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amirfahd
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I was wondering if nuclear power is being used in pushing and thrusting Space Rockets when launching out from the earth?
Cheers.
Amir Fahd.
Cheers.
Amir Fahd.
Hi, Amir. In short the answer to your question is - No. Nuclear rockets, and those would be nuclear thermal, are not used in Earth's atmosphere.amirfahd said:I was wondering if nuclear power is being used in pushing and thrusting Space Rockets when launching out from the earth?
Cheers.
Amir Fahd.
No. A subcritical system would require a massive driver, so its specific energy would be way too low.If subcritical fuels like thorium are ever harnessed, these could further lower risks.
sanman,sanman said:Technologies like pebble bed could be used, which have high stability and lesser risk for heat buildup,
wxrocks,wxrocks said:. Pardon if this is in error -- but I think the Voyager spacecraft s had nuclear powered batteries.
Morbius said:However, in case of a rocket failure, the heat source will be EXTERNAL - it will be the
friction of the fast moving reactor with the atmosphere. That high heat transfer area
now works to effectively conduct heat INTO the pellet - which is the LAST THING you
want to do if you want the pellet to survive instead of being dispersed.
Candyman,theCandyman said:Could you elaborate on this? Heat transfer is in the negative thermal gradient direction, so why would the pellet heat up further?
LURCH,LURCH said:Unfortunately, even if we set aside the risk of atmospheric contamination caused by catastrophic structural failure, the use of a nuclear reaction for thrust to launch a rocket into space requires venting radioactive waste directly to the atmosphere (through the thrust nozzles). .
Not quite. The rocket is 'accelerating', and the mass of the pebble bed resists acceleration, and that resistance provides the force on the support structure (core support) which transmits that force to the pressure vessel. That is in addition to the coolant pressure!Regarding force of the pebble bed on the pressure vessel, that would only be the result of the force generated by the propellant flowing through the bed.
And that would be unacceptable in the environment/atmosphere. Dispersal of a heavy metal (U) would be undesirable, as would dispersal of radioactive fission products in the atmosphere.In the event of a catastrophic failure, then the pebbles would be released and not stay concentrated together
sanman,sanman said:Regarding force of the pebble bed on the pressure vessel, that would only be the result of the force generated by the propellant flowing through the bed.
In the event of a catastrophic failure, then the pebbles would be released and not stay concentrated together, so they would no longer have critical mass. The thermal throttling principle would also prevent a runaway reactor meltdown. But if the pebbles were released in orbit, then their higher surface area would make them more likely to vaporize on re-entry, rather than survive as concentrated hazardous chunks of fallout.
The diffuse dispersal of the radioactive material into the natural environment from which it came (we didn't manufacture U-235, Mother Nature did)
The pebbles could be ballistic shaped, in order to better accommodate the high speed propellant flow, but you could also have the propellant flowing at lower density through the bed, and then later being concentrated into higher velocity at a nozzle throat.
What other nuclear reactor design could be more accommodating than this?
Morbius said:sanman,
As Astronuc already pointed out - the above is incorrect. You missed considering the
"inertial force" of an accelerating object.
You don't want the pellets to vaporize - that just disperses the radioactivity - which is
what you DON'T want to do. You want the reactor to survive intact without dispersing
its radioactivity. You WANT the reactor to remain in one chunk for recovery. If it stays
in one chunk, then you clean up by recovering the chunk. You can't clean up the
radioactivity if it is dispersed.
You are not considering the radioactive material we DID make; namely the fission
products. It's not just the U-235 from the ground. A fresh nuclear power plant fuel
element is only slightly radioactive, and you can handle it and stand next to it with
no problem.
However, after the fuel has been irradiated - it now contains in addition to U-235, the
fission products; the remnants of fissioned U-235 atoms. There are now materials
like Iodine-131, Iodine-135, Strontium-90, Cesium-135... The spent fuel element is
now INTENSELY radioactive. You can no longer stand next to it or handle it directly.
It has to be kept under at least 20-30 feet of water as shielding in spent fuel pools.
It is this INTENSELY radioactive material that would be dispersed - not just relatively
benign U-235. You DON"T want to disperse the fission products.
Nuclear rockets have already been designed and tested. LLNL's "Project Pluto":
http://www.llnl.gov/str/Hacker.html
[scroll down about half-way]
There were also the NERVA and Kiwi reactor rockets:
http://en.wikipedia.org/wiki/NERVA
http://www.fas.org/nuke/space/c04rover.htm
http://www.daviddarling.info/encyclopedia/K/KIWI.html
NONE of these reactor designs are pebble beds.
Dr. Gregory Greenman
Physicist
sanman,sanman said:To be frank, a conventional rocket has to also contend with inertial forces on the chemical fuel load. There's nothing special there. In the case of nuclear fuel, it's going to have less mass than chemical fuel, hence less inertial force to contend with.
Waitasec -- how long is this nuclear-powered ascent taking, anyway? The typical Space Shuttle ascent takes about 8 minutes from ground to orbit. I can't believe that 8 minutes worth of fission-reaction power is going to produce horrendous amounts of radioactive waste.
