An artificial satellite is a human-made object intentionally placed into orbit around a celestial body, most often Earth. These machines represent a profound achievement of engineering, operating high above the atmosphere. They form a vast infrastructure that underpins much of contemporary global civilization. Since the first satellite launch in 1957, these devices have evolved into complex platforms that connect, observe, and measure the planet, enabling technologies deeply integrated into daily life.
Fundamental Design and Purpose
Every artificial satellite is fundamentally composed of two primary functional blocks: the bus and the payload. The bus acts as the spacecraft’s core platform, housing all necessary subsystems to keep the satellite operational in space. This structure includes the electrical power system, typically using solar panels and batteries for storage during eclipses. It also incorporates the propulsion system, which uses small thrusters to make fine adjustments to the satellite’s orbit and orientation.
The bus also contains the attitude control system, which uses sensors and reaction wheels or magnetorquers to maintain the satellite’s specific pointing direction. This is essential for keeping instruments or antennas accurately aimed. Additionally, a thermal control system uses insulation and radiators to protect sensitive electronics from extreme temperature fluctuations. The payload, in contrast, is the mission-specific equipment designed to perform the satellite’s intended task, such as a high-resolution camera, scientific sensor, or communication transponder.
A satellite remains in orbit not by continuous engine power but by achieving a precise balance between two forces: the Earth’s gravitational pull and the satellite’s forward motion, known as orbital velocity. Once the necessary speed is reached, the satellite continuously “falls” toward the Earth, but its rapid horizontal velocity causes it to constantly miss the planet’s curved surface. The required orbital speed is inversely related to altitude; the closer a satellite is to Earth, the faster it must travel to counteract the stronger gravitational force. For instance, an object in low orbit must travel at approximately 27,400 kilometers per hour to maintain its trajectory.
Categorizing Satellites by Orbit
Satellites are placed into various orbits, with the altitude and path determining their capabilities and limitations. The Low Earth Orbit (LEO) is the region nearest to Earth, spanning altitudes from about 160 to 2,000 kilometers. Satellites in LEO have orbital periods as short as 90 to 120 minutes, circling the globe multiple times a day. This proximity minimizes communication delay, or latency, making LEO systems highly responsive for real-time applications.
Further out is the Medium Earth Orbit (MEO), which occupies the space between LEO and the highest orbits, ranging from 2,000 kilometers up to the geostationary belt (35,786 kilometers). MEO satellites have orbital periods of several hours, offering a compromise between the low latency of LEO and the wide coverage of higher orbits. Satellites in this region can cover larger areas for extended periods compared to their LEO counterparts.
The Geostationary Orbit (GEO) is a high-altitude orbit 35,786 kilometers above the Earth’s equator. A satellite placed here travels at a speed that exactly matches the Earth’s rotation, causing it to appear stationary relative to a fixed point on the ground. This provides continuous, stable coverage over a massive geographical area. However, the great distance introduces a noticeable signal lag, or high latency, which impacts time-sensitive communications.
Essential Roles in Modern Life
Artificial satellites perform functions across communication, navigation, and Earth observation that sustain modern global society. Communication satellites, particularly those in the GEO belt, utilize transponders to receive signals from one ground station and retransmit them to another, facilitating global television broadcasting and long-distance telephone calls. Newer constellations of small satellites in LEO are now providing high-speed, low-latency internet access to remote and underserved areas worldwide.
Navigation is served primarily by Global Navigation Satellite Systems (GNSS), such as the United States’ Global Positioning System (GPS), which operate in MEO. These satellites transmit precise timing and position data, allowing ground receivers to calculate their exact location on Earth. This capability is foundational for services including personal navigation in smartphones, air traffic control, precision agriculture, and the synchronization of global financial networks.
The third major role is Earth observation, which involves monitoring the planet for environmental, meteorological, and security purposes. Weather satellites, often positioned in GEO, provide continuous, wide-area imagery that allows meteorologists to track large storm systems and predict weather patterns. Other Earth observation satellites, predominantly in LEO, use high-resolution cameras and sensors to collect detailed data for climate change tracking, disaster response, and intelligence gathering. These instruments monitor everything from sea-level rise and deforestation to the movement of ice sheets and urban expansion.