Satellites serve five major purposes: communication, navigation, Earth observation, scientific research, and military surveillance. Every time you check a weather forecast, use a maps app, or stream a TV channel, you’re relying on at least one satellite orbiting somewhere between 300 and 36,000 kilometers above the Earth’s surface. As of 2024, thousands of active satellites circle the planet, and each one falls into one or more of these functional categories.
Communication
The most widespread use of satellites is relaying signals. Phone calls, television broadcasts, internet data, and radio transmissions all bounce through satellites to reach places that ground-based infrastructure can’t easily serve. A satellite TV dish on your roof, for example, points at a single satellite hovering roughly 35,786 km above the equator. At that altitude, the satellite completes one orbit every 24 hours, matching Earth’s rotation so it appears to stay in the same spot in the sky. That’s why the dish never needs to move.
Newer satellite internet constellations like Starlink take a different approach. They fly in low-Earth orbit (between 300 and 2,000 km up), which dramatically cuts the time a signal takes to travel up and back down. Low-orbit internet satellites typically deliver latency of 20 to 40 milliseconds under clear skies, comparable to many home broadband connections. Traditional high-orbit satellite internet averages around 600 milliseconds, with spikes above 1,500 milliseconds during heavy rain. The tradeoff is that low-orbit satellites pass overhead quickly, staying in view of any ground point for only about 10 minutes, so you need hundreds or thousands of them working in coordination to provide uninterrupted service.
Navigation
The GPS system you use to navigate while driving relies on a constellation of satellites in medium-Earth orbit, between 2,000 and 35,000 km up. Satellites at this altitude move slowly enough across the sky to stay visible from a given location for hours, yet they’re positioned to cover every latitude on Earth, including the poles. That combination makes medium-Earth orbit ideal for navigation.
GPS works by having your device receive time-stamped signals from at least four satellites simultaneously, then calculating your position based on the tiny differences in how long each signal took to arrive. The current global average accuracy is within 8 meters horizontally and 13 meters vertically at 95% confidence. Beyond driving directions, GPS technology supports land surveying, tracking tectonic plate movement, resource exploration, and precision agriculture.
Earth Observation and Weather
Satellites in low-Earth orbit carry cameras and sensors that photograph the planet’s surface in visible light, infrared, and other wavelengths. Because they fly relatively close to the ground, their telescopes can capture high-resolution images that would be impossible from higher altitudes. These images feed into an enormous range of applications: tracking deforestation, monitoring crop health, mapping urban growth, assessing wildfire damage, and measuring how glaciers and ice sheets change over time.
Weather satellites are a specialized branch of Earth observation. Some orbit at low altitude, sweeping across different parts of the planet with each pass. Others sit in geostationary orbit above the equator, watching an entire hemisphere continuously. Together, they monitor cloud patterns, storm systems, ocean temperatures, and atmospheric conditions. The five-day weather forecast on your phone exists because of these satellites feeding data into computer models around the clock.
Climate science depends heavily on satellite data as well. Instruments in orbit track key climate indicators including global surface temperature, atmospheric carbon dioxide levels, sea level changes, and the extent of Arctic and Antarctic ice. These measurements, collected consistently over decades, form the backbone of our understanding of how Earth’s climate is shifting.
Scientific Research
Some satellites point their instruments not at Earth but outward into space. The James Webb Space Telescope, launched in 2021, studies every phase of cosmic history: from the first light that appeared after the Big Bang, to the formation of galaxies and stars, to the chemistry of atmospheres on planets orbiting other stars. Its predecessor, the Hubble Space Telescope, has been doing similar work since 1990.
Space-based telescopes have a fundamental advantage over ground-based ones. Earth’s atmosphere blurs and absorbs certain wavelengths of light, especially infrared. A telescope in orbit avoids that interference entirely, producing sharper images and detecting faint signals that would never reach the ground. Other science satellites measure the Sun’s output, map Earth’s gravitational and magnetic fields, detect cosmic rays, and study the behavior of materials in microgravity.
Military and Intelligence
Governments operate satellites for reconnaissance, secure communications, missile launch detection, and battlefield coordination. Military imaging satellites function much like civilian Earth-observation satellites but typically carry more powerful optics and transmit data through encrypted channels. Early warning satellites detect the heat signatures of missile launches within seconds. Secure communication satellites ensure that military commands can be relayed globally without relying on ground networks that could be disrupted.
How Orbit Height Shapes the Mission
The altitude a satellite flies at isn’t arbitrary. It’s chosen to match the mission. Low-Earth orbit (300 to 2,000 km) is best for tasks that need high resolution or fast signal times: Earth imaging, low-latency internet, and crewed space stations. Medium-Earth orbit (2,000 to 35,000 km) suits navigation systems that need to stay visible for hours at a time across all latitudes. Geostationary orbit (35,786 km) is reserved for missions that need a satellite to hover over one fixed spot: television broadcasting, continuous weather monitoring, and certain communications relays.
Satellites in lower orbits are generally smaller, cheaper to build, and shorter-lived. They experience more atmospheric drag, which gradually pulls them back toward Earth, so they need to be replaced more frequently. Higher-orbit satellites cost more to launch but can operate for 15 years or longer. Large low-orbit constellations compensate for individual satellite lifetimes by constantly cycling in replacements, which also builds in resilience. If one satellite fails or gets knocked out, the rest of the constellation picks up the slack.
The First Satellite and What It Proved
The first artificial satellite, Sputnik 1, launched on October 4, 1957. It was a polished metal sphere just 58 centimeters across with no scientific instruments onboard, only four radio antennas broadcasting simple pulses. Even so, scientists extracted useful data from it. The way its orbit gradually decayed revealed the density of the upper atmosphere, and the behavior of its radio signals provided information about the ionosphere, the electrically charged layer of atmosphere that affects radio communication. Sputnik proved that placing an object in stable orbit was possible, and within a few years, satellites were already being built for every purpose they serve today.