How Satellites Work: Orbits, Technology, and Applications

How Orbits Determine Function

The altitude and inclination of a satellite's orbit directly determine what it can do. Satellites in low Earth orbit between 200 and 2,000 kilometers travel at roughly 7.8 kilometers per second and complete one orbit every 90 to 120 minutes. Their proximity to the surface makes them ideal for detailed Earth observation and imaging, scientific research in microgravity, and communication with low latency but limited coverage area per satellite. The International Space Station, Hubble Space Telescope, and imaging satellites like those operated by Planet Labs all occupy LEO.

Medium Earth orbit, from about 2,000 to 35,786 kilometers, hosts navigation constellations. The Global Positioning System operates at roughly 20,200 kilometers altitude with 31 satellites in six orbital planes, ensuring that at least four satellites are visible from any point on Earth at any time. Each GPS satellite broadcasts precise timing signals from onboard atomic clocks, and receivers on the ground calculate their position by measuring the time differences between signals from multiple satellites. The accuracy of civilian GPS receivers has improved from roughly 100 meters in the 1990s to under 3 meters today, with differential corrections achieving centimeter-level precision for surveying and autonomous vehicles.

Geostationary orbit at 35,786 kilometers altitude is uniquely valuable because satellites there match Earth's rotation rate, appearing to hover over a fixed point on the equator. A single geostationary satellite can see roughly one-third of the planet's surface, making this orbit ideal for broadcast television, weather monitoring, and communications relay. Major weather satellites like GOES in the United States and Meteosat in Europe provide continuous imagery of the same hemisphere, tracking storm development in real time. The tradeoff is distance: signals take roughly 240 milliseconds for a round trip to geostationary orbit and back, introducing noticeable latency in voice calls and making the orbit unsuitable for applications requiring low-latency interaction.

Satellite Subsystems

Every satellite consists of a payload, the instruments that perform its mission, and a bus, the supporting systems that keep the payload powered, pointed, communicating, and thermally regulated. The power subsystem typically uses solar panels to convert sunlight into electricity, with batteries providing power during eclipse periods when the satellite passes through Earth's shadow. Solar panel technology has improved steadily, with modern multi-junction gallium arsenide cells achieving efficiencies above 30 percent.

The attitude determination and control system keeps the satellite pointed in the correct direction using a combination of sensors and actuators. Star trackers identify the satellite's orientation by matching observed star patterns against a catalog. Sun sensors and Earth horizon sensors provide additional reference data. Reaction wheels, spinning masses inside the satellite, allow precise pointing adjustments without expending propellant by transferring angular momentum between the wheel and the spacecraft body. When the wheels accumulate too much momentum, magnetic torquers or small thrusters desaturate them by dumping the excess angular momentum.

The thermal control system manages temperatures that can range from minus 150 degrees Celsius in shadow to over 120 degrees in direct sunlight. Multi-layer insulation blankets reflect solar radiation, heat pipes transfer excess heat from electronics to radiator panels, and heaters prevent components from getting too cold during eclipse. Some instruments, particularly infrared sensors, require active cooling to temperatures near absolute zero using cryogenic systems or mechanical coolers.

Communication Satellites

Communication satellites relay signals between ground stations, ships, aircraft, and other satellites, forming the backbone of global telecommunications. Traditional communication satellites in geostationary orbit carry transponders that receive signals on one frequency, amplify them, and retransmit them on another frequency. A single large geostationary satellite can provide bandwidth for thousands of simultaneous telephone calls, hundreds of television channels, and broadband internet service across an entire continent.

The emergence of large low-Earth-orbit constellations has introduced a new model for satellite communications. SpaceX's Starlink network, with over 5,000 satellites as of 2025, provides broadband internet service with latencies of 20 to 40 milliseconds, comparable to terrestrial cable connections and far lower than geostationary alternatives. Each satellite communicates with ground terminals using phased-array antennas that electronically steer their beams to track the rapidly moving satellites. Laser inter-satellite links allow data to be routed through the constellation in space, reducing dependence on ground infrastructure and enabling service over oceans and remote regions.

Earth Observation

Earth observation satellites carry instruments that image the planet's surface and atmosphere across multiple wavelengths. Optical sensors capture visible and near-infrared light for mapping, agriculture monitoring, urban planning, and disaster response. Synthetic aperture radar satellites like Sentinel-1 produce all-weather, day-and-night imagery by bouncing microwave pulses off the surface and analyzing the reflected signals. SAR can detect ground movement of just millimeters, useful for monitoring volcanic deformation, glacier flow, and urban subsidence. Multispectral and hyperspectral sensors measure reflected light in dozens or hundreds of narrow wavelength bands, allowing precise identification of crop types, mineral deposits, water quality, and atmospheric pollutants.

The commercial Earth observation market has grown rapidly, with companies like Maxar, Planet, and BlackBridge operating large constellations that collectively image the entire land surface of Earth every day. This frequency enables change detection applications that were previously impossible, from tracking construction activity and monitoring supply chains to providing daily updates on agricultural conditions and deforestation rates. Government agencies use the same data for border security, environmental compliance, and disaster management.

Space Debris and Sustainability

The rapid growth in satellite numbers has intensified concerns about space debris and the long-term sustainability of the orbital environment. LEO satellites experience atmospheric drag that gradually lowers their orbits, causing natural re-entry within years or decades depending on altitude. Satellites in higher orbits remain indefinitely. International guidelines now recommend that LEO satellites be designed to deorbit within 25 years of end of mission, and some regulators are pushing for five-year limits. Active debris removal missions, using robotic arms or nets to capture defunct satellites, are being developed but have not yet operated at scale. Responsible orbital stewardship is becoming as critical to the future of satellite operations as the technology itself.

Satellite Manufacturing and Launch

Modern satellites are built in cleanroom facilities where engineers assemble thousands of components into spacecraft designed to operate without maintenance for 15 years or more. The manufacturing process includes extensive vibration testing to simulate launch conditions, thermal vacuum testing to verify operation in the extreme temperature swings of space, and electromagnetic compatibility testing to ensure that the satellite's own electronic systems do not interfere with each other. A typical geostationary communications satellite takes two to three years from contract signing to launch readiness and costs between 150 and 400 million dollars.

The selection of launch orbit depends on the satellite's mission. Geostationary satellites must reach an altitude of roughly 35,786 kilometers above the equator, where their orbital period matches Earth's rotation, keeping them fixed over a single point on the ground. Low Earth orbit satellites operate at altitudes between 200 and 2,000 kilometers and circle the planet every 90 to 130 minutes, providing global coverage as Earth rotates beneath their orbital planes. Medium Earth orbit, between roughly 2,000 and 35,786 kilometers, hosts navigation constellations like GPS, Galileo, and GLONASS, where the orbital period allows optimal geometric coverage of the planet's surface.

Rideshare launches have dramatically reduced costs for small satellite operators. Companies like SpaceX, Rocket Lab, and others offer dedicated small satellite launches or shared rides on larger missions, enabling startups and universities to access orbit for a fraction of what a dedicated launch would cost. This accessibility has driven a surge in satellite innovation across Earth observation, communications, weather monitoring, and scientific research.