Mission type | Planetary and heliosphere exploration |
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Operator | NASA / ARC |
COSPAR ID | 1973-019A |
SATCAT no. | 6421 |
Website | Pioneer Project website (archived) NASA Archive page |
Mission duration | 22 years, 7 months and 19 days |
Spacecraft properties | |
Manufacturer | TRW |
Launch mass | 258.5 kg [1] |
Power | 155 watts (at launch) |
Start of mission | |
Launch date | April 6, 1973, 02:11:00 UTC [1] |
Rocket | Atlas SLV-3D Centaur-D1A Star-37E |
Launch site | Cape Canaveral LC-36B |
End of mission | |
Last contact | November 24, 1995 |
Flyby of Jupiter | |
Closest approach | December 3, 1974 |
Distance | 43,000 kilometers (27,000 miles) |
Flyby of Saturn | |
Closest approach | September 1,1979 |
Distance | 21,000 kilometers (13,000 miles) |
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Pioneer 11 (also known as Pioneer G) is a NASA robotic space probe launched on April 5,1973,to study the asteroid belt,the environment around Jupiter and Saturn,the solar wind,and cosmic rays. [2] It was the first probe to encounter Saturn,the second to fly through the asteroid belt,and the second to fly by Jupiter. Later,Pioneer 11 became the second of five artificial objects to achieve an escape velocity allowing it to leave the Solar System. 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] [4]
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:
Subsequent planning for an encounter with Saturn added many more goals:
Pioneer 11 was built by TRW and managed as part of the Pioneer program by NASA Ames Research Center. [6] A backup unit,Pioneer H,is currently on display in the "Milestones of Flight" exhibit at the National Air and Space Museum in Washington,D.C. [7] Many elements of the mission proved to be critical in the planning of the Voyager program. [8] : 266–8
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. [2] : 42
Pioneer 11 has one additional instrument more than Pioneer 10,a flux-gate magnetometer. [11]
Helium Vector Magnetometer (HVM) | |
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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. [12]
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Quadrispherical Plasma Analyzer | |
Peer through a hole in the large dish-shaped antenna to detect particles of the solar wind originating from the Sun. [13]
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Charged Particle Instrument (CPI) | |
Detects cosmic rays in the Solar System. [15]
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Cosmic Ray Telescope (CRT) | |
Collects data on the composition of the cosmic ray particles and their energy ranges. [16]
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Geiger Tube Telescope (GTT) | |
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. [17]
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Trapped Radiation Detector (TRD) | |
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. [18]
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Meteoroid Detectors | |
Twelve panels of pressurized cell detectors mounted on the back of the main dish antenna record penetrating impacts of small meteoroids. [19]
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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. [20]
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Ultraviolet Photometer | |
Ultraviolet light is sensed to determine the quantities of hydrogen and helium in space and on Jupiter and Saturn. [21]
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Imaging Photopolarimeter (IPP) | |
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. [22]
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Infrared Radiometer | |
Provides information on cloud temperature and the output of heat from Jupiter and Saturn. [23]
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Triaxial Fluxgate Magnetometer | |
Measures the magnetic fields of both Jupiter and Saturn. This instrument is not carried on Pioneer 10. [24]
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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 Canaveral,Florida aboard an Atlas-Centaur launch vehicle,with a Star-37E propulsion module. Its twin probe, Pioneer 10 ,had been launched on March 3,1972.
Pioneer 11 was launched on a trajectory directly aimed at Jupiter without any prior gravitational assists. [25] 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. [26] It also made two mid-course corrections,on April 11,1973 and November 7,1974. [4] [27]
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. [28] 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. [4]
Pioneer 11 passed by Saturn on September 1, 1979, at a distance of 21,000 km (13,000 mi) from Saturn's cloud tops.
By this time, Voyager 1 and Voyager 2 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 probes would use to test the route before the Voyagers 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 were 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 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.
