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, over 14,000 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.