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Old 12-06-2017, 11:20 PM   #11
Michael Thayne
 
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Default Re: [Spaceships] Mass-driver realism

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They both come under the category of "buildable at TL 7, but a really stupid idea".
Which? The nuclear rockets, or is mass driver propulsion a stupid idea?
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Old 12-06-2017, 11:36 PM   #12
Anthony
 
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Default Re: [Spaceships] Mass-driver realism

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Which? The nuclear rockets, or is mass driver propulsion a stupid idea?
The nuclear rockets.
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Old 12-07-2017, 03:10 AM   #13
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Default Re: [Spaceships] Mass-driver realism

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Looking at this more, I'm kind of wondering why mass drivers weren't listed in Spaceships as TL8—sure mass driver propulsion hasn't been developed yet, but neither have Orion drives or nuclear thermal rockets, both TL7.
Actually, the NERVA project did test fire a nuclear thermal rocket and a small scale Orion (using conventional explosives) was flight tested before Orion was shut down by JFK. So both were fairly well developed in TL7.

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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Old 12-07-2017, 09:55 AM   #14
Michael Thayne
 
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Default Re: [Spaceships] Mass-driver realism

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Originally Posted by Gnaskar View Post
Actually, the NERVA project did test fire a nuclear thermal rocket and a small scale Orion (using conventional explosives) was flight tested before Orion was shut down by JFK. So both were fairly well developed in TL7.

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.
Yeesh, you're right. Actually, the mass driver in Spaceships appears to be about 40 times more energy efficient than the beam weapons. Which means unless the Spaceships weapons are only 2.5% energy-efficient, this is a straight-up violation of the laws of thermodynamics.
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Old 12-07-2017, 10:02 AM   #15
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Default 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.
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Old 12-07-2017, 11:20 AM   #16
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Default Re: [Spaceships] Mass-driver realism

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Tangentially, why is NTR a really stupid idea?
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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Old 12-07-2017, 01:13 PM   #17
Fred Brackin
 
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Default Re: [Spaceships] Mass-driver realism

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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.
As a measure of how much fun the 60s were, NASA actually blew up a NERVA while in use (ground test, all NERVA test fires were ground-based) to test how bad a crash would be. The answer was not very by the standards of the time.

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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Old 12-07-2017, 02:55 PM   #18
AlexanderHowl
 
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Default 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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Old 12-07-2017, 05:45 PM   #19
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Default Re: [Spaceships] Mass-driver realism

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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...
And getting prophylactic thyroidectomies at age 14... :)

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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Old 12-07-2017, 05:52 PM   #20
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Default 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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