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Space probe


A space probe is a robotic spacecraft that leaves Earth orbit and explores space. It may approach the Moon; enter interplanetary space; flyby, orbit, or land on other planetary bodies; or approach interstellar space.

See List of active Solar System probes for a list of active probes; the space agencies of the USSR (now Russia and Ukraine), the United States, the European Union, Japan, China and India 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. Approximately fifteen missions are currently operational.

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 simplest practical method is a Hohmann transfer orbit. More complex techniques, such as gravitational slingshots, can be more fuel-efficient, though they may require the probe to spend more time in transit. Some high Delta-V missions (such as those with high inclination changes) can only be performed, within the limits of modern propulsion, using gravitational slingshots. A technique using very little propulsion, but requiring a considerable amount of time, is to follow a trajectory on the Interplanetary Transport Network.


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