|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|
|426 d 0 h 32 m 24.6 s|
|Synodic orbital period||Not defined|
|Orbital velocity||9 285 m/s|
|Equatorial radius||600 000 m|
|Equatorial circumference||3 769 911 m|
|Surface area||4.5238934×1012 m2|
|Standard gravitational parameter||3.5316000×1012 m3/s2|
|Density||58 484.090 kg/m3|
|Surface gravity||9.81 m/s2 (1 g)|
|Escape velocity||3 431.03 m/s|
|Sidereal rotation period||21 549.425 s|
|5 h 59 m 9.4 s|
|Solar day||21 600.000 s|
|5 h 59 m 60 s|
|Sidereal rotational velocity||174.94 m/s|
|Synchronous orbit||2 863.33 km|
|Sphere of influence||84 159 286 m [Note 1]|
|Atmospheric pressure||101.325 kPa|
|Atmospheric height||70 000 m|
|Temperaturemin||-86.20 °C 186.95 K|
|Temperaturemax||15 °C 288.15 K|
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 6767 m in altitude at the coordinates 46°21'32" E 61°35'53" 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 33 location biomes at KSC, these are comprised of each building and their props, the crawlerway, the flag, and KSC itself; these give a jumpstart to gathering Science points in Career mode.
List of biomes
Kerbin has a thick, warm atmosphere with a mass of approximately 4.7×1016 kilograms, a sea level pressure of 101.325 kilopascals (1 atmosphere), and a depth of 70,000 meters. The atmosphere contains oxygen and can support combustion. Kerbin is the only planet or moon with a breathable atmosphere.
The average molecular weight of Kerbin air is 28.9644 g/mol, and its adiabatic index is 1.40. This suggests that Kerbin likely has an earthlike nitrogen-oxygen atmosphere. The air-fuel ratio of jet engines operating in Kerbin's atmosphere suggests that the percentage of oxygen is similar to that of Earth's atmosphere (about 21%).
Like all other atmospheres in the game, Kerbin's atmosphere fades exponentially as altitude increases. The scale height varies with altitude, which is a change from pre-1.0 versions of the game. The pressure-altitude profile is globally constant and independent of temperature. The following table gives the atmospheric pressure at various altitudes above sea level.
|Altitude (m)||Pressure (Pa)|
|2 500||69 652|
|5 000||45 675|
|7 500||28 962|
|10 000||17 965|
|15 000||6 715|
|20 000||2 526|
Kerbin's atmosphere can be divided into three major layers, comparable to Earth's troposphere, stratosphere and mesosphere. In the lower and upper layers, temperature decreases as altitude increases, while the middle layer spans of a region of increasing temperature. The boundary between the lower and middle layers occurs at an altitude of about 16 km at low latitudes, and about 9 km at high latitudes. The boundary between the middle and upper layer occurs at an altitude of about 41 km.
Air temperatures also vary with latitude and time of day. At the equator, sea level temperature varies between a nighttime low of 32 oC and a daytime high of 41 oC. At the poles, the temperature varies between -35 oC and -30 oC. The global mean sea level temperature is approximately 13.5 oC. Since Kerbin has no axial tilt, there are no seasonal temperature variations.
The atmosphere of Kerbin is patterned after Earth's U.S. Standard Atmosphere (USSA), though with the vertical height scale reduced by 20%. Kerbin's "base" temperature and atmospheric pressure can be very closely approximated using the equations of the USSA, where Kerbin's geometric altitude, z, is converted to Earth's geopotential altitude, h, using the following equation:
- h = 7963.75·z / (6371 + 1.25·z)
The base temperature is the temperature less latitudinal and diurnal adjustments; it is roughly equal to the global mean temperature.
The thickness of Kerbin's atmosphere makes it suitable for aerobraking and the use of parachutes to save fuel during reentry and landing. Because of the presence of oxygen, jet engines can operate in Kerbin's atmosphere.
A synchronous orbit is achieved with a semi-major axis of 3 463.33 km. Kerbisynchronous Equatorial Orbit (KEO) has a circularly uniform altitude of 2 863.33 km and a speed of 1 009.81 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 1 581.76 km with an orbital velocity of 1 272.28 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|
|Time warp||Minimum Altitude|
|5×||70 000 m (above the atmosphere)|
|10×||70 000 m (above the atmosphere)|
|50×||70 000 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.
- Added biomes
- 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
- “Some Major Orbit Types” uses that, the Wikipedia article mentions 0.74105, and “Orbital Parameters of a Molniya Orbit” uses 0.72.