Why KSP's planets have the same gravity as ours

[gutza1]

As you know, The planets in KSP are ten times as small as real planets, but have the same gravity. For example, Kerbin has the same gravity and mass as Earth. Many people says that the planets have the density of lead, but I have a different theory. My theory is that in the KSP universe, gravity is ten times as strong as in our world. Feel free to discuss my theory's plausibility (Assume that KSP is in a parallel universe.)

[Ravenchant]

Hm. A planet with 1/11 the diameter of another, equally dense planet would have 0.075% of the mass, and 9,1% of its surface gravity. The gravitational constant being 11x larger would make sense.

[Retread]

According to the wiki, Kerbin has a density of 58,484 kg/m³, roughly 5 times the density of lead. Earth's average density (according to wikipedia) is 5.515 g/cm³, or 5,515 kg/m³.

So either Kerbin is super-dense, or it exists in a universe with a completely different gravitational constant from our own, take your pick.

Or it's just a game...

[arq]

They couldn't just make Kerbin a nice round 10m/s^2? I guess it doesn't matter so much when you have the computer to do TWRs for you...

[Coupon]

No, the only reason they made everything smaller is because smaller distances are better in the game. Since they have the same gravity, it's the same anyway.

[bsalis]

So either Kerbin is super-dense, or it exists in a universe with a completely different gravitational constant from our own, take your pick.

I pick a different gravitational constant. There's no reason the game has to have identical physics. The way I have viewed it is that whatever physics you see in the game is what they really are in the game world. So, patched two-body approximation is how gravity actually works, not N-body.

[Epthelyn]

You can be clever and change the laws of physics to suit the Kerbal universe...

...or you can just pretend there's a material making up most of the planets in the system which is denser than anything known the real world.

Your choice

I prefer to think of it as the last one, because I know what the gravitational constant is but not the mass and volume of planets. I have to look up those things, so I might as well just keep G as a constant and vary the others from reality to non-reality.

[obi_juan]

According to the wiki, Kerbin has a density of 58,484 kg/m³, roughly 5 times the density of lead. Earth's average density (according to wikipedia) is 5.515 g/cm³, or 5,515 kg/m³.

So either Kerbin is super-dense, or it exists in a universe with a completely different gravitational constant from our own, take your pick.

No, the gravitational constant will be different if the density of Kerbin were only 5.5 g/m³... to have the same surface gravity the only option is be more dense... and now the question is: How?

For this are several possibilities:

1) The materials that form Kerbin have a higher density... That is not possible, the density of the Ir (Iridium) is 22.5 g/m³ lower than Kerbin density so there are not elements on the periodic table to archive that density

2) There are a singularity in the center of the planet (singularity, I was thinking on a black hole). To find more information about these singularities in a closed space read the books from Gregory Benford "Artifact" and "Cosm". But all the planets of Kerbol solar system have a high density, son in that case all the planets need to have singularities in the center.

3) The other possibility is that the planets have a core of 'degenerate matter' (hypothetical situation when all the electrons share the space with the protons in the nuclei of the elements, like in a neutron star) the lower density for that degenerate matter is 1,000,000,000 kg/m³ so with only a small portion the density of Kerbol system will be explained.

But moving to the reality, is a game... And the size of the planets are made to make a quick and easy game when our ships have in the space 6000m/s delta-V we send them to another planets. In our solar system with less than 11,000m/s we can not leave the earth.

To make a realistic game, but funny to play, you need to change the distances of the solar system, so they change avery thing but with the actual physic that we know the need to change something, the density is the more harmless parameter.

[LaydeeDem]

They are only small for gameplay reasons. When KSP was in its infancy, we didn't have timewarp or a map view. In the proper scale, checking to see if you were in orbit would have been hell. The small planets are vestigial from an older version. Just like how you can still find the pre-PQS terrain in KSP's API, or a ton of other strange, unused classes like asteroid fields and the WarpDrive. (They are all outdated, don't get excited.)

Now that we do have timewarp and map mode, real scale planets are possible and they have been done: http://forum.kerbalspaceprogram.com/threads/55145-0-22-WIP-Alpha-Real-Solar-System-v5-2

[stupid_chris]

According to the knowledge base in the game, the planets are all the mass we would expect them to be in our Universe, so I don't believe the different Universe theory holds tight. My guess is that all the planets are giant Dyson shells.

[Liowen]

A

Or it's just a game...

This is why.

Gave rep for this for answer!

[chaos_forge]

Although the cited in-game masses for the planets don't support this, I like to think that the Kerbol system exists in a different universe with a higher gravitational constant.

[ouion]

probably the planets are the same size as in real life,but scale down so the computer can handled it.

