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définition - Pioneer_11

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Wikipedia

Pioneer 11

                   
Pioneer 11
Pioneer 11 at Saturn.gif
Pioneer 11 at Saturn (artist's impression)
Operator ARC / NASA
Major contractors TRW
Mission type Flyby
Flyby of Jupiter, Saturn
Launch date 1973-04-06 02:11:00 UTC
(39 years, 2 months and 13 days ago)
Launch vehicle Atlas/Centaur/TE364-4
Launch site Space Launch Complex 36A
Cape Canaveral Air Force Station
Mission duration

Apr 6, 1973 - Sep 30, 1995
(22 years, 5 months, 25 days)
(lost communication)

Jupiter flyby
(completed 1975-01-01)
Saturn flyby
(completed 1979-10-05)
Interstellar mission
(completed 1995-09-30)
COSPAR ID 1973-019A
Homepage Pioneer Project website(archived)
NASA Archive
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.[1] 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.

Contents

  Mission background

  History

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:

  • 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.
  • 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 data.
  • 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 waves at 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 was built by TRW and managed as part of the Pioneer program by NASA Ames Research Center.[3] 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..[4] Many elements of the mission proved to be critical in the planning of the Voyager Program[5]:266-8.

  Pioneer plaque

Pioneer Plaque

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.[6]

  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.[1]:42

  Attitude control and propulsion

Pioneer 10 - Pioneer 11 - thrusters - p43.jpg

Orientation of the spacecraft was maintained with six 4.5-N,[7] hydrazine monopropellant 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 performing conical scanning maneuvers to track Earth in its orbit[8], a star sensor able to reference Canopus, and two sun sensors.[1]:42-43

  Communications

The space probe included a redundant system of 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, used a convolutional encoder, a form of error correction, to avoid sending corrupted data.[1]:43

  Power

SNAP-19 RTG
Pioneer 11 used 4 SNAP-19 radioisotope thermoelectric generators (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.[1]:44-45

  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.[1]:38

  Scientific instruments

Helium Vector Magnetometer (HVM)
Pioneer 10-11 - P50 - fx.jpg 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.[9]
Quadrispherical Plasma Analyzer
Pioneer 10-11 - P51b - fx.jpg Peers through a hole in the large dish-shaped antenna to detect particles of the solar wind originating from the Sun.[10]
Charged Particle Instrument (CPI)
Pioneer 10-11 - P52a - fx.jpg Detects cosmic rays in the Solar System.[12]
Cosmic Ray Telescope (CRT)
Pioneer 10-11 - P52b - fx.jpg Collects data on the composition of the cosmic ray particles and their energy ranges.[13]
Geiger Tube Telescope (GTT)
Pioneer 10-11 - p53 - fx.jpg
Surveys the intensities, energy spectra, and angular distributions of electrons and protons along the spacecraft's path through the radiation belts of Jupiter.[14]
Trapped Radiation Detector (TRD)
Pioneer 10-11 - P54 - fx.jpg

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.[15]

Meteoroid Detectors
Pioneer 10-11 - P56 - fx.jpg Twelve panels of pressurized cell detectors mounted on the back of the main dish antenna record penetrating impacts of small meteoroids.[16]
Asteroid/Meteoroid Detector (AMD)
Pioneer 10-11 - P55b - fx.jpg 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.[17]
Ultraviolet Photometer
Pioneer 10-11 - P57a - fx.jpg Ultraviolet light is sensed to determine the quantities of hydrogen and helium in space and on Jupiter.[18]
Imaging Photopolarimeter (IPP)
Pioneer 10-11 - P60 - fx.jpg 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.[19]
Infrared Radiometer
P58 - fx.jpg Provides information on cloud temperature and the output of heat from Jupiter.[20]
  • Principal investigator: Andrew Ingersoll / California Institute of Technology[11]

  Mission profile

Timeline of travel
Date Event
1973-04-06
Spacecraft launched at 02:11:00.
1974-04-19
Passage through the asteroid belt.
1974-11-03
Start Jupiter observation phase.
1979-07-31
Start Saturn observation phase.
1979-10-05
Begin Pioneer Interstellar Mission.
[1]:61-94[21][22]

  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 Canaveral, Florida aboard an Atlas/Centaur launch vehicle. Twin probe, Pioneer 10, had previously launched a year before on March 3, 1972.

Pioneer 11 launching from Space Launch Complex 36A
Pioneer 11 launching from Space Launch Complex 36A.  
Media related to Pioneer 11 at Wikimedia Commons

  Encounter with Jupiter

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.[21] 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.

Pioneer 11 Jupiter encounter
Pioneer 11 Jupiter encounter.  
Approach on Jupiter
Approach on Jupiter.  
The Great Red Spot imaged by Pioneer 11
The Great Red Spot imaged by Pioneer 11.  
The Great Red Spot prior to closest approach
The Great Red Spot prior to closest approach.  
Cloud bands along the edge of Jupiter
Cloud bands along the edge of Jupiter.  
Beginning polar gravity assist
Beginning polar gravity assist  
Jupiter polar region from 1,079,000 km
Jupiter polar region from 1,079,000 km.  
Io imaged from 756,000 km
Io imaged from 756,000 km.  
Media related to Pioneer 11 Jupiter encounter at Wikimedia Commons

  Saturn encounter

  Pioneer 11 and Saturn rings on September 1, 1979 (artist's impression)

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.

