Pioneer 11 is a 259-kilogram (569
lb-Codes:*.lb, the Internet country code top-level domain for Lebanon*Labrador's former postal abbreviation*Lloyd Aéreo Boliviano airline's IATA code*Luxembourgish language's ISO 639 alpha-2 code*Lebanon's ISO 3166-1 alpha-2 country code...
)
roboticA robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...
space probeA robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...
launched by
NASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
on April 6, 1973 to study the
asteroid beltThe asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...
, the environment around
JupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
and
SaturnSaturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
,
solar windThe solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
,
cosmic rayCosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
s, and eventually the far reaches of the solar system and
heliosphereThe heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself...
. It was the first probe to encounter
SaturnThe exploration of Saturn has been solely done by robotic probes. Like all gas giants, there is no solid surface for a solid probe to land on. Most missions therefore have been flybys, although the Cassini–Huygens spacecraft is currently in orbit....
and the second to fly through the asteroid belt and by
JupiterThe exploration of Jupiter has to date been conducted via close observations by automated spacecraft. It began with the arrival of Pioneer 10 into the Jovian system in 1973, and, , has continued with seven further spacecraft missions...
. Due to power constraints and the vast distance of the probe, communication has been lost since November 30, 1995.
History
Approved in February 1969,
Pioneer 11 and twin probe
Pioneer 10Pioneer 10 is a 258-kilogram robotic space probe that completed the first interplanetary mission to Jupiter, and became the first spacecraft to achieve escape velocity from the Solar System. The project was managed by the NASA Ames Research Center and the contract for the construction of the...
, 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:
- Explore the interplanetary medium beyond the orbit of Mars
- Investigate the nature of the asteroid belt from the scientific standpoint and assess the belt's possible hazard to missions to the outer planets.
- Explore the environment of Jupiter.
Subsequent planning for an encounter with Saturn added many more goals:
- Map the magnetic field of Saturn and determine its intensity, direction, and structure.
- Determine how many electrons and protons of various energies are distributed along the trajectory of the spacecraft through the Saturn system.
- Map the interaction of the Saturn system with the solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
.
- Measure the temperature of Saturn's atmosphere and that of Titan, the large satellite of Saturn.
- Determine the structure of the upper atmosphere of Saturn where molecules are expected to be electrically charged and form an ionosphere.
- Map the thermal structure of Saturn's atmosphere by infrared observations coupled with radio occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
data.
- Obtain shooting squirrels and spin-scan images of the Saturnian system in two colors during the encounter sequence and polarimetry spacecraft.
- As a precursor to the Mariner Jupiter/Saturn mission
The Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...
, verify the environment of the ring plane to find out where it may be safely crossed by the Mariner spacecraft without serious damage.
Pioneer 11 was built by
TRWTRW Inc. was an American corporation involved in a variety of businesses, mainly aerospace, automotive, and credit reporting. It was a pioneer in multiple fields including electronic components, integrated circuits, computers, software and systems engineering. TRW built many spacecraft,...
and managed as part of the
Pioneer programThe Pioneer program is a series of United States unmanned space missions that was designed for planetary exploration. There were a number of such missions in the program, but the most notable were Pioneer 10 and Pioneer 11, which explored the outer planets and left the solar system...
by
NASA Ames Research CenterThe Ames Research Center , is one of the United States of America's National Aeronautics and Space Administration 10 major field centers.The centre is located in Moffett Field in California's Silicon Valley, near the high-tech companies, entrepreneurial ventures, universities, and other...
. A backup unit,
Pioneer HPioneer H is an unlaunched unmanned space mission that was part of the US Pioneer program for a planned 1974 launch. Had this mission and spacecraft been launched, it would have been designated Pioneer 12; that designation was later applied to the Pioneer Venus Orbiter.The probe would have been...
, is currently on display in the "Milestones of Flight" exhibit at the
National Air and Space MuseumThe National Air and Space Museum of the Smithsonian Institution holds the largest collection of historic aircraft and spacecraft in the world. It was established in 1976. Located in Washington, D.C., United States, it is a center for research into the history and science of aviation and...
in
Washington, D.C.Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....
