# Difference between revisions of "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 also the Earth analog for the game and 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. Doing so 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. Many interplanetary missions expend over half of their delta-V in reaching Kerbin orbit. Many Earth-based interplanetary spaceflights also do so, 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 ”

## Topography

Topographical representation of Kerbin's surface as of .18.2. Click for high resolution. by Zeroignite

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 6761 m in altitude.

#### Craters

Terrain model centered on one of Kerbin's most pronounced craters

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 reentry. 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. 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.

## Atmosphere

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).[3] The atmospheric pressure on Kerbin at an altitude expressed in meters, generally is:

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

The thickness of Kerbin's atmosphere makes it suitable for aerobraking and using parachutes to save fuel during reentry. Debris is not affected by air resistance above approximately 10 km: 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 harmless re entry and supersonic air effects as of 0.19.

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.[4] The optimal velocity after a gravity turn has been started is less than the corresponding value in the table. [5]

Altitude (m) Velocity (m/s)
75 107
1000 114
2000 124
3000 136
4000 152
5000 169
6000 188
7000 209
8000 232
9000 256
10000 281
12500 348
15000 419
20000 566
32000 2250

## Orbits

File:Screenshot39.png
A Stayputnik Orbiter

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.

## 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:

Body Delta-V
Mun ~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
KEO (comparison) ~1120 m/s

## Reference Frames

Time warp Minimum Altitude
Any
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

## Gallery

Spoiler: Spoiler images

## Changes

0.21
• Terrain revised to produce more detailed and interesting landforms.
0.19.1
0.19
• New mesh for the launchpad and area (no launchtower anymore).
• New mesh for the runway, with lights and sloping edges for rovers.
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.
0.7.3
• Initial Release

## Trivia

Kerbin's continents are derived from libnoise [7], though they have been increasingly modified with time.

## 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. Forum thread 16000, "[KGSS] Examining Kerbin's atmosphere"