A space probe, or simply probe, is an uncrewed spacecraft that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; or enter interstellar space.
The space agencies of the USSR (then later Russia), the United States, the European Union, Japan, China, India, and Israel have collectively launched probes to several planets and moons of the Solar System, as well as to a number of asteroids and comets.
Further information: List of Solar System probes
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After the launch of the first artificial satellite, Sputnik 1, the first space probe Pioneer 0 was launched one year later, on 17 August 1958. However, it had not succeeded on achieving lunar orbit, due to Thor missile's error. The Soviet then soon followed with the failed launch of Luna E-1 No.1 on 23 September 1958, another lunar probe which is aimed to impact the moon. Both countries failed to reach the Moon repeatingly, until 4 January 1959 when Luna 1 orbited around the Moon, then the Sun.
A space probe generally need an antenna to communicate back with Earth.
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.