- Pioneer 11
Caption= Pioneer 11 at Saturn (artist's impression)
Name= Pioneer 11
Mission_Type= Fly-by, Deep Space
Jupiter, Saturn, Outer Solar System
Mass= 259 kg
Ames Research Center- NASA
6 April 1973at 02:11:00 UTC (age in days|1973|04|06 days ago)
Mission_Duration = undefined (age in days|1973|04|06|1995|09|30 days from launch to end of mission operations on release date and age|1995|09|30, last contact was November 1995)
Pioneer 11 was the second mission (after its sister probe
Pioneer 10) to investigate Jupiter and the outer solar systemand the first to explore the planet Saturn and its main rings. Pioneer 11 (also called "Pioneer G", part of the Pioneer program) used Jupiter's massin a gravity assistto alter its trajectorytoward Saturn. The spacecraft made a successful Saturn flyby and then followed an escape trajectory from the solar system.
Its objectives were to 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. It was developed out of
NASA Ames Research Centeras part of the Pioneer series (6-12) of spacecraft that include Pioneer Venus.
spacecraftwas launched from Cape Canaveralon 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
Sunsensors. 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.
Rather than a traditional lens camera, Pioneer used its spin to scan scenes line-by-line (
spin-scan). Its imaging system ( photopolarimeter) could record brightness values of one narrow spot ( pixel) at a time in two wavelengths corresponding to Redand Bluelight. A combination of craft rotation and gradual forward or backward movement of this "pixel" allowed color images to be reconstructed using computers back at JPL (Earth). It is roughly comparable to early mechanical televisionscanners.
Instruments on the Pioneer 11 probe studied the interplanetary and planetary
magnetic fields; solar windproperties; cosmic rays; the transition region of the heliosphere; neutral hydrogenabundance; distribution, size, mass, flux, and velocity of dustparticles; 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 argonand nitrogengas 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 mechanicsand occultation phenomena.
Pioneer 11 instrument list:
* Helium Vector
* Geiger Tube Telescope
* Trapped Radiation Detector
* Asteroid-Meteoroid Experiment
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.
It passed by Saturn on
September 1, 1979, at a distance of 21,000 km from Saturn's cloud tops.
By this time
Voyager 1and Voyager 2had 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 a few thousand kilometers from it. 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, 1979at 14:52 UTCat a distance of 2500 km and Mimasat 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 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.
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
telemetryceased on September 30, 1995when 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 latitudeof 17.4 degrees above the solar equatorial planeand 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 ( Voyagers 1 and 2, Pioneers 10 and 11, and New Horizons). [http://www.heavens-above.com/solar-escape.asp]
Earth's motion has carried it out of alignment with the spacecraft antenna. As it cannot be maneuvered to point back at our planet, it's now impossible to establish further communication from Earth with the probe and know if it is still transmitting a signal.The spacecraft is headed toward the constellation of Aquila (The Eagle), Northwest of the constellation of
Sagittarius. Barring incident, Pioneer 11 will pass near one of the stars in the constellation in about 4 million years. [ [http://www.nasa.gov/centers/ames/missions/archive/pioneer.html NASA - The Pioneer Missions] ]
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.
*1990 - passes the orbit of Pluto
September 30, 1995- Routine daily mission operations stopped. Pioneer 11 is 6.5 billion km from Earth.
*November, 1995 - Last communication with Pioneer 11.
The Pioneer plaque
Like its sister ship, Pioneer 10, Pioneer 11 carried a plaque with a message from
humankind. The Pioneer plaques are identical in that they depict a Jupiter flyby. However, Pioneer 11 was redirected to Saturn making its plaque somewhat out of date. 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.
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
Dopplerfrequency 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.Fact|date=July 2008
Unmanned space missions
* [http://www.nasa.gov/mission_pages/pioneer/index.html Pioneer Project Home Page]
* [http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Pioneer_11 Pioneer 11 Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [http://www.strykfoto.org/pioneersaturn.htm Ted Stryk's Pioneer 11 at Saturn page]
* [http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1973-019A NSSDC Pioneer 11 page]
* [http://history.nasa.gov/SP-349/sp349.htm "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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