What Is a Satellite? Types, Orbits, and How Satellites Work

Every time you check the weather forecast, use GPS to navigate, watch satellite TV, or even look at a photo of a hurricane from space, you are relying on satellites. These remarkable machines orbit Earth by the thousands, quietly enabling modern life in ways most people never think about. This guide explains what satellites are, how they reach orbit, the different types and orbits they use, and why they matter more than ever.

What Exactly Is a Satellite?

In the broadest sense, a satellite is any object that orbits another object in space. By that definition, the Moon is Earth's natural satellite, and Earth itself is a satellite of the Sun. But when most people say "satellite," they mean the human-made machines we have placed into orbit around our planet.

As of 2025, there are more than 10,000 active artificial satellites orbiting Earth. They range in size from tiny CubeSats no bigger than a loaf of bread to school-bus-sized spacecraft weighing several tonnes. These machines perform an astonishing variety of tasks: relaying television signals, providing internet access to remote villages, photographing every corner of the planet, guiding aircraft and ships, monitoring the climate, peering into deep space, and much more.

What keeps a satellite in orbit? The same force that keeps the Moon from flying away: gravity. A satellite is essentially falling toward Earth constantly, but it is moving forward fast enough that the curve of its fall matches the curve of the Earth. The result is a continuous free-fall around the planet, an orbit, that can last for years or even decades without any fuel.

A Brief History of Satellites

The Space Age began on October 4, 1957, when the Soviet Union launched Sputnik 1, the world's first artificial satellite. About the size of a beach ball and weighing just 83 kilograms, Sputnik did little more than transmit a simple radio beep. But that beep changed the world. It proved that human-made objects could reach orbit, and it triggered the space race between the United States and the Soviet Union.

The United States answered with Explorer 1 in January 1958. Unlike Sputnik, Explorer 1 carried scientific instruments and made a major discovery: the Van Allen radiation belts surrounding Earth. This established a pattern that continues today, where satellites serve as platforms for scientific discovery.

The first communications satellite, Telstar 1, launched in 1962 and relayed the first live transatlantic television signal. Suddenly, people on different continents could watch the same event in real time. Within a few years, geostationary communications satellites were providing permanent relay links, transforming global telecommunications.

The GPS constellation began in 1978 when the U.S. military launched the first Navigation System with Timing and Ranging (Navstar) satellite. By the mid-1990s the full constellation was operational, and in 2000 the U.S. government removed selective availability, giving civilians access to the same precision that the military enjoyed. GPS has since become so embedded in daily life that it is difficult to imagine a world without it.

Today, the satellite industry has exploded. More satellites were launched in 2023 alone than in the first 50 years of the Space Age combined, driven largely by mega-constellations like SpaceX's Starlink. Over 80 countries now operate at least one satellite, and the global space economy is valued at over $400 billion annually.

How Satellites Get to Space

Every satellite begins its journey on the ground, mounted inside the nose cone (fairing) of a launch vehicle. Rockets burn propellant to generate enough thrust to overcome Earth's gravity and atmospheric drag, accelerating the satellite to orbital velocity, roughly 7.8 kilometers per second for low Earth orbit.

Once the rocket reaches the target altitude, the satellite is released from a deployer or dispenser. Some missions carry a single large satellite, while rideshare missions pack dozens or even over a hundred small satellites onto a single rocket, dramatically lowering the cost per kilogram to orbit. SpaceX's Falcon 9, for instance, routinely deploys 20 to 60 Starlink satellites per launch.

The cost of reaching orbit has dropped dramatically over the past two decades. In the Space Shuttle era, it cost roughly $54,000 per kilogram to reach low Earth orbit. Today, a Falcon 9 launch brings that figure below $3,000 per kilogram, and SpaceX's Starship aims to push costs below $100 per kilogram. This plummeting launch cost is one of the primary drivers of the satellite boom.

