Planet Probes: Landers, Flybys, and Gravity Assist


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A probe is a robot investigation tool, about the size of a car, that is launched by rockets. Probes have a destination schedule: a predetermined target, then investigate. The close up views of planets, moons, comets, and asteroids have been provided by the probes launched into our solar system. Before probes were created scientists used the human eye and telescope to view the planets. Mars is the only planet that Earth telescopes can provide surface photographs.

The Voyager probe is equipped with a camera platform holding a wide-angle lens for close-ups and a narrow angle lens for shots at a distance. Voyager's thrusters are tiny jets used for changing the direction of the probe, and for power it uses a nuclear generator. For finding and measuring the planets' magnetic fields, Voyager uses a magnetometer, and has two long antennas for discovering planets giving off radio waves. Once this is collected, the dish sends this data back to controllers on the Earth.

Whenever a probe needs extra help to reach its goal, a rocket or the space shuttle uses a technique called gravity assist to send it on its way. Gravity assist is creating a flight path that will take the probe close to planet, then using the gravity from the planet to speed it up and change its direction. The Ulysses probe was assisted by the gravity of Jupiter in 1992 to make a pass under the Sun in 1994.

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Flyby probes will survey the target area when flying past it, orbiting it, or landing on its target, often from several thousands kilometers away. Between 1979 and 1989, Voyagers 1 and 2 made successful flybys to Jupiter, Uranus, and Neptune. Some flyby probes may have more than one target or method.

Orbiters are the probes that travel to a moon or planet, then enters the moon or planet orbit. The instruments will then turn on and begin an investigation of the selected target. In August and September 1975, Vikings 1 and 2 were launched; in July and September of 1976 Vikings 1 and 2 landed on Mars; in May 1989 Magellan was launched; and in August 1990, Magellan orbited the planet Venus.

Landers naturally land. The two Viking probes visiting Mars had an orbiter and a lander. Probes have landed on Mars, the Moon, and Venus. When a lander is in orbit, a separation occurs between the lander and the probe. It then uses a parachute for brakes and to make a solid landing it uses retrorockets. In 1997, Pathfinder landed on Mars, but did not go into orbit first; once reaching the surface, Sojourner, a small robot rover vehicle was released.


1. Couper, Heather and Nigel Henbest. Space Encyclopedia DK Publishing, Inc.: NY 1999

2. Editors. Secrets of the Universe. International Master Publishing: US. 1999