$Unique_ID{bob01159} $Pretitle{} $Title{Pioneer Chapter 4: Part 1 - Pioneer Science at New Frontiers} $Subtitle{} $Author{Fimmel, Richard O.;Allen, James Van;Burgess, Eric} $Affiliation{Ames Research Center;University Of Iowa;Science Writer} $Subject{saturn jupiter solar particles magnetic wind field measured spacecraft fields see pictures see figures } $Date{1980} $Log{See Plasma Analyzer*0115901.scf } Title: Pioneer Book: Pioneer: First To Jupiter, Saturn, And Beyond Author: Fimmel, Richard O.;Allen, James Van;Burgess, Eric Affiliation: Ames Research Center;University Of Iowa;Science Writer Date: 1980 Chapter 4: Part 1 - Pioneer Science at New Frontiers The scientific payloads of Pioneers 10 and 11 for the missions to Jupiter and Saturn were virtually identical. They were designed to gather new knowledge about interplanetary space beyond Mars and about the Jovian and Saturnian systems. Several of the science instruments measured particles, fields, and radiation, while an imaging photopolarimeter provided spin-can imaging and analysis of scattered light. Additionally, the radio signals from the spacecraft were used to measure the gravitational fields of Jupiter and Saturn and their major satellites and to investigate the atmospheres of the two planets. The Pioneers performed several experiments in interplanetary space between Earth and the target planets and beyond: Mapped the magnetic field in interplanetary space. Determined how the solar wind changed with distance from the Sun and, during the flight of Pioneer 11 to Saturn, how the solar wind changed high above the plane of the ecliptic. Measured solar and galactic cosmic ray particles. Studied interactions among the interplanetary magnetic field, the solar wind, and cosmic rays. Searched for a transition region of the heliosphere - the region where the influence of the Sun on interplanetary space ends - in two opposite directions. Measured the amount of neutral atomic hydrogen in interplanetary space and near Jupiter and Saturn. Ascertained the distribution of dust particles in interplanetary space in the outer Solar System. Determined the sizes, masses, fluxes, and velocities of small particles in the asteroid belt, thus providing information on the probability of damage by such particles to spacecraft passing through this region. Searched for gravitational radiation impinging on the Solar System by means of its effects on the spacecraft's velocity as revealed on the microwave radio link between Earth and the spacecraft. Searched for the gravitational effects of large undiscovered objects orbiting the Sun. Within the systems of Jupiter and Saturn, the Pioneer spacecraft performed a more involved series of experiments: Mapped the magnetic fields of the planets their intensity, direction, and structure. Determined how many electrons and protons of various energies were distributed along the trajectory of each spacecraft through the planetary magnetospheres and, for Saturn, determined how the rings affect the distribution of those particles; for both planets, determined how the particles were affected by the satellites. Searched for auroras in the polar atmospheres of the two planets. Obtained information to help interpret the observed characteristics of the two main types of radio waves from Jupiter - decimetric and decametric. Mapped how the two planets interact with the solar wind. Measured the temperature of the atmospheres of the two planets and of those of some of their larger satellites. Determined the structure of the upper atmospheres of Jupiter and Saturn, where molecules are ionized by solar radiation to produce an ionosphere. Mapped the thermal structure of the two planets by measuring their infrared radiation, and deduced how much more heat each planet radiates into space than it absorbs from the Sun. Obtained spin-can images of Jupiter and Saturn in two colors during the encounter sequences, and close-up images of special planetary features (the Great Red Spot and polar regions of Jupiter and the rings of Saturn); made polarimetry measurements of Jupiter and Saturn and of some of their large satellites. Probed the upper atmospheres of Jupiter and Saturn with S-band radio waves at occultation; similarly, probed the Galilean satellite Io to establish whether it has an atmosphere. Investigated, at relatively close range, several of the Galilean satellites of Jupiter, and Saturn's largest satellite, Titan, by spin-scan imaging and other measurements to determine their sizes and other physical characteristics. Determined