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Kerbal EVA suit vs real EVA suits


Gordon Fecyk

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On a challenge thread on getting to Minmus and the Mun and back in one trip, a discussion came up on the mass of kerbals and their EVA suits. Based on the before / after mass of a basic craft and adding a kerbal to a command seat, a kerbal has 0.09 t mass. MechJeb apparently reports it as 94 kg. Now take the kerbal and remove the EVA fuel, and you still get 0.09 t, but somehow that suit has 600 m/s dV according to the Wiki.

@Teilnehmer did some math and figured the EVA fuel was 10 kg based on the max acceleration of 3.2 m/s2 but that would mean the exhaust velocity was 5.4 km/s! If the stuff was actually the same as monopropellant, that would make EVA fuel 20 kg but that still puts the exhaust velocity at 2.5 km/s and I'm pretty sure I wouldn't want that on my back. Especially since real monopropellants are pretty volatile stuff. Modern EVA suits use compressed Nitrogen and apparently that suit only has 25 m/s dV.

Now EVA fuel in KSP comes from hammerspace currently and a kerbal in a command seat is still 0.09 t with a full or empty EVA pack. But is this sort of EVA suit a real possibility?

(I found an old thread on this regarding the mass of kerbals, but the advice against necro-posting applies.)

Edited by Gordon Fecyk
speed != velocity
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A Gemini flight was originally supposed to test a USAF peroxide jet pack, complete with steel wool spacesuit pants. But even that wouldn't provide the requisite dV. The pack would have to be stripped down, much larger and heavier than an MMU - let alone a Kerbal jetpack. In my own fanfic an EVA from Mun orbit to surface included several KIS supplementary tanks and nitromethane instead of standard H2O2.

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I don't know which one of you caused this thought, but somewhere the idea of nitrous oxide as a monopropellant came up. And it seems plausible oddly.

To get 600 m/s out of N2O for a dry-mass 75 kg being including EVA suit, you'd need 30 kg of the stuff based on a possible ISP of 180 s. That's still 1.7 km/s exhaust velocity apparently, but maybe that can be adjusted. And maybe we wouldn't need 600 m/s and then could get away with a lower ISP (and safer exhaust), and less of the stuff to carry around.

Sure it means carrying around a heating element that can reach 577 OC... ouch.

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If a kerbal mass around 45 kg then yes it's possible in-game.

IRL... I don't know. Assuming scale goes likewise for propellant vs. dead mass I think it'd be quite lumpy... And dangerous.

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  • 4 weeks later...
9 hours ago, PhysicsBrain said:

The power source to heat it would have to be like two RTG's.. Not a good idea.

Rtg is heat over long time, not burst. 
Chemical would be better, add it to exhaust, yes it would be more mass 

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Numerous rocket packs have been built for use on Earth, hydrogen peroxide is the most common fuel. On Earth at least the 750 C exhaust seems manageable, although it does only have to thrust one way.

A 30 second flight time with such a rocket pack equates to about 300 m/s of delta-V. So if the Kerbals are willing to toss safety and common sense out the window (and it's generally accepted they are) 600 m/s doesn't seem so unbelievable, especially as thrust is lower. That said, the propellant mass would be higher than the game seems to imply.

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