Does having a Kerbal in a cockpit affect its mass?

[whistlehead]

Title says it all. I ask because my submission to the BSC albatross thread has two cockpits both waaaay off centre, and I'm wondering if having only one crew affects its flight.

(It = the cockpit)

Edited November 1, 2013 by whistlehead

[kahlzun]

It shouldn't do: the only time kerbals add mass is to the external seats.

Easy way to tell, bail one of them out, and see if the mass shown on the map screen changes..

[numerobis]

All reports I've seen say that kerbals are massless in the cockpit.

kahlzun's test though is inconclusive: the map screen only lists the mass of the ship. If you use the ship to push a kerbal (or some parts that you decoupled), that doesn't get added to the listed mass. You'd have to test whether your speed is going up as fast as you expect when you thrust.

[Starwhip]

I don't think they do. You could experiment somehow. Maybe EVA a Kerbal in orbit, switch back to the ship, and go to the information panel. Then do the same with the Kerbal in the cockpit and compare the masses.

[Smidge204]

Small rocket and fuel tank, command capsule and small probe core. Launch straight up with and without a Kerbal in it, see if there's a difference in altitude reached. Can't test it myself right now though

I get the feeling that Kerbals don't add mass if they're inside. If this is still unanswered when I get home I'll test and share results here.

=Smidge=

[Dispatcher]

The mass of a Kerbalnaut (whenever actually applied in the game) is about 0.18 units of mass. When finesse counts, I do add that in for each Kerbal, just in case. As for balancing a craft with only one crew in a multi crew craft, I'd have no idea.

[Blue]

HERE COMES THE SCIENCE!!

Well. Now we know. And that's half the battle. And that's terrible.

Kerbals weigh exactly 0kg. Or rather, Kerbals have 0 mass and weigh 0N.

[Smidge204]

Well. Now we know. And that's half the battle.

Kerbals weigh exactly 0kg. Or rather, Kerbals have 0 mass and weigh 0N.

Could also be that the information window is not properly reporting the value, and the mass is still figured into the calculations.

Hence, more testing needed.

=Smidge=

[Zad Fnark]

I doubt it. The Ship info in MechJeb never regestered a change.

ZF-

[wasmic]

Could also be that the information window is not properly reporting the value, and the mass is still figured into the calculations.

Hence, more testing needed.

=Smidge=

Kerbals on EVA are entirely different vessels, and assuming that the ship info doesn't show mass properly, without any evidence, makes no sense, logically.

[Smidge204]

I didn't assume anything. It's a hypothesis that needs testing.

Edit: Okay, ran the test with 0-7 Kerbals on the same rocket - No difference in max height for the same fuel. In fact, the rocket with only Jeb in it went 4 meters higher (6305m) than the empty rocket (6301m) which is just how good a pilot he is!

=Smidge=

Edited October 31, 2013 by Smidge204

[Superfluous J]

I didn't assume anything. It's a hypothesis that needs testing.

=Smidge=

Challenge accepted.

I created a ship, 11 lander cans (I think they're the best weight/kerbal ratio out there at 0.6 tons per Kerbal). I had to have a Kerbal in one of them (though I could have used the little Okto now that I think about it, but oh well) but the other 10 were empty. Under those, I had a single reaction wheel to keep things stable and then a large SRB. I went to the launch pad and launched it 3 times. As soon as the engine died I got an apogee reading with Kerbal Engineer.

1: 9986km

2: 9995km

3: 9997km

Average: 9993km

I then loaded up the 10 previously empty cans with Kerbals, and did 3 more launches in the same way.

1: 9977km

2: 9987km

3: 9987km

Average: 9984km

The error in this is roughly 0.1 percent. (10km out of 10,000km). So either 10 Kerbals weighs 0.1 percent of the total mass of the ship (which was 14.78 tons), or 1 kerbal weighs 0.001478 tons or 1.478kg or about 3 pounds) or they weigh nothing and my error is just that, an error.

I'm going with it's an error

[nismobg]

When you exit capsule in the water isnt it reacting ? If it is then there is mass.

[Ghost13]

As far as I know from flying expirience, no kerbals dosn't have any weight.

[TaranisElsu]

Based on all the testing that I have done while developing my mods: No, Kerbals do not add any weight to the ship while inside. A Kerbal on EVA weights 0.09 tons (90 kg), and that weight IS added to the ship when they sit in an external seat.

[whistlehead]

Ok, I think that's the answer - no difference. Thanks!

[Vanamonde]

I tried a couple of experiments to answer this empirically, but the results were equivocal and inconclusive.

Firstly, I threw this odd rocket together.

Bill is in the capsule whose lights are on, and the other one is empty. I got the ship rotating quickly, then ejected the segment with the capsules. If there is a Kerbal's mass in one but not the other, the barycenter of the capsule segment should be off of geometrical center, and I hoped that by watching along the axis of the launch stage in chase mode, I could see the capsule segment rotating around a slightly different axis. Unfortunately, the ejection is so violent that the capsule segment started precessing.

Sorry that's so dark, but I had to fly it in Kerbin's shadow so the lights on the capsule were evident. If you can't make that out, the capsule segment has flipped around and its former axis is now perpendicular to the launch stage. Maybe somebody else can figure out a way to make this principal work as a test?

So then I built this odd rocket.

Bob is again in the lit capsule, on the left. After leaving atmo I triggered the chutes and ejected the capules,

then watched them fall. If there is a Kerbal's mass in one, it should fall ever so slightly faster than the empty. Confounding my expectations, the empty one first pulled slightly ahead,

then filled one caught up to a degree,

then when the chutes opened the empty one yanked to the side as if its internal weight was not symmetrical,

and then they stayed neck-and-neck to touchdown.

Make of this what you will.

[Smidge204]

Maybe try using a docking port instead of a decoupler? Should be less violent.

If there is a Kerbal's mass in one, it should fall ever so slightly faster than the empty.

Might want to reconsider that hypothesis...

=Smidge=

[hobbsyoyo]

A capsule that is empty will not fall slower than a full one eveb if Kerbals do have mass. Gravity acts on all objects the exact same regardless of mass. Haven't you seen the video from Apollo where the astronaut dropped a feather and a rock and they fell at the same speed?

[Vanamonde]

Yeah, I should have been more specific; my thinking was that the capsule with the Kerbal's mass in it should punch through air resistance slightly faster (same cross-section, different mass), which is why I performed the test in atmo. Of course, it's quite possible that isn't right, either. I've got a persistent headcold that has left me feeling mildly drunk all week.

[Troberg]

I didn't notice any difference between the unmanned test launches and fully crewed launch of my 164 kerbal permanent Eve base. That should have made a difference...

[Lexif]

Yeah, I should have been more specific; my thinking was that the capsule with the Kerbal's mass in it should punch through air resistance slightly faster (same cross-section, different mass), which is why I performed the test in atmo.

Drag also should not depend on mass. But that's exactly where the aerodynamic model of KSP goes wrong, as in KSP drag is proportional to mass (everything else being equal). Try dropping full and empty, otherwise identical, fuel tanks. So your test is valid.

Get well soon!

[UberFuber]

Drag also should not depend on mass. But that's exactly where the aerodynamic model of KSP goes wrong, as in KSP drag is proportional to mass (everything else being equal). Try dropping full and empty, otherwise identical, fuel tanks. So your test is valid.

Get well soon!

Drag doesn't depend on mass, but drag is a force, and the acceleration (or in term of drag, deceleration) it imparts on the craft should be inversely proportional to its mass (so the heavier the craft, the less it decelerates from drag).