Why are parts so heavy?

[Kurld]

For instance, the Mk2 lander. It weighs, what 2+ tons? This seems too heavy to me. The Apollo ascent stage included RCS, liquid fuel and engine, etc. for 2200m/s delta v and was nearly 2x as large in every dimension and yet only had mass of 4.7 tons. The Mk2 can should only have mass of about 600kg even including an engine and fuel.

Other parts seem similarly skewed.

I'm not complaining, but really want to understand the design decision behind making parts have such mass. How would it impact gameplay if the parts had a more "realistic" mass.

I put "realistic" in quotes because I am open to the possibility I am way off base in my understanding of what scaled down stuff "should" weigh.

[Scarecrow88]

This is a game and doesn't mimic the real world - just compare the size of the planets. The game is what it is.

[magnemoe]

Done for balance, its very easy to launch an small probe but far harder to launch larger stuff.

[MiniMatt]

There are still undoubtedly some balance passes to be done but as others above have intimated, game first, realism second. So long as parts end up balanced against each other I've no particular desire to see them balanced to reality.

The Mk2 Lander Can does look a little heavy compared to it's Mk1 counterpart (in that it's far far more mass efficient to have two separate 1-kerbal cans than a single 2-kerbonaut can) but that could indicate the Mk1 can is too light as much as the Mk2 being too heavy.

edit: also perhaps noteworthy that not all mechanics are in place. Things like heat tolerance are meaningless stats right now. When other game mechanics are in place that design process of juggling many different pros and cons to reach your perfect-ish solution will consider more variables in the concept of balance.

Edited September 16, 2013 by MiniMatt

[Kurld]

I understand it's a game (geez louise I've sure put in the hours on it). And I really don't have any problem with the weight or size of whatever. It's fun, after all. I am just wondering at the rationale. To put it another way, would the game somehow be less fun it the stats were more realistic? (of the parts at least... I understand and fully support the decision not to have a scale-size planet/solar system.. it would take forever to do anything.)

[Kurld]

I'm asking from the perspective of a software engineer and (non pro) game designer.

[NASI Director]

I don't know if it's been noticed yet, but the Apollo lander was something more like 14 tonnes.

[Kerbart]

Remember that earth spacecraft are made from hitech materials.

Kerbal craft are pieced together from garbage cans, swimming pools, sewage pipe and other nondescript materials.

[Maddmatts]

It's not just a game. It's an early-access game. Anything about it can change in the future.

There are other odd weights like how a 1m nosecone + 1m to 2m adapter is lighter than a 2m nosecone.

[lincourtl]

I don't know if it's been noticed yet, but the Apollo lander was something more like 14 tonnes.

Yeah, the ascent and descent stages combined were 16 tons -- 5 tons for the ascent stage and 11 tons for the descent stage. That's not counting the LRV, but that was just under a quarter ton.

[softweir]

... To put it another way, would the game somehow be less fun it the stats were more realistic?

Yes! It has been pointed out that an accurate Saturn-5 first stage would, in the Kerbal universe, have enough delta-v to act as a single-stage-to-Mun vehicle. That is, it could launch, go all the way to the Mun, land, re-launch and get a crew back in just one stage! While some people enjoy that sort of thing (and have downloaded mods that enable them to) it would render the game somewhat less challenging.

However, I am sure that there will be at least one rebalancing pass on the parts before the game reaches Release.

[Kurld]

That's a good point, softweir. I suppose if you make the distances smaller, you do have to limit performance somehow to keep things interesting.

[rosenkranz]

one might also consider mass density. Earth is only about as dense as iron (thus the general assumption that it has a primarilly iron core. Kerbin on the other hand, to have the same gravity as earth but be a 1/10th the size would have to have a ginormace mass density.

It's not really a stretch to think that density issue might carry over into components built from available materials. Does that make any sense?

[-Velocity-]

one might also consider mass density. Earth is only about as dense as iron (thus the general assumption that it has a primarilly iron core. Kerbin on the other hand, to have the same gravity as earth but be a 1/10th the size would have to have a ginormace mass density.

It's not really a stretch to think that density issue might carry over into components built from available materials. Does that make any sense?

No, not that I've seen. What I've seen, by looking at mass and volume of fuel tanks, suggests that the density of KSP rocket components are supposed to be similar to real life, actually. Rocket fuel in KSP is the same density as rocket fuel IRL.

There is an alternate, more sensical interpretation to the purported "high density" of KSP solar system bodies. The more sensical interpretation is that the gravitational constant is higher in the "kerbal universe". Keep in mind that the planets are on rails, thus we cannot apply a known force to a body and see how much it accelerates- so the only way that we "know" the mass of objects is through the gravitational force they exert. We also cannot launch a really huge rocket and measure the gravitational acceleration of some small object towards this huge rocket in space. So we are only guessing the masses of planets via their gravity, using the assumption that the gravitational constant is the same as our universe.

