A flyby is a type of mission where a spacecraft flies by a celestial body, such as a planet, moon, or comet, at a relatively close distance without going into orbit around it.
The main purpose of a flyby is to study the target body and its environment using the spacecraft's instruments, as well as to gather data for future missions. Flybys are often used to make initial reconnaissance of a target and to plan more detailed missions, such as orbiter or lander missions.
Examples of flyby missions include:
- Mariner 2, the first spacecraft to flyby Venus in 1962
- Pioneer 10 and 11, the first spacecraft to flyby Jupiter and its moons in the 1970s
- Voyager 1 and 2, which flew by Jupiter, Saturn, Uranus, and Neptune in the 1970s and 1980s
- Galileo, which flew by Jupiter and its moons multiple times in the 1990s
- Cassini-Huygens, which flew by Venus, Earth and Jupiter before entering orbit around Saturn in the 2000s.
- New Horizons, which flew by Pluto in 2015
- Hayabusa2, which flew by asteroid Ryugu in 2018 and collected samples before returning to Earth.
Flybys are considered as cost-effective and relatively low-risk method of exploring space and gathering data and images of celestial bodies as compared to orbiters and landers.