On February 25, 1990, Pioneer 11 became the fourth human-made object to pass beyond the orbit of the planets. [29]
By 1995, Pioneer 11 could no longer power any of its detectors, so the decision was made to shut it down. [30] 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." [31] 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. [30] 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. [4] [32]
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As of January 20, 2023, Pioneer 11 is estimated to be 111.678 AU (16.7068 billion km; 10.3811 billion mi) from the Earth and 110.764 AU (16.5701 billion km; 10.2962 billion mi) from the Sun. It was traveling at 11.176 km/s (40,230 km/h; 25,000 mph) relative to the Sun and traveling outward at about 2.36 AU per year. [34] [35] The spacecraft is heading in the direction of the constellation Scutum near the current position (January 2023) RA 18h 54m dec -8° 59' (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 [36] and will pass near the star Lambda Aquilae in about four million years. [37]
Pioneer 11 has now been overtaken by the two Voyager probes launched in 1977, and Voyager 1 became 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. [38]
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". [39] 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. [40] [41]
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. [42]
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". [43]
The Mariner program was conducted by the American space agency NASA to explore other planets. Between 1962 and late 1973, NASA's Jet Propulsion Laboratory (JPL) designed and built 10 robotic interplanetary probes named Mariner to explore the inner Solar System - visiting the planets Venus, Mars and Mercury for the first time, and returning to Venus and Mars for additional close observations.
The Pioneer programs were two series of United States lunar and planetary space probes exploration. The first program, which ran from 1958 to 1960, unsuccessfully attempted to send spacecraft to orbit the Moon, successfully sent one spacecraft to fly by the Moon, and successfully sent one spacecraft to investigate interplanetary space between the orbits of Earth and Venus. The second program, which ran from 1965 to 1992, sent four spacecraft to measure interplanetary space weather, two to explore Jupiter and Saturn, and two to explore Venus. The two outer planet probes, Pioneer 10 and Pioneer 11, became the first two of five artificial objects to achieve the escape velocity that will allow them to leave the Solar System, and carried a golden plaque each depicting a man and a woman and information about the origin and the creators of the probes, in case any extraterrestrials find them someday.
Voyager 1 is a space probe launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System and the interstellar space beyond the Sun's heliosphere. It was launched 16 days after its twin Voyager 2. It communicates through the NASA Deep Space Network (DSN) to receive routine commands and to transmit data to Earth. Real-time distance and velocity data is provided by NASA and JPL. At a distance of 162.7 AU from Earth as of March 2024, it is the most distant human-made object from Earth.
Voyager 2 is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, Voyager 1, on a trajectory that took longer to reach gas giants Jupiter and Saturn but enabled further encounters with ice giants Uranus and Neptune. Voyager 2 remains the only spacecraft to have visited either of the ice giant planets, and was the third of five spacecraft to achieve Solar escape velocity, which will allow it to leave the Solar System.
Pioneer 10 is a NASA space probe launched in 1972 that completed the first mission to the planet Jupiter. Pioneer 10 became the first of five planetary probes and 11 artificial objects to achieve the escape velocity needed to leave the Solar System. This space exploration project was conducted by the NASA Ames Research Center in California. The space probe was manufactured by TRW Inc.
Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine-and-a-half times that of Earth. It has only one-eighth the average density of Earth, but is over 95 times more massive. Even though Saturn is nearly the size of Jupiter, Saturn has less than one-third of Jupiter's mass. Saturn orbits the Sun at a distance of 9.59 AU (1,434 million km) with an orbital period of 29.45 years.
The Voyager program is an American scientific program that employs two interstellar probes, Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable alignment of the two gas giants Jupiter and Saturn and the ice giants, Uranus and Neptune, to fly near them while collecting data for transmission back to Earth. After launch, the decision was made to send Voyager 2 near Uranus and Neptune to collect data for transmission back to Earth.
