"We have your satellite. If you want it back send twenty billion in Martian money."
Graffiti at NASA laboratory, Pasadena, California
A space probe is a satellite that leaves the grip of Earth's gravity and moves off to flyby, or orbit, another solar system body. The first target was the moon. There were three U.S. attempts in 1958, Pioneer 2, and 3, which all failed. The U.S.S.R. had the first success in January 1959 with the Luna 1 probe, which was launched with the objective of impacting the lunar surface. It flew by, missing by 3,700 miles (5,950 km), but at least it got there. The U.S.'s Pioneer 4 flew past at a miss distance of 37,300 miles (60,000 km).
The greatest early successes were Luna 2 (September 1959) and Luna 3 (October 1959), the first hitting the moon Just east of the Sea of Serenity and the second imaging the far side of the moon for the first time. The 1960s saw a host of lunar missions that was to culminate in the first moon landing.
The first successful planetary space probe reached Venus in 1962, and the U.S.S.R.'s Venera 7 probe soft landed there in 1970. In June and August 1976 the U.S.'s Viking t and 2 probes achieved the first successful landings on Mars and returned images from the planet's surface. Voyager 1 and 2 have since become interstellar space probes and areon their way to the stars.
