An artificial satellite is any human-made object placed into orbit around Earth or another celestial body. The word “satellite” itself simply means any object orbiting a larger one, so the Moon is a natural satellite of Earth, and Earth is technically a satellite of the Sun. What makes a satellite “artificial” is that people built it and launched it into space. Since the first one reached orbit in 1957, thousands have followed, and today they underpin everything from weather forecasts to GPS navigation to the internet connection on a transatlantic flight.
How Artificial Satellites Differ From Natural Ones
Natural satellites are moons and other celestial objects that formed through gravitational processes over billions of years. Artificial satellites are engineered, launched on rockets, and placed into precise orbits to carry out specific jobs. They range from objects smaller than a shoebox (called CubeSats) to structures the size of a school bus. What they share is the same basic physics: they move fast enough that their forward momentum balances Earth’s gravitational pull, keeping them in a continuous free fall around the planet rather than crashing into it or drifting away.
The First Artificial Satellite
On October 4, 1957, the Soviet Union launched Sputnik 1, changing the course of history. It was about the size of a beach ball, 58 centimeters in diameter, and weighed just 83.6 kilograms. Sputnik completed one orbit every 98 minutes on an elliptical path around Earth. It carried no cameras or scientific instruments beyond a radio transmitter, but its steady beeping signal, picked up by amateur radio operators worldwide, proved that a human-made object could survive in orbit. The launch kicked off the Space Age and triggered the space race between the United States and the Soviet Union.
Types of Orbits
Where a satellite orbits determines what it can do. Orbits are grouped into three main zones based on altitude.
Low Earth Orbit (LEO) covers altitudes up to 2,000 kilometers. This is where the International Space Station flies, along with most Earth-observation and imaging satellites. Being closer to the surface means higher-resolution views and lower launch costs, but satellites here move fast, circling the planet roughly every 90 minutes.
Medium Earth Orbit (MEO) spans from 2,000 to about 35,586 kilometers. This zone is best known for navigation satellite networks like GPS, Europe’s Galileo, Russia’s GLONASS, and China’s Beidou. At these altitudes, a satellite’s orbital period is long enough that a relatively small constellation can provide continuous global coverage.
Geostationary Orbit (GEO) sits at roughly 35,786 kilometers above the equator. A satellite here orbits at the same rate Earth rotates, so it appears to hover over one fixed point on the surface. That makes GEO ideal for weather monitoring and communications, because a ground antenna can point at the same spot in the sky permanently without needing to track a moving target.
What’s Inside a Satellite
Despite the huge variety of missions, nearly every satellite shares the same basic architecture: a bus and a payload. The payload is the mission-specific equipment, whether that’s a camera, a radar sensor, a communications relay, or a scientific instrument. The bus is everything else that keeps the payload alive and working.
A typical satellite bus contains six core subsystems. The electrical power subsystem converts sunlight into electricity using solar panels and stores energy in batteries for periods when the satellite passes through Earth’s shadow. The attitude control subsystem keeps the satellite pointed in the right direction, using small spinning wheels or tiny thrusters. The communication subsystem handles sending data to the ground and receiving commands. A command and data handling system acts as the onboard computer, coordinating operations. The propulsion system provides thrust for orbit adjustments and end-of-life maneuvers. And the thermal control subsystem manages temperatures, which can swing from extreme heat in direct sunlight to extreme cold in shadow.
Power in the Vacuum of Space
Solar panels are the dominant power source for satellites. Photovoltaic cells convert sunlight directly into electricity, and they work well for any mission within the inner solar system. The catch is that solar cells produce nothing when the satellite is in Earth’s shadow, a period called eclipse. In low Earth orbit, a satellite can pass through eclipse every 90 minutes, so onboard batteries are essential to bridge those gaps.
