The Pioneer program marked the first attempt by the United States to explore the solar system and to reach the Moon. Although the Pioneer probes did not reach the Moon, the probes did provide critical information on the radiation belts around Earth and gathered other significant astronomical data. Later missions in the series successfully orbited the Sun.
The name “Pioneer” has been applied to four distinct groups of lunar and interplanetary spacecraft. Although all thirteen Pioneer spacecraft were numbered consecutively, the series differed greatly in design and mission. The two groups launched before 1970 consisted of five lunar missions—launched between 1958 and 1960—and four interplanetary missions—launched between 1965 and 1969. Several additional missions failed during launch.
In the wake of the early successes in space exploration by the Soviet Union, the United States struggled to catch up. The initial response to the success of the Soviet space program was somewhat chaotic, with separate branches of the U.S. military independently planning its own space missions. “Pioneer” actually stemmed from this interservice rivalry among the Air Force
Because the Soviet Union had not launched a mission to the Moon by early 1958, U.S. secretary of defense Neil H. McElroy endorsed lunar missions as a way of reasserting U.S. technological leadership. The first U.S. attempt to reach the Moon was launched by the USAF on August 17, 1958, less than a year after the Soviet Union’s launching of the first artificial satellite. If successful, the mission would surpass any achievement by the Soviet Union and supply a valuable boost to American morale. Unfortunately, the rocket exploded only 77 seconds after launch. This mission had no official designation but was later called Pioneer 0.
Engineers assemble the Pioneer spacecraft at TRW in Southern California.
A newly created defense department agency, the Advanced Research Projects Agency
The next USAF launch, officially designated Pioneer 1, came on October 11. A malfunction during the separation of the third stage of the rocket kept the spacecraft from acquiring enough velocity to reach the Moon. It reached an altitude of 115,000 kilometers (71,700 miles) before falling back to Earth. Nevertheless, Pioneer 1 traveled farther from Earth than any previous human-made object.
Pioneer 2 was launched on November 8. Because the third stage failed to ignite, the spacecraft reached an altitude of only 1,550 kilometers (963 miles), and the flight produced no significant data. Pioneer 3, launched on December 6, was planned as a mission to photograph the Moon at close range, but it, too, failed when its third stage ceased firing prematurely. Pioneer 3 reached an altitude of 107,500 kilometers (63,580 miles) and provided additional data on what came to be called the Van Allen radiation belts, which are belts of energetic subatomic particles from the Sun that are trapped by Earth’s magnetic field.
The Soviet probe Luna 1 successfully flew beyond the Moon on January 2, 1959, and thus deprived the U.S. space program of yet another chance to take the lead. Since the photographic mission of Pioneer 3 had failed, space physicist James Van Allen successfully advocated that the next mission be redesigned to measure radiation in space. Pioneer 4, launched on March 3, passed 59,000 kilometers (37,300 miles) from the Moon and was tracked to a distance of 400,000 miles (650,000 kilometers). On September 2, the Soviet probe Luna 2 became the first human artifact to reach the Moon. The United States had lost the race to the Moon, at least for the moment.
Pioneer 5, the final probe in the first Pioneer group, was in some ways a bridge to the second series: It was not intended as a lunar probe but was specifically intended for heliocentric orbit. Pioneer 5 originally was conceived as a mission to fly past Venus but was not ready in time for the launch window. It finally was launched on March 11, 1960, and was successfully tracked to a then-record distance of 44 million kilometers (27.5 million miles).
In 1963, the NASA Ames Research Center in Sunnyvale, California, was awarded a block of four Pioneer missions and a budget of $40 million to build them. Founding director Smith J. DeFrance and his successor H. Julian Allen oversaw the programs. The second series of Pioneers were small spin-stabilized spacecraft specifically designed to orbit the Sun and retrieve data on interplanetary conditions. Although using spin to stabilize a spacecraft sounds simple, it is a surprisingly complex task. Nonspherical bodies rotate in very complex ways. A number of early missions had already failed when the spacecraft began rotating around a different axis than the one planned, or rotated in the wrong direction. Design of the later Pioneer spacecraft required extremely careful balancing of instruments to guarantee stable spin, plus corrections after spin-testing. In addition, the spacecraft were intended to measure magnetic fields in space, and therefore the materials used and the electrical circuitry had to be carefully chosen to minimize magnetic fields due to the spacecraft itself. In cases where onboard magnetism was absolutely unavoidable, small magnets were placed on the spacecraft to cancel out magnetic fields. By later communications standards, the Pioneers were unbelievably primitive. Depending on distance from Earth, data from the Pioneers was transmitted at rates ranging from a low of 8 bits (one byte) per second to a high of 512 bits (64 bytes) per second.