Pioneer 11 image of Saturn (image F81). Taken on 1979/08/26, showing the satellite Rhea
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.  
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
Outgoing Pioneer 11 image of Saturn taken on 1979/09/03.  
Pioneer 11 image of Titan
Pioneer 11 image of Saturn's moon Titan  
Media related to Pioneer 11 Saturn encounter at Wikimedia Commons

  Interstellar mission

  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 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.[23][24]

  Current status

  Simulated view of the position of Pioneer 11 as of 8 Feb 2012 showing spacecraft trajectory since launch.

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.[25]

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."[26]

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."

Pioneer 10 has now been overtaken by the two Voyager probes, launched in 1977, and Voyager 1 is now the most distant object built by humans.[27]

  See also

  References

  1. ^ a b c d e f g Fimmel, R. O.; W. Swindell, and E. Burgess (1974). SP-349/396 PIONEER ODYSSEY. NASA-Ames Research Center. ISBN SP-349. http://history.nasa.gov/SP-349/ch8.htm. Retrieved 2011-01-09. 
  2. ^ Mark, Hans: "SP-349/396 PIONEER ODYSSEY", Chapter 5, NASA-Ames Research Center, 1974 | http://history.nasa.gov/SP-349/ch5.htm
  3. ^ NASA - The Pioneer Missions
  4. ^ "Milestones of Flight". Smithsonian National Air and Space Museum. http://www.nasm.si.edu/exhibitions/gal100/index.cfm#pioneer10. 
  5. ^ William E. Burrows, Exploring Space, (New York: Random House, 1990)
  6. ^ Carl Sagan, Linda Salzman Sagan and Frank Drake (1972-02-25). "A Message from Earth". Science 175 (4024): 881–884. Bibcode 1972Sci...175..881S. DOI:10.1126/science.175.4024.881. PMID 17781060. http://www.sciencemag.org/cgi/reprint/175/4024/881.pdf.  Paper on the background of the plaque. Pages available online: 1, 2, 3, 4
  7. ^ Wade, Mark. "Pioneer 10-11". Encyclopedia Astronautica. http://astronautix.com/craft/pior1011.htm. Retrieved 2011-02-08. 
  8. ^ "Weebau Spaceflight Encyclopedia". 9 November 2010. http://weebau.com/satplan/pioneer%2010.htm. Retrieved 12 January 2012. 
  9. ^ "Magnetic Fields". NASA / National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1973-019A-08. Retrieved 2011-02-19. 
  10. ^ "Quadrispherical Plasma Analyzer". NASA / National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1972-012A-13. Retrieved 2011-02-19. 
  11. ^ a b c d e f g h i j Simpson 2001, p. 146.
  12. ^ "Charged Particle Instrument (CPI)". NASA / National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1972-012A-02. Retrieved 2011-02-19. 
  13. ^ "Cosmic-Ray Spectra". NASA / National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1972-012A-12. Retrieved 2011-02-19. 
  14. ^ "Geiger Tube Telescope (GTT)". NASA / National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1972-012A-11. Retrieved 2011-02-19. 
  15. ^ "Jovian Trapped Radiation". NASA / National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1972-012A-05. Retrieved 2011-02-19. 
  16. ^ "Meteoroid Detectors". NASA / National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1972-012A-04. Retrieved 2011-02-19. 
  17. ^ "Asteroid/Meteoroid Astronomy". NASA / National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1972-012A-03. Retrieved 2011-02-19. 
  18. ^ "Ultraviolet Photometry". NASA / National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1972-012A-06. Retrieved 2011-02-19. 
  19. ^ "Imaging Photopolarimeter (IPP)". NASA / National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1972-012A-07. Retrieved 2011-02-19. 
  20. ^ "Infrared Radiometers". NASA / National Space Science Data Center. http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1972-012A-08. Retrieved 2011-02-19. 
  21. ^ a b "Pioneer 11 Mission Information". http://starbrite.jpl.nasa.gov/pds/viewMissionProfile.jsp?MISSION_NAME=PIONEER+11. Retrieved 2011-01-23. 
  22. ^ Muller, Daniel (2010). "Pioneer 11 Full Mission Timeline". Daniel Muller. http://www.dmuller.net/spaceflight/mission.php?mission=pioneer11&appear=black&showimg=yes. Retrieved 2011-01-09. 
  23. ^ "Conference on The Pioneer Anomaly - Observations, Attempts at Explanation, Further Exploration". http://www.zarm.uni-bremen.de/Pioneer/. 
  24. ^ "The Pioneer Explorer Collaboration: Investigation of the Pioneer Anomaly at ISSI". February 18, 2008. http://www.issi.unibe.ch/teams/Pioneer/. Retrieved January 10, 2009. 
  25. ^ Spacecraft escaping the Solar System
  26. ^ "Pioneer 11 to End Operations after Epic Career". NASA / Ames Research Center. September 29, 1995. http://nssdc.gsfc.nasa.gov/planetary/text/pioneer-11_endops.txt. Retrieved August 07, 2011. 
  27. ^ Where are the Voyagers

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