Short answers, pulled from the story.
Sputnik 1 was the first artificial satellite, launched by the Soviet Union on the 4th of October 1957 under the Sputnik program with Sergei Korolev as chief designer. It helped identify the density of high atmospheric layers and provided data on radio-signal distribution in the ionosphere.
As of the 28th of June 2025, there are 12,952 satellites in Earth's orbit. Of those, 8,530 belong to the United States, 1,559 to Russia, and 908 to China.
Satellites are used for communication relay, weather forecasting, navigation such as GPS, broadcasting, scientific research, and Earth observation. Military uses include reconnaissance, early warning, signals intelligence, and potentially weapon delivery.
Satellites reach orbital velocity and occupy an orbit high enough to avoid orbital decay from atmospheric drag and above their Roche limit. Most use chemical or ion propulsion with reaction wheels to adjust or maintain their orbit and control their three axes of rotation.
Explorer 1 became the United States' first artificial satellite on the 31st of January 1958. Information from its radiation detector led to the discovery of the Earth's Van Allen radiation belts.
The International Space Station is the largest artificial satellite ever. Crewed spacecraft that remain in orbit, like space stations, are counted as artificial satellites.
Satellites raise concerns over resource use and pollution, with aluminium making up around 40% of a satellite's mass and rocket launches releasing black carbon, carbon dioxide, nitrogen oxides, aluminium, and water vapour. Roughly 70% of deorbited satellites end up in the ocean and are rarely recovered, and the brightness of the night skies has risen by up to 10% above natural levels.