The 10-cent Pioneer commemorative stamp was issued on February 28, 1975, at Mountain View, California, and paid the domestic first-class rate for letters weighing less than one half ounce. Designed by Robert T. McCall and printed at the Bureau of Engraving and Printing on the Giori presses, the stamp shares numerous design elements with USA Scott 1557. Although they have different designers and dates of issue, the two stamps are catalogued together under the heading "U.S. Unmanned Accomplishments in Space."
In March of 1972, scientists launched the interstellar spacecraft Pioneer 10 to gather information about Jupiter while also receiving signals and information from Earth. Pioneer was expected to last for twenty-one months in the solar system and deliver accurate information over that period of time. The fastest manmade object to enter space from Earth, the spacecraft was to begin collecting data at the Asteroid Belt and Jupiter and continue to relay information about other areas and phenomena of the solar system. By July, the spacecraft had reached the Asteroid Belt between Mars and Jupiter. During its traversal of the Belt, it transmitted information about the Asteroid Belt for scientists to analyze. In December, Pioneer captured the first photos of Jupiter.
As suspected by scientists, the photographs proved that the solar system's largest planet was indeed predominately liquid. Pioneer 10 charted Jupiter's radiation belts for further observation and data and discovered the planet's magnetic fields. Pioneer 10 then continued past Jupiter and became the first spacecraft to travel beyond Pluto. During its working life, it traversed Jupiter twice and recorded data regarding solar winds and cosmic rays. Pioneer 10 actually worked for more than thirty years, with readable signals detected as late as January 2003. Another attempt at contacting the satellite, made in March 2006, was unsuccessful, and attempts will likely not be made again. Pioneer 10 is now more than 7.5 billion miles from Earth and headed toward the Taurus constellation.
"Missions: Pioneer 10 and 11." NASA. http://www.nasa.gov/centers/glenn/about/history/pioneer.html (accessed September 3, 2008).
Kloetzel, James E., ed. 2006 Specialized Catalogue of United States Stamps & Covers. 84th ed. Sidney, Ohio: Scott Publishing Co., 2005.