After deployment, most satellites use their own small thrusters to fine-tune their orbit, a process called orbit raising or orbit insertion. Some satellites are placed directly into their operational orbit, while others, particularly those headed for geostationary orbit, must perform a series of engine burns over days or weeks to reach their final position 35,786 kilometers above the equator.

Parts of a Satellite

Despite enormous variation in size and mission, virtually every satellite shares the same basic architecture: a bus and a payload.

The Satellite Bus

The bus is the spacecraft's backbone. It provides all the support systems the payload needs to function:

• Structure: The physical frame that holds everything together and withstands the violent vibrations of launch.
• Power system: Solar panels convert sunlight into electricity, while rechargeable batteries store energy for use when the satellite passes through Earth's shadow (eclipse periods). A typical communications satellite's solar arrays generate 10-20 kilowatts, while a small CubeSat might produce just a few watts.
• Propulsion: Small thrusters (chemical, electric, or cold-gas) allow the satellite to adjust its orbit, maintain its position, and eventually deorbit at end of life. Electric propulsion systems, such as ion thrusters, are increasingly common because they use far less propellant.
• Thermal control: Satellites experience extreme temperature swings, from over 120 degrees Celsius in direct sunlight to minus 150 degrees in shadow. Radiators, heaters, insulation blankets, and heat pipes keep components within safe operating temperatures.
• Attitude control: Reaction wheels, magnetorquers, and star trackers keep the satellite oriented correctly so its antennas point at Earth and its solar panels face the Sun.
• On-board computer: The satellite's brain processes commands from the ground, manages all subsystems, and increasingly runs sophisticated software for autonomous operations.

The Payload

The payload is the mission-specific equipment: a camera for Earth observation, a transponder for communications, a scientific instrument for research, or a navigation signal generator for positioning. Everything else on the satellite exists to support the payload. The payload determines the satellite's purpose and value.

Antennas

Every satellite needs antennas to communicate with ground stations and, in many cases, with end users. These range from small omnidirectional antennas for basic telemetry to large parabolic dishes several meters across for high-throughput data links. Phased-array antennas, which can electronically steer their beams without moving parts, are increasingly used on modern satellites like those in the Starlink constellation.

Satellite Orbits Explained

Where a satellite orbits determines nearly everything about what it can do, how long signals take to reach it, how much of the Earth it can see, and how long it will last. There are several major orbital regimes, each suited to different missions.

Low Earth Orbit (LEO): 160-2,000 km

LEO is the closest orbital zone to Earth and the most crowded. Satellites here complete an orbit in roughly 90 minutes, traveling at about 7.8 km/s. Because they are close, LEO satellites enjoy low signal latency (under 30 milliseconds round-trip) and can capture high-resolution images of Earth's surface. However, each satellite can only see a small area at any given time, so LEO applications that need global coverage, like Starlink internet or the Iridium phone network, require large constellations of hundreds or thousands of satellites.

Notable LEO residents include the International Space Station (about 420 km), the Starlink constellation (~550 km), and Planet Labs' Earth-imaging fleet (~475 km). LEO satellites experience atmospheric drag, which slowly lowers their orbit. Without periodic reboosts, they will eventually re-enter the atmosphere and burn up, which is actually a feature for sustainability since it prevents long-lived debris.

Medium Earth Orbit (MEO): 2,000-35,786 km

MEO is the domain of navigation constellations. The U.S. GPS constellation orbits at about 20,200 km, taking approximately 12 hours to circle the Earth. Europe's Galileo system and China's BeiDou also occupy MEO orbits. At this altitude, each satellite can see a large swath of Earth's surface, so a constellation of 24-30 satellites can provide continuous global coverage. Signal latency is moderate, around 100 milliseconds.

Geostationary Orbit (GEO): 35,786 km

At exactly 35,786 km above the equator, a satellite's orbital period matches Earth's rotation: 24 hours. From the ground, the satellite appears to hang motionless in the sky. This is enormously useful for applications like television broadcasting and weather monitoring, because ground antennas can be permanently pointed at one spot in the sky. A single GEO satellite can see roughly one-third of Earth's surface, so just three satellites can provide near-global coverage (excluding the polar regions).

