Approved in February 1969, Pioneer 11 and its twin probe, Pioneer 10, were the first to be designed for exploring the outer Solar System. Yielding to multiple proposals throughout the 1960s, early mission objectives were defined as:
Obtain spin-scan images of the Saturnian system in two colors during the encounter sequence and polarimetry measurements of the planet.
Probe the ring system and the atmosphere of Saturn with S-band radio occultation.
Determine more precisely the masses of Saturn and its larger satellites by accurate observations of the effects of their gravitational fields on the motion of the spacecraft.
As a precursor to the Mariner Jupiter/Saturn mission, verify the environment of the ring plane to find out where it may be safely crossed by the Mariner spacecraft without serious damage.[2]
Pioneer 11 during the installation of its protective shroud
Spacecraft design
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The Pioneer 11 bus measures 36 centimeters (14 in) deep and with six 76-centimeter-long (30 in) panels forming the hexagonal structure. The bus houses propellant to control the orientation of the probe and eight of the twelve scientific instruments. The spacecraft has a mass of 259 kilograms.[6]
Attitude control and propulsion
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Orientation of the spacecraft was maintained with six 4.5-N,[7]hydrazinemonopropellant thrusters: pair one maintains a constant spin-rate of 4.8 rpm, pair two controls the forward thrust, pair three controls attitude. Information for the orientation is provided by performing conical scanning maneuvers to track Earth in its orbit,[8] a star sensor able to reference Canopus, and two Sun sensors.[9]
Communications
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The space probe includes a redundant system transceivers, one attached to the high-gain antenna, the other to an omni-antenna and medium-gain antenna. Each transceiver is 8 watts and transmits data across the S-band using 2110 MHz for the uplink from Earth and 2292 MHz for the downlink to Earth with the Deep Space Network tracking the signal. Prior to transmitting data, the probe uses a convolutional encoder to allow correction of errors in the received data on Earth.[10]
Power
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Pioneer 11 uses four SNAP-19 radioisotope thermoelectric generators (RTGs) (see diagram). They are positioned on two three-rod trusses, each 3 meters (9 feet 10 inches) in length and 120 degrees apart. This was expected to be a safe distance from the sensitive scientific experiments carried on board. Combined, the RTGs provided 155 watts at launch, and decayed to 140 W in transit to Jupiter. The spacecraft requires 100 W to power all systems.[11]
Computer
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Much of the computation for the mission was performed on Earth and transmitted to the probe, where it is able to retain in memory, up to five commands of the 222 possible entries by ground controllers. The spacecraft includes two command decoders and a command distribution unit, a very limited form of a processor, to direct operations on the spacecraft. This system requires that mission operators prepare commands long in advance of transmitting them to the probe. A data storage unit is included to record up to 6,144 bytes of information gathered by the instruments. The digital telemetry unit is then used to prepare the collected data in one of the thirteen possible formats before transmitting it back to Earth.[12]
Scientific instruments
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Pioneer 11 has one additional instrument more than Pioneer 10, a flux-gate magnetometer.[13]
Measures the fine structure of the interplanetary magnetic field, mapped the Jovian magnetic field, and provides magnetic field measurements to evaluate solar wind interaction with Jupiter.[14]
Surveys the intensities, energy spectra, and angular distributions of electrons and protons along the spacecraft's path through the radiation belts of Jupiter and Saturn.[19]
Includes an unfocused Cerenkov counter that detects the light emitted in a particular direction as particles passed through it recording electrons of energy, 0.5 to 12 MeV, an electron scatter detector for electrons of energy, 100 to 400 keV, and a minimum ionizing detector consisting of a solid-state diode that measured minimum ionizing particles (<3 MeV) and protons in the range of 50 to 350 MeV.[20]
Principal investigator: R. Fillius / University of California San Diego[16]
Twelve panels of pressurized cell detectors mounted on the back of the main dish antenna record penetrating impacts of small meteoroids.[21]
Principal investigator: William Kinard / NASA Langley Research Center[16]
Data: NSSDC data archive list
Asteroid/Meteoroid Detector (AMD)
Meteoroid-asteroid detector looks into space with four non-imaging telescopes to track particles ranging from close by bits of dust to distant large asteroids.[22]
Principal investigator: Robert Soberman / General Electric Company[16]
The imaging experiment relies upon the spin of the spacecraft to sweep a small telescope across the planet in narrow strips only 0.03 degrees wide, looking at the planet in red and blue light. These strips are then processed to build up a visual image of the planet.[24]
Principal investigator:Tom Gehrels / University of Arizona[16]
Pioneer 11 was launched on a trajectory directly aimed at Jupiter without any prior gravitational assists.[27] In May 1974, Pioneer was retargeted to fly past Jupiter on a north–south trajectory, enabling a Saturn flyby in 1979. The maneuver used 17 pounds (7.7 kilograms) of propellant, lasted 42 minutes and 36 seconds, and increased Pioneer 11's speed by 230 km/h.[28] It also made two mid-course corrections, on April 11, 1973 and November 7, 1974.[1]
NASA map showing trajectories of the Pioneer 10, Pioneer 11, Voyager 1, and Voyager 2 spacecraft.
