Orbiters

An orbiter is a spacecraft or natural celestial body that travels in an orbital path around another body. In spaceflight, the term is most often applied to artificial satellites designed to observe, study, or relay information while remaining in orbit rather than landing. Natural orbiters include moons, which are held in orbit by the gravity of their primary planet.

Artificial orbiters are launched into orbit around planets, moons, or other bodies to perform scientific experiments, remote sensing, communications relays, or navigation support. They operate in various orbital regimes chosen to optimize coverage, resolution, and mission lifetime. Common Earth-centric orbits include low Earth orbit (LEO, roughly 160 to 2,000 km altitude), medium Earth orbit (MEO, around 2,000 to 35,786 km), and geostationary orbit (GEO, about 35,786 km) where the satellite appears fixed over the equator. Around other planets, orbiters typically occupy parking or highly inclined orbits tailored to their science goals and may undergo multiple orbital phases during a mission.

Orbiters enable a wide range of missions, from astronomical observation and planetary mapping to weather monitoring and communications. Notable examples include Earth-observing and space-telescope satellites in LEO, Mars Reconnaissance Orbiter, Lunar Reconnaissance Orbiter, and Venus Express. The operation of an orbiter requires propulsion for orbit maintenance, power generation, thermal control, and onboard instrumentation. At end of mission, planners may decommission the craft by moving it to a disposal orbit, performing a controlled reentry, or allowing natural orbital decay, depending on location and risk.