The trade-off is latency. A signal must travel 35,786 km up and 35,786 km back down, resulting in a minimum round-trip delay of about 240 milliseconds, noticeable in voice calls and problematic for real-time applications. GEO slots above the equator are a limited and valuable resource, managed by the International Telecommunication Union (ITU). Roughly 560 active satellites currently occupy GEO.

Sun-Synchronous Orbit (SSO)

SSO is a special type of LEO orbit (typically 600-800 km) in which the satellite passes over any given point on Earth at the same local solar time on every orbit. This consistent lighting is ideal for Earth observation, because images taken on different days have comparable shadows and illumination, making it easier to detect changes over time. Most optical Earth observation satellites, including those operated by Planet Labs and Maxar Technologies, use SSO.

Highly Elliptical Orbit (HEO)

HEO satellites follow elongated oval orbits, swinging close to Earth at their lowest point (perigee) and far away at their highest (apogee). They spend most of their time near apogee, where they move slowly and can dwell over high-latitude regions that GEO satellites cannot see well. Russia's Molniya orbits, designed for communications coverage of northern latitudes, are a classic example. HEO is also used for certain scientific and early-warning missions.

Communications Satellites

Communications satellites are the workhorses of the commercial space industry, generating the majority of satellite-industry revenue. They relay signals between points on Earth that cannot easily be connected by cables or terrestrial towers.

Television broadcasting remains a major application. GEO satellites operated by companies like SES and Intelsat beam hundreds of channels to small dish antennas on rooftops worldwide. A single satellite can serve millions of viewers simultaneously.

Satellite internet is the fastest-growing segment. SpaceX's Starlink constellation has deployed over 6,000 LEO satellites to deliver broadband with download speeds of 50-200 Mbps and latency of 20-40 milliseconds. OneWeb (now part of Eutelsat) focuses on enterprise and government connectivity, while Amazon's Project Kuiper is preparing to deploy 3,236 satellites. These LEO constellations are transforming connectivity for rural communities, maritime vessels, and aircraft.

Mobile satellite phones like those on the Iridium network provide voice and data coverage anywhere on Earth, including oceans, deserts, and polar regions where no cell tower exists. Iridium's constellation of 66 active satellites in LEO ensures that at least one satellite is always overhead from any point on the planet.

How does satellite communication work? In a typical scenario, a ground station (or user terminal) transmits a signal up to the satellite (the uplink). The satellite's transponder amplifies the signal, shifts it to a different frequency, and retransmits it back to Earth (the downlink), where another ground station or user terminal receives it. Modern high-throughput satellites can handle hundreds of gigabits per second of data, rivaling undersea fiber-optic cables.

Earth Observation Satellites

Earth observation (EO) satellites look down at our planet, collecting imagery and data across the electromagnetic spectrum. The applications are vast and growing.

Optical imaging satellites capture photographs of Earth's surface at resolutions ranging from 30 centimeters (enough to see individual cars) to hundreds of meters (useful for large-scale land-use mapping). Maxar Technologies operates the highest-resolution commercial satellites, while Planet Labs images the entire Earth daily using a fleet of over 200 small satellites, sacrificing resolution for frequency.

Synthetic aperture radar (SAR) satellites, like those operated by Capella Space and ICEYE, use radar to image the surface regardless of weather or darkness. Because radar penetrates clouds and works at night, SAR is invaluable for disaster response, maritime surveillance, and defense. SAR satellites can detect changes in ground elevation down to millimeters, useful for monitoring land subsidence, volcanic activity, and infrastructure stability.

Weather satellites are perhaps the most directly life-saving application. The U.S. GOES satellites in GEO provide continuous coverage of the Western Hemisphere, tracking hurricanes, thunderstorms, and wildfires in real time. Polar-orbiting weather satellites like those in the NOAA and EUMETSAT fleets provide global coverage and feed data into numerical weather prediction models that power your daily forecast. These satellites have dramatically improved forecast accuracy, giving communities days of warning before severe weather strikes.

