|Kerbin as seen from orbit.|
|Planet of Kerbol|
|Semi-major axis||13 599 840 256 m [Note 1]|
|Apoapsis||13 599 840 256 m [Note 1]|
|Periapsis||13 599 840 256 m [Note 1]|
|Orbital inclination||0 °|
|Argument of periapsis||0 °|
|Longitude of the ascending node||0 °|
|Mean anomaly||3.14 rad (at 0s UT)|
|Sidereal orbital period||9 203 545 s|
|106 d 12 h 32 m 24.6 s|
|Synodic orbital period||Not defined|
|Orbital Velocity||9284.5 m/s|
|Equatorial radius||600 000 m|
|Surface area||4.5238934×1012 m2|
|Standard gravitational parameter||3.5316000×1012 m3/s2|
|Density||58 484.791 kg/m3|
|Surface gravity||9.81 m/s2 (1 g)|
|Escape velocity||3 431.03 m/s|
|Sidereal rotation period||21 600.000 s|
|6 h 0 m 0 s|
|Solar day||21 650.813 s|
|6 h 0 m 50.8 s|
|Sidereal rotational velocity||174.53 m/s|
|Synchronous orbit||2 868.75 km|
|Sphere of influence||84 159 286 m[Note 1]|
|Atmosphere present||✓ Yes|
|Atmospheric Pressure||101.325 kPa|
|Scale height||5000 m|
|Atmospheric height||69 077.553 m|
|Temperaturemin||-40.19 °C 232.96 K|
|Temperaturemax||20 °C 293.15 K|
|Oxygen present||✓ Yes|
Kerbin is the home planet of the Kerbals, the location of the Space Center, and the main focus of Kerbal Space Program. It is also the Earth analog for the game and has two moons named Mun and Minmus.
Kerbin is the third planet in orbit around the star Kerbol. It is the third largest celestial body that orbits Kerbol, following Jool and Eve. Jool's moon Tylo has the same radius of Kerbin, though it may be classified as larger, as the highest point on Tylo is about 5 km higher than the highest point on Kerbin. However, Tylo has only 80% of Kerbin's mass.
Reaching a stable orbit around Kerbin is one of the first milestones a player might achieve in the game. Doing so with a fuel-optimal ascent requires a delta-v of ≈4500 m/s, (or about 3500 if one is using Ferram Aerospace Research mod) and is the second highest value after Eve. Many interplanetary missions expend over half of their delta-V in reaching Kerbin orbit. The energy required to escape a body from a given altitude is always exactly twice the kinetic energy of a circular orbit around the body at that height, leading one observer to remark:
|“|| If you can get your ship into orbit, you're halfway to anywhere.
— Robert Heinlein, quoted on page 194 of A Step Farther Out by Jerry Pournelle
|“|| A unique world, Kerbin has flat plains, soaring mountains and wide, blue oceans. Home to the Kerbals, it has just the right conditions to support a vast, seemingly undepletable population of the eager green creatures.
Reaching a stable orbit around Kerbin is one of the first things budding space programs strive for. It is said that he who can get his ship into orbit is halfway to anywhere.
— Kerbal Astronomical Society
Kerbin has a roughly equal distribution of surface liquid water and solid land, with polar icecaps and scattered deserts. Some of its mountains exceed 6 km in height, with the tallest peak being 6764 m in altitude at the coordinates 46.3° E 61.6° N. The lowest point is almost 1.4 km deep and about 313° south-west of the Kerbal Space Center.
Unlike other bodies in its system, Kerbin has few visible craters because its environment would erode craters from the few meteors that avoid the gravity or surface of its large moon and survive entry. Nevertheless, some geological formations indicate that bodies have violently collided with Kerbin: two planetary features appear to be impact craters that are coincidentally separated by nearly 180 degrees. The least eroded, and therefore presumably youngest, of the two (both are in excess of 100 km diameter) lies along the coastline. The uplift is easily visible as a series of islands, and the feature has a central peak that pokes up through the water (also known as a rebound peak.) The other, and older of the two, is near the prime meridian in the northern hemisphere and is more easily missed, but its uplift rims are visible, and it has a central rebound peak.
Before 0.90 Kerbin was one of the few bodies with multiple biomes, Kerbin was second only to the Mun in number of biomes it has. Following the 0.90 update all celestial bodies have Biomes. Science experiments can be performed at all biomes, though Kerbin's low multipliers result in less impressive results than more distant worlds. Kerbin's biomes show a loose correlation with Earth's biomes and geographic features. Uniquely, Kerbin has eleven special location biomes at KSC, these are comprised of each building, the crawlerway, and KSC itself; these give a jumpstart to gathering Science points in Career mode. Other biomes on Kerbin include grasslands, hillsides, mountains, deserts, the poles, and some others.
