Technicians work on the Ulysses space probe.

A space probe is a scientific space exploration mission in which a robotic spacecraft leaves the gravity well of Earth and approaches the Moon or enters interplanetary or interstellar space; approximately twenty are currently extant. The space agencies of the USSR (now Russia and Ukraine), the United States, the European Union, Japan and China have in the aggregate launched probes to several planets and moons of the solar system as well as to a number of asteroids and comets.

Types

A space probe destined for a planet or other astronomical body can be classified as a "flyby", an "impactor", an "orbiter" or a "lander" mission. Historically, flyby missions proved easiest to accomplish, as they did not require the precise navigation needed for an impact, nor the need for additional propulsion to conduct a maneuver to enter orbit. Upon landing some landers have released "rovers" which travel across the surface of the astronomical body upon which they have landed.

The Genesis probe was a sample return mission requiring very little fuel.

Interplanetary trajectories

Once a probe has left the vicinity of Earth, its trajectory will likely take it along an orbit around the Sun similar to the Earth's orbit. To reach another planet, the conceptually simplest means is to execute a Hohmann transfer orbit maneuver. More complex techniques, such as gravitational slingshots, can be more efficient, though they may require the probe to spend more time in transit. A technique using very little propulsion, but possibly requiring a considerable amount of time, is to follow a trajectory on the Interplanetary Transport Network.

Some notable probes

Luna 1:
The first successful space probe was the Soviet Luna 1 flyby of the Moon in 1959. Luna 1 reached the escape velocity of the Earth, and passed within of the Moon's surface after 83 hours of flight. It then went into orbit around the Sun, between the orbits of Earth and Mars.

The Huygens landing site on Titan.

Spirit and Opportunity:
The Mars Exploration Rovers, Spirit and Opportunity landed on Mars to explore the Martian surface and geology, and search for clues to past water activity on Mars. They were each launched in 2003 and landed in 2004. As of January 24, 2007, both Spirit and Opportunity have lasted for more than three years on Mars--when they were intended to last only three months. On February 6, 2007, Opportunity had traversed more than on the surface of Mars.^[1]

Locations of Voyager 1 and Voyager 2.

Voyager 1 is the farthest human-made object from Earth, traveling away from both the Earth and the Sun at a relatively faster speed than any other probe. As of May 9, 2008, Voyager 1 is over 15.89 terameters (15.89 meters, or 15.89 km, 106.26 AU, 14.72 light-hours, or 9.87 billion miles) from the Sun. At this distance, signals from Voyager 1 take more than fourteen hours to reach its control center at the Jet Propulsion Laboratory. Voyager 1 and Voyager 2 have achieved solar escape velocity, meaning that its trajectory will not return it to the solar system.

Along with Pioneer 10, Pioneer 11, and its sister ship Voyager 2, Voyager 1 is an interstellar probe.

References

• Deep Space: The NASA Mission Reports / edited by Robert Godwin (2005) ISBN 1894959159

See also

• List of planetary probes
• List of space agencies

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