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How much more efficient would Nuclear Fission rockets be?
Using existing technology if we were to build a Fission rocket then how much
more efficient would than a Chemical rocket would it be? I believe conventional rockets are capable of speeds around 8km/s. What sort of speeds could a Fission rocket get up to? |
#2
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How much more efficient would Nuclear Fission rockets be?
"Rats" wrote in message ...
Using existing technology if we were to build a Fission rocket then how much more efficient would than a Chemical rocket would it be? Rocket efficency is measured in terms of "specific impulse". Or to use english units: pounds thrust produced by the rocket divided by pounds mass of propellent consumed per second = lb_thrust/lb_prop/sec= Isp The very best chemical rockets use Liquid Hydrogen - Liquid Oxygen propellent and get an Isp of around 450 in english units. The nuclear powered NERVA rocket engines built and tested by NASA in the 1960s got an Isp as high as about 900 if I recall right. One of the basic reasons the Nerva project was shut down was that the Nerva design had to be put in orbit by chemical rockets as it could not get to orbit on its own as the thrust to weight ratio was too low. Designs that were never tested full scale, specifically the "Dumbo" project, should have been able to produce Isps of as high as about 1200. In addition it could reach earth orbit in one stage, again in theory. Dumbo fuel elements were tested in nuclear reactors and found to work well, however a full scale dumbo nuclear reactor design was never built. Another project was the Orian project that used a totally different approach of detonating nuclear explosives (bombs) to propell very large spacecraft that used a thick shield plate. In theory it should work. Test models were built and flown in the 1950s using chemical explosives to propell the model. In principle it should work fine, and be very fuel efficent and able to lift huge payloads and go very fast indeed. The enviromental ad legal concerns are the problem. Lately a revised design that uses the principle of the Orian system but micro nuclear explosions that are set off by pinching tiny pieces of nuclear fuel rather than a traditional nuclear bomb is being studied. The ISP on an Orian system in theory can be very high indeed, as I recall and figure of 10,000 was considerd low. I believe conventional rockets are capable of speeds around 8km/s. That is not correct. In thory any rocket can achieve any velocity if you have enough propellent. The formula is as follows: DeltaV=Isp*g*LN(M0/M1) Whe DeltaV is the required change in velocity Isp= specific impulse as discussed above. g= gravitational constant 32.2 ft/sec/sec in english units M0 is the initial mass of the rocket+ propellent M1 is the final (after rocket burn) mass of rocket + remaining propellent and LN() is the natural log of whatever is inside the parenthesis (). What sort of speeds could a Fission rocket get up to? A whole lot faster than a chemical fueled rocket with the same mass ratio, example assume that the mass ratio is 5 =M0/M1 then the LH2-LOX rocket with and ISP of 450 is going at 7.11 km/sec the Nerva rocket with LH2 Propellent heated in a Nerva nuclear reactor to an ISP of 900 is going at 14.22 km/sec the Dumbo rocket with LH2 Propellent heated in a Dumbo nuclear reactor to an ISP of 1200 is going at 18.95 km/sec and the minimal Orion rocket is booking along at 157.96 km/sec |
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How much more efficient would Nuclear Fission rockets be?
"Rats" wrote in message ... Using existing technology if we were to build a Fission rocket then how much more efficient would than a Chemical rocket would it be? I believe conventional rockets are capable of speeds around 8km/s. What sort of speeds could a Fission rocket get up to? The rough rule is twice the exhaust velocity. After that the required mass ratios tend to get ridiculous. LOX/LH2 will get you an exhaust velocity of maybe 4.4km/s in vacuum. The most energetic chemical propellants I'm aware of is the tripropellant LOx/LH2/beryllium, at about 5.3 km/s. For a NERVA-type engine, figure about 8 - 9km/s exhaust using LH2. Regards Jonathan Wilson |
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How much more efficient would Nuclear Fission rockets be?
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#5
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How much more efficient would Nuclear Fission rockets be?
Christopher M. Jones wrote:
"Rats" wrote in message ... Using existing technology if we were to build a Fission rocket then how much more efficient would than a Chemical rocket would it be? I believe conventional rockets are capable of speeds around 8km/s. What sort of speeds could a Fission rocket get up to? Chemical rockets are capable of speeds up to the speed of light, given sufficient mass ratios and staging (note: Nitpick: Say one stage has a 5Km/s ISP, and each stage is double the weight of the last. 300000/5 (neglecting relativity) is 60000 stages. I make that a mass ratio of 63057948700178233572600261579236409495216587841434 361062005234596045 40006238697171501101348715304065265065961166212456 929797807660184547 23814941962225280444496680617986892514285389144879 868315356003294016 snip some 263 lines If the final payload is one atom, the first stage will weigh considerably more than the whole universe. |
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How much more efficient would Nuclear Fission rockets be?
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#7
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How much more efficient would Nuclear Fission rockets be?