Since pebble bed chain reaction is based on proximity of the pellets to each other, then you don't move them together until you're ready to initiate your launch.
True, but none of them is younger than 50 years old, either.
Only nuclear power offers the wide energy margins necessary for versatile and convenient access to space.
Morbius said:sanman,
Conventional rocket fuels DO deal with this. However, consider the liquid fueled
shuttle main engines. The fuel is a liquid - it's not going to have problem with the
inertial force. The liquid fuel doesn't have to maintain any structural integrity.
However, the pellets and the reactor do.
Time is only part of the issue. What's the power of the reactor? The amount of fission
products is going to be dependent not on just time; but on the total energy the reactor
has to deliver.
THINK about it. I could use your argument above with a nuclear bomb:
However a nuclear bomb DOES produce a lot of radioactivity - because it produces so
much ENERGY! The time is NOT the determining factor.
Right, and then you do move them together and the rocket takes off, and then sometime
during the ascent, there is some type of failure, it loses directional control and the
aerodynamic forces tear your rocket apart. What then? How do you prevent the
contamination due to the radioactivity produced?
We may have to forego launching from Earth with nuclear rockets, and transport
people and material to space with chemical rockets as we have done for the past
40 some years. Then use the nuclear rocket assembled in orbit to take it from there.
Dr. Gregory Greenman
Physicist
Let's not forget that in addition to the core, one still needs the hydrogen propellant of approximately the same mass as one would have in a chemical system - not however to provide chemical energy, but simply to serve as the working fluid/propellant.sanman said:Look, the fact is that chemical fuel tanks don't deform horrendously in a chemical rocket. With nuclear fuel, you're talking about a much lower mass of fuel, and in pellet form if it's a pebble bed. The containment system for chemical fuel is going to weigh much more than the containment for nuclear fuel used to provide 8 minutes of power.
Please provide calculations comparing the fission product yield of a Hiroshima size weapon and a pebble bed core providing the same energy of the Space Shuttle. Keep it simple - just calculate the MCi or I-131, Cs-137 and Sr-90 for the given energy produced.I don't believe that lifting the mass of the Space Shuttle to orbit would generate the amount of radioactive waste as a Hiroshima bomb. For one thing, your radiation is inside an enclosed structure, and it's going through a moderator, etc.
Again please provide the calculations - other one is making unsubstantiated statements.Again, how much radioactive waste is going to be produced from lifting a Space Shuttle sized mass to orbit? I don't think it's going to be a lot. Anyhow, your trajectory could be over the ocean.
Individual fuel assemblies would be pack in special containers - something we considered in the past. It is quite easy to test also with dummy fuel assemblies made of W-Mo alloy or WC-Mo cermet of roughly the same density as fuel. The containers are designed to have high drag and then impact limiting heads.Oh, and how pray tell will we get the nuclear elements of that nuclear rocket to orbit? Or will we have to harvest the ore from space? What happens if the orbital nuclear rockets suffer some accident, and tumble towards Earth? Again, I think that we can handle the safety issues of a nuclear launch vehicle just fine, and it will end up being a more robust system for transport, since it will have the higher energy margin necessary to provide a safer trip.
sanman,sanman said:Look, I said 8 minutes worth of power -- that's clearly enough to derive the energy for a known launch mass. Suppose we talk about the mass of the Space Shuttle, for the sake of argument. I don't believe that lifting the mass of the Space Shuttle to orbit would generate the amount of radioactive waste as a Hiroshima bomb. For one thing, your radiation is inside an enclosed structure, and it's going through a moderator, etc.
You're GUESSING! You haven't done the calculation. That's NOT the way to doAgain, how much radioactive waste is going to be produced from lifting a Space Shuttle sized mass to orbit? I don't think it's going to be a lot.
Oh, and how pray tell will we get the nuclear elements of that nuclear rocket to orbit? Or will we have to harvest the ore from space? What happens if the orbital nuclear rockets suffer some accident, and tumble towards Earth? .
Good start, and I know you know that's not all the energy required, but I think I have an easier and more accurate way:Morbius said:Consider just the energy of the orbiting orbiter. Under "Technical Data" at:
http://en.wikipedia.org/wiki/Space_Shuttle
The gross weight of the orbiter is 109,000 kg = 1.09e5 kg
The speed is 7,743 m/s
Therefore the energy of the orbiting shuttle is:
E = 1/2 * (1.09e5 kg)(7,743 m/s)^2 = 3.27e12 Joules
The conversion from Joules to Kilotons may be found at:
http://en.wikipedia.org/wiki/1_E12_J
1 Kiloton = 4.186e12 Joules
Therefore the energy in the space shuttle represents
E = 3.27e12 Joules / ( 4.186e12 J/KT ) = 0.78 KT
A rail gun just needs a very large current source, and it doesn't have to be nuclear, but possibly a dedicated peaking plant or high energy storage system, since a rail gun represents an electrical transient compared to most loads.cmc21us said:I think there are several applications that could be beneficial to the space industry.