The problem is that assuming the gravitational constant is the same leads to the conclusion that Kerbals build their rockets out of extremely light materials that are not representative of what their planets are made of. This is not true to real life; our rockets are not 1/20 the average density of Earth, they are more like maybe 1/3.

So in the absence of any real ability to test the masses of the planets outside their gravitational forces, the more sensical explanation is that the gravitational constant in the "Kerbal universe" is higher than in our universe, and that the materials the Kerbals build their rockets out of are, in fact, representative of the materials their planet is made out of. After all, the density of fuel is what it should be, why should metals be any different?

[RawChicken]

Maybe someone somewhere can edit all game data and make a "Real World simulator", but since then, KSP is a game and it should not be compared to real life. There is too much "magic" occurring in KSP to think of it as a real life simulator.

[NovaSilisko]

The more sensical interpretation is that the gravitational constant is higher in the "kerbal universe".

Yes! That's what I've been saying forever! That's a keystone of my semi-official canon

I kinda want to make a mod to experiment, though - realistic gravity values for all planets based on their size, and real-world density. By that logic, kerbin would have about 0.02g~ at the surface. Who needs rockets, just flap your arms and hit escape velocity.

[Tygroux]

We have 3 variables to consider.

Mass, Thrust, and Fuel Efficiency.

We know that the distance are 1/10th of real life, but the gravity is still the same.

I guess that means that

Thrust should be the same as RL (or else we're gonna need bigger engines to take off than in RL).

Mass shoud le the same as RL (or else we're gonna have inertia skewed up, and landing will be more difficult than RL)

(Note than the two comes together. The Thrust/Weight/Gravity/Physics constraints ratios should stay realists, or at list immersives.)

Now, the parts i'm not sure of:

Since we have less distance to travel, we need less fuel, so lower ISP than RL.

I'm not sure of it, since staying stable at the same altitude is taking the same amount of energy(and fuel) RL and on kebin.

And accelerationg 100tons by 2000m/s is taking the same amount of fuel whatever the G constant.

But since distance are smaller, going far enough so the gravity became negligible is far easier.

So... I guess the game have the chose to be realist in low orbit, or interplanetary travel, but cannot do both.

Also that would explain why my rocket VTOL sucks fuel so fast... They are calibrated for 1/10th the gravity.

[Temstar]

The more sensical interpretation is that the gravitational constant is higher in the "kerbal universe".

But then the large structures of the universe that is dependant on gravity will be radially different in the kerbal universe. Galaxies won't form the way they do as fusion in stars will work differently. If the gravitational constant is higher than fusion could be ignited with much less hydrogen and the universe will be filled with tiny dwarf stars. The larger stars will be super compressed from the higher gravity as they start to form and either be blown apart by runaway fusion reaction or collapse directly into (very small by our standards) black holes.

[thereaverofdarkness]

I like to think that Kerbal rocket parts are designed very poorly in comparison to Human rocket parts, and out of materials that are heavier and weaker. After all, since it is easier for Kerbals to get into space, might they become satisfied more quickly with their rocket part developments? I imagine they use much more iron and much less titanium in construction, which would explain why Kerbal rockets smaller than a Saturn V will collapse under their own weight.

But then the large structures of the universe that is dependant on gravity will be radially different in the kerbal universe. Galaxies won't form the way they do as fusion in stars will work differently. If the gravitational constant is higher than fusion could be ignited with much less hydrogen and the universe will be filled with tiny dwarf stars. The larger stars will be super compressed from the higher gravity as they start to form and either be blown apart by runaway fusion reaction or collapse directly into (very small by our standards) black holes.

That fits perfectly. Stars are smaller and the amount of mass needed to achieve singularity is less. There is no upper limit to the mass of a Quasar, but the only thing different in KSP is the size of the stars. A universe like that might be prone to developing neutron stars and black holes much more rapidly than ours, but there will still be peaceful galaxies filled with main sequence stars. Basically the Kerbals could say the same about the theoretical possibility of a universe like ours, that planets would have to be much bigger to generate substantial gravity, that stars would have to be much bigger to fuse hydrogen, and that black holes would not form nearly as easily. It's all just a relative difference and in no way makes either universe unfeasible.

Edited September 17, 2013 by thereaverofdarkness

[TheDarkStar]

We have 3 variables to consider.

Mass, Thrust, and Fuel Efficiency.

We know that the distance are 1/10th of real life, but the gravity is still the same.

I guess that means that

Thrust should be the same as RL (or else we're gonna need bigger engines to take off than in RL).