. Many elements of the mission proved to be critical in the planning of the
Voyager ProgramThe Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...
.
Pioneer plaque
Pioneer 10 and Pioneer 11 carry a gold-anodized aluminum
plaqueA commemorative plaque, or simply plaque, is a plate of metal, ceramic, stone, wood, or other material, typically attached to a wall, stone, or other vertical surface, and bearing text in memory of an important figure or event...
in the event that either spacecraft is ever found by intelligent life-forms 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.
Spacecraft design
The
Pioneer 11 bus measures 36 centimeters deep and with six 76-centimeters-long panels forming the hexagonal structure. The bus houses propellant to control the orientation of the probe and eight of the eleven scientific instruments. The spacecraft had a mass of 260 kilograms.
Attitude control and propulsion
- Orientation of the spacecraft was maintained with six 4.5-N, hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
monopropellantA monopropellant rocket is a rocket that uses a single chemical as its propellant.-Chemical-reaction monopropellant rockets:...
thrusters: pair one maintained a constant spin-rate of 4.8-rpm, pair two controlled the forward thrust, pair three controlled attitude. Information for the orientation was provided by a star sensor able to reference CanopusCanopus |Alpha]] Carinae) is the brightest star in the southern constellation of Carina and Argo Navis, and the second brightest star in the night-time sky, after Sirius. Canopus's visual magnitude is −0.72, and it has an absolute magnitude of −5.53.Canopus is a supergiant of spectral...
, and two sun sensors.
Communications
- The space probe included a redundant system of transceiver
A transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s...
s, one attached to the high-gain antennaA high-gain antenna is an antenna with a focused, narrow radiowave beam width. This narrow beam width allows more precise targeting of the radio signal - also known as a directional 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 NetworkThe Deep Space Network, or DSN, is a world-wide network of large antennas and communication facilities that supports interplanetary spacecraft missions. It also performs radio and radar astronomy observations for the exploration of the solar system and the universe, and supports selected...
tracking the signal. Prior to transmitting data, used a convolutional encoderIn telecommunication, a convolutional code is a type of error-correcting code in which* each m-bit information symbol to be encoded is transformed into an n-bit symbol, where m/n is the code rate and...
, a form of error correction, to avoid sending corrupted data.
Power
- Pioneer 11 used 4 SNAP-19 radioisotope thermoelectric generator
A radioisotope thermoelectric generator is an electrical generator that obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples.RTGs can be...
s (RTG) (see diagram). They were positioned on 2 three-rod trusses, each 3 meters (10 ft) 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 140w in transit to Jupiter. The spacecraft required 100w to power all systems.
Computer
- Much of the computation for the mission was performed on Earth and transmitted to the probe, where it was able to retain in memory, up to five commands of the 222 possible entries by ground controllers. The spacecraft included two command decoders and a command distribution unit, a very limited form of processor, to direct operations on the spacecraft. This system required that mission operators prepare commands long in advance of transmitting them to the probe. A data storage unit was included to record up to 6,144-bytes of information gathered by the instruments. The digital telemetry unit would then be used to prepare the collected data in one of the thirteen possible formats before transmitting it back to Earth.
Scientific instruments
| Helium Vector Magnetometer A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...
(HVM) |
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Measures the fine structure of the interplanetary magnetic field, maps the Jovian magnetic field, and provides magnetic field measurements to evaluate solar wind interaction with Jupiter.
- Principal investigator: Edward Smith / JPL
- Data: PDS/PPI data catalog, [ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/pioneer/pioneer11/mag/ NSSDC data archive]
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Quadrispherical PlasmaIn physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
Analyzer |
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Peers through a hole in the large dish-shaped antenna to detect particles of the solar wind originating from the Sun.
