See some key dates relating to early discoveries about natural and artificial satellites in this timeline.
6th century BCE – Ancient Greek geocentric model
Ancient Greek astronomers believe the Earth is the centre of the Universe and that all celestial bodies orbit the Earth. Anaximander describes this in c550 BCE. Aristotle (384–322 BCE) and Claudius Ptolemy (c100–c170 CE) develop more complex geocentric models.
14th century – Ibn al-Shatir anticipates Copernicus
Islamic astronomer Ibn al-Shatir (1304–1375) of the Maragha school accepts the geocentric model but produces configurations that challenge the Ptolemaic model. His calculations are similar to the later calculations of Copernicus.
1543 – Copernicus’s heliocentric model
Polish astronomer Copernicus (1473–1543) proposes that the Sun is stationary in the centre of the Universe and the Earth and other planets revolve around it. The church suppresses this controversial idea but it revolutionises astronomy.
1572 – Tycho Brahe’s accurate measurements
Danish astronomer Tycho (Tyge) Brahe (1546–1601) designs and builds instruments that allow him to accurately observe stellar and planetary positions. His records of the motion of Mars are later used by Kepler.
1609–1610 – Galileo and heliocentrism
Italian astronomer Galileo Galilei’s improvements to the telescope allow him to observe Venus’s phases, the largest satellites of Jupiter, a supernova and sunspots. His discoveries prove the Copernican heliocentric system. The Roman Inquisition finds him guilty of heresy.
1610 – Kepler uses the term ‘satellite’
German astronomer Johannes Kepler (1571–1630) uses the term ‘satellite’ to describe the moons orbiting Jupiter. He develops the three laws of planetary motion, and his accurate astronomical tables provide evidence for the Copernican heliocentric model.
1687 – Newton and gravity
Sir Isaac Newton (1642–1727) publishes Principia in which he states the three laws of motion and describes universal gravity. This lays the foundation for our understanding of rockets, satellites and orbits.
1869–1879 – First fictional artificial satellites
The first fictional depictions of satellites being launched into orbit are published in Edward Everett Hale’s short story The Brick Moon (1869) and Jules Verne’s The Begum’s Fortune (1879).
1903 – First orbit of Earth calculated
Russian Konstantin Tsiolkovsky (1857–1935) proposes using rocketry to launch spacecraft. He calculates the orbital speed required for a minimal orbit around the Earth at 8 km/s and that a multi-stage rocket fuelled by liquid propellants could be used to achieve this.
1928 – First description of a space station
Slovenian Herman Potočnik (1892–1929) describes geostationary satellites and communication between them and Earth using radio. He also describes a space station in detail and the use of orbiting spacecraft for detailed observation of the Earth and scientific experiments.
1945 – Satellite communications system proposed
British science fiction writer and inventor Arthur C Clarke (1917–2008) publishes an article that shows how geostationary satellites could be used for worldwide radio and television broadcasts and communication.
1957 – First artificial satellite launch
The Soviet Union launches Sputnik, the first artificial satellite to orbit around the Earth. It has a mass of 83.6 kg and travels in an elliptical orbit at a height above the Earth between 939 km and 215 km. It travels at 29,000 km/h and takes 96.2 minutes for each orbit.
1960 – First successful weather satellite
NASA launches Tiros-1, the first weather satellite considered a success. It transmits infrared images of Earth’s cloud cover and is able to detect and chart hurricanes. This begins the Tiros programme, which is followed by the Nimbus programme of weather satellites.
1961 – First person to orbit Earth
Russian cosmonaut Yuri Gagarin (1934–1968) becomes the first person to orbit the Earth in his Vostok spacecraft. After this, he becomes an international celebrity and undertakes several overseas tours.
1962 – First communications satellite
The first live transatlantic telecast is broadcast using Telstar-1, a low-orbit satellite. Later, an international global satellite consortium (Intelsat) is formed, which manages a constellation of communications satellites providing international broadcast services.
