Pioneer 11 (also called Pioneer G) was the second mission of the Pioneer program The Pioneer program is a series of United States unmanned space missions that was designed for planetary exploration. There were a number of such missions in the program, but the most notable were Pioneer 10 and Pioneer 11, which explored the outer planets and left the solar system. Both carry a golden plaque, depicting a man and a woman and (after its sister probe Pioneer 10 Pioneer 10 was the first spacecraft to travel through the asteroid belt, on July 15, 1972, and to make direct observations of Jupiter, which it passed by on December 3, 1973. It was launched from Cape Canaveral Air Force Station's Launch Complex 36A on March 3, 1972 at 01:49:00 UTC. Pioneer 10 is heading in the direction of Aldebaran, located in) to investigate Jupiter Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with a mass slightly less than one-thousandth of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn, Uranus and Neptune. Together, these and the outer solar system The Solar System[a] consists of the Sun and those celestial objects bound to it by gravity, all of which were formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets[e] whose orbits are almost circular and, and the first to explore Saturn Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus the Babylonian Ninurta and to the Hindu Shani. Saturn's symbol represents the god's sickle (Unicode: ♄) and its main rings. Pioneer 11 used Jupiter's mass In physics, mass commonly refers to any of three properties of matter, which have been shown experimentally to be equivalent: Inertial mass, active gravitational mass and passive gravitational mass. In everyday usage, mass is often taken to mean weight, but in scientific use, they refer to different properties in a gravity assist In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of a spacecraft, typically in order to save propellant, time, and expense. Gravity assistance can be used to accelerate, to alter its trajectory A trajectory is the path a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass. A trajectory can be described mathematically either by the geometry of the path, toward Saturn. The unmanned spacecraft A spacecraft is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and space tourism. Spacecraft and space travel are common themes in works of science fiction was developed by NASA Ames Research Center NASA's Ames Research Center , located at Moffett Field, California, was founded on December 20, 1939 as the second National Advisory Committee for Aeronautics (NACA) laboratory, and became part of NASA in 1958, as part of the turnover from NACA. The center was named after Joseph Sweetman Ames, a founding member and longtime chairman (1919–1939) as part of the Pioneer spacecraft series (6-12), and was launched from Cape Canaveral Air Force Station Cape Canaveral Air Force Station is an installation of the United States Air Force Space Command's 45th Space Wing, headquartered at nearby Patrick Air Force Base. Located on Cape Canaveral in the state of Florida, CCAFS is the primary launch head of America's Eastern Range with four launch pads currently active. The facility is south-southeast of on April 5, 1973.^[1][2]

Its objectives were to study the interplanetary and planetary magnetic fields; solar wind The solar wind is a stream of charged particles ejected from the upper atmosphere of the sun. It mostly consists of electrons and protons with energies usually between 10 and 100 eV. The stream of particles varies in temperature and speed over time. These particles can escape the sun's gravity because of their high kinetic energy and the high properties; cosmic rays Cosmic rays are energetic particles originating from outer space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are simple protons, with nearly 10% being helium nuclei , and slightly under 1% are heavier elements, electrons (beta particles), or gamma ray photons. The term ray is a misnomer, as cosmic; transition region of the heliosphere The heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar space can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself; neutral hydrogen abundance; distribution, size, mass, flux, and velocity of dust particles; Jovian aurorae; Jovian radio waves Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Like all other electromagnetic waves, they travel at the speed of light. Naturally-occurring radio waves are made by lightning, or by astronomical objects. Artificially-generated radio waves are used for fixed and mobile; the atmospheres An atmosphere is a layer of gases that may surround a material body of sufficient mass,and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low. Some planets consist mainly of various gases, but only their outer layer is their of planets and satellites A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called the primary. Technically, the term natural satellite could refer to a planet orbiting a star, or a dwarf galaxy orbiting a major galaxy, but it is normally synonymous with moon and used to identify non-artificial satellites of planets, dwarf; and the surfaces of Jupiter, Saturn, and some of their satellites.

Pioneer 11 completed a successful Saturn flyby in 1979, and it is now estimated to be following an escape trajectory from the solar system.

There is no longer communication with the spacecraft; the last contact was in November 1995.^[3]

Design

Pioneer 11 is 2.9 meters long and has a 2.74-meter-diameter high-gain antenna An antenna is a transducer designed to transmit or receive electromagnetic waves. In other words, antennas convert electromagnetic waves into electrical currents and vice versa. They are used with waves in the radio part of the electromagnetic spectrum, that is, radio waves, and are a necessary part of all radio equipment. Antennas are used in, topped with a medium-gain antenna. A low-gain, omnidirectional antenna is mounted below the high-gain dish. The spacecraft contains four SNAP-19 radioisotope thermoelectric generators A radioisotope thermoelectric generator is an electrical generator that obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples (RTGs), which generated 144 W The watt is a derived unit of power in the International System of Units (SI), named after the Scottish engineer James Watt (1736–1819). The unit measures the rate of energy conversion. It is defined as one joule per second at Jupiter, but had decreased to 100 W by the time it reached Saturn.

