A satellite is any object orbiting a celestial body, called its primary. Satellites can be naturally created orbiting bodies (planets, moons, asteroids), or artificial objects (probes, space stations, etc.).
Any celestial body that orbits a larger body is a natural satellite. Planets are satellites of Kerbol. Moons are satellites of planets. Asteroids may be satellites of either Kerbol or planets, depending on their primaries. It's also possible for asteroids orbiting Kerbol to become captured naturally by a planet, depending on their size and entry angle.
- → Main article: Probe
Artificial satellites can be used for unmanned flights to test rocket designs, or to travel to other planetary bodies to collect scientific data. With the addition of the career mode and science mode, satellites are not available until later in the game due to the lack of command probes. Satellites are great for long distance voyages, especially for inexperienced players because they do not risk the lives of any Kerbals. The major defect of satellites and probes in general is high electricity consumption leading to the end of functionality for the craft's vital systems. In order to counteract this, many satellites are equipped with extra batteries and solar panels to store and generate electricity.