Mass shoud le the same as RL (or else we're gonna have inertia skewed up, and landing will be more difficult than RL)

(Note than the two comes together. The Thrust/Weight/Gravity/Physics constraints ratios should stay realists, or at list immersives.)

Now, the parts i'm not sure of:

Since we have less distance to travel, we need less fuel, so lower ISP than RL.

I'm not sure of it, since staying stable at the same altitude is taking the same amount of energy(and fuel) RL and on kebin.

And accelerationg 100tons by 2000m/s is taking the same amount of fuel whatever the G constant.

But since distance are smaller, going far enough so the gravity became negligible is far easier.

So... I guess the game have the chose to be realist in low orbit, or interplanetary travel, but cannot do both.

Also that would explain why my rocket VTOL sucks fuel so fast... They are calibrated for 1/10th the gravity.

The devs lowered the planet sizes because otherwise just going to orbit would take about 11000 m/s and 15 minutes (even with the same gravity). Jool is actually about earth-sized. I_SPs are also slightly lower than real life (at least for the LV-N and the ion engine).

[-Velocity-]

But then the large structures of the universe that is dependant on gravity will be radially different in the kerbal universe. Galaxies won't form the way they do as fusion in stars will work differently. If the gravitational constant is higher than fusion could be ignited with much less hydrogen and the universe will be filled with tiny dwarf stars. The larger stars will be super compressed from the higher gravity as they start to form and either be blown apart by runaway fusion reaction or collapse directly into (very small by our standards) black holes.

Well, there's a limit to how far we should take this. Trying to actually model the evolution of the Kerbal universe just goes WAY too far. And if KSP planets are really as dense as they are, it ALREADY implies that the KSP universe does not follow our laws of physics! So no matter what, the KSP universe has to follow different laws of physics than ours. We need to recognize this fact and stop giving bogus, made up, phony estimates for planetary density when there is no real way to directly test the mass of planetary bodies. That we don't know the mass and we don't know the gravitational constant implies we don't know ANYTHING regarding the density of planetary bodies. Hell, you could even say the mass of planetary bodies is almost infinite, since no matter how many rockets you crash into them, their orbits won't change one iota.

In the end, the only thing we DO know the densities of are rockets. We can just extrapolate from real life rocket densities what the density of Kerbin, and thus, the other planets, is likely to be, and it is not these super-high values that the KSP wiki bogusly claims. It's simply the approach that makes the most sense.

Edited September 18, 2013 by |Velocity|

[Respawn]

The kerbal universe has the same gravitational constant as our universe, i'm pretty sure..

I've been using it to plan my orbits and intercepts, and the answers i get is exactly right (Depending on how many decimal places i use.)

i.e: if you want an orbit with a specific period and want to know what altitude you need.

cuberoot(("orbital period in sec"², times gravitational constant, times inertial mass of the planet) divided by (4pi²))

you get your desired semi-major axis. simply subtract planets radii and you have your orbital altitude for circular orbit.

And this holds true for all planets and moons as far as i've tested.

If you redefine G you would also need to redefine mass and distance to end up coming out with the same numbers.

If G is 10 times higher the inertal mass would be 10 times higher so either the mass number would have to be 1/100'th or 1m would have to be redefined cuberoot(1/100)

and if distances is redefined kN (thrusts) would have to be redefined, and probably alot of other things i can't come up with atm.

Redefining G has a lot of consequences if you still want your standard real world math formulas to apply.

So instead i believe they just said hm.. lets make it smaller and just say it's more dense.

[The Error]

I'll state it all in layman's terms.

Because Kerbin is so incredibly dense (It has far more gravity than it should), everything that's built out of stuff on Kerbin (rocket parts) is also Made of Heavyum. Thus, it's like building your rocket out of granite, but that's all the Kerbs have. More boosters will fix it.

[Garek]

cuberoot(("orbital period in sec"², times gravitational constant, times inertial mass of the planet) divided by (4pi²))

you get your desired semi-major axis. simply subtract planets radii and you have your orbital altitude for circular orbit.

And this holds true for all planets and moons as far as i've tested.

But as far as I know, we get the inertial mass of the planet only by deriving it from the gravitational constant and the planets gravity, so if we were to assume a different gravitational constant, we just get a different inertial mass and your formula still works.

[Tygroux]

The devs lowered the planet sizes because otherwise just going to orbit would take about 11000 m/s and 15 minutes (even with the same gravity). Jool is actually about earth-sized. I_SPs are also slightly lower than real life (at least for the LV-N and the ion engine).

I don't mean to be aggressive, but i don't see how it's relevant to my post, you are the 21313th person to say it, and everybody knows that.

Useless post is useless.