Satelliiti

Satelliiti are objects that orbit a larger body, such as a planet or dwarf planet. They include natural satellites, such as moons, and artificial satellites, which are human-made spacecraft placed into orbit for a variety of purposes. Artificial satellites carry instruments and payloads to support communications, Earth observation, navigation, science, and weather monitoring.

Orbits vary by altitude and orientation. Common regimes include low Earth orbit (LEO), roughly 160 to 2,000 kilometers above Earth; medium Earth orbit; and geostationary orbit at about 35,786 kilometers, where a satellite remains above a fixed point on the equator. Polar and sun-synchronous orbits pass over the poles, providing global coverage.

Most satellites consist of a bus, which provides power, structure, propulsion, and attitude control, and a payload, which defines mission objectives. Power is usually supplied by solar panels with onboard batteries. Some satellites use electric propulsion for station-keeping or deorbiting. Communications links with ground stations enable command and data return.

Historically, the launch of Sputnik 1 in 1957 marked the beginning of artificial satellites and the space age. Since then, thousands of satellites have been launched. Earth’s Moon is the largest natural satellite of Earth, and natural satellites in other planetary systems continue to be objects of scientific study.

Challenges include space debris, regulatory coordination, signal interference, and collision risk. Effective space traffic management and end-of-life disposal strategies are important for sustainable operation of orbital environments.