Pioneer 11

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Characteristics of the mission:
Name	Pioneer 11
Nation	United States
Objective(s)	Study the interplanetary and planetary magnetic fields; solar wind properties; cosmic rays; transition region of the heliosphere; neutral hydrogen abundance; distribution, size, mass, flux, and velocity of dust particles; Jovian aurorae; Jovian radio waves; the atmospheres of planets and satellites; and the surfaces of Jupiter, Saturn, and some of their satellites.
Craft	Pioneer-G
Craft – Weight	259 kg
Administration and planning of mission	Ames Research Center - NASA
Launch vehicle	Atlas/Centaur/TE364-4
Date and time of launch	06 April 1973 at 02:11:00 UTC
Launched from	Cape Canaveral
Scientific instruments/ Technology experiments	Helium Vector Magnetometer Plasma Analyzer Charged Particle Instrument Cosmic Ray Telescope Geiger Tube Telescope Trapped Radiation Detector Meteoroid Detector Asteroid-Meteoroid Experiment Ultraviolet Photometer Imaging Photopolarimeter Infrared Radiometer Flux-Gate Magnetometer

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Pioneer 11 was the second mission to investigate Jupiter and the outer solar system and the first to explore the planet Saturn and its main rings. Pioneer 11 (also called Pioneer G), unlike Pioneer 10 which only visited Jupiter, used Jupiter's mass in a gravitational slingshot to alter its trajectory toward Saturn. It passed close to Saturn and then it followed an escape trajectory from the solar system.

The spacecraft was launched from Cape Canaveral on April 6, 1973. It is 2.9 meters long and has a 2.74-meter-diameter high-gain antenna, topped with a medium-gain antenna. A low-gain, omnidirectional antenna is mounted below the high-gain dish. The spacecraft contains two radioisotope thermoelectric generators (RTGs), which generated 144 W at Jupiter, but had decreased to 100 W by the time it reached Saturn. There were three reference sensors: a star (Canopus) sensor, and two Sun sensors. Attitude position could be calculated from the reference direction to Earth and Sun, with the known direction to Canopus as backup. Pioneer 11's star sensor gain and threshold settings were modified, based on experience gained from the settings used on Pioneer 10. Three pairs of rocket thrusters provided spin-axis control (maintained at 4.8 rpm) and change the spacecraft's velocity. The thrusters could be either fired steadily or pulsed, by command.

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Instruments studied the interplanetary and planetary magnetic fields; solar wind properties; cosmic rays; the transition region of the heliosphere; neutral hydrogen abundance; distribution, size, mass, flux, and velocity of dust particles; Jovian aurorae; Jovian radio waves; the atmospheres of planets and satellites; and higher layers of the atmospheres of Jupiter and Saturn, and the surfaces of some of their satellites. The instruments carried for these experiments were a magnetometer, a plasma analyzer (for solar wind), a charged-particle detector, an ion detector, non-imaging telescopes with overlapping fields of view to detect sunlight reflected from passing meteoroids, sealed pressurized cells of argon and nitrogen gas for measuring penetration of meteoroids, an ultraviolet photometer, an infrared radiometer, and an imaging photopolarimeter, which produced photographs and measured their polarization. Further scientific information was obtained from celestial mechanics and occultation phenomena.

1 Jupiter Encounter
2 Saturn Encounter
3 Outer regions of the Solar system
4 Timeline
5 The Pioneer Plaque
6 Pioneer anomaly
7 See also
8 External links

[edit] Jupiter Encounter

During its closest approach, December 4, 1974, Pioneer 11 passed to within 34,000 km of Jupiter's cloud tops and obtained dramatic images of the Great Red Spot, made the first observation of the immense polar regions, and determined the mass of Jupiter's moon, Callisto. Using Jupiter's mass in a gravitational slingshot, the probe altered its trajectory towards Saturn.

Great Red Spot by Pioneer 11 (image C3)

The polar region of Jupiter by Pioneer 11 showing the knotted nature of the cloud cover

View of Jupiter by Pioneer 11

View of Jupiter by Pioneer 11 (image C6)

[edit] Saturn Encounter

It 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.) 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.)

Instruments located two previously undiscovered small moons 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 amazing 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 1979/09/01

Outgoing Pioneer 11 image of Saturn taken on 1979/09/03

[edit] Outer regions of the Solar system

Pioneer 11 explored the outer regions of our Solar system, studying the Solar Wind and cosmic rays entering our portion of the Milky Way. The spacecraft has operated on a backup transmitter since launch. Instrument power sharing began in February 1985 due to declining generator power output. Science operations and daily telemetry ceased on September 30, 1995 when the RTG power level was insufficient to operate any experiments. As of the end of 1995, when its mission ended, the spacecraft was located at 44.7 AU from the Sun at a nearly asymptotic latitude of 17.4 degrees above the solar equatorial plane and was heading outward at ~2.4 AU/year (11.6 km/s); this is the lowest velocity of the five spacecraft now escaping the Solar System.[1]

Earth's motion has carried it out of alignment with the spacecraft antenna; as this cannot be maneuvered to point back at the Earth, it's unknown whether the spacecraft is still transmitting a signal. The spacecraft is headed toward the constellation of Aquila (The Eagle), Northwest of the constellation of Sagittarius. Pioneer 11 will pass near one of the stars in the constellation in about 4 million years.

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[edit] Timeline

April 6, 1973 - Launch
April 19, 1974 - Safe passage through the Asteroid belt
December 2, 1974 - Flyby of Jupiter.
September 1, 1979 - Flyby of Saturn.
February, 1985 - Instrument power sharing began due to declining generator power output.
September 30, 1995 - Routine daily mission operations stopped. Pioneer 11 is 6.5 billion km from Earth.
November, 1995 - Last communication with Pioneer 11.

[edit] The Pioneer Plaque

Main article: Pioneer plaque

The plaque on board the Pioneer spacecraft

Like its sister ship, Pioneer 10, Pioneer 11 carried a plaque with a message from humankind. If the space probe is ever found by extraterrestrial intelligences, this message is meant to provide information about the origin of the spacecraft. It includes a drawing depicting a man, a woman, the transition of a hydrogen atom, and the location of the Sun and Earth in the galaxy.

[edit] Pioneer anomaly

Main article: 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.

[edit] See also

[edit] External links

Pioneer Project Home Page
NSSDC Pioneer 11 page
Pioneer Odyssey, NASA SP-396, 1977 - This is an entire book about the Pioneer 10 and 11 project, with all pictures and diagrams, on-line! Scroll down to click on the "Table of Contents" link.

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