How Satellites Work: Orbital Mechanics, Main Types and Everyday Uses

A satellite stays up by falling. Once a rocket gives it enough sideways speed, Earth's gravity keeps pulling it toward the ground, but the planet's surface curves away at the same rate the satellite falls, so it never actually reaches the surface. NASA's Earth Observatory describes this balance as the basic physics behind every artificial satellite: lower orbits require higher speed to avoid falling back, while higher orbits allow slower speeds.

The physics: altitude, eccentricity, inclination

According to NASA's Science division, three parameters define any satellite's path. Altitude sets the orbital speed and the time needed to complete one loop around Earth. Eccentricity describes whether the path is a circle or a stretched ellipse. Inclination is the tilt of the orbital plane relative to the equator. Together these three numbers determine what portion of Earth a satellite can see and how often it passes overhead.

NASA gives concrete examples: its Aqua satellite, at 705 kilometers altitude, completes one orbit every 99 minutes, while a satellite parked in the geostationary belt at roughly 36,000 kilometers takes nearly 24 hours to go around once, matching Earth's own rotation.

Main orbit families

Space agencies group most satellites into a handful of standard orbit types, each suited to a different mission. The European Space Agency (ESA) and NASA describe the same basic set, with largely matching altitude ranges.

ESA notes that geostationary satellites travel from west to east directly above the equator at about 3 kilometers per second, exactly matching Earth's spin, so they appear to hover over one fixed point on the ground. NASA's catalog adds that GPS-type satellites sit in a 'semi-synchronous' orbit at about 20,200 kilometers, completing two orbits every day, while the Molniya orbit is a highly elongated ellipse (eccentricity 0.722) that spends most of its roughly 12-hour period over high northern latitudes, which is why it has historically served Arctic communications.

Beyond orbits that circle Earth, some spacecraft are placed at Lagrange points — gravitationally balanced locations roughly 1.5 million kilometers from Earth, according to ESA — where deep-space observatories can operate with minimal interference from Earth and the Sun. Others leave Earth orbit entirely for a heliocentric path around the Sun once they reach escape velocity.

What satellites are used for

Orbit choice tracks directly to mission type. The U.S. government's official GPS information site, GPS.gov, describes the Global Positioning System as built on three parts: a constellation of 24 operating satellites that continuously broadcast position and timing signals (the space segment); worldwide tracking and command stations that keep the satellites in their proper orbits and correct their clocks (the control segment); and the receivers that calculate location and time from those signals (the user segment).

• Communications satellites relay television, phone, radio and internet signals, mostly from medium and geostationary orbit.
• Navigation satellites such as GPS, Galileo, GLONASS and BeiDou broadcast precise time and position signals from medium Earth orbit so ground receivers can calculate their own location.
• Earth observation satellites, often in polar or sun-synchronous low orbits, image the surface for weather forecasting, agriculture, mapping and disaster response.
• Scientific satellites study the Sun, cosmic radiation and distant astronomical objects, sometimes from Earth orbit and sometimes from Lagrange points.
• Low Earth orbit broadband constellations, such as the thousands of Starlink satellites tracked by independent catalogs, provide internet access by relaying signals between ground stations and receivers.

Keeping satellites in orbit

Orbits are not maintenance-free. NASA's Earth Observatory notes that low Earth orbit satellites experience atmospheric drag and must periodically boost their altitude: Aqua-class satellites need this as often as every two to three weeks when the Sun is highly active, but only about four times a year when solar activity is low, since solar activity changes the density of the upper atmosphere. Satellites at all altitudes also need occasional corrections for gravitational perturbations and to avoid collisions with debris or other spacecraft.

Tracking the overall population of satellites is an ongoing task for independent observers. Jonathan's Space Report, a long-running tracking project, counted 16,988 active payloads in Earth orbit as of October 12, 2026, of which 11,114 were Starlink satellites; the vast majority of active satellites were classified as being in lower Low Earth Orbit.