voir la définition de Wikipedia
Pioneer 11 at Saturn (artist's impression)
|Operator||ARC / NASA|
|Flyby of||Jupiter, Saturn|
|Launch date||1973-04-06 02:11:00 UTC
(39 years, 2 months and 13 days ago)
|Launch site||Space Launch Complex 36A
Cape Canaveral Air Force Station
Apr 6, 1973 - Sep 30, 1995
|Homepage||Pioneer Project website(archived)
|Mass||259 kg (570 lb)|
|Power||165.0 W (4 SNAP-19 RTGs)|
Pioneer 11 (also known as Pioneer G) is a 259-kilogram (569 lb) robotic space probe launched by NASA on April 6, 1973 to study the asteroid belt, the environment around Jupiter and Saturn, solar wind, cosmic rays, and eventually the far reaches of the solar system and heliosphere. It was the first probe to encounter Saturn and the second to fly through the asteroid belt and by Jupiter. Due to power constraints and the vast distance of the probe, communication has been lost since November 30, 1995.
Approved in February 1969, Pioneer 11 and 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. 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.. Many elements of the mission proved to be critical in the planning of the Voyager Program:266-8.
Pioneer 10 and Pioneer 11 carry a gold-anodized aluminum plaque 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.
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.:42
|Helium Vector Magnetometer (HVM)|
|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.|
|Quadrispherical Plasma Analyzer|
|Peers through a hole in the large dish-shaped antenna to detect particles of the solar wind originating from the Sun.|
|Charged Particle Instrument (CPI)|
|Detects cosmic rays in the Solar System.|
|Cosmic Ray Telescope (CRT)|
|Collects data on the composition of the cosmic ray particles and their energy ranges.|
|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.|
|Trapped Radiation Detector (TRD)|
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.
|Twelve panels of pressurized cell detectors mounted on the back of the main dish antenna record penetrating impacts of small meteoroids.|
|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.|
|Ultraviolet light is sensed to determine the quantities of hydrogen and helium in space and on Jupiter.|
|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 were then processed to build up a visual image of the planet.|
|Provides information on cloud temperature and the output of heat from Jupiter.
|Timeline of travel|
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. Twin probe, Pioneer 10, had previously launched a year before on March 3, 1972.
Media related to Pioneer 11 at Wikimedia Commons
In November and December 1974, During its closest approach, December 2, 1974, Pioneer 11 reached closest approach to Jupiter, passing 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. Utilizing the gravitational pull of Jupiter, a gravity assist was used to alter the trajectory of the probe, towards Saturn.
Media related to Pioneer 11 Jupiter encounter at Wikimedia Commons
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 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 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 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 2500 km and Mimas 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, Titan, 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.
Media related to Pioneer 11 Saturn encounter at Wikimedia Commons
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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 Doppler 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.
As of February 8, 2012, Pioneer 11 is about 85.013 astronomical units (1.27178×1010 km) from the Sun. It is at an elliptic latitude of 14.3 degrees and at a declination of -8.82 degrees. It is traveling at about 11.391 km/s relative to the Sun and is traveling outward at about 2.403 AU per year. Pioneer 11 is at a right ascension of 18.763 hours, and at an ecliptic latitude of 14.3 degrees. Sunlight takes 11.9 hours to get to Pioneer 11 at its approximate distance. Pioneer 11 is traveling in roughly the opposite direction from Pioneer 10. 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 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."
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 10 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."
|Wikimedia Commons has media related to: Pioneer program|
|Previous mission: Pioneer 10||Next mission: Pioneer H|
|Pioneer 0 · Pioneer 1 · Pioneer 2 · Pioneer 3 · Pioneer 4 · Pioneer P-1 (W) · Pioneer P-3 (X) · Pioneer P-30 (Y) · Pioneer P-31 (Z)|
|Pioneer 5 (P-2) · Pioneer 6, 7, 8, 9, and E · Pioneer 10 · Pioneer 11 · Pioneer H · Pioneer Venus project|
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