1) I've always wondered what the potential would be for a nuclear powered rail gun typ launcher on the side of a mountain. Not reasonable for the delivery of personnel; but a possibliity for material?
2) My second thought would be a nuclear core as a heat source connected to a sterling engine. Not useful for propulsion but high potential for power on longer operations (Moon, Mars or beyond...)
The Brayton cycle may be closed (using recirculation) or open (using atmosphere). The Brayton cycle refers to a gas cycle in which a compressor increases the pressure on the working fluid, which is passed through the heat source and then passed through a turbine. A Brayton cycle based on a combustion (air-fuel) energy source, which exhauts to the atmosphere is obviously open. A system which used a nuclear or solar heat source, and which recirculates the gas working fluid is closed. One major aspect of the Brayton cycle is the gas working fluid, which requires a compressor to increase pressure and density of the working fluid which is then heated as passed into a turbine, where the fluid's energy is transformed into mechanical energy by the turbine.cmc21us said:On the space power supply, I like the sterling as it is a closed cycle. I think Brayton is an open circuit using some uncontained gas supply. (Is this correct?) Ideally, a sterling would have only one charge of working gas ever. In any case, a small make up source would be prudent. Added benefit, close into the sun it could actually be run on solar radiation via a concetrator (same machine multiple fuel/power source). Big fan.
In space, the heat transfer has to be accomplished by radiation, and there is a mass penalty associated with the fact that for a given power level, the mass of the radiator increases at T(reject) decreases. There is a trade of between thermal to mechanical conversion efficiency (which is maximized by minimizing Tcold) and overall system mass, which is often dominated by the radiator.cmc21us said:I did think about that after the post. With the extreme temperatures of space cooling the working gas after heating should not be too difficult. Do you think the Brayton would provide a higher power for the mass? I think the generator coupling might be mare easily accomplished (microturbines are using a high speed generator directly coupled to the mover without reduction gears)?
Yeah, that's along the lines of the closed Baryton system. In this case, the primary thermal source is solar energy so there is a solar collector which focuses the light onto the heater. That heater could just as easily be a nuclear reactor, so the primary system is not too different, and the balance of plant is much the same.cmc21us said:Hey Astronuc
I have not yet purchased the paper but is this something like what we were discussing?
A Brayton cycle solar dynamic heat receiver for space
Sedgwick, L.M. Nordwall, H.L. Kaufmann, K.J. Johnson, S.D.
Boeing Aerosp. & Electron., Seattle, WA;
This paper appears in: Energy Conversion Engineering Conference, 1989. IECEC-89., Proceedings of the 24th Intersociety
Publication Date: 6-11 Aug 1989
On page(s): 905-909 vol.2
Meeting Date: 08/06/1989 - 08/11/1989
Location: Washington, DC, USA
References Cited: 13
INSPEC Accession Number: 3676704
Digital Object Identifier: 10.1109/IECEC.1989.74576
Posted online: 2002-08-06 16:52:43.0
Abstract
The detailed design of a heat receiver developed to meet the requirements of the US Space Station Freedom, which will be assembled and operated in low Earth orbit beginning in the mid-1990s, is described. The heat receiver supplies thermal energy to a nominal 25 kW closed-Brayton-cycle power conversion unit. The receiver employs an integral thermal energy storage system utilizing the latent heat of a eutectic-salt phase-change mixture to store energy for eclipse operation. The salt is contained within a felt metal matrix which enhances heat transfer and controls the salt void distribution during solidification
Space rockets and space aircrafts use powerful engines to generate thrust, which propels them out of Earth's atmosphere and into space. The engines burn a mixture of fuel and oxidizer, creating a controlled explosion that pushes the spacecraft forward. Once in space, rockets and aircrafts use their thrusters to maneuver and change direction.
There are several types of space rockets and space aircrafts, including launch vehicles, space shuttles, and space probes. Launch vehicles are used to transport satellites and spacecraft into orbit around Earth. Space shuttles are reusable spacecraft that can take off and land like a plane, and are used to transport astronauts and cargo to and from space. Space probes are unmanned spacecraft that are sent to explore other planets and objects in our solar system.
Space rockets and space aircrafts use navigation systems and guidance controls to stay on course. These systems use sensors, such as gyroscopes and accelerometers, to measure the spacecraft's orientation and velocity. Based on this data, the spacecraft's computer calculates the correct trajectory and adjusts the thrusters accordingly to keep it on course.
Space rockets and space aircrafts are made of lightweight and durable materials, such as aluminum, titanium, and carbon fiber. These materials are able to withstand the extreme conditions of space, including high temperatures, radiation, and pressure differentials. They are also designed to be aerodynamic and reduce drag during launch and re-entry into Earth's atmosphere.
Space rockets and space aircrafts have different methods of landing depending on their design. Some space shuttles are able to land like a plane on a runway, using their wings and landing gear. Others may use parachutes or airbags to soften their landing. Space probes often use a technique called aerobraking, where they use the friction of a planet's atmosphere to slow down and enter orbit for landing. Reusable rockets, such as SpaceX's Falcon 9, are able to land vertically on a designated platform using their engines.