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dV of Kerbal on EVA

Leafbaron

By Leafbaron
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Leafbaron

Leafbaron

Posted
Posted

Hey ya'll

I was just curious what the dV of a Kerbal on EVA was. I found a post from 2013 that claimed 500 m/s. But with all the changes since then, I'm curious if its the same, better, or worse. Currently at work so I can't test. However, if you know or are able to test please let me know!

If not I will launch a kerbal into LKO and completely burn his EVA monoprop and see what the change in velocity is and report back. 

Thanks,

-Leafy

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Dman979

Dman979

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Posted

IIRC, it was about 300 m/s.

 

I don't think that your plan will work too well. X dV will not get you a direct X increase in orbital speed, because of the Oberth Effect, where you're burning, etc.

I think the best way to find out would be to send one on EVA and see their mass, then run them dry and see the mass. Then see what the ISP of the thruster is, and plug that info into the Rocket Equation.

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Deutherius

Deutherius

Posted
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12 minutes ago, Dman979 said:

IIRC, it was about 300 m/s.

 

I don't think that your plan will work too well. X dV will not get you a direct X increase in orbital speed, because of the Oberth Effect, where you're burning, etc.

I think the best way to find out would be to send one on EVA and see their mass, then run them dry and see the mass. Then see what the ISP of the thruster is, and plug that info into the Rocket Equation.

I think that kerbals on EVA have a mass of 90 kg at all times, regardless of fuel quantity.

Dunno about changes, but you can still comfortably deorbit from 50 km Minmus orbit, land, reorbit and rendezvous with fuel to spare, so I"d guss it's a little more than 300 m/s.

 

^yup, a "little" more.

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Sharpy

Sharpy

Posted
Posted (edited)

Jebediah Kerman weighs as much as 19 units of liquid fuel. At 5kg per unit, that's 95kg.

Jh2zlU8.png

 

And the scales are very sensitive. At both 18 and 20 units of fuel, the indicator was waaay off.

VgwdtR8.png\3OkUEoE.png

ps. he weighs the same standing on top of the command chair. He weighs nothing when holding a ladder.

Edited by Sharpy
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Dman979

Dman979

Posted
Posted
1 hour ago, Sharpy said:

He weighs nothing when holding a ladder.

Interesting. Nothing at all? If there's an LFO tank on one side, and he's on the other, balanced, doe it tip when he holds the ladder?

Also, how does firing RCS affect this?

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Sharpy

Sharpy

Posted
Posted (edited)
6 minutes ago, Dman979 said:

Interesting. Nothing at all? If there's an LFO tank on one side, and he's on the other, balanced, doe it tip when he holds the ladder?

Also, how does firing RCS affect this?

There are two LFO tanks of equal mass on the two sides. The first test went: let Jeb out of the cabin. Get him to the ladder. Decouple the pods on two ends. Lower the scales - that allows them to swing.  The scales remained perfectly balanced. Then I switched to Jeb and let go of the ladder. Next thing, he's sliding off the arm as it swings rapidly towards the ground. So, F, to grab the ladder, quick! Then pump fuel off to the third tank (empty tank in the axis). And got a Kerbal Carousel as Jeb swings around to the other side :)

You can't use the jetpack while on the ladder, but you should be able to push the scales when standing freely.

Edited by Sharpy
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Archgeek

Archgeek

Posted
Posted
1 hour ago, Sharpy said:

Jebediah Kerman weighs as much as 19 units of liquid fuel. At 5kg per unit, that's 95kg.

And the scales are very sensitive. At both 18 and 20 units of fuel, the indicator was waaay off.

ps. he weighs the same standing on top of the command chair. He weighs nothing when holding a ladder.

That kerbal balance scale is the best thing I've seen this week.

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EpicSpaceTroll139

EpicSpaceTroll139

Posted
Posted (edited)

I just looked at the kerbalEVA.cfg and the kerbalEVAfemale.cfg in my game (version 1.2). Both say this:

"initialMass = 3.125
 massMultiplier = 0.03"

So if I understand things correctly that gives a mass of 0.09375t = 93.75kg. That's a pretty accurate scale @Sharpy!

As far as I can tell the "initial" doesn't mean anything because the Kerbal's mass doesn't change while it's on EVA.  

They have 5 units of propellant and their

"PropellantConsumption = 0.025"

which is supported by the in-game resources view.

This gives 200 seconds of thrust. (Also supported by in-game view/experience).

Their thrust in a single direction seems to be somehow defined by this line

"linPower = 10"

There doesn't seem to be any kind of obvious multiplier that applies to it, and it's definitely not in N or KN. :huh:

If we can figure out what exactly the thrust is, we can use F=ma --> a = F/m to find the acceleration, and then just multiply that by 200 seconds to get the exact dV capability.

 

On a side note I also found a rather amusing line:

splatThreshold = 150

But they don't go splat! They go poof!

Edited by EpicSpaceTroll139
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EpicSpaceTroll139

EpicSpaceTroll139

Posted
Posted (edited)

Ok I gave up on figuring out the thrust and using that to calculate dV. Maybe I could get a mod to measure my acceleration or something, but I'm too lazy to get that. I performed a similar experiment to @Sharpy's EVA experiment, except I put myself at 1000000000000000000000000m = 1000000 Exameters (displayed as 999999E for whatever weird game reason). Out here the sun's gravity is negligible. I'm not sure of the exact value but the gui said "Gav Force (weight): 0.000kN and my orbital velocity read 0.0 at the start. Anyways, I ended up reaching 639.6m/s.

Given that the grav force measurement is 0.000kN, this means that I could have had +- (discard the -) 0.0005kN of gravity (most likely less, it might have zeroed out at a lower altitude). Napkin math means this gives me an error margin of 1.067m/s 1.1m/s

HuPyimZ.jpg

ibwNjvs.jpg

Edited by EpicSpaceTroll139
sig figs
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OrbitalBuzzsaw

OrbitalBuzzsaw

Posted
Posted
4 hours ago, Deutherius said:

I think that kerbals on EVA have a mass of 90 kg at all times, regardless of fuel quantity.

Dunno about changes, but you can still comfortably deorbit from 50 km Minmus orbit, land, reorbit and rendezvous with fuel to spare, so I"d guss it's a little more than 300 m/s.

 

^yup, a "little" more.

94kG, according to KER

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