Animation of Pioneer 11's trajectory from April 6, 1973 to December 31, 1980 Pioneer 11·Earth·Jupiter·Saturn
Animation of Pioneer 11's trajectory around Jupiter from November 30, 1974 to December 5, 1974 Pioneer 11·Jupiter·Io·Europa·Ganymede·Callisto
Animation of Pioneer 11 around Saturn Pioneer 11· Saturn· Epimetheus· Janus· Mimas· Enceladus
Encounter with Jupiter
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Pioneer 11 flew past Jupiter in November and December 1974. During its closest approach, on December 2, it passed 42,828 kilometers (26,612 mi) above the cloud tops. The probe obtained detailed images of the Great Red Spot, transmitted the first images of the immense polar regions, and determined the mass of Jupiter's moon Callisto. Using the gravitational pull of Jupiter, a gravity assist was used to alter the trajectory of the probe towards Saturn and gain velocity. On April 16, 1975, following the Jupiter encounter, the micrometeoroid detector was turned off.[1]
Media related to Pioneer 11 Jupiter encounter at Wikimedia Commons
Encounter with Saturn
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Pioneer 11 passed by Saturn on September 1, 1979, at a distance of 21,000 km (13,000 mi) from Saturn's cloud tops.[29]
By this time, Voyager 1 and Voyager 2 had already passed Jupiter and were en route to Saturn, so it was decided Pioneer 11 would pass through the Saturn ring plane at the same position Voyager 2 would later have to fly through in order to reach Uranus and Neptune. If there were faint ring particles capable of damaging a probe in that area, mission planners felt it was better to learn about it via Pioneer.[29] Thus, Pioneer 11 was acting as a "pioneer" in a true sense of the word; if danger were detected, then Voyager 2 could be redirected further away from the rings but miss the opportunity to visit the ice giants in the process.
Pioneer 11 imaged—and nearly collided with—one of Saturn's small moons, passing at a distance of no more than 4,000 kilometers (2,500 mi). The object was tentatively identified as Epimetheus, a moon discovered the previous day from Pioneer's imaging, and suspected from earlier observations by Earth-based telescopes. After the Voyager flybys, it became known that there are two similarly sized moons (Epimetheus and Janus) in the same orbit, so there is some uncertainty about which one was the object of Pioneer's near-miss. Pioneer 11 encountered Janus on September 1, 1979, at 14:52 UTC, at a distance of 2,500 km (1,600 mi). At 16:20 UTC the same day, Pioneer 11 encountered Mimas at a distance of 103,000 km (64,000 mi).
Besides Epimetheus, instruments located another previously undiscovered small moon and an additional ring, charted Saturn's magnetosphere and magnetic field, and found its planet-size moon, Titan, to be too cold for life. Hurtling underneath the ring plane, the probe sent back pictures of Saturn's rings. The rings, which normally seem bright when observed from Earth, appeared dark in the Pioneer pictures, and the dark gaps in the rings seen from Earth appeared as bright rings.
