What a satellite is
An artificial satellite is any human-made object that orbits another body, usually the Earth. It stays in orbit because it moves sideways fast enough that, as it falls toward the planet, the surface curves away beneath it. Reaching that speed takes a large rocket, which is why satellites only became possible in the middle of the twentieth century. Theorists had described the idea earlier, and the people involved are the subject of our article on satellite pioneers.
The first launches, 1957 to 1958
The first artificial satellite was the Soviet Sputnik 1, launched on October 4, 1957, covered in our article on the Sputnik launch. Sputnik 2 followed in November 1957, carrying the dog Laika. The United States launched Explorer 1 on January 31, 1958, and the instruments on it contributed to the discovery of the radiation belts around Earth later named after James Van Allen. These early satellites were mostly scientific or demonstration missions, and their lifetimes were short.
Satellites find a purpose
Within a few years, designers began to ask what satellites could do that nothing else could. The uses that followed can be grouped by type.
- Weather satellites: TIROS-1 in 1960 showed cloud patterns from orbit. This work is covered in our article on weather satellites.
- Communications satellites: Echo 1 (1960) was a large reflective balloon that bounced signals, and Telstar 1 (1962) relayed television and telephone signals across the Atlantic. Later geostationary satellites, such as Early Bird in 1965, offered commercial service.
- Navigation satellites: the Navy’s Transit system began service in the 1960s, followed by GPS from the 1970s onwards.
- Earth observation satellites: the Landsat program, which began in 1972, supplied repeated images of land for mapping, farming and forestry, and began a long record of changes in land use.
- Military reconnaissance: both superpowers launched photographic and signals satellites in the 1960s. Details were kept secret at the time, and some were declassified decades later.
- Scientific satellites: observatories studying the Sun, the cosmos and the Earth’s environment. The Hubble Space Telescope, launched in 1990, is one of the best-known examples.
Orbits shape purposes
Different jobs need different orbits.
- Low Earth orbit (a few hundred kilometers) suits imaging satellites, crewed stations and many communications constellations. It is close to the ground, so signals have a short delay, but each satellite sees only a small area.
- Medium Earth orbit (around 20,000 kilometers) is used by navigation systems including GPS, because a satellite there stays in view for hours and a small number of satellites can cover the world.
- Geostationary orbit (about 35,786 kilometers above the equator) matches the Earth’s rotation so that a satellite appears fixed in the sky. It suits television relays and some weather satellites. The idea is credited to Arthur C. Clarke’s 1945 proposal, as covered in our article on communications satellites.
- Polar and sun-synchronous orbits pass over the poles and allow repeated views under similar lighting, which is useful for observation.
Technology that made satellites smaller
Early satellites were limited by the weight of electronics. Transistors and then integrated circuits reduced the weight of equipment, and solar panels replaced short-lived batteries. Satellites such as Vanguard 1 in 1958 used solar cells and were useful for years. The development of solar power, a subject discussed in our article on solar panels, was therefore closely linked with spaceflight. Later improvements included better rockets, onboard computers, more efficient radio links and, more recently, small satellites that can be built and launched cheaply.
A commercial and strategic infrastructure
By the early twenty-first century, satellites had become part of everyday infrastructure. Television reached remote areas by satellite, as with satellite radio and direct-to-home broadcasting, and weather forecasts, ship tracking, phone calls in remote regions and bank timing relied on them. GPS had become the best-known example. In recent years, large constellations of small satellites in low orbit have been launched to provide internet access, raising the number of active satellites into the thousands. Exact counts change quickly.
Costs and problems
The success of satellites has brought challenges. Rockets, once launched, discard parts that may stay in orbit, and defunct satellites remain there too. Space debris is a growing concern because collisions can generate more fragments, and operators must plan for end-of-life disposal. Astronomers have raised concerns about bright satellites in images of the night sky. Satellites are also vulnerable to interference and to deliberate attack, and international discussions about space rules continue.
An overview of the arc
The history can be divided roughly into four phases: a pioneering period of demonstration satellites from 1957, the establishment of weather, communications and navigation services in the 1960s and 1970s, the growth of commercial markets in the 1980s and 1990s, and the recent expansion of small-satellite constellations. Each stage built on advances in electronics, power and launch capability. The path from Sputnik’s simple beeping sphere to the satellites that supply a phone with its location is a clear example of a single idea being developed into many different tools.