Satellite

A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. Satellites have many important jobs, like helping with communication, weather forecasting, navigation through systems like GPS, broadcasting TV and radio, doing scientific research, and watching over the Earth. They can also be used for military purposes such as reconnaissance and sending important signals.

Most satellites have their own way to make electricity, often using solar panels, and they carry special tools called transponders to talk to people on the ground. Many satellites are built using a standardized bus to save money, and some small ones are called CubeSats. Satellites can work together in groups known as constellations.

The first artificial satellite ever launched was the Soviet Union's Sputnik 1 on October 4, 1957. By June 28, 2025, there were over 12,000 satellites orbiting Earth, with most belonging to the United States, Russia, and China. These satellites help us in many ways every day, from checking the weather to finding our way with GPS.

History

See also: Timeline of first artificial satellites by country

The idea of satellites has been around for a long time. In 1687, Isaac Newton used a thought experiment called "Newton's cannonball" to explain how natural satellites move. Later, in 1869, Edward Everett Hale wrote a story called "The Brick Moon" where a satellite was launched into orbit. In 1903, Konstantin Tsiolkovsky wrote about using rockets to launch spacecraft and calculated how fast a satellite would need to go to stay in orbit.

The first artificial satellite was Sputnik 1, launched by the Soviet Union on October 4, 1957. It helped scientists learn about Earth's atmosphere and radio signals in space. This launch started the Space Race between the Soviet Union and the United States. The United States launched its first satellite, Explorer 1, on January 31, 1958, which discovered radiation belts around Earth. Since then, many countries have launched their own satellites for communication, weather forecasting, and scientific research.

Components

Most satellites use special engines to stay in the right place in space. They also have parts that help them point in the correct direction. Near Earth, satellites feel the pull of Earth's gravity and the Sun's energy, so they need to be careful to stay steady. Farther away, the pull of the Moon and Sun matters more.

Satellites get power mostly from solar panels that turn sunlight into energy. When there's no sunlight, like inside a rocket or at night in space, they use batteries to keep working.

Applications

Main article: Communications satellite

Main article: Reconnaissance satellite

Main article: Space telescope

Main articles: Space weapon, Anti-satellite weapon, and Early warning satellite

Satellites have many important uses. They help us watch the Earth from space, which helps scientists study weather, natural disasters, and changes in our planet. They can also help people talk to each other over long distances and help us find our way using tools like GPS.

Some satellites are used to look at stars and other objects far away in space. Others are used for special experiments, like carrying living things into space to learn more about how they live. Satellites can also help us learn about our universe and how things work in space.

Environmental impact

The environmental impact of satellites is becoming more important as more are launched into space. Satellites and their launches use many resources and can release pollutants into the atmosphere. For example, the metal aluminium, which is commonly used in satellites, has negative effects on the environment because of how it is mined and processed.

Rocket launches release pollutants like black carbon and nitrogen oxides into the atmosphere, which can harm the ozone layer. Satellites in orbit can also release chemicals and degrade materials, adding more pollutants. The increasing number of satellites can brighten the night sky, which may affect animals that rely on stars for navigation. As satellites end their lives, they often fall back to Earth, adding more pollution to the atmosphere and oceans. Researchers are looking into ways to reduce these effects, such as using wooden materials for satellites.

Main articles: Satellite observation, Space debris

Interference

Space debris poses dangers to satellites in orbit and could lead to a situation called Kessler syndrome, which might make future space missions very difficult. As more satellite constellations, like SpaceX Starlink, are launched, they can interfere with astronomical research. Organizations like the IAU are working on ways to reduce these harmful effects.

Satellites can also face radio interference from land-based transmitters, which can disrupt their signals. This is especially a concern for GPS satellites, but it can affect satellite phone and television signals too. Sometimes, Earth stations accidentally send signals at the wrong time or frequency, which can block legitimate satellite communications. Satellite operators use special tools to detect and manage these issues.

Regulation

As more satellites are launched, problems like space debris and light pollution are growing. However, there hasn't been much progress in rules to manage these issues at national or international levels.

Usually, responsibility for any problems caused is handled by the Liability Convention.

Operation

Satellite operation has become more diverse and continues to grow in many ways. To operate a satellite, you need money, factories to build it, rockets to launch it, and special equipment on the ground to control it. This infrastructure helps satellites do important jobs like talking to people far away, watching the weather, and guiding cars with GPS.

List

See also: List of heaviest spacecraft

This is a list of some heavy satellites that orbit Earth. It does not include space stations or spacecraft that go beyond Earth’s orbit. The list includes satellites located at a special point called the Sun-Earth Lagrange point 2.