The first spacecraft in orbit
A satellite is any object that orbits another, and people had known the physics of orbits long before they could build one. What changed in the 1950s was access to rockets powerful enough to reach orbital speed. Both the United States and the Soviet Union announced plans to launch satellites as part of the International Geophysical Year, a scientific effort that ran from mid-1957 to the end of 1958.
The Soviet Union reached orbit first. Sputnik 1, launched on October 4, 1957, weighed roughly 83 kilograms and carried a radio transmitter that sent beeps for about three weeks. Its scientific value was limited, but the signal could be tracked by amateur radio operators, and observers learned about the upper atmosphere from how its orbit slowly decayed. It reentered in early 1958. Sputnik 2 followed in November, carrying the dog Laika.
Explorer 1 and the radiation belts
The United States launched its first satellite, Explorer 1, on January 31, 1958, after an attempt with the Vanguard rocket had failed late in 1957. Explorer 1 carried a cosmic ray detector designed by a team led by James Van Allen. The instrument’s unexpected readings were later interpreted as evidence of zones of charged particles trapped by Earth’s magnetic field, now called the Van Allen radiation belts. It was one of the first major discoveries made from space.
Vanguard 1, launched in March 1958, was a small satellite that measured details of Earth’s shape through its orbit. It is often described as the oldest human-made object still in orbit, although such claims are worth checking if precision matters. Together these missions showed that a satellite could give data that was impossible to gather from the ground.
Looking down at the weather
Early satellite designers soon asked what orbit could show about Earth itself. In April 1960, the United States launched TIROS-1, usually described as the first successful weather satellite. It carried television cameras that sent back images of cloud patterns. The pictures were rough compared with today’s, but they showed that large storm systems could be seen from above as a whole.
Meteorologists began to use satellite images in forecasting during the 1960s, and later generations of spacecraft added more instruments and better coverage. The modern basis for tracking storms and understanding weather systems builds on this early work. Another line of development, beginning in 1972 with the U.S. Landsat program, then called the Earth Resources Technology Satellite, used orbit for repeated imaging of land, which grew into the field of remote sensing.
Relays, navigation and observation
Early satellites also tested communications. Echo 1, launched in 1960, was a large reflective balloon that bounced radio signals between ground stations. Telstar 1, launched in 1962, was an active relay that retransmitted signals, and it carried early transatlantic television transmissions. Syncom satellites, in the early 1960s, demonstrated geosynchronous orbit, where a satellite stays above one spot on Earth. These steps led to the commercial communications systems that followed; the later story of satellite communication builds on them.
Navigation was another early use. The U.S. Navy’s Transit system, which began operating in the 1960s, let ships determine their position from satellite signals. Its ideas were refined into the later system behind GPS positioning on phones. Military reconnaissance was also an early use, with programs such as the American Corona satellites returning film capsules from orbit. Much of that work stayed secret for decades.
Science beyond Earth’s neighborhood
Satellites were also used to look outward. Observatories above the atmosphere can detect ultraviolet, X-ray and other light that air blocks. Early solar and astronomical satellites of the 1960s and 1970s began that work, and they led to the large space telescopes that came later. Robotic probes then left Earth orbit entirely, visiting the Moon and nearby planets.
Why the early period mattered
The first decade of satellites set a pattern still in use: a small number of prototype missions proving a concept, followed by operational systems built on them. Many of the services that are routine now, from weather maps to global television links, started as experiments whose usefulness was uncertain at the time. Early engineers also discovered the hazards: radiation, extreme temperatures, and the difficulty of fixing anything once it was in orbit.