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Post by quarkster on Sept 29, 2016 14:29:20 GMT
I was just trying to design a magnetoplasmodynamic thruster and they are all kinds of messed up. Increasing fuel flow increases exhaust velocity. Increasing chamber radius makes it easier to dissociate and ionize the propellant. Chamber length has zero effect on thruster performance. I may very well have missed some other things.
Also, and this may be a design decision rather than a mistake, but I should not be able to put a gigawatt through an object the size of a paint bucket and expect it to survive.
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Post by darloth on Sept 30, 2016 15:19:33 GMT
Not to mention - in the ship designer, using 20 of these doesn't draw any more power than using 1 of them, even though they now provide 20x the thrust.
(It's still not ENOUGH thrust, but still - it's supposed to cost energy, right?)
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Post by quarkster on Sept 30, 2016 15:53:04 GMT
I was planning on using them to steer a deathstar. My thinking was that it would either be steering or firing the gigawatt laser, but not both, so insanely powerful MPDTs might be a good choice.
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Post by qswitched on Sept 30, 2016 18:06:46 GMT
Most of the initial issues mentioned seem par for the course for MPD thrusters. Chamber length of an MPD thruster has very little effect after an initial length (dependent on the power involved), this is well documented. Mass flow rate heavily affects the resistivity of the coolant and thus all sorts of performance metrics change, unlike in NTRs, etc. Not to mention - in the ship designer, using 20 of these doesn't draw any more power than using 1 of them, even though they now provide 20x the thrust This is a known bug though. |
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Post by quarkster on Sept 30, 2016 21:35:22 GMT
Most of the initial issues mentioned seem par for the course for MPD thrusters. Chamber length of an MPD thruster has very little effect after an initial length (dependent on the power involved) One of these days you'll believe me the first time. |
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Post by qswitched on Sept 30, 2016 22:19:10 GMT
I'll double check the MPD papers (I'm much more versed in thermal/combustion rockets than electric rockets), but I'm not too terribly surprised by the results you've posted. If anything, this indicates that thruster length needs to be able to go less than 1 cm, down to millimeters or even micrometers.
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Post by quarkster on Oct 1, 2016 0:04:31 GMT
This invariance occurs at both the smallest and largest scales, and real MPDT chambers are about as long as they are wide.
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