Institute. (accessed last: 4/16/04). Gas Core Reactors. [Online] available: http://www.inspi.ufl.edu/research/gcr/index.html
5: Unknown author. (accessed last: 4/16/04). Gas Core Nuclear Rocket. [Online] available: http://www.islandone.org/APC/Nuclear/08.html
6: Unknown author. (accessed last: 4/16/04). Nuclear Rocket Technologies. [Online] available: http://www.lascruces.com/~mrpbar/rocket.html
7: Sahu, J., Nietubicz, C. (September, 1985). Navier-stokes computations of projectile base flow with and without mass injection. AIAA Journal. Pg. 1348-1355.
See also Gaseous fission reactors are a hypothetical type of nuclear reactor proposed for use in space travel. ...
Jump to: navigation, search A remote camera captures a close-up view of a Space Shuttle Main Engine during a test firing at the John C. Stennis Space Center in Hancock County, Mississippi Spacecraft propulsion is used to change the velocity of spacecraft and artificial satellites, or in short, to...
A nuclear lightbulb is a specific type of gas core nuclear reactor that is operated at such high temperature (aprox. ...
Nuclear materail consists of materials used in nuclear systems. ...
Atomic physics (or atom physics) is physics of the electron hull of atoms. ...
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