- Principal investigator: Aaron Barnes / NASA Ames Research Center (archived website)
- Data: PDS/PPI data catalog, [ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/pioneer/pioneer11/plasma/ NSSDC data archive]
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| Charged Particle In physics, a charged particle is a particle with an electric charge. It may be either a subatomic particle or an ion. A collection of charged particles, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its...
Instrument (CPI) |
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Detects cosmic rays in the Solar System.
- Principal investigator: John Simpson / University of Chicago
- Data: [ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/pioneer/pioneer11/particle/cpi/ NSSDC data archive]
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Cosmic RayCosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
Telescope (CRT) |
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Collects data on the composition of the cosmic ray particles and their energy ranges.
- Principal investigator: Frank McDonald / NASA Goddard Space Flight Center
- Data: PDS/PPI data catalog, [ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/pioneer/pioneer11/particle/crt/ NSSDC data archive]
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| Geiger Tube Telescope The Geiger Tube Telescope is a scientific instrument that measures the intensities, energy spectra, and angular distribution of energetic electrons and protons in interplanetary space and near Jupiter and Saturn....
(GTT) |
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Surveys the intensities, energy spectra, and angular distributions of electrons and protons along the spacecraft's path through the radiation belts of Jupiter.
- Principal investigator: James Van Allen / University of Iowa (website)
- Data: PDS/PPI data catalog, [ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/pioneer/pioneer11/particle/gtt/ NSSDC data archive], [ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/pioneer/pioneer11/geiger_tube_telescope_%28gtt%29/jupiter_encounter_data/ NSSDC Jupiter data archive]
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| Trapped Radiation In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
Detector (TRD) |
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Includes an unfocused Cerenkov counter that detects the light emitted in a particular direction as particles pass 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 measures minimum ionizing particles (<3 MeV) and protons in the range of 50 to 350 MeV.
- Principal investigator: R. Fillius / University of California San Diego
- Data: [ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/pioneer/pioneer11/particle/trd/ NSSDC hourly data archive], [ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/pioneer/pioneer11/jovian_trapped_radiation/saturn_enctr_binary_reduction_dat/ NSSDC Saturn data archive]
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MeteoroidA meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite...
Detectors |
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Twelve panels of pressurized cell detectors mounted on the back of the main dish antenna record penetrating impacts of small meteoroids.
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| Asteroid/Meteoroid Detector (AMD) |
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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.
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| Ultraviolet Photometer In its widest sense, a photometer is an instrument for measuring light intensity or optical properties of solutions or surfaces. Photometers are used to measure:*Illuminance*Irradiance*Light absorption*Scattering of light*Reflection of light*Fluorescence...
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Ultraviolet light is sensed to determine the quantities of hydrogen and helium in space and on Jupiter.
- Principal investigator: Darrell Judge / University of Southern California
- Data: PDS/PPI data catalog, [ftp://nssdcftp.gsfc.nasa.gov/spacecraft_data/pioneer/pioneer11/uv/ NSSDC data archive]
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| Imaging Photopolarimeter A polarimeter is a scientific instrument used to measure the angle of rotation caused by passing polarized light through an optically active substance....
(IPP) |
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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 were then processed to build up a visual image of the planet.
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Infrared RadiometerA radiometer is a device for measuring the radiant flux of electromagnetic radiation. Generally, the term radiometer denotes an infrared radiation detector, yet it also includes detectors operating on any electromagnetic wavelength....
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Provides information on cloud temperature and the output of heat from Jupiter.
- Principal investigator: Andrew Ingersoll / California Institute of Technology
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Mission profile
| Timeline of travel |
EWLINE
| Date |
Event |
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Spacecraft launched at 02:11:00. |
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Passage through the asteroid beltThe asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...