Multispectral and hyperspectral sensors observe Earth in wavelengths beyond visible light, revealing information invisible to the human eye: crop health, water quality, mineral deposits, and atmospheric composition. Farmers use satellite-derived vegetation indices to optimize irrigation and fertilizer application. Environmental agencies monitor deforestation, ocean health, and air quality. Insurers assess disaster damage. The Earth observation market is growing rapidly as analytics and AI make satellite data accessible to non-expert users.

Navigation Satellites

Global Navigation Satellite Systems (GNSS) are among the most important satellite applications, underpinning transportation, agriculture, finance, telecommunications, and emergency services worldwide.

GPS (United States) is the most widely used system, consisting of 31 operational satellites in MEO at about 20,200 km altitude. Each satellite continuously broadcasts precise time signals and its own orbital position. A GPS receiver on the ground picks up signals from at least four satellites and uses a technique called trilateration to calculate its exact position: each satellite signal defines a sphere of possible positions, and the intersection of four or more spheres pinpoints the receiver's location in three dimensions plus time.

Standard GPS accuracy is about 3-5 meters for civilian users. Augmentation systems like WAAS (aviation), RTK (surveying), and PPP (precise point positioning) push accuracy to centimeter or even millimeter levels. GPS timing is so precise that it underpins the synchronization of cellular networks, power grids, financial trading systems, and internet infrastructure.

GLONASS (Russia) provides independent global coverage with 24 satellites. Galileo (European Union) offers civilian accuracy of about one meter and is designed for interoperability with GPS. BeiDou (China) completed its global constellation in 2020 with 35 satellites. Most modern smartphones and navigation devices receive signals from multiple GNSS systems simultaneously, improving accuracy and reliability.

Science and Weather Satellites

Some of humanity's greatest scientific discoveries have come from satellites. The Hubble Space Telescope, launched in 1990, revolutionized our understanding of the universe with its stunning images of distant galaxies, nebulae, and exoplanets. Its successor, the James Webb Space Telescope (JWST), launched in 2021, observes in infrared wavelengths and has already peered back to the earliest galaxies formed after the Big Bang.

Climate-monitoring satellites track greenhouse gas concentrations, ice sheet thickness, sea level rise, ocean temperatures, and deforestation rates. NASA's Earth Observing System, ESA's Copernicus program, and Japan's GOSAT satellites provide critical data that informs climate policy and scientific understanding of global warming.

Solar observation satellites like NASA's Solar Dynamics Observatory (SDO) and ESA's Solar Orbiter watch the Sun continuously, monitoring solar flares and coronal mass ejections that can disrupt power grids, satellite operations, and radio communications on Earth. Early warning of space weather events has become essential as our technology infrastructure grows more dependent on electronics.

Weather satellites deserve special emphasis for their direct life-saving impact. Before satellite weather monitoring, hurricanes could strike coastlines with little warning. Today, geostationary weather satellites provide continuous imagery of developing storms, while polar-orbiting satellites supply temperature and humidity profiles that feed into forecast models. Studies estimate that satellite-based weather forecasting saves thousands of lives and billions of dollars in property damage annually by enabling timely evacuations and preparations.

Military and Intelligence Satellites

Military applications were a driving force behind satellite development from the very beginning, and they remain a major part of the space landscape today.

Reconnaissance satellites provide detailed imagery of military installations, troop movements, and weapons programs. The United States' National Reconnaissance Office (NRO) operates classified imaging satellites believed to achieve resolutions of 10 centimeters or better. Other spacefaring nations, including Russia, China, India, and several European countries, operate their own reconnaissance systems.

Early-warning satellites use infrared sensors to detect the heat signatures of ballistic missile launches within seconds. The U.S. Space-Based Infrared System (SBIRS) in GEO and newer Next-Generation Overhead Persistent Infrared (OPIR) satellites are critical components of nuclear deterrence and missile defense architectures.

