Pioneer 11 Provided the First Up-close View of Ringed Planet Saturn
Sister Ships Pioneers 10, 11, Were First Probes to Leave the Solar System
By Bob Granath
The first spacecraft to approach the planet Saturn was launched 50 years ago on a 1.5 billion mile trip to Earth’s distant neighbor. During its 22-year mission, Pioneer 11 studied the asteroid belt, the solar wind, cosmic rays and the environment around the planets Jupiter and Saturn. The probe was part of the United States’ efforts leading the reconnaissance of each planet in the solar system.
On April 5, 1973, NASA’s Pioneer 11 lifted off atop an Atlas Centaur rocket from Launch Complex 36B at Cape Kennedy Air Force Station (now Cape Canaveral Space Force Station). Along with sister ship Pioneer 10, the two spacecraft were the first to venture through the perilous asteroid belt between Mars and Jupiter. Launched a year earlier, Pioneer 10 was the first mission from Earth to study the planet Jupiter.
During the mid-1960s, the United States and Soviet Union began sending probes to the planets closest to Earth – Venus and Mars. However, it was not until the 1970s that spacecraft were launched farther away toward Mercury, Jupiter and Saturn. The most significant step was Voyager 2, also referred to as the “Grand Tour.” Launched from Cape Canaveral in 1977, it passed Jupiter in 1979, Saturn in 1981, Uranus in 1986 and Neptune in 1989.
Eventually, Pioneers 10 and 11 also became the first human-made objects to achieve the needed velocity to leave the solar system. Since then, Voyagers 1 and 2, along with the New Horizons probe passed the region past Pluto known as the heliopause.
When New Horizons’ principal investigator Dr. Alan Stern of the Research and Development at the Southwest Research Institute in Boulder, Colorado, spoke to employees at NASA’s Kennedy Space Center in 2015, he recalled the early days of the “space race.”
“I’m proud of the tradition that began in 1962 with Mariner to Venus,” said Stern, a former associate administrator for NASA’s Science Mission Directorate. “The United States was first to every planet in the solar system.”
The 571-pound Pioneer 11 measured 9 1/2 feet long and at its widest dimension was the 9-foot diameter high gain antenna. It traveled past Jupiter on Dec. 3, 1974, using the giant planet’s gravity to thrust it to a velocity of 110,000 mph to Saturn. While passing Jupiter, the spacecraft took dramatic images of the giant planet’s “red spot.” It also made the first surveillance of Jupiter’s vast polar regions and determined the size of the Jovian moon, Callisto.
Pioneer 11’s closest approach to Saturn was on Sept. 1, 1979, passing within 13,000 miles of the ringed planet. While taking the first close-up photographs, the probe’s instruments located two previously undiscovered moons. Saturn’s magnetosphere and magnetic field also were charted. Data returned allowed scientists to measure the heat radiation from Saturn’s interior and determine that its planet-size moon, Titan, is too cold to support life at a frigid -289 degrees Fahrenheit.
Traveling beneath the plane of the rings, Pioneer 11 discovered a never before seen ring. It also sent back amazing images of Saturn’s rings that normally appear bright when observed from Earth, but indicated dark gaps.
Due to power constraints and the vast distance to the probe, the last routine contact with the spacecraft was on Sept. 30, 1995, and the last good engineering data was received on Nov. 24, that year.
Since then, the next spacecraft to arrive was in November 1980, Voyager 1 flew past the Saturn system transmitting the first high-resolution photographs of the planet, its rings and surface features of various moons. During August 1981, Voyager 2 flew past Saturn taking additional close-up pictures of the planet’s moons and discovering changes in the rings. Voyager 2 also studied Saturn’s atmosphere with radar measuring temperature and density. Following the fly-by, Saturn’s gravity helped direct the probe’s trajectory towards Uranus.
NASA’s Cassini-Huygens spacecraft became the first to orbit Saturn on July 1, 2004. A month earlier, the probe conducted a close flyby of Saturn’s moon, Phoebe, sending back high-resolution photographs and data. The orbiter released the Huygens probe on Dec. 25, 2004 descending to the surface of Titan landing on Jan. 14, 2005. It provided additional data about the atmosphere before landing. During March 2006, Cassini aided NASA scientists in discovering evidence of liquid water reservoirs on Saturn’s moon Enceladus that erupt in geysers.
“Centuries from now, people will read about how, in one short period of time, a little over 50 years,” said Stern, “we started from scratch eventually exploring across the solar system.”
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