The probe includes three reference sensors: a star (Canopus) sensor, and two Sun The Sun is the star at the center of the Solar System. It has a diameter of about 1,392,000 kilometers , about 109 times that of Earth, and its mass (about 2 × 1030 kilograms, 330,000 times that of Earth) accounts for about 99.86% of the total mass of the Solar System. About three quarters of the Sun's mass consists of hydrogen, while the rest is 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 A thruster is a small propulsive device used by spacecraft and watercraft for station keeping, attitude control, or long duration low thrust acceleration provided spin-axis control (maintained at 4.8 rpm) and change the spacecraft's velocity In physics, velocity is the rate of change of position. It is a vector physical quantity; both magnitude and direction are required to define it. The scalar absolute value of velocity is speed, a quantity that is measured in meters per second (m/s or ms−1) when using the SI (metric) system. 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 In digital imaging, a pixel is a single point in a raster image. The pixel is the smallest addressable screen element; it is the smallest unit of picture that can be controlled. Each pixel has its own address. The address of a pixel corresponds to its coordinates. Pixels are normally arranged in a 2-dimensional grid, and are often represented) at a time in two wavelengths corresponding to Red The word red comes from the Old English rēad. Further back, the word can be traced to the Proto-Germanic rauthaz and the Proto-Indo European root reudh-. In Sanskrit, the word rudhira means red or blood. In the English language, the word red is associated with the color of blood, certain flowers , and ripe fruits (e.g. apples, cherries). Fire is and Blue Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal mixture of red and green light. On a colour wheel light. 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 television Mechanical television was a television system that used mechanical or electromechanical devices to capture and display images. However, the images themselves were usually transmitted electronically and via radio waves. The reason for this dual nature of mechanical television lies in the history of technology. Mechanical television mechanics came scanners.

Instruments

Instruments on the Pioneer 11 probe studied the interplanetary and planetary magnetic fields Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field; solar wind The solar wind is a stream of charged particles ejected from the upper atmosphere of the sun. It mostly consists of electrons and protons with energies usually between 10 and 100 eV. The stream of particles varies in temperature and speed over time. These particles can escape the sun's gravity because of their high kinetic energy and the high properties; cosmic rays Cosmic rays are energetic particles originating from outer space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are simple protons, with nearly 10% being helium nuclei , and slightly under 1% are heavier elements, electrons (beta particles), or gamma ray photons. The term ray is a misnomer, as cosmic; the transition region of the heliosphere The heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar space can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself; neutral hydrogen abundance; distribution, size, mass, flux One could argue, based on the work of James Clerk Maxwell, that the transport definition precedes the more recent way the term is used in electromagnetism. The specific quote from Maxwell is "In the case of fluxes, we have to take the integral, over a surface, of the flux through every element of the surface. The result of this operation is, and velocity of dust Dust is a general name for solid particles with diameters less than 20 thou . Particles in the atmosphere arise from various sources such as soil dust lifted up by wind, volcanic eruptions, and pollution. Dust in homes, offices, and other human environments contains small amounts of plant pollen, human and animal hairs, textile fibers, paper particles; Jovian aurorae; Jovian radio waves Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Like all other electromagnetic waves, they travel at the speed of light. Naturally-occurring radio waves are made by lightning, or by astronomical objects. Artificially-generated radio waves are used for fixed and mobile; the atmospheres An atmosphere is a layer of gases that may surround a material body of sufficient mass, by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low. Some planets consist mainly of various gases, but only their outer layer is their atmosphere (see gas giants) of planets and satellites A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called the primary. Technically, the term natural satellite could refer to a planet orbiting a star, or a dwarf galaxy orbiting a major galaxy, but it is normally synonymous with moon and used to identify non-artificial satellites of planets, dwarf; 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 magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. Magnetism varies from place to place and differences in Earth's magnetic field can be caused by the differing nature of rocks and the interaction between charged particles from the Sun and the, a plasma analyzer (for solar wind The solar wind is a stream of charged particles ejected from the upper atmosphere of the sun. It mostly consists of electrons and protons with energies usually between 10 and 100 eV. The stream of particles varies in temperature and speed over time. These particles can escape the sun's gravity because of their high kinetic energy and the high), a charged-particle detector In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a particle accelerator. Modern detectors are also used, an ion detector, non-imaging telescopes A telescope is an instrument designed for the observation of remote objects by the collection of electromagnetic radiation. The first known practically functioning telescopes were invented in the Netherlands at the beginning of the 17th century. "Telescopes" can refer to a whole range of instruments operating in most regions of the with overlapping fields of view to detect sunlight reflected from passing meteoroids A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteor reaches the ground and survives impact, then it is called a meteorite. Many meteors appearing seconds or minutes apart are, sealed pressurized cells of argon Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table (noble gases). Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide. The complete octet (eight electrons) in the outer atomic shell makes it and nitrogen Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere gas for measuring penetration of meteoroids, an ultraviolet photometer, an infrared radiometer, and an imaging photopolarimeter, which produced photographs and measured their polarization Polarization is a property of certain types of waves that describes the orientation of their oscillations. Electromagnetic waves such as light exhibit polarization; acoustic waves (sound waves) in a gas or liquid do not have polarization because the direction of vibration and direction of propagation are the same. Further scientific information was obtained from celestial mechanics Celestial mechanics is the branch of astronomy that deals with the motions of celestial objects. The field applies principles of physics, historically classical mechanics, to astronomical objects such as stars and planets to produce ephemeris data. Orbital mechanics is a subfield which focuses on the orbits of artificial satellites. Lunar theory and occultation phenomena.

