# Kerbin

Kerbin is the home planet of the Kerbals, the location of the Space Center, and the main focus of Kerbal Space Program. It is the Earth analog for the game. It has two moons, named Mün and Minmus.

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[1] requires a delta-V of ≈4500 m/s,[2] 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."[3])

## Topography

 Topographical image of Kerbin from 0.17.1. The terrain is slightly different in the latest version.[4] 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.

## Atmosphere

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).[5] In general, the atmospheric pressure on Kerbin, at an altitude expressed in meters, is:

${\displaystyle p_{k}=e^{-altitude/5000}}$

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).[6]

Altitude (m) Velocity (m/s)
0 97.3
1000 110
3000 130
5000 160
8000 215
10000 260
15000 425
32000 2250
File:Screenshot39.png
A Stayputnick Orbiter

## Orbits

Geosynchronous orbit is achieved at an altitude of 0.00 m (1008.9 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 0.00 m/s.

## Interplanetary Travel

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:

Body Delta-V
Mün ~860 m/s
Minmus ~930 m/s
Eve ~1033 m/s
Duna ~1060 m/s
Moho ~1676 m/s
Jool ~1915 m/s
Eeloo ~2100 m/s

## Reference Frames

Paid (0.17) Demo (0.13.3)
Rotational/Inertial transition 100,000 m 70,000 m
Warp Minimum Altitude
1x Any
2x n/a 0 m
5x 69,078 m (above the atmosphere)
10x 69,078 m (above the atmosphere)
50x 69,078 m 150,000 m
100x 120,000 m 300,000 m
1,000x 240,000 m 600,000 m
10,000x 480,000 m 1,200,000 m
100,000x 600,000 m n/a

## Changes

0.18
• Terrain overhaul: Entire planet redo. Deserts, darker and greener grass, islands, darker ocean/water, snow capped mountains. Looks more realistic.
• Airport added to island off of KSC coastline. (Not a launching point)
0.17
• Improved atmosphere visuals.
0.15
0.14.2
• 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.
0.12
0.11
• Terrain overhaul, oceans became wet.
0.10.1
• Atmosphere extended from ~34,500 m to ~69,000 m.
?
• Initial Release

## Notes

1. 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.
2. See this challenge on the forum and a popular Kerbin delta-V chart
3. Robert Heinlein, quoted on page 194 of A Step Farther Out by Jerry Pournelle.
4. http://forum.kerbalspaceprogram.com/entry.php/247-A-Brave-New-World
5. Forum thread 16000, "[KGSS] Examining Kerbin's atmosphere"