1970 – China launches its first satellite
China launches its first satellite Dongfanghong 1 into Earth orbit on its Long March rocket, becoming the fifth nation to achieve independent launch capability. The other nations are the Soviet Union (1957), the USA (1958), France (1965) and Japan (1970).
1971 – First space station launched
The Soviet Union launches the first space station Salyut 1. It is monolithic – constructed and launched in one piece. When all its supplies and equipment are used up, it is abandoned. The Salyut programme continues until 1986.
1972 – Beginning of Landsat programme
The Earth Resources Technology Satellite is launched. This begins the longest-running programme of satellite imagery of the Earth, later renamed Landsat. Landsat instruments acquire millions of images that are used to evaluate natural and human changes to the Earth.
1979 – ESA’s first launch
The European Space Agency (ESA) launches Ariane-1, which is designed primarily to put two telecommunications satellites into orbit. This begins ESA’s space programme that continues into the present.
1981 – First space shuttle launched
The first space shuttle Columbia is launched with astronauts John W Young and Robert L Crippen. This is the beginning the American Space Shuttle programme, which takes astronauts and satellites into orbit around the Earth. This programme continues for 30 years.
1990 – Hubble Space Telescope
The Hubble Space Telescope is carried into orbit by the Space Shuttle. Its orbit outside the Earth’s atmosphere allows it to take sharp images that lead to breakthroughs in astrophysics, for example, determining the rate of the Universe’s expansion.
1994 – First GPS constellation
The first global positioning system constellation becomes operational. It consists of 24 geosynchronous satellites. GPS is a space-based satellite navigation system that provides location and time information in all weather, anywhere on or near the Earth.
1998 – International Space Station launched
The first component of the modular International Space Station is launched. It is an international collaboration involving Russia, the USA, the European Union, Japan and Canada. It serves as a microgravity and space environment research laboratory.
2004 – Satellite launched to 'chase comet'
In March the European Space Agency launches the Rosetta from French Guiana. The Rosetta, carrying the lander probe Philae, is destined to rendezvous with Comet 67P in 2014.
2012 – 1000 satellites orbit the Earth
More than a thousand active satellites orbit the Earth. The exact number of operational satellites is difficult to determine for security reasons, but the UCS (Union of Concerned Scientists) satellites database lists 1016 active satellites.
2014 – Probe lands on comet
In August the spacecraft Rosetta is the first to catch up with a comet and land the probe Philae on the comet 67P/Churyumov-Gerasimenko.
25 May 2017 – World's first private orbital launch site
Rocket Lab launches their Electron rocket from their Mahia Peninsula based orbital launch site, in New Zealand. Rocket Lab's Mahia facility is the world's first private orbital launch site and is part of a programme of work to make launching a satellite more cost effective in order to open space up to more organisations.
21 January 2018 – New Zealand's first satellite
Rocket Lab successfully deployed 4 small satellites on their second test launch from Mahia. Three were for US based corporations but the fourth 'secret satellite' was a New Zealand effort – the Humanity Star. The Humanity Star was a geodesic sphere made from carbon fibre with 65 highly reflective panels. Rocket Lab CEO Peter Beck said he wanted the first New Zealand satellite to be something special for everyone, "The humanity star is a way of looking beyond our immediate situation, whatever that may be, and understanding we are all in this together as one species."
11 November 2018 – First commercial rocket launch from New Zealand
Rocket Lab achieves their first official commercial deployment from Mahia. 'It's Business Time', took off at 4.50 pm on Sunday 11 November. It lifted six satellites and a technology demonstrator into low Earth orbit.
28 June 2022 – testing a return to the Moon
NASA is leading the Artemis programme – aiming to return humans to the Moon. As part of this, Rocket Lab launched the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) spacecraft to test a unique lunar orbit intended for use by the new lunar space station/outpost that will orbit the Moon.
In the article, Our solar system – revolutionary ideas we look at how since the earliest times, humans have made observations of the night sky. These observations led to the development of models to explain the movement of these natural satellites.