Kerbin is the third planet in orbit around the star Kerbol. It is the third largest planet (after Jool and Eve) and the fourth largest celestial object around Kerbol (with Tylo, a moon of Jool, being slightly larger).
Reaching a stable orbit around Kerbin is one of the first milestones a player might achieve in the game. Achieving such an orbit with a fuel-optimal ascent requires a delta-V of ≈4500 m/s, the second largest of all celestial bodies with a solid surface after Eve. For many interplanetary missions, this represents over half of the flight's total delta-V requirement. This is also true of Earth-based interplanetary spaceflights, leading one observer to remark that:
|“|| 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
Kerbin has a roughly equal distribution of surface liquid water and solid land, with polar icecaps and scattered deserts. There are mountains exceeding 4 km in height, with the tallest peak being just under 4044 m in altitude.
Unlike other bodies in its system, Kerbin has few visible craters. This could be attributed to many causes. The environment would cause erosion of many geological features. Also due to its atmosphere, and large moon, fewer meteorites would make it to its surface. However, some geological formations would lead one to believe Kerbin has been subjected to violent collisions in the past. It has two features that appear to be impact craters, separated coincidentally by nearly 180 degrees. The least eroded, and presumably youngest, of the two (both are in excess of 100 km diameter) is located along the coastline. The uplift is easily visible as a series of islands and it has a central peak poking out of the water. The other, and older of the two, is located near the prime meridian in the northern hemisphere. It is more easily missed, but its uplift rims are visible and it has a central rebound peak.
Kerbin's atmosphere contains oxygen and extends to roughly 69,078 meters. Its atmosphere becomes exponentially less dense as altitude increases (with a scale height of 5 km). In general, the atmospheric pressure on Kerbin, at an altitude expressed in meters, is:
The thickness of Kerbin's atmosphere makes it suitable for aerobraking and using parachutes, useful for saving on fuel when spacecraft return to Kerbin. Note that debris is not affected by air resistance above approximately 10 km, so spent stages may continue in a stable orbit even if they are going through thick atmosphere that would stop an active craft (0.19). Crafts will experience re entry and supersonic air effects as of 0.19. This however will not damage or burn it.
The following table gives approximation of terminal velocities at different Kerbin altitudes. These 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. 
|Altitude (m)||Velocity (m/s)|
Geosynchronous orbit is achieved at an altitude of 0.00 m and a speed of Expression error: Unexpected < operator. 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 semi-synchronous orbit with an orbital period of 1/2 of Kerbin's rotation period (3 hours or 10800 seconds) is achieved at an altitude of 0.00 m with an orbital velocity of Expression error: Unexpected < operator. m/s.
The Hill Sphere (the radius around the planet at which moons are gravitationally stable) of Kerbin is 136 185km, 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 as follows:
|KEO (comparison)||~1120 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.
- 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 , 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"