Earth

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* System

**Earth** is the third planet from the Sun, the largest of the inner planets of the solar system and the location of the Space Center, where rockets are built and launched in.

It is one of five celestial bodies that has an atmosphere. The other celestial bodies that has an atmosphere are the Sun, Mars, Venus, Europa and Jupiter.

Earth has one natural satellite, the Moon. This makes Earth one of the three celestial bodies with natural satellites. The other 2 celestial bodies that have natural satellites are Mars and Jupiter, with Mars having 2 and Jupiter having four. It is the starting point for rockets that go to space.

Earth has an atmosphere that is thick enough for rockets to slow down when deploying a parachute without any destruction, and thin enough to not cause any problems while launching from it.

After building a rocket in the Vehicle Assembly Building, the rocket is rolled out from the VAB and transferred to the launch pad. This is where it will start its mission. Most rockets are launched from Earth.

## Earth's natural satellite

The **moon** is Earth's only natural satellite. It is roughly 4 times smaller than Earth, and it has a low gravity — it is around 1/6 of Earth's gravity. It has no atmosphere and has a rocky surface. Many players land a lander or a rover on the moon before heading to Mars. Several activities can be done on the moon (e.g. a flyby mission or building a colony in orbit (a space station) or on the surface).

## Atmosphere

 File:Atmoearth.png
Earth's atmosphere is thick. It has a blue hue and the atmospheric density on Earth is 0.005 in SFS value. Earth's atmosphere can be used for aerobraking and aerocapture. Earth's atmosphere extends up to 30 kilometers above ground level. When zooming out from Earth, there will be a small blue blurring effect because of the atmosphere.

Earth's atmospheric curve is 10, which is a moderate value for typical atmospheres. See Planet Editor Tutorial for more details on planetary atmospheres in the game.

Earth's atmosphere decreases in density quickly by altitude in the first 1000 meters, then it starts to fade moderately, fading slower by altitude (as seen by the graph below) until it becomes very thin, and then fades very slowly until reaching the Karman line, where it becomes non-existent. Beyond that point, there is no atmospheric drag that is making the rocket slow down. At 2,000 meters, Earth's atmosphere is half as dense as the atmosphere found at sea level, and at about 4,900 meters, Earth's atmosphere is one-fifth as dense than found at sea level. Earth's atmosphere fades the fastest at around 3,100 meters. The Earth's atmosphere density decreases to 0.0001 at around 13 kilometers. Above that point the atmosphere can be used with aerobraking.

 File:Earth Atmo Graph.png

### Atmospheric flight

Earth's atmosphere is not enough to cause significant problems such as slowing down of rockets due to atmospheric friction when going up into the atmosphere because of its moderate *curve* value and its moderate atmospheric pressure.

Earth's atmosphere can sufficiently slow down a rocket descending with a parachute or two, but in some cases, it's not being slowed down enough, causing minor damage to the rocket.

When flying a plane in Earth's atmosphere, make sure it has some aerodynamic parts to avoid spinning.

Setting a trajectory below 8 kilometers during a return mission can cause problems on descent, such as an unwanted rotations during reentry, and even burning up into the atmosphere during reentry.

When traveling fast into Earth's atmosphere, the rocket will most likely burn up, unless it has many heat shields.

## Terrain

The terrain on earth is covered in rolling hills, like Mars, but they are low in height and a little spread apart, and unlike Venus and/or Io, which have tall mountains/volcanoes that makes a hazard who lands on the edge or slopes of those structures. Landing on rough surfaces such as a steep hill would cause the rocket to tip over, and fall to the ground. Try to land on a surface that has a relatively flat surface.

The height of the hills are around 35 meters at their highest. There are smaller hills that are 5 meters and one meter high.

### Flat zones

Earth has one flat zone in its terrain. It is the only planet that has a flat zone in the game. The flat zone is located at the Space Center. Some SFS players use this flat zone as a Runway for airplanes.

## Landmarks

Earth has no landmarks. But there is one facility on Earth where rockets are launched. It's called the *Space Center*.

 File:Space Center.png

### Space Center

The **Space Center** is a place on Earth where rockets are launched. It has four buildings. They are the Mission Center, the Research and Development, the Vehicle Assembly Building and the launch pad.

The launch pad is the place where rockets lift off and start their mission. The VAB is where rockets are built.

## Information

* Geostationary orbit: 550 kilometers above the surface
* Earth is the planet where rockets can be launched from.
* It has a green hue, unlike the blue color we see in space in real life.
* Its natural satellite, Mgrunde, is orbiting around the same altitude as if a rocket is orbiting around 1/3 the geostationary orbit in real life.
* Earth is undersized by 3.5 kilometers when comparing to the real 1:20 scale. The real 1:20 scale Earth has a radius of 318550 meters, about 1% larger than the in-game radius.

## What to do

Earth is the home planet and the celestial body from where you start. There are several activities to do on Earth without leaving the ground and reaching space:

* Building earth rovers
* Testing rockets before launch
* Building weather stations
* Do scientific research
* Building launch towers
* Launching satellites into orbit
* Communication satellite
* Sub-orbital flight
* Space stations
* Building aircraft
* Practically anything can be built

Starting small is advised first. You could practice launching a rocket by building a basic rocket and send it into a suborbital flight. The next thing you can do are orbital flights. Then you can go to the moon, then you do complex things such as interplanetary spaceflight, and building space stations!

Earth can be also used for gravity assists. These gravity assists are powerful enough to send a rocket past Mars's orbit, and with the help of Venus gravity assists, the rocket can be sent to Jupiter.

Getting orbit on Earth from other planets is easy. Getting to orbit from the surface is also easy, but it requires high-thrust engines to lift it off from the ground.

## Achievements

There are nine achievements on Earth:

1. Reached 1000 meters altitude
2. Reached 5 kilometers altitude
3. Reached 10 kilometers altitude
4. Reached 15 kilometers altitude
5. Passed the Karman Line, leaving the atmosphere and reaching space
6. Reached low Earth orbit
7. Reached high Earth orbit
8. Performed a space walk in low Earth orbit
9. Reentered Earth’s atmosphere, max temperature [temperature]

## Gallery

Earthsurface.pngA section of Earth's surfaceEarth–Moon system.pngThe Earth and Moon in physics viewRocket launch 2.pngA rocket launchReentry.pngA capsule re-entering Earth's atmosphereParachute landing.pngA capsule landing on Earth from orbit

## Trivia

* The Karman Line is technically the Von Kármán Line, but is not referred to as this in game.
* In the real life the Kármán line measures 100 kilometers but in the game the Kármán line measures 30 kilometers.
* There are 5 types of orbits on Earth:
	+ Low Earth orbit
	+ Medium Earth orbit
	+ Geostationary orbit
	+ Geostationary transfer orbit
	+ High Earth orbit.
* Earth is the only planet to have a man-made structure and the rocky only planet that has no landmarks in-game.
* It is the only planet in the Solar System that is not named after a Roman or Greek god or goddess.
* Earth is one of the celestial bodies in the solar system that have a body of liquid on its surface, i.e. water. The other celestial body that inherits that trait is Titan, a moon of Saturn, which has lakes and seas of liquid methane, ethane and propane.
* Earth is one of the rarest planets in the universe to have complex life such as humans.

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