Pioneer 11 instrument list:

• Helium Vector Magnetometer A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. Magnetism varies from place to place and differences in Earth's magnetic field can be caused by the differing nature of rocks and the interaction between charged particles from the Sun and the
• Plasma Analyzer
• Charged Particle In physics, a charged particle is a particle with an electric charge. It may be either a subatomic particle or an ion. A collection of charged particles, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its properties are quite different from solids, liquids and Instrument
• Cosmic Ray Cosmic rays are energetic particles originating from outer space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are simple protons, with nearly 10% being helium nuclei , and slightly under 1% are heavier elements, electrons (beta particles), or gamma ray photons. The term ray is a misnomer, as cosmic Telescope
• Geiger Tube hubble
• Trapped Radiation Detector
• Meteoroid A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteor reaches the ground and survives impact, then it is called a meteorite. Many meteors appearing seconds or minutes apart are Detector
• Asteroid-Meteoroid Experiment
• Ultraviolet Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than x-rays, in the range 10 nm to 400 nm, and energies from 3eV to 124 eV. It is so named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the colour violet Photometer
• Imaging Photopolarimeter
• Infrared Radiometer
• Flux-Gate Magnetometer

Jupiter encounter

During its closest approach, December 2, 1974^[4], 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.

Saturn encounter

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 a 2500 miles. 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 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 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 (Voyagers 1 and 2, Pioneers 10 and 11, and New Horizons). [1]

Earth's motion has carried it out of alignment with the spacecraft antenna. As the antenna cannot be maneuvered to point back at our planet, it is no longer possible with current technology to establish further communication from Earth with the probe.

The spacecraft is headed toward the constellation of Aquila (The Eagle), Northwest of the constellation of Sagittarius. Barring incident, Pioneer 11 will pass near the star Lambda (λ) Aquilae ^[5] in about 4 million years time.^[6]

Timeline

• April 5, 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 1, 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, since Pioneer 11 was redirected to Saturn, this depiction would be somewhat erroneous. 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.

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.^[7][8]

See also

• Unmanned space missions
• Pioneer plaque
• Pioneer 10
• Voyager program
• Cassini–Huygens
• S band

References

1. ^ http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Pioneer_11
2. ^ http://www.nasa.gov/centers/ames/missions/archive/pioneer.html
3. ^ http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Pioneer_11
4. ^ http://starbrite.jpl.nasa.gov/pds/viewMissionProfile.jsp?MISSION_NAME=PIONEER%2011
5. ^ DK Eyewitness Space Encyclopedia: Leaving the Solar System - Where are they now?
6. ^ NASA - The Pioneer Missions
7. ^ "Conference on The Pioneer Anomaly - Observations, Attempts at Explanation, Further Exploration". http://www.zarm.uni-bremen.de/Pioneer/.
8. ^ "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.

External links

• Pioneer Project Home Page
• Pioneer 11 Profile by NASA's Solar System Exploration
• Ted Stryk's Pioneer 11 at Saturn 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.

Categories: Pioneer program | Jupiter spacecraft | Radio frequency propagation | Saturn spacecraft | 1973 in space exploration | Spacecraft escaping the Solar System | Inactive extraterrestrial probes

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