PIONEER 10 SPACECRAFT ~ JUPITER 1556 Plate Block of 4 x 10 cents US Postage stamps

On February 28, 1975 in Mountain View, CA; the USPS comemmorated Pioneer 10, the first spacecraft to travel through the asteroid belt, on July 15, 1972, and to make direct observations of Jupiter, which it passed by on December 3, 1973. It was launched from Cape Canaveral Air Force Station's Launch Complex 36A on March 3, 1972. Pioneer 10 is heading in the direction of Aldebaran, located in Taurus. By some definitions, Pioneer 10 has become the first artificial object to leave the solar system. It is the first human-built object to have been set upon a trajectory leading out of the solar system. However, according to the estimated trajectory, it has not yet passed the heliopause or the Oort cloud. Its objectives were to study the interplanetary and planetary magnetic fields, solar wind parameters, cosmic rays, transition region of the heliosphere, neutral hydrogen abundance, distribution, size, mass, flux, and velocity of dust particles, Jovian aurorae, Jovian radio waves, atmosphere of Jupiter and some of its satellites (particularly Io), and to photograph Jupiter and its satellites. There is no longer communication with the probe; the last contact was in 2003 and in 2006 a final attempt at contact failed.