Kerbin's atmosphere contains oxygen and extends to roughly 69,078 meters. Its atmosphere exponentially rarefies with altitude with a scale height of 5 km. The atmospheric pressure on Kerbin at an altitude expressed in meters, generally is:
The thickness of Kerbin's atmosphere makes it suitable for aerobraking and using parachutes to save fuel during reentry and landing. Since version 0.19, harmless supersonic and shock heating/reentry effects have been applied to objects flying above certain velocities. Debris flying in the lower atmosphere disappears once 2 km from an active craft, but above approx. 23 km (where atmospheric pressure is less than 0.01 atm) debris persists. Spent stages may continue in a stable orbit even if they are going through thick atmosphere that would destabilize the orbit of an active craft[outdated].
The following table gives approximation of terminal velocities at different Kerbin altitudes, which are also the velocities at which a ship should travel for a fuel-optimal vertical ascent from Kerbin, given the game's model of atmospheric drag. The optimal velocity after a gravity turn has been started is less than the corresponding value in the table.
Terminal Velocity Table
|Altitude (m)||Velocity (m/s)|
A synchronous orbit is achieved with a semi-major axis of 3 468.75 km. Kerbisynchronous Equatorial Orbit (KEO) has a circularly uniform altitude of 2 868.75 km and a speed of 1 009.02 m/s. From a 70 km low equatorial orbit, the periapsis maneuver requires 676.5 m/s and the apoapsis maneuver requires 434.9 m/s. A syncronous Tundra orbit with eccentricity of 0.2864 and inclination of 63 degrees is achieved at 3799.7/1937.7 km. Inclination correlates with eccentricity: higher inclined orbits need to be more eccentric, while equatorial orbit may be circular, essentially KEO.
A semi-synchronous orbit with an orbital period of ½ of Kerbin's rotation period (2 h 59 m 34.7 s or 10774.7 seconds) is achieved at an altitude of 1 585.18 km with an orbital velocity of 1 271.28 m/s. A semi-syncronous Molniya orbit with eccentricity of 0.742 and inclination of 63 degrees can not be achieved, because the periapsis would be 36 km below the ground. The highest eccentricity of a semi-synchronous orbit with a periapsis of 70 km is 0.693 with an apoapsis of 3100.36 km.
The Hill sphere (the radius around the planet at which moons are gravitationally stable) of Kerbin is 136 185 km, or roughly 227 Kerbin radii.
From the lowest stable orbit around Kerbin (70 km), the amount of delta-V needed to reach the orbits of other celestials is:
|Kerbol escape||~2740 m/s|
|Paid (0.19.1)||Demo (0.18.3)|
|Rotational/Inertial transition||100 000 m||100 000 m|
|5×||69 078 m (above the atmosphere)|
|10×||69 078 m (above the atmosphere)|
|50×||69 078 m (above the atmosphere)|
|100×||120 000 m|
|1 000×||240 000 m|
|10 000×||480 000 m|
|100 000×||600 000 m|
Topographical map of Kerbin as of version 0.21
A projection map of Kerbin, as of 0.14.1 and before (including the old demo).
Topographical image of Kerbin from 0.17.1. The terrain is slightly different in the latest version.
- Rotational speed changed so solar day is now 6 hours (previously sidereal day was 6 hours). (Rotation speed not actually changed)
- Biomes added.
- Terrain revised to produce more detailed and interesting landforms.
- Fixed ladders on the fuel tanks near the launchpad.
- New mesh for the launchpad and area (no launchtower anymore).
- New mesh for the runway, with lights and sloping edges for rovers.
- Terrain overhaul: Entire planet redo. Deserts, darker and greener grass, islands, darker ocean/water, snow capped mountains. Looks more realistic.
- Several Easter Eggs added.
- Airport added to island off of KSC coastline. (Not a launching point)
- Improved atmosphere visuals.
- Minmus added.
- Much more varied and taller terrain added. Prior to this, some mountain ranges exceeded 600 m in height, but the tallest point was at an altitude of approximately 900 m.
- Mün added.
- Terrain overhaul, oceans became wet.
- Atmosphere extended from ~34,500 m to ~69,000 m.
- Initial Release
Kerbin's continents are derived from libnoise, a coherent noise generating library, though they have been increasingly modified with time.
- A fuel-optimal ascent is one which (a) minimizes velocity losses to gravity and atmospheric drag and (b) launches eastward (toward the 90 degree heading) to gain 174.5 m/s of orbital velocity for free, thanks to Kerbin's rotation.
- See this challenge on the forum and a popular Kerbin delta-V chart
- Forum thread 16000, "[KGSS] Examining Kerbin's atmosphere"
- “Some Major Orbit Types” uses that, the Wikipedia article mentions 0.74105, and “Orbital Parameters of a Molniya Orbit” uses 0.72.