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.
Kerbin shows signs of having been impacted by an asteroid or comet. That is visible in the large crater in the western hemisphere. The crater's central peak is visible from orbit and was caused by the compression followed by the rebound of material in the center of the crater.
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 10000m, 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).
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 ascent from Kerbin, given the game's model of atmospheric drag (0.18.1).
|Altitude (m)||Velocity (m/s)|
Geosynchronous orbit is achieved at an altitude of 0.00 m (1008.9 m/s). From a 70km low equatorial orbit, the periapsis maneuver requires 676.5m/s and the apoapsis maneuver requires 434.9m/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 0.00 m/s.
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|
A projection map of Kerbin, as of 0.14.1 and before (including the demo).
Topographical image of Kerbin from 0.17.1. The terrain is slightly different in the latest version.
- 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
- 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"