12-06-2017, 10:20 PM | #11 |
Join Date: May 2010
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Re: [Spaceships] Mass-driver realism
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12-07-2017, 02:10 AM | #13 | |
Join Date: Feb 2016
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Re: [Spaceships] Mass-driver realism
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The work done with Mass Drivers in the same period were more focused on using them to shoot material into lunar orbit (or the lagrange points anyway) than on useful propulsion of spacecraft. A mass driver rocket with the kind of stats listed in Spaceships is pretty scifi even by modern standards. It fires off it's propellant at ~6-9,000 m/s (roughly 3-4 times that of a modern railgun, meaning 10 times the energy). Worse still, in order to get an acceleration of 0.01G, it has to fire away the propellant at a sustained rate of measured in kilograms or even tons per second. Railguns require massive capacitor banks to recharge between shots, while this theoretical mass driver needs a constant supply of power. Basically, Mass Drivers are TL9 because they require a TL9 power source. NTRs and Orions are TL7 because we actually built working prototypes of them in the Cold War. |
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12-07-2017, 08:55 AM | #14 | |
Join Date: May 2010
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Re: [Spaceships] Mass-driver realism
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12-07-2017, 09:02 AM | #15 |
Join Date: May 2010
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Re: [Spaceships] Mass-driver realism
*Does more math*
Incidentally, it seems that the energy requirements for emag weapons are much more in line with listed beam weapon energy outputs. So this really is a case of the mass driver engine being screwy in isolation. Tangentially, why is NTR a really stupid idea? My understanding is that NASA still assumes we'll use one for a manned Mars mission, at least if they get funding for one in the foreseeable future. |
12-07-2017, 10:20 AM | #16 |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: [Spaceships] Mass-driver realism
Because they were designing it for ground to orbit use, and even the best rockets are prone to crashing or blowing up. Depending on the details, the exhaust might also be radioactive.
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12-07-2017, 12:13 PM | #17 | |
Join Date: Aug 2007
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Re: [Spaceships] Mass-driver realism
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Probably the real issue was thrust-to-weight ratio. That was about 3 lbs of thrust to 1 lb of engine. Then you add in fuel mass and it's just not very practical even with double the Delta-V of a chemical rocket. However, the NERVAs that were tested really shown in one area and that was endurance. Normal/average burn time for a liquid fuel motor was about 2 minutes. Making the Shuttle Main Engines able to burn for more than 8 minutes is probably one of the things that may have made them overly expensive and complicated. One of the NERVA tests ran for over 40 minutes without any trouble and longer burns were probably possible. So once you were in orbit and didn't have to exceed 1G you could use a NERVA that was 10x smaller but run it for 10x as long. The radioactive fuel in the engine was also much less radioactive before you put it into firing mode. So risks during launch would be significantly reduced.
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Fred Brackin |
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12-07-2017, 01:55 PM | #18 |
Join Date: Feb 2016
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Re: [Spaceships] Mass-driver realism
The Orion Project was a fun idea. While everyone blames the treaties for scrapping it, the real reason why no one in power cared is because they did not see the utility of sending destroyers into orbit in the 1960s (especially since the Soviets would have done the same). We would have colonies on Titan and be sending manned missions to Triton right now if we had kept going with the Orion. Oh well, missed opportunities...
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12-07-2017, 04:45 PM | #19 | |
Join Date: Aug 2010
Location: The Land of Enchantment
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Re: [Spaceships] Mass-driver realism
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I mean, really, detonating nuclear weapons in the atmosphere? Unless you boost to orbit first- like those schemes that used a couple of dozen SRBs- building a space industry around Orion is insane. Cool as hell, but insane.
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I'd need to get a grant and go shoot a thousand goats to figure it out. |
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12-07-2017, 04:52 PM | #20 |
Join Date: Feb 2016
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Re: [Spaceships] Mass-driver realism
It depends on the type of device you are using. I am sure that there would have been serious work on pure fusion devices (using something more affordable and less dangerous than tritium) if there had been an economic incentive for such devices.
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