Natural vs Artificial Satellites
The Moon is Earth's natural satellite. Since Sputnik 1 in 1957, humans have launched thousands of artificial satellites for communications, navigation, Earth observation, weather forecasting, scientific research, and military purposes. As of early 2026, 18,000+ operational satellites orbit Earth.
How Do They Stay in Orbit?
A satellite stays in orbit by moving fast enough that its forward momentum balances the gravitational pull of Earth. In low Earth orbit (~400 km), this requires a speed of approximately 7.7 km/s (27,700 km/h). The higher the orbit, the slower the required velocity and the longer each orbit takes.
Types by Purpose
Communications: Relay voice, data, and video. Includes geostationary TV/internet sats and LEO broadband constellations like Starlink.
Navigation: GPS, Galileo, GLONASS, BeiDou — providing position, timing and navigation services.
Earth Observation: Monitor weather, climate, land use, agriculture, natural disasters. Includes Landsat, Sentinel, and commercial imaging fleets like Planet Labs.
Scientific: Space telescopes (Hubble, JWST), particle physics, heliophysics, and astronomy missions.
Military: Reconnaissance, signals intelligence, missile early warning, and secure communications.
Satellite Anatomy
Most satellites share common subsystems: a bus (structural frame), power system (solar panels + batteries), attitude control (reaction wheels, thrusters), communications (antennas, transponders), and a payload (the mission-specific instrument or sensor). Modern LEO satellites like Starlink weigh 260–800 kg; large geostationary platforms can exceed 6,000 kg.