Cassini–Huygens, commonly called Cassini, was a space-research mission by NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, including its rings and natural satellites. The Flagship-class robotic spacecraft comprised both NASA's Cassini space probe and ESA's Huygens lander, which landed on Saturn's largest moon, Titan. Cassini was the fourth space probe to visit Saturn and the first to enter its orbit, where it stayed from 2004 to 2017. The two craft took their names from the astronomers Giovanni Cassini and Christiaan Huygens.
A gravity assist, gravity assist maneuver, swing-by, or generally a gravitational slingshot in orbital mechanics, is a type of spaceflight flyby which makes use of the relative movement and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft, typically to save propellant and reduce expense.
New Horizons is an interplanetary space probe launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institute (SwRI), with a team led by Alan Stern, the spacecraft was launched in 2006 with the primary mission to perform a flyby study of the Pluto system in 2015, and a secondary mission to fly by and study one or more other Kuiper belt objects (KBOs) in the decade to follow, which became a mission to 486958 Arrokoth. It is the fifth space probe to achieve the escape velocity needed to leave the Solar System.
This article provides a timeline of the Cassini–Huygens mission. Cassini was a collaboration between the United States' NASA, the European Space Agency ("ESA"), and the Italian Space Agency ("ASI") to send a probe to study the Saturnian system, including the planet, its rings, and its natural satellites. The Flagship-class uncrewed robotic spacecraft comprised both NASA's Cassini probe, and ESA's Huygens lander which was designed to land on Saturn's largest moon, Titan. Cassini was the fourth space probe to visit Saturn and the first to enter its orbit. The craft were named after astronomers Giovanni Cassini and Christiaan Huygens.
The Grand Tour is a NASA program that would have sent two groups of robotic probes to all the planets of the outer Solar System. It called for four spacecraft, two of which would visit Jupiter, Saturn, and Pluto, while the other two would visit Jupiter, Uranus, and Neptune. The enormous cost of the project, around $1 billion, led to its cancellation and replacement with Mariner Jupiter-Saturn, which became the Voyager program.
The exploration of Jupiter has been conducted via close observations by automated spacecraft. It began with the arrival of Pioneer 10 into the Jovian system in 1973, and, as of 2023, has continued with eight further spacecraft missions in the vicinity of Jupiter. All of these missions were undertaken by the National Aeronautics and Space Administration (NASA), and all but two were flybys taking detailed observations without landing or entering orbit. These probes make Jupiter the most visited of the Solar System's outer planets as all missions to the outer Solar System have used Jupiter flybys. On 5 July 2016, spacecraft Juno arrived and entered the planet's orbit—the second craft ever to do so. Sending a craft to Jupiter is difficult, mostly due to large fuel requirements and the effects of the planet's harsh radiation environment.
The exploration of Uranus has, to date, been through telescopes and a lone probe by NASA's Voyager 2 spacecraft, which made its closest approach to Uranus on January 24, 1986. Voyager 2 discovered 10 moons, studied the planet's cold atmosphere, and examined its ring system, discovering two new rings. It also imaged Uranus' five large moons, revealing that their surfaces are covered with impact craters and canyons.
The exploration of Saturn has been solely performed by crewless probes. Three missions were flybys, which formed an extended foundation of knowledge about the system. The Cassini–Huygens spacecraft, launched in 1997, was in orbit from 2004 to 2017.
Neptune has been directly explored by one space probe, Voyager 2, in 1989. As of 2024, there are no confirmed future missions to visit the Neptunian system, although a tentative Chinese mission has been planned for launch in 2024. NASA, ESA, and independent academic groups have proposed future scientific missions to visit Neptune. Some mission plans are still active, while others have been abandoned or put on hold.
The discrepancy caused by the anomaly amounts to about 248,500 miles (399,900 kilometres), or roughly the distance between Earth and the Moon. That's how much farther the probes should have traveled in their 34 years, if our understanding of gravity is correct.