. |
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Start Jupiter observation phase.
| Time |
Event |
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Encounter with Jovian system. |
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CallistoCallisto named after the Greek mythological figure of Callisto) is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. Callisto has about 99% the diameter of the...
flyby at 786,500 km. |
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GanymedeGanymede is a satellite of Jupiter and the largest moon in the Solar System. It is the seventh moon and third Galilean satellite outward from Jupiter. Completing an orbit in roughly seven days, Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively...
flyby at 692,300 km. |
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IoIo ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....
flyby at 314,000 km. |
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EuropaEuropa Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This surface is striated by cracks and...
flyby at 586,700 km. |
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Jupiter shadow entry. |
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Jupiter occultationAn occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
entry. |
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JupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
closest approach at 42,828 km. |
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Jupiter shadow exit. |
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Jupiter occultation exit. |
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AmaltheaAmalthea is the third moon of Jupiter in order of distance from the planet. It was discovered on September 9, 1892, by Edward Emerson Barnard and named after Amalthea, a nymph in Greek mythology. It is also known as '....
flyby at 127,500 km. |
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Phase stop. |
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Start Saturn observation phase.
| Time |
Event |
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Encounter with Saturnian system. |
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IapetusIapetus ), occasionally Japetus , is the third-largest moon of Saturn, and eleventh in the Solar System. It was discovered by Giovanni Domenico Cassini in 1671...
flyby at 1,032,535 km. |
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PhoebePhoebe is an irregular satellite of Saturn. It was discovered by William Henry Pickering on 17 March 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Observatory near Arequipa, Peru, by DeLisle Stewart...
flyby at 13,713,574 km. |
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HyperionHyperion , also known as Saturn VII, is a moon of Saturn discovered by William Cranch Bond, George Phillips Bond and William Lassell in 1848. It is distinguished by its irregular shape, its chaotic rotation, and its unexplained sponge-like appearance...
flyby at 666,153 km. |
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Descending ring plane crossing. |
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EpimetheusEpimetheus is an inner satellite of Saturn. It is also known as Saturn XI. It is named after the mythological Epimetheus, brother of Prometheus.-Discovery:Epimetheus occupies essentially the same orbit as the moon Janus...
flyby at 6,676 km. |
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AtlasAtlas is an inner satellite of Saturn.Atlas was discovered by Richard Terrile in 1980 from Voyager photos and was designated '. In 1983 it was officially named after Atlas of Greek mythology, because it "holds the rings on its shoulders" like the Titan Atlas held the sky up above the Earth...
flyby at 45,960 km. |
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DioneDione is a moon of Saturn discovered by Cassini in 1684. It is named after the titan Dione of Greek mythology. It is also designated Saturn IV.- Name :...
flyby at 291,556 km. |
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MimasMimas is a moon of Saturn which was discovered in 1789 by William Herschel. It is named after Mimas, a son of Gaia in Greek mythology, and is also designated Saturn I....
flyby at 104,263 km. |
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Saturn Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
closest approach at 20,591 km. |
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Saturn occultationAn occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
entry. |
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Saturn shadow entry. |
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JanusJanus is an inner satellite of Saturn. It is also known as Saturn X . It is named after the mythological Janus.-Discovery and orbit:Janus occupies practically the same orbit as the moon Epimetheus...
flyby at 228,988 km. |
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Saturn occultation exit. |
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Saturn shadow exit. |
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Ascending ring plane crossing. |
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TethysTethys or Saturn III is a mid-sized moon of Saturn about across. It was discovered by G. D. Cassini in 1684 and is named after titan Tethys of Greek mythology. Tethys is pronounced |Odysseus]] is about 400 km in diameter, while the largest graben—Ithaca Chasma is about 100 km wide and...
flyby at 329,197 km. |
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Enceladus Enceladus is the sixth-largest of the moons of Saturn. It was discovered in 1789 by William Herschel. Until the two Voyager spacecraft passed near it in the early 1980s very little was known about this small moon besides the identification of water ice on its surface...
flyby at 222,027 km. |
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CalypsoCalypso is a moon of Saturn. It was discovered in 1980, from ground-based observations, by Dan Pascu, P. Kenneth Seidelmann, William A. Baum, and Douglas G. Currie, and was provisionally designated ' . Several other apparitions of it were recorded in the following months: , , , and...
