got around to building a plasma engine ship on kspi

[noobsrtoast]

what even, can plasma engines actually produce that kind of specific impulse irl, if so, why are not using them for everything, this is amazing 

[FreeThinker]

Are you refering to KSPI MPD (Magnetoplasmadynamic thruster)? the Isp maximum for this engine 11213s was the original value cooked up by Fractal, which might sound a bit on the high side but not if you consider some some other sources like MPD on atom rocket  where is list a maximum Isp of even 32,008 s. I dicided to leave this number alone for now. Also understand this value is for Hydrogen, which molecular size is small and light but as a consequence, is much less dense that KSP High Isp propellant Xenon. If you consider that Xenon only give 12.34% of the Isp of Hydrogen Isp,The 11213s   Isp actualy realy low. as using Xenon as a propellant would only produce 1383s which is is only 33% of Ksp Ion engine @ 4200s. Considering this a fair Isp should be  11213s / 0.33 = 34035s.

On the other hand other soursces likw on Wikipedia mention a maximum exhaust speed of  110 km/s which would translate in to 110.000 / 9.81 = 11213s

Notie that hydrogen beside being lower density, requires bulky tanks,also require low temperature cryogenic storage, which cost a lot of power at earth distance from the sun. HYdrogen also has the nasty happit of escaping though the tank wals, precisely because of its small molecular size. Despite this, it would be usefull for long range mission past the astroid belt.

Because of balance reason, KSPI MPD has very high power tillarance for it engine. This will allow you get get meaningfull thrust provider you have sufficient power. In relsity they are much more limited in power, causing you to crete only newtons of thrust instead of kilo newtons. Relaisitcly this would mean that any mission with such engine will require a long time. Now that doesn't mean they aren't usefull. For some mission like unmaanded tankes they are technically ideal as they can afford to spend year enroute. For Manned mission on the otherhands, MPD are often too slow. Trips longer than a 2 years are simply unacceptable due to a range of problems. So it's much more likely they use nuclear propulsion for that.

 

 

Edited March 9, 2016 by FreeThinker

[Rushligh]

In KSPI Ammonium seems to be the most potent propellant (at lease if you have your engines scaled up)

You'll notice however that these engines require a lot of electric charge... as in the charge of a small plant. until we master making micro-fusion power plants, that technology won't be applicable IRL any time soon.
also, heat. all the thermals... to much heat...