A group of satellites working together as a system to provide coverage, such as global internet, navigation, or Earth imaging.
A single satellite can only see part of the Earth at any moment, especially in low orbit. A constellation coordinates many satellites in carefully planned orbits so that, together, they provide continuous or frequent coverage.
Navigation systems such as GPS, Galileo, GLONASS, and BeiDou each use a constellation of satellites in medium Earth orbit so receivers can always see enough of them to calculate position. More recently, companies have launched large low Earth orbit constellations, numbering in the thousands of satellites, to deliver broadband internet to remote areas, ships, and aircraft. Earth observation constellations photograph the planet frequently for agriculture, disaster response, and climate monitoring. Concerns include space debris, collision avoidance, and the brightness of satellites disrupting astronomy.
Gathering information about the Earth's surface, oceans, and atmosphere using satellites, aircraft, and drones, often as imagery and sensor data.
Geostationary OrbitA circular orbit about 35,786 km above the equator where a satellite circles at the same rate Earth rotates, so it appears fixed in the sky.
LatencyThe time delay between a request being sent and a response beginning to arrive, usually measured in milliseconds.
Low Earth OrbitThe region of space roughly 160 to 2,000 km above Earth, home to the International Space Station and many communication satellites.
How rocket boosters land themselves, what happens between flights, how the Space Shuttle differs from Falcon 9 and why reuse changed the economics of getting to orbit.