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Old 08-09-2020, 01:42 PM   #21
AlexanderHowl
 
Join Date: Feb 2016
Default Re: [Spaceships] Can't find the right propulsion system

I would honestly go with a higher delta-v system. A nuclear thermal rocket provides 0.5g and 0.45 mps per fuel tanks at TL9+. It could even be used for shuttle taxis from the surface to orbit and back.
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Old 08-09-2020, 04:04 PM   #22
Anthony
 
Join Date: Feb 2005
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Default Re: [Spaceships] Can't find the right propulsion system

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Originally Posted by AlexanderHowl View Post
I would honestly go with a higher delta-v system. A nuclear thermal rocket provides 0.5g and 0.45 mps per fuel tanks at TL9+. It could even be used for shuttle taxis from the surface to orbit and back.
In general the more delta-V per tank, the more destructive the exhaust. Depending on the details of how it's to be used, it might be better to not use a reaction drive at all (use something like tethers, or something that interacts with EM fields created by a larger vehicle).
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Old 08-09-2020, 05:27 PM   #23
AlexanderHowl
 
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Default Re: [Spaceships] Can't find the right propulsion system

Well, destructive potential is a related to thrust and delta-v. Doubling thrust usually means doubling mass flow or doubling exhaust velocity. Increasing mass flow will decrease delta-v proportionally to the increase in thrust while increasing exhaust velocity will increase delta-v proportionally to the increase in thrust. Energy is proportional to the square of exhaust increase.

For example, compare the TL9 HEDM rocket (2g/0.5 mps) to the TL9 fission thermal rocket (0.5g/0.45 mps). The former possesses ~2x the exhaust velocity, burns twice as much reaction mass per second, so it is putting out ~8x the energy of latter. While a TL9+ HEDM rocket has exhaust with a temperature of over 26,000 K, the fission rocket is only running at around 6,500 K. While dangerous to unprotected systems, a TL9+ fission thermal rocket is much safer than the TL9 HEDM rocket, dealing ~1/3 as much damage to anything caught in its exhaust flow.
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Old 08-09-2020, 07:04 PM   #24
Anthony
 
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Default Re: [Spaceships] Can't find the right propulsion system

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Originally Posted by AlexanderHowl View Post
For example, compare the TL9 HEDM rocket (2g/0.5 mps) to the TL9 fission thermal rocket (0.5g/0.45 mps). The former possesses ~2x the exhaust velocity, burns twice as much reaction mass per second, so it is putting out ~8x the energy of latter.
No it doesn't. The TL9 HEDM rocket has 11% higher exhaust velocity and 4x greater thrust, and thus is putting out 4.44x as much energy, but since you only have to burn it for 1/4 as long the net hazard is 11% higher. It's also running at about a 23% higher temperature (temperature varies with the square of exhaust velocity and not correlated with thrust). In any case, HEDM is also a bad choice, most thrusters intended for purposes like this are things like cold gas thrusters with exhaust velocities up to maybe 1 km/sec and thus delta-V per tank of .03mps or so.
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Last edited by Anthony; 08-09-2020 at 07:07 PM.
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Old 08-09-2020, 09:13 PM   #25
Rupert
 
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Default Re: [Spaceships] Can't find the right propulsion system

Of the rockets available in Spaceships, the ones that seem to produce decent thrust without too much burning doom or issues with casual anti-matter ownership seem to me to be the basic chemical rocket and a nuclear thermal rocket using water as reaction mass (or hydrogen if delta-vee is more important than thrust). One means having highly volatile fuel and oxidant sitting round, the other having fissile materials readily available to all and sundry.
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Old 08-09-2020, 09:29 PM   #26
Anthony
 
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Default Re: [Spaceships] Can't find the right propulsion system

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Of the rockets available in Spaceships, the ones that seem to produce decent thrust without too much burning doom...
Might want to just tune down your concept of decent thrust. For comparison, a NASA MMU has a total acceleration of about 0.009G with a total burn duration of 450s for a total delta-V of about 40 meters/sec. You might want a tad more performance, but reaching a safe walking speed of 1 yard per second takes 0.09s at 1G, so 0.05G is probably plenty.
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Old 08-09-2020, 09:53 PM   #27
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Default Re: [Spaceships] Can't find the right propulsion system

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Might want to just tune down your concept of decent thrust. For comparison, a NASA MMU has a total acceleration of about 0.009G with a total burn duration of 450s for a total delta-V of about 40 meters/sec. You might want a tad more performance, but reaching a safe walking speed of 1 yard per second takes 0.09s at 1G, so 0.05G is probably plenty.
Even 0.05G if you don't want a large fraction of the module's mass to be rocket gives fairly limited choices using Spaceships. Chemical, HEDM, NTR, light-bulb, fusion torch if available. I'm not counting nuclear pulse drives or nuclear salt-water because if anti-matter isn't desirable I very much doubt they would be either.

A smaller-system (1/3 size) NTR with a single 1/3rd size fuel tank would give 0.167G and 0.15 mps DV using hydrogen or 0.5G and 0.05 mps DV with water. I think you could probably make a pretty simple, reliable, and failsafe NTR unit at TL10, especially if getting optimal thrust/weight and specific impulse out of it wasn't the priority.
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Old 08-09-2020, 11:12 PM   #28
Anthony
 
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Default Re: [Spaceships] Can't find the right propulsion system

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A smaller-system (1/3 size) NTR with a single 1/3rd size fuel tank would give 0.167G and 0.15 mps DV using hydrogen or 0.5G and 0.05 mps DV with water. I think you could probably make a pretty simple, reliable, and failsafe NTR unit at TL10, especially if getting optimal thrust/weight and specific impulse out of it wasn't the priority.
The basic power output of a rocket is 0.5 * thrust * exhaust velocity; for a 1 ton ship managing 0.167G, the thrust is 1480N, at 0.45mps/tank exhaust velocity is 14,400m/s, and thus your 'small' system is still belching out more than ten megawatts.

If you want something that isn't ridiculously dangerous, accept low performance; something like 0.05g at 0.09mps/tank is within the reach of storable liquid rockets.
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Old 08-09-2020, 11:51 PM   #29
Say, it isn't that bad!
 
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Default Re: [Spaceships] Can't find the right propulsion system

Hmm... suggestion: Spaceships... 9?: Work Pods and Smallcraft?
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Old 08-10-2020, 08:25 AM   #30
TGLS
 
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Default Re: [Spaceships] Can't find the right propulsion system

Hm... Low thrust rockets:

Remote Heated Hydrogen: Hydrogen heated by laser/solar power to 5800 K. 0.3 mps per tank/0.01g
Microwave Water Rocket: Water heated using microwaves to 3100 K. High Power System. 0.3 mps per tank/0.06g
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