[Retread]

No, the gravitational constant will be different if the density of Kerbin were only 5.5 g/m³... to have the same surface gravity the only option is be more dense... and now the question is: How?

I think you're mixing up the gravitational constant (big G, 6.67384 × 10-11 m³/kg.s²) with the acceleration due to gravity at the earth's surface (little g, 9.81 m/s²). G is constant, no matter where in our universe you go (according to Newton, anyway), where g is just a convenient way of expressing the acceleration almost all of us are subjected to every day of our lives.

[Wheffle]

Maybe Kerbal meters and Kerbal grams are different units of measurement than ours, and the Kerbals are all actually giants...

A twist in the plot!

[stargazer1235]

You must look at this question from a game play stance. If you where to scale the size of planets to their gravity then theoretically speaking, Kerbin would have a lower gravity then our Moon and then the Mun would have the gravity of Gilly. The point is that it would be two easy to do things like getting into orbit or landing if the gravity was scaled with the size of a planet.

[Hyratel]

No, the only reason they made everything smaller is because smaller distances are better in the game. Since they have the same gravity, it's the same anyway.

lol no it's not. low Kerbin orbit (130km) is 2200m/s. Earth's low orbit is in the neighborhood of 7300m/s for 200km altitude.

probably the planets are the same size as in real life,but scale down so the computer can handled it.

untrue! in fact, there is an entire mod dedicated to doing this, RealSolarSystem! -> http://forum.kerbalspaceprogram.com/threads/55145

this is what is required to launch 20 tons to 150km equatorial Earth orbit. 9500m/s dV sitting on the pad. (I say Earth because when you use RSS, the differences start to blur)

[Hex6t6]

I'm pretty sure the Gravity constant is the same in the Kerbal Universe as real life. I used the real life Gravity constant (6.67*10^-11) in some equations, and they seemed to work pretty well, so it's more likely that the celestial bodies are indeed just incredibly dense. Of course, there is the good point that it is just a game, but I like that people are coming together to try to explain stuff

[DocMoriarty]

The only reason why the planets are so dense in KSP is that the Kerbals are decendants of potatoes! Yeah!

[Leafbaron]

If Kerbin were to be equally dense to earth but 1/10 its size, like it is, what would the gravitational constant have to be (Big G) in order to produce acceleration of 9.81 m/s/s surface gravity (little g)?

using g_p= G*M/r² to find gravitational accerleration. I got G equaling 7.0775612e^-11Nm²/kg², so really really not that far off from our universes 6.673e^-11Nm²/kg²

r= 600,000m

M= 4.989854443662e²² kg (kerbins volume times the density of earth)

Edited December 2, 2016 by Leafbaron

[katateochi]

or.....the gravitational constant AND the density of Kerbin are the same as on Earth. but....there is also the existence of another hypothetical elementary particle known as the Squaditon which results in higher gravitational forces in the Kerbal universe as the same mass would exert in our universe.  (There is also an inverse Squaditon particle which is believed to only exists in asteroids and acts to completely cancel out all gravitational forces, hence why you can't put anything in orbit around them).

[kerbiloid]

If the gravity constant were the same, but planets were denser, they would be highly overstressed and blow up after the very first drill pierced into its rocky surface.
Or collapsed under their weight.

Also why the oceans and atmospheres have ususal density then?

[monstah]

13 hours ago, Leafbaron said:

If Kerbin were to be equally dense to earth but 1/10 its size, like it is, what would the gravitational constant have to be (Big G) in order to produce acceleration of 9.81 m/s/s surface gravity (little g)?

using g_p= G*M/r² to find gravitational accerleration. I got G equaling 7.0775612e^-11Nm²/kg², so really really not that far off from our universes 6.673e^-11Nm²/kg²

r= 600,000m

M= 4.989854443662e²² kg (kerbins volume times the density of earth)

That's really overthinking, dude. Surface g is linear on both radius and density. Same density, 1/10th radius = 1/10th surface g, given same G. For same surface g, multiply G by 10.

3 minutes ago, kerbiloid said:

If the gravity constant were the same, but planets were denser, they would be highly overstressed and blow up after the very first drill pierced into its rocky surface.
Or collapsed under their weight.

Also why the oceans and atmospheres have ususal density then?

Different fine structure constant, I guess? vOv

[kerbiloid]

3 minutes ago, monstah said:

Different fine structure constant, I guess? vOv

Not so different as they still can into chemistry in usual way.

(Though, maybe that's a reason why KSP engines are so weak and heavy. Chemistry differs a little.

upd.: and fuel is dense. Maybe they need to pour lead powder to make it burn.)

 

Edited December 2, 2016 by kerbiloid

[monstah]

Just now, kerbiloid said:

Not so different as they still can into chemistry in usual way.

They can do chemistry, but that doesn't mean it's the same as ours.