Pioneer 11 image of Saturn taken on 1979/08/26
Pioneer 11 image of Saturn taken on 1979/09/01
Pioneer 11 image of Saturn taken on 1979/09/01
Outgoing Pioneer 11 image of Saturn taken on 1979/09/03
Pioneer 11 image of Saturn's moon Titan
Media related to Pioneer 11 Saturn encounter at Wikimedia Commons
Interstellar mission
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On February 25, 1990, Pioneer 11 became the fourth human-made object to pass beyond the orbit of the planets.[30]
By 1995, Pioneer 11 could no longer power any of its detectors, so the decision was made to shut it down.[31] On September 29, 1995, NASA's Ames Research Center, responsible for managing the project, issued a press release that began, "After nearly 22 years of exploration out to the farthest reaches of the Solar System, one of the most durable and productive space missions in history will come to a close." It indicated NASA would use its Deep Space Network antennas to listen "once or twice a month" for the spacecraft's signal, until "some time in late 1996" when "its transmitter will fall silent altogether." NASA Administrator Daniel Goldin characterized Pioneer 11 as "the little spacecraft that could, a venerable explorer that has taught us a great deal about the Solar System and, in the end, about our own innate drive to learn. Pioneer 11 is what NASA is all about – exploration beyond the frontier."[32] Besides announcing the end of operations, the dispatch provided a historical list of Pioneer 11 mission achievements.
NASA terminated routine contact with the spacecraft on September 30, 1995, but continued to make contact for about two hours every two to four weeks.[31] Scientists received a few minutes of good engineering data on November 24, 1995, but then lost final contact once Earth moved out of view of the spacecraft's antenna.[1][33]
Due to power constraints and the vast distance to the probe, the last routine contact with the spacecraft was on September 30, 1995, and the last good engineering data was received on November 24, 1995.[3][1]
As of June 24, 2024, Pioneer 11 is estimated to be 113.121 AU (16.9227 billion km; 10.5153 billion mi) from the Earth and 114.089 AU (17.0675 billion km; 10.6052 billion mi) from the Sun. It was traveling at 11.155 km/s (40,160 km/h; 24,950 mph) relative to the Sun and traveling outward at about 2.35 AU per year.[36][37] The spacecraft is heading in the direction of the constellation Scutum near the current position (June 2024) RA 18h 54m dec -8° 46' (J2000.0), close to Messier 26. In 928,000 years, it will pass within 0.25 parsecs (0.82 light-years) of the K dwarf TYC 992-192-1[38] and will pass near the star Lambda Aquilae in about four million years.[39]
Pioneer 11 has been overtaken by the two Voyager probes launched in 1977. Voyager 1 has become the most distant object built by humans and will remain so for the foreseeable future, as no probe launched since Voyager has the speed to overtake it.[40]
Pioneer anomaly
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Analysis of the radio tracking data from the Pioneer 10 and 11 spacecraft at distances between 20 and 70 AU from the Sun had consistently indicated the presence of a small but anomalous Doppler frequency drift. The drift can be interpreted as due to a constant acceleration of (8.74 ± 1.33) × 10−10 m/s2 directed towards the Sun. Although it was suspected that there was a systematic origin to the effect, none was found. As a result, there has been sustained interest in the nature of this so-called "Pioneer anomaly".[41] Extended analysis of mission data by Slava Turyshev and colleagues determined the source of the anomaly to be asymmetric thermal radiation and the resulting thermal recoil force acting on the face of the Pioneers away from the Sun.[42][43]
Pioneer plaque
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Pioneer 10 and 11 both carry a gold-anodized aluminum plaque in the event that either spacecraft is ever found by intelligent lifeforms from other planetary systems. The plaques feature the nude figures of a human male and female along with several symbols that are designed to provide information about the origin of the spacecraft.[44]
Commemoration
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In 1991, Pioneer 11 was honored on one of 10 United States Postage Service stamps commemorating uncrewed spacecraft exploring each of the then nine planets and the Moon. Pioneer 11 was the spacecraft featured with Jupiter. Pluto was listed as "Not yet explored".[45]
Gallery
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Pioneer 11 and Saturn rings on September 1, 1979 (artist concept)
^D. Savage; Ann Hutchison (September 28, 1995). "Pioneer 11 to End Operations after Epic Career" (TXT). nssdc.gsfc.nasa.gov. NASA / Ames. Retrieved August 7, 2011.
