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Space Topics: Past MissionsPioneer 10 and 11
On March 2, 1972, Pioneer 10 was launched on an Atlas/Centaur rocket from Cape Canaveral. Pioneer 10 was Earth’s first space probe to an outer planet, encountering Jupiter on December 4, 1973. Pioneer 11 followed its sister ship to Jupiter, and continued on to encounter Saturn on September 1, 1979. With their primary missions completed, the two spacecraft embarked on escape orbits to opposite sides of the solar system, traveling nearly along the ecliptic, the imaginary plane described by Earth’s orbit about the Sun. Pioneer 10 became the first human artifact to pass beyond the orbit of the farthest known planet, Pluto, in June 1983. The Pioneer AnomalyPioneer 10 and 11 are traveling quickly -- but not as quickly as expected. Each year, they fall behind in their projected travel by about 5,000 kilometers (3,000 miles). Jet Propulsion Laboratory scientist John Anderson and his colleagues have been searching for an explanation for this "Pioneer Anomaly" since 1980. But as of yet, they have found nothing conclusive; no spacecraft behavior or previously unknown property of the outer solar system can explain the deceleration of the Pioneer spacecraft. The Planetary Society, using support from its members, is currently sponsoring the recovery of Doppler and spacecraft status data, as well as analysis of that data. A switch failure in the Pioneer 11 radio system on October 1, 1990 disabled the generation of coherent Doppler signals that we use for tracking, so we received no more data from that craft to help us solve the anomaly. On March 31, 1997, Pioneer 11 was finally shut off, but it continues on its way toward the constellation Aquila (the Eagle). It may pass by Lambda Aquila, the magnitude 3.4 star that marks the Eagle’s tail, in about 4 million years. The Pioneer 10 mission officially ended on March 31, 1997, when the spacecraft was 67 AU from the Sun, but it kept on working and generating data for our study. (An AU, or Astronomical Unit, is the mean distance of Earth from the Sun, about 150 million kilometers or 93 million miles.) Eventually, though, we lost our collaborator. On February 11, 2000, Pioneer 10 received its last message from Earth and was heard from no more. At a velocity relative to the Sun of 12.24 kilometers (7.6 miles) per second, Pioneer 10 will continue into interstellar space, heading for Aldebaran, the red star that forms the eye of the bull in the constellation Taurus. |
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