Pioneer 6 was launched on December 16, 1965, on an orbit that carried it between Earth and Venus. Pioneer 7 (launched on August 17, 1966) and Pioneer 8 (December 13, 1967) orbit between Earth and Mars, and Pioneer 9 (November 8, 1968) orbits between Earth and Venus. A final spacecraft, provisionally named Pioneer E, failed on launch on August 7, 1969.
Although the early Pioneer spacecraft failed to gain the lead in space exploration for the United States, and were of small size and simple design, they nevertheless contributed significantly to knowledge of the environment of deep space. In the late 1950’s and early 1960’s, human ignorance about conditions in space was almost total. Little was known about how electronics would function in space, about radiation in space, and about meteor impact hazards in space. By exploring Earth’s radiation belts and by providing data on the solar wind (charged particles streaming outward from the Sun), the Pioneer probes showed that the radiation environment in space not only was more hazardous than ever suspected but also far more complex.
Until the early 1970’s, the Pioneer probes made up the primary system for detecting solar disturbances and for providing early warning to Earth. During the Apollo program, the probes transmitted information hourly to warn scientists of dangerous solar eruptions. Furthermore, the probes also showed that the danger from impacts by small meteors had been vastly overestimated, and that meteors did not pose a significant hazard to spacecraft.
Many early U.S. missions in space failed because, in many cases, the missions were overly ambitious and planners were overly confident. Attempting to reach the Moon only eight months after the launching of the first U.S. satellite proved to be a far too ambitious goal. Gradually, mission planners learned that spacecraft had to be rigorously and thoroughly tested and that redundant components were necessary to guard against failure. As these lessons and facts were absorbed, the success rate climbed steeply. The durability of the later Pioneer probes testifies to the value of simple design, realistic goals, and thorough testing.
The interplanetary Pioneer probes have proven to be the most long-lived of any existing spacecraft. Although routine contact has not been maintained because of the demands of later and more advanced missions, NASA made brief contact with Pioneer 6 on December 8, 2000, to mark the thirty-fifth anniversary of its launch.
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Bugos, Glenn E. Atmosphere of Freedom: Sixty Years at the NASA Ames Research Center. NASA SP-4314. Washington, D.C.: Scientific and Technical Information Branch, 2000. Describes the role of the Ames Research Center in many early missions, including Pioneer. -
Hall, R. Cargill. Lunar Impact: A History of Project Ranger. NASA SP-4210. Washington, D.C.: Scientific and Technical Information Branch, 1977. Although a chronology of the Ranger program, this work discusses historical predecessors, including the early Pioneer series. Available at http://history.nasa .gov/SP-4210/pages/TOC.htm. -
National Space Sciences Data Center (NSSDC) Master Catalog. Spacecraft Query Form. NASA Goddard Space Flight Center, 2006. Entry to a database on satellites and space probes. Can be searched by name, date, or keyword and includes both U.S. and foreign missions. Available at http://nssdc.gsfc.nasa.gov/database/sc-query.html. -
Nicks, Oran. The Far Travelers: The Exploring Machines. NASA SP-480. Washington, D.C.: Scientific and Technical Information Branch, 1985. A popular account of the first twenty-five years of space exploration by a former director of NASA’s lunar and planetary programs, and who was closely involved in the execution of the final Pioneer missions. The chapter “Spinners Last Forever” celebrates the phenomenal longevity of Pioneers 6 through 9. -
Wolverton, Mark. The Depths of Space: The Story of the Pioneer Planetary Probes. Washington, D.C.: Joseph Henry Press, 2004. An excellent study of the Pioneer program and its space probes. Includes illustrations.
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