Question about planet Kerbal

[FalloutBoy]

Hi,

Is Kerbal meant to be Earthlike and have similar conditions to Earth such as the level of gravity?

I am asking as I built a simple rocket and using Mechjeb told it to limit its acceleration to 4m/s which should be enough to counteract normal Earth gravity ; however it did nothing and only began to climb when I changed acceleration to 10m/s.

Now having one foot in each world I happen to know how to convert metric and imperial measure.

Earth Gravity = -10 fps

There a 3'4" to 1 metre so therefore Earth gravity is 10/3'4" = 3m/s.

Yet on Kerbal my craft needs 10m/s to overcome gravity at sea level - is my thinking floored or is kerbal a heavy gravity world?

10m/s = 3'4" per metre = 33'4" ( 33 feet four inches ) per second almost 3.4 x the gravity of Earth.

Would really appreciate if someone could clear this up for me.

[robly18]

Actually, earth's gravity pulls at just under 10 m/s if I remember correctly. Not 10 feet per second.

[Guest]

All this is covered in the wiki: http://wiki.kerbalspaceprogram.com/wiki/Kerbin

But the short answer is that Kerbin's gravity is 9.81 m/s^2, just like Earth.

[Eric S]

Not sure where you got the wrong numbers, but earth's gravity is 9.8 m/s, and Kerbin matches it. OK, google says it's 9.78 m/s so I was off a bit.

EDIT: I'm sorry, were we doing that as a chorus? I thought we were doing it in rounds.

[Panichio]

By the way, I see this mistake a lot, but it's 'Kerbin', not 'Kerbal'. Kerbals are the little green guys.

[Guest]

I'm sorry, were we doing that as a chorus? I thought we were doing it in rounds.

As long as we're all singing off the same sheet of music, it's good!

And "Kerbal", when used as a noun, refers to the inhabitants of Kerbin. "Kerbal" as a verb means the act of reducing an otherwise serviceable spacecraft or aeroplane into a flaming pile of junk, usually in the most ridiculous possible way.

Edited April 29, 2013 by Guest

[Warscribe]

its usually 9.81 m/s² at sea level. 9.78m/s² must be some high ground, Eric.

[ThatBum]

Use the ingame accelerometers, they show the gravity in gees and m/s².

Kerbin seems to be half the size but twice the density of Earth, or thereabouts. The geography is supposed to be like Earth before the supercontinent broke up. Evidenced by Afrikerb, the part of land KSC is on.

[CalculusWarrior]

And "Kerbal", when used as a noun, refers to the inhabitants of Kerbin. "Kerbal" as a verb means the act of reducing an otherwise serviceable spacecraft or aeroplane into a flaming pile of junk, usually in the most ridiculous possible way.

I manage to Kerbal my rockets every day...

[EndlessWaves]

Kerbin seems to be half the size but twice the density of Earth, or thereabouts.

Kerbin is 1/100th the size of earth but ten times the density.

The gravity, by cosmic co-incidence, is exactly the same acceleration on Kerbin's surface as Earth's but because it's much smaller the gravity falls off much faster. In a 250km Kerbin orbit gravity has halved, in the same height earth orbit it's still above 9m/s²

Edited April 29, 2013 by EndlessWaves

[CalculusWarrior]

Have the devs said whether they will eventually scale up the planets sizes or not? I guess it would involve adding a lot more surface to the planets and might not be the best for lag, eh?

[theflyingfish]

Kerbin is about 1/26th the size of Earth, yet it has the same mass, giving it about the same density as lead. The entire Kerbol System is about 1/20th the size of the real system. The devs did this to increase playability before time warp was added, so that orbits were minutes rather than hours long. It stuck around afterwards, because the devs decided that the game was more fun at a scaled down size, rather than at realistic distances. But because all of the planets have the same masses as in real life, maneuvers still require a realistic amount of fuel.

TLDR, Kerbin is supposed to be like Earth, with the same surface gravity and environment but at a much reduced scale.

[Tremzack]

Kerbin is 1/100th the size of earth but ten times the mass.

I heard someone say it was 1/11 scale....URRRG conflicting sources!!!!!

[Spatzimaus]

Kerbin is 1/100th the size of earth but ten times the mass.

Not even close. Kerbin is about 1/1200th the size of Earth (a radius about 10.5 times smaller than Earth's) but has about 1/110th the mass. These ratios give it the exact same surface gravity as Earth, 9.81 m/s^2. (It's not exactly a 1/10 ratio; the Earth's mean radius is 6371km, and Kerbin is 600km. But you can call it that and not be too far off) Unfortunately, this gives it about eleven times the density of Earth, a little over 50 kg/m^3, which is more than twice the density of the densest metals. In other words, it's physically impossible unless the core of the planet is made of degenerate matter from an exploded neutron star or something. Since all of the other bodies in the Kerbin system have similar ratios, it's not possible for this to be true of Kerbin.

And a similar scaling happens with Kerbin's Sun, which is also not physically possible; you can't produce energy through fusion on anything heavier than Iron, and a star of mass less than 0.08 solar masses won't have a high enough central pressure to fuse even hydrogen. Kerbin's Sun has about one-tenth of the minimum mass, making it only ~8 times more massive than Jupiter.

But scientific accuracy wasn't really as important as making a system with manageable distances and shallow gravity wells.

[vencaslac]

the value of 9.81m/s^2 also varies with latitude as earth is not perfectly spherical like kerbin is - i think the proper term is oblate spheroid - as its' rotation makes it bulge at the equator so the farther away from the equator you go the less mass is between you and the earth's center of mass, making gravity slightly weaker

[Spatzimaus]

the value of 9.81m/s^2 also varies with latitude as earth is not perfectly spherical like kerbin is - i think the proper term is oblate spheroid - as its' rotation makes it bulge at the equator so the farther away from the equator you go the less mass is between you and the earth's center of mass, making gravity slightly weaker

No. The whole point of that "bulge" is that it's an equipotential, to where the force felt at each point at sea level is the same regardless of latitude. Yes, there's less mass between you and the center of mass if you move toward the poles, but there's also less distance, so the force is the same. If the forces differed, then all of the world's water would flow "downhill" towards the spot that had higher gravity. So, all points at "sea level" have the same gravitational force, regardles of their actual distance from the center.

The Earth has a lot of smaller variations in gravty as well, with "sea level" varying from that oblate spheroid by up to ~100m depending on where you are on the surface. Look up "World Geodetic Survey '84" for more information on this. The only people who really care about this are the ones who need to fly things at really low altitudes, or who make GPS devices, but it's been well-studied for more than a century.