The Mission Timeline
- Sputnik 1 (USSR). A 58 cm aluminium sphere, beeping on radio, becomes the first artificial satellite and starts the Space Age.
- Vostok 1. Yuri Gagarin completes one orbit of Earth, the first human in space.
- Apollo 11 (NASA). Neil Armstrong and Buzz Aldrin land in the Sea of Tranquillity while Michael Collins orbits above.
- Voyager 2 and Voyager 1 launch. Voyager 2 remains the only spacecraft to visit Uranus and Neptune; Voyager 1 entered interstellar space in August 2012.
- Hubble Space Telescope launches on Space Shuttle Discovery (STS-31). A flawed mirror is corrected by astronauts in December 1993.
- Cassini-Huygens (NASA, ESA, ASI) launches for Saturn. Huygens lands on Titan in 2005; Cassini ends with a dive into Saturn on 15 September 2017.
- International Space Station. The first module, Zarya, launches; crews have lived aboard continuously since 2 November 2000.
- Rosetta's Philae (ESA) lands on comet 67P/Churyumov–Gerasimenko, the first landing on a comet.
- New Horizons (NASA) flies past Pluto after a journey of nine and a half years.
- Perseverance (NASA) lands in Jezero Crater on Mars. Its helicopter Ingenuity makes the first powered flight on another planet on 19 April 2021.
- James Webb Space Telescope (NASA, ESA, CSA) launches on an Ariane 5 from Kourou, French Guiana.
- Chandrayaan-3 (ISRO) lands near the Moon's south pole, making India the fourth nation to soft-land on the Moon.
Sixty-six years in twelve lines
Each entry built on the engineering and science of the one before, just as this primer builds step by step.
How they get there →How Spacecraft Actually Travel
Rockets do not fly straight at their targets. To reach orbit, a vehicle must travel sideways at about 7.8 km per second, fast enough that it keeps falling around Earth instead of back to it. Leaving Earth entirely takes roughly 11.2 km per second.
Between planets, mission designers use transfer orbits. The classic Hohmann transfer, described by German engineer Walter Hohmann in 1925, is an ellipse that touches the departure planet's orbit at one end and the target's at the other. It is fuel-efficient but slow, and launch windows open only when the planets line up; for Mars, about every 26 months.
Gravity assists add speed for free. By swinging close to a planet, a spacecraft borrows a tiny fraction of the planet's orbital momentum. Voyager 2 used a rare alignment of the outer planets to visit Jupiter, Saturn, Uranus and Neptune on one journey.
Why Put Telescopes in Space?
Earth's atmosphere blurs starlight and absorbs whole bands of the spectrum, including most ultraviolet, X-ray and large parts of infrared light. Above it, telescopes see sharply and in colours our eyes never will.
Hubble orbits roughly 540 km up and observes mainly in visible and ultraviolet light; its Deep Field images revealed thousands of galaxies in a patch of sky that looked empty. Webb works in the infrared with a 6.5-metre mirror made of 18 gold-coated hexagonal segments. It orbits the Sun near the second Lagrange point, L2, about 1.5 million km from Earth, shaded by a sunshield the size of a tennis court. Infrared lets it see through dust and catch light from the earliest galaxies, stretched to longer wavelengths by the expansion of the universe.
The Agencies Behind the Missions
Spaceflight is expensive enough that most big missions are shared. These are the names you will see most.
NASA
Founded 1958. Apollo, Voyager, Hubble, the Mars rovers and the Artemis programme, whose uncrewed Artemis I flew around the Moon in 2022.
See its missions →ESA
Founded 1975, with over twenty member states. Rosetta, Huygens, Gaia's star map and partner on Hubble and Webb.
Titan and Huygens →ISRO, JAXA, CNSA
India's ISRO (1969) landed Chandrayaan-3. Japan's JAXA returned asteroid samples with Hayabusa2. China's CNSA brought far-side lunar samples home with Chang'e 6.
Questions about missions →You Have Reached Zero
From naked eye to interstellar space, the countdown is complete. Now go back outside: the faint smudge of Andromeda, the steady glint of Jupiter and the moving dot of the ISS will all mean far more than they did at Step 01.