flyby at 109,916 km. |
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RheaRhea is the second-largest moon of Saturn and the ninth largest moon in the Solar System. It was discovered in 1672 by Giovanni Domenico Cassini.-Name:Rhea is named after the Titan Rhea of Greek mythology, "mother of the gods"...
flyby at 345,303 km. |
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TitanTitan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
flyby at 362,962 km. |
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Phase stop. |
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Begin Pioneer Interstellar Mission. |
| More |
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Instrument power sharing began due to declining generator power output. |
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Passed the orbit of PlutoPluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
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Routine daily mission operations stopped. Pioneer 11 is 6.5 billion km from Earth. |
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Last signal received. |
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Launch and trajectory
The
Pioneer 11 probe was launched on April 6, 1973 at 02:11:00 UTC, by the National Aeronautics and Space Administration from Space Launch Complex 36A at
Cape CanaveralCape Canaveral Air Force Station is an installation of the United States Air Force Space Command's 45th Space Wing, headquartered at nearby Patrick Air Force Base. Located on Cape Canaveral in the state of Florida, CCAFS is the primary launch head of America's Eastern Range with four launch pads...
, Florida aboard an
Atlas/CentaurThe Atlas-Centaur was an American expendable launch system designed and built by General Dynamics Convair Division in San Diego, CA. It was derived from the SM-65 Atlas missile. It was a member of the Atlas family of rockets, and was used for 61 orbital launches between 1962 and 1983. It was...
launch vehicle. Twin probe,
Pioneer 10Pioneer 10 is a 258-kilogram robotic space probe that completed the first interplanetary mission to Jupiter, and became the first spacecraft to achieve escape velocity from the Solar System. The project was managed by the NASA Ames Research Center and the contract for the construction of the...
, had previously launched a year before on March 3, 1972.
Encounter with Jupiter
In November and December 1974, During its closest approach, December 2, 1974,
Pioneer 11 reached closest approach to Jupiter, passing 42828 kilometres (26,612.2 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
CallistoCallisto named after the Greek mythological figure of Callisto) is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. Callisto has about 99% the diameter of the...
. Utilizing the gravitational pull of Jupiter, a gravity assist was used to alter the trajectory of the probe, towards Saturn.
Saturn encounter
Pioneer 11 passed by Saturn on September 1, 1979, at a distance of 21,000 km from Saturn's cloud tops.
By this time
Voyager 1The Voyager 1 spacecraft is a 722-kilogram space probe launched by NASA in 1977, to study the outer Solar System and eventually interstellar space. Operating for as of today , the spacecraft receives routine commands and transmits data back to the Deep Space Network. At a distance of as of...
and
Voyager 2The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...
had already passed Jupiter and were also en route to Saturn, so it was decided to target Pioneer 11 to pass through the Saturn ring plane at the same position that the soon-to-come Voyager probe would use in order to test the route before Voyager arrived. If there were faint ring particles that could damage a probe in that area, mission planners felt it was better to learn about it via Pioneer. Thus, Pioneer 11 was acting as a "pioneer" in a true sense of the word; if danger was detected, then the Voyager probes could be rerouted further away from the rings, but missing the opportunity to visit Uranus and Neptune in the process.
Pioneer 11 imaged and nearly collided with one of Saturn's small moons, passing at a distance of no more than 4000 kilometres (2,485.5 mi). The object was tentatively identified as
EpimetheusEpimetheus is an inner satellite of Saturn. It is also known as Saturn XI. It is named after the mythological Epimetheus, brother of Prometheus.-Discovery:Epimetheus occupies essentially the same orbit as the moon Janus...
, a moon discovered the previous day from Pioneer's imaging, and suspected from earlier observations by Earth-based telescopes. After the
VoyagerThe Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...
flybys, it became known that there are two similarly-sized moons (Epimetheus and
JanusJanus is an inner satellite of Saturn. It is also known as Saturn X . It is named after the mythological Janus.-Discovery and orbit:Janus occupies practically the same orbit as the moon Epimetheus...