^Elizabeth Howell (September 26, 2012). "Pioneer 11: Up Close with Jupiter & Saturn". Space.com. Retrieved December 10, 2017.
^Daniel Muller. "Pioneer 11 Full Mission Timeline". Spaceflight Realtime Simulations and Information. Archived from the original on March 4, 2016. Retrieved January 9, 2011.
^"Spacecraft escaping the Solar System". Heavens Above. Retrieved August 24, 2022.
^"Pioneer 11 - Live Position". www.theskylive.com. Retrieved July 19, 2015.
^C. A. L. Bailer-Jones; D. Farnocchia (April 3, 2019). "Future Stellar Flybys of the Voyager and Pioneer spacecraft". Research Notes of the AAS. 3 (4): 59. arXiv:1912.03503. Bibcode:2019RNAAS...3...59B. doi:10.3847/2515-5172/ab158e. S2CID 134524048.
^"Hardware, Leaving the Solar System: Where are they now?". DK Eyewitness - Encyclopedia of Space and the Universe. 2001. ISBN 978-0-789-40881-5.
^"Voyager - Mission Status". voyager.jpl.nasa.gov. NASA / JPL. Retrieved December 15, 2021.
^Robert Roy Britt (October 18, 2004). "The Problem with Gravity: New Mission Would Probe Strange Puzzle". Space.com. Retrieved June 7, 2011.
^"Pioneer Anomaly Solved!". The Planetary Society. Archived from the original on April 22, 2012. Retrieved April 20, 2012.
^S. G. Turyshev; V. T. Toth; G. Kinsella; et al. (June 12, 2012). "Support for the Thermal Origin of the Pioneer Anomaly". Physical Review Letters. 108 (24): 241101. arXiv:1204.2507. Bibcode:2012PhRvL.108x1101T. doi:10.1103/PhysRevLett.108.241101. PMID 23004253.
^C. Sagan; L. S. Sagan; F. Drake (February 25, 1972). "A Message from Earth". Science. 175 (4024): 881–884. Bibcode:1972Sci...175..881S. doi:10.1126/science.175.4024.881. PMID 17781060.
^Syd Kronish (October 27, 1991). "Space Launches are Featured". The Index Journal. South Carolina, USA. p. 21. Retrieved December 5, 2017 – via Newspapers.com.
Bibliography
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Burrows, W. E. (1990). Exploring Space: Voyages in the Solar System and Beyond (first ed.). New York: Random House. ISBN 978-0-394-56983-3.
Fimmel, R. O.; Swindell, W.; Burgess, E. (1974). Pioneer Odyssey: Encounter with a Giant. Washington, D.C.: NASA / Ames. ISBN 978-1-493-71200-7. OCLC 3211441. NASA-SP-349/396.
Fimmel, R. O.; van Allen, J. A.; Burgess, E. (1980). "Pioneer: First to Jupiter, Saturn, and Beyond" (PDF). NASA Special Publication. 446. Washington, D.C.: NASA / Ames. ASIN B000IRXYN0. Bibcode:1980NASSP.446.....F. NASA-SP-446.
Simpson, J. A. (2001). "The Cosmic Radiation". In Johan A. M. Bleeker; Johannes Geiss; Martin C. E. Huber (eds.). The Century of Space Science. Vol. 1. Springer. p. 146. ISBN 978-0-7923-7196-0.
External links
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Wikimedia Commons has media related to Pioneer 11.
Pioneer 11 Profile by NASA's Solar System Exploration