"Ian Stirling" wrote in message ... Christopher M. Jones wrote: "Rats" wrote in message ... Using existing technology if we were to build a Fission rocket then how much more efficient would than a Chemical rocket would it be? I believe conventional rockets are capable of speeds around 8km/s. What sort of speeds could a Fission rocket get up to? Chemical rockets are capable of speeds up to the speed of light, given sufficient mass ratios and staging (note: Nitpick: Say one stage has a 5Km/s ISP, and each stage is double the weight of the last. 300000/5 (neglecting relativity) is 60000 stages. I make that a mass ratio of 63057948700178233572600261579236409495216587841434 361062005234596045 40006238697171501101348715304065265065961166212456 929797807660184547 23814941962225280444496680617986892514285389144879 868315356003294016 snip some 263 lines If the final payload is one atom, the first stage will weigh considerably more than the whole universe. Or, to work the problem the other way - starting with the mass of the Universe (3 x 10^55 g, http://curious.astro.cornell.edu/que...php?number=342) we have a total mass ratio of 1.8 x10^79 (assuming the payload is one hydrogen atom) we can make the mass ratio larger by a factor of 1836.1527 by assuming the payload is an electron, but this is supposed to be a *chemical rocket* using reactions between atoms and we wouldn't want to get *ridiculous* about this! This gives a maximum of 263 stages (with the same assumptions as Ian's) and a burnout velocity of 1300 km/sec or 0.44% c. (Note that a large majority of the mass of the Universe is invisible, non-baryonic dark matter. This calculation assumes that this mass can be converted to usable fuel.) Carey Sublette |
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How much more efficient would Nuclear Fission rockets be?
Ian Stirling wrote in message .. .
Christopher M. Jones wrote: Chemical rockets are capable of speeds up to the speed of light, given sufficient mass ratios and staging (note: Nitpick: Say one stage has a 5Km/s ISP, and each stage is double the weight of the last. 300000/5 (neglecting relativity) is 60000 stages. I make that a mass ratio of 63057948700178233572600261579236409495216587841434 361062005234596045 40006238697171501101348715304065265065961166212456 929797807660184547 23814941962225280444496680617986892514285389144879 868315356003294016 snip some 263 lines If the final payload is one atom, the first stage will weigh considerably more than the whole universe. You snipped the full quote, here's what I wrote: "Chemical rockets are capable of speeds up to the speed of light, given sufficient mass ratios and staging (note: quite a lot of dry humor there)." The difficulty of obtaining more propellant mass than the mass of the known Universe is merely an engineering problem. |
#9
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How much more efficient would Nuclear Fission rockets be?
Christopher M. Jones wrote:
Ian Stirling wrote in message .. . Christopher M. Jones wrote: Chemical rockets are capable of speeds up to the speed of light, given sufficient mass ratios and staging (note: Nitpick: Say one stage has a 5Km/s ISP, and each stage is double the weight of the last. 300000/5 (neglecting relativity) is 60000 stages. I make that a mass ratio of 63057948700178233572600261579236409495216587841434 361062005234596045 40006238697171501101348715304065265065961166212456 929797807660184547 23814941962225280444496680617986892514285389144879 868315356003294016 snip some 263 lines If the final payload is one atom, the first stage will weigh considerably more than the whole universe. You snipped the full quote, here's what I wrote: "Chemical rockets are capable of speeds up to the speed of light, given sufficient mass ratios and staging (note: quite a lot of dry humor there)." I know, that was why there was the Nitpick:. It was also to point out to those that might just be lurking how mind-bogglingly fast C is, compared to chemical rockets. The difficulty of obtaining more propellant mass than the mass of the known Universe is merely an engineering problem. |
#10
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How much more efficient would Nuclear Fission rockets be?
"Ian Stirling" wrote in message ... Christopher M. Jones wrote: "Rats" wrote in message ... Using existing technology if we were to build a Fission rocket then how much more efficient would than a Chemical rocket would it be? I believe conventional rockets are capable of speeds around 8km/s. What sort of speeds could a Fission rocket get up to? Chemical rockets are capable of speeds up to the speed of light, given sufficient mass ratios and staging (note: Nitpick: Say one stage has a 5Km/s ISP, and each stage is double the weight of the last. 300000/5 (neglecting relativity) is 60000 stages. I make that a mass ratio of 63057948700178233572600261579236409495216587841434 361062005234596045 40006238697171501101348715304065265065961166212456 929797807660184547 23814941962225280444496680617986892514285389144879 868315356003294016 snip some 263 lines If the final payload is one atom, the first stage will weigh considerably more than the whole universe. Or, to work the problem the other way - starting with the mass of the Universe (3 x 10^55 g, http://curious.astro.cornell.edu/que...php?number=342) we have a total mass ratio of 1.8 x10^79 (assuming the payload is one hydrogen atom) we can make the mass ratio larger by a factor of 1836.1527 by assuming the payload is an electron, but this is supposed to be a *chemical rocket* using reactions between atoms and we wouldn't want to get *ridiculous* about this! This gives a maximum of 263 stages (with the same assumptions as Ian's) and a burnout velocity of 1300 km/sec or 0.44% c. (Note that a large majority of the mass of the Universe is invisible, non-baryonic dark matter. This calculation assumes that this mass can be converted to usable fuel.) Carey Sublette |
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