Most modern satellites use lithium-ion batteries, the same basic chemistry found in smartphones and electric cars. Older designs relied on nickel-cadmium or nickel-hydrogen cells. Solar panels also degrade over time from radiation exposure and aging, so engineers design power systems with enough margin to keep the satellite running at end-of-life performance, not just beginning-of-life performance. For deep-space missions far from the Sun, where solar panels become impractical, satellites use radioisotope generators that convert heat from decaying nuclear material into electricity.
How Satellites Communicate With Earth
Satellites talk to ground stations using radio waves. A transmitter on the satellite encodes digital data onto a high-frequency electromagnetic wave, amplifies the signal, and sends it through an antenna. On the ground, a receiving antenna collects the signal, amplifies it, and demodulates it back into usable data. The process works in reverse for commands sent up from Earth.
Different missions use different radio frequency bands. Lower frequencies like L-band (1 to 2 GHz) work well for mobile satellite phones and legacy networks like Iridium and Globalstar. Higher frequencies like Ku-band (12 to 18 GHz) and Ka-band (27 to 40 GHz) carry far more data and are the standard for large communications satellites. Ka-band systems on smaller satellites have demonstrated downlink speeds over 100 megabits per second. The tradeoff is that higher frequencies are more susceptible to interference from rain and atmospheric conditions.
How GPS Satellites Pinpoint Your Location
Navigation is one of the most familiar satellite applications, and it relies on a clever use of radio signals and timing. GPS satellites continuously broadcast signals that include two pieces of information: the satellite’s exact position in orbit and the precise time the signal was sent, measured by onboard atomic clocks.
Your GPS receiver picks up these signals and calculates how long each one took to arrive. Since radio waves travel at very close to the speed of light (299,792,458 meters per second), multiplying that travel time by the speed gives the distance between you and the satellite. With distance measurements from at least three satellites, a process called trilateration narrows your position to a single point on Earth’s surface. In practice, receivers use four or more satellites to also correct for timing errors and atmospheric delays that slightly slow the signals.
The Growing Problem of Space Debris
As of recent tracking data, there are roughly 8,900 active satellites in orbit, but they share that space with about 35,800 inactive objects, including dead satellites, spent rocket stages, and fragments from past collisions and explosions. In 1978, NASA scientist Don Kessler predicted that cascading collisions between orbiting objects could produce a chain reaction, generating debris faster than Earth’s atmosphere can drag it down. This scenario, now called the Kessler Syndrome, wouldn’t be a sudden catastrophe. It would unfold over decades, gradually making certain orbital zones so cluttered that operating satellites there becomes dangerously risky.
Some regions of low Earth orbit are already considered unstable in this sense. The current estimated rate of catastrophic collisions between tracked objects is about one every ten years. Each collision produces thousands of new fragments, and even a paint chip traveling at orbital velocity (around 28,000 kilometers per hour) can damage a satellite.
What Happens When a Satellite Dies
International guidelines require that satellites in low Earth orbit be removed within 25 years after their mission ends, either by letting atmospheric drag pull them down to burn up on reentry or by boosting them into a less congested “graveyard” orbit. These rules were established through the Inter-Agency Space Debris Coordination Committee, a body including NASA, the European Space Agency, and Japan’s JAXA, and were endorsed by the United Nations in 2007.
Of the available disposal methods (direct retrieval, atmospheric reentry, and relocation to a storage orbit), atmospheric reentry is considered the most practical for most missions. The satellite fires its thrusters to lower its orbit until air resistance does the rest, and the vast majority of the hardware burns up during descent. For satellites in geostationary orbit, where reentry would require an impractical amount of fuel, operators instead boost them a few hundred kilometers higher into a graveyard orbit, safely above the operational zone.
The 25-year guideline is increasingly seen as too slow. In 2023, the World Economic Forum recommended targeting five years or less for post-mission removal, and new U.S. regulations now require commercial launch operators to dispose of rocket upper stages within 30 days of mission completion through controlled reentry, graveyard orbit placement, or Earth escape trajectory.