) 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 2500 km and
MimasMimas is a moon of Saturn which was discovered in 1789 by William Herschel. It is named after Mimas, a son of Gaia in Greek mythology, and is also designated Saturn I....
at 16:20 UTC the same day at 103000 km.
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,
TitanTitan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
, to be too cold for life. Hurtling underneath the ring plane, Pioneer 11 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 anomaly
Analysis of the radio tracking data from the Pioneer 10 and 11 spacecraft at distances between 20–70 AU from the Sun has consistently indicated the presence of an anomalous, small
DopplerThe Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
frequency drift. The drift can be interpreted as being due to a constant acceleration of (8.74 ± 1.33) × 10
−10 m/s² directed towards the Sun. Although it is suspected that there is a systematic origin to the effect, none has been found. As a result, the nature of this anomaly has become of growing interest.
Current status
As of April 1, 2011, Pioneer 11 is about 82.972 AU from the Sun. It is at an elliptic latitude of 14.3 degrees, at a declination of -8.73 degrees. It is traveling at about 11.413 km/s and is traveling outward at about 2.408
AU-Science:*Absorbance Units, a reporting unit in spectroscopy*Astronomical unit, the average distance between the Earth and the Sun *Atomic units, a system of units convenient for atomic physics and other fields...
per year.
Pioneer 11 is at a right ascension of 18.759 hours, and at an ecliptic latitude of 3.0 degrees. Sunlight takes 11.54 hours to get to Pioneer 11 at its approximate distance. Pioneer 11 is traveling in roughly the opposite direction from
Pioneer 10Pioneer 10 is a 258-kilogram robotic space probe that completed the first interplanetary mission to Jupiter, and became the first spacecraft to achieve escape velocity from the Solar System. The project was managed by the NASA Ames Research Center and the contract for the construction of the...
. Pioneer 11 is heading in the direction of the constellation Scutum. Whereas Pioneer 10 is moving away from the center of the galaxy, Pioneer 11 is moving towards it.
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 NetworkThe Deep Space Network, or DSN, is a world-wide network of large antennas and communication facilities that supports interplanetary spacecraft missions. It also performs radio and radar astronomy observations for the exploration of the solar system and the universe, and supports selected...
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 GoldinDaniel Saul Goldin served as the 9th and longest-tenured Administrator of NASA from April 1, 1992, to November 17, 2001. He was appointed by President George H. W. Bush and also served under President William Jefferson Clinton and George W...
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."
Besides announcing the end of operations, the dispatch provides an historical list of Pioneer 11 mission achievements. It also provided status of the preceding probe, "
Pioneer 10Pioneer 10 is a 258-kilogram robotic space probe that completed the first interplanetary mission to Jupiter, and became the first spacecraft to achieve escape velocity from the Solar System. The project was managed by the NASA Ames Research Center and the contract for the construction of the...
continues to return scientific data and may have enough power to last until 1999. At almost six billion miles, Pioneer 10 is the most distant object built by humans."
Pioneer 10 has now been overtaken by the two Voyager probes, launched in 1977, and
Voyager 1The Voyager 1 spacecraft is a 722-kilogram space probe launched by NASA in 1977, to study the outer Solar System and eventually interstellar space. Operating for as of today , the spacecraft receives routine commands and transmits data back to the Deep Space Network. At a distance of as of...
is currently (2011) the most distant object built by humans.
See also
- Unmanned space missions
- Pioneer 10
Pioneer 10 is a 258-kilogram robotic space probe that completed the first interplanetary mission to Jupiter, and became the first spacecraft to achieve escape velocity from the Solar System. The project was managed by the NASA Ames Research Center and the contract for the construction of the...
- Voyager program
The Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...
- Cassini–Huygens
- S band
The S band is defined by an IEEE standard for radio waves with frequencies that range from 2 to 4 GHz, crossing the conventional boundary between UHF and SHF at 3.0 GHz. It is part of the microwave band of the electromagnetic spectrum...
External links