Secure military communications satellites, like the U.S. Advanced Extremely High Frequency (AEHF) system and the UK's Skynet network, provide jam-resistant, encrypted links for military command and control. Signals intelligence (SIGINT) satellites intercept electronic communications and radar emissions.

Space is increasingly viewed as a warfighting domain. The United States established the U.S. Space Force in 2019, and several other nations have created dedicated space military commands. Anti-satellite (ASAT) weapons have been tested by the United States, Russia, China, and India. The growing dependence on satellites for military operations has made space security a top national-security priority for all major powers.

Satellite Mega-Constellations

One of the defining trends of the 2020s is the rise of satellite mega-constellations: networks of hundreds or thousands of coordinated satellites working together. The concept is not entirely new, as Iridium deployed 66 satellites in the late 1990s, but the current wave operates at an entirely different scale.

SpaceX's Starlink is the clear leader, with over 6,000 satellites in orbit and authorization for more than 12,000, with applications for up to 42,000. Starlink alone accounts for more than half of all active satellites. OneWeb (now Eutelsat OneWeb) has completed its initial 648-satellite constellation for enterprise broadband. Amazon's Project Kuiper plans 3,236 satellites and has begun prototype launches. China's Guowang constellation is planned for 13,000 satellites.

Why so many satellites? Coverage, redundancy, and low latency. In LEO, each satellite covers only a small footprint, so you need many to ensure that at least one is always overhead for every user. Multiple overlapping satellites provide redundancy: if one fails, others seamlessly take over. And LEO's proximity to Earth means signal latency is low enough for video calls, gaming, and other real-time applications that are impractical with GEO satellites.

Mega-constellations raise significant concerns. Light pollution is a major issue for astronomers, as thousands of bright satellites create streaks in telescope images. Operators are working on sunshade designs and darkening coatings, but the problem is far from solved. Orbital debris risk increases with more objects in orbit: even with high reliability, a constellation of 10,000 satellites will experience failures, and dead satellites can become collision hazards. Radio frequency spectrum congestion is another challenge, as constellations compete for limited bandwidth with existing services and each other.

The Future of Satellites

The satellite industry is evolving rapidly, driven by technological innovation and decreasing costs. Several trends are shaping what comes next.

Smaller and cheaper satellites are democratizing access to space. CubeSats, which follow a standardized form factor starting at just 10 cm x 10 cm x 10 cm (a 1U CubeSat), have enabled universities, startups, and developing nations to operate their own spacecraft for a fraction of traditional costs. A 1U CubeSat can be built and launched for under $100,000, compared to hundreds of millions for a traditional large satellite.

Artificial intelligence is moving to orbit. Rather than downlinking all raw data to ground stations for processing, next-generation satellites can analyze imagery and sensor data on board, transmitting only the most relevant information. This reduces bandwidth requirements and enables faster response times for applications like disaster detection and maritime monitoring.

Inter-satellite laser links (optical inter-satellite links) allow satellites to communicate with each other directly using laser beams, creating a mesh network in space. Starlink is already deploying laser links on its satellites, enabling data to route through space rather than bouncing down to ground stations and back up. In some cases, this space-based routing is actually faster than terrestrial fiber optics because light travels faster in vacuum than in glass.

In-orbit servicing is an emerging capability. Companies are developing spacecraft that can dock with existing satellites to refuel them, repair components, or reposition them to new orbits, extending the useful life of expensive assets. Northrop Grumman's Mission Extension Vehicle has already demonstrated this with GEO communications satellites.

Space manufacturing may eventually produce goods in the unique microgravity environment of orbit, from ultra-pure fiber optics to pharmaceutical crystals. While still in early experimental stages, in-space manufacturing could become a significant economic driver.

The space economy, currently valued at over $400 billion, is projected to exceed $1 trillion by the mid-2030s. Satellites will be at the heart of that growth, becoming more capable, more numerous, and more integral to daily life on Earth. Whether you are navigating to a restaurant, checking tomorrow's weather, or streaming a live broadcast from the other side of the planet, satellites are the invisible infrastructure making it all possible.