the shape of the external gravitational fields of Jupiter and Saturn and inferred the internal mass distribution and structure of those fields. Determined more precisely the masses of Jupiter and its Galilean satellites, and the masses of Saturn, the rings of Saturn, and of the Saturnian satellites, Rhea, Iapetus, and Titan, by accurate observations of the effects of their gravitational fields on the motion of the spacecraft. Provided information to calculate with greater precision the orbits and ephemerides of Jupiter and its Galilean satellites, and of Saturn and Titan. Determined the maximum radiation dosage for planning future missions. Eleven scientific instruments and experiments were selected from more than 150 proposals submitted to NASA Headquarters in response to the original request for proposed onboard experiments for the original Pioneer mission to Jupiter. These instruments, and two noninstrumented experiments, are described in the following subsections. In addition, a high-field magnetometer was later selected for Pioneer 11 to ensure adequate coverage of higher magnetic field strengths that might be encountered. This instrument - a flux-gate magnetometer - is also described. Magnetic Fields Magnetic fields permeate the plasma of electrically charged particles in interplanetary space as it spreads out from the Sun across the Solar System. Before the Pioneer missions to Jupiter and Saturn, these effects had been observed and measured only to the orbit of Mars. Scientists were still uncertain about many specific details concerning the interplanetary medium and particularly the configuration of the magnetic field beyond the orbit of Mars to the outer regions of the Solar System. The outer boundaries of the Sun's influence were, and still are, vague, and interactions between the plasma and the magnetic fields of the Solar System and those of the nearby interstellar medium still puzzle scientists. Pioneers 10 and 11 will continue to explore the regions beyond the orbit of Saturn and will provide data that will help define the transition region of the solar influence, or the heliopause. Of even greater importance was the objective of measuring the detailed magnetic fields of Jupiter and Saturn and the configurations throughout the magnetospheres of these planets. Principal investigator: Edward J. Smith Jet Propulsion Laboratory, Pasadena, California Coinvestigators: Palmer Dyal and David S. Colburn Ames Research Center, NASA, Moffett Field, California Charles P. Sonett University of Arizona, Tucson, Arizona Douglas E. Jones Brigham Young University, Provo, Utah Paul J. Coleman, Jr. University of California at Los Angeles Leverett Davis, Jr. California Institute of Technology, Pasadena, California This experiment used a sensitive magnetometer mounted on the tip of a lightweight boom extending 6.6 m (21.5 ft) from the center of the spacecraft to reduce the effects of even the minute amount of residual magnetic field of the spacecraft and to help balance the spin-stabilized Pioneer spacecraft. The helium vector magnetometer measured the fine structure of the interplanetary field, mapped the fields of Jupiter and Saturn, and provided field measurements to evaluate the interaction of the solar wind with the two planets. The magnetometer operated in any one of eight ranges, the lowest of which covered magnetic field strengths from +0.01 to +4.0 gamma (1 gamma = 10^-5 gauss); the highest measured field strengths up to +140,000 gamma (i.e., +1.4 gauss). (The surface field of Earth is about 0.5 gauss.) The ranges were selected by ground command or automatically by the instrument as it reached the limits of a given range. The sensor for the magnetometer consisted of a cell filled with helium that was excited by electrical discharge at radio frequencies and by infrared optical pumping. Changes in helium absorption caused by magnetic fields passing through the magnetometer were measured by an infrared optical detector. Flux-Gate Magnetometer Experiment Pioneer 11 carried another instrument for measuring the magnetic field, a flux-gate magnetometer. This instrument was designed to measure the intense planetary fields of Jupiter and Saturn and to extend the measuring capability of the spacecraft beyond the range provided by the helium vector magnetometer. The scientific objectives were to study the intrinsic magnetic fields of Jupiter and Saturn by carrying out measurements during the closest approach phases of the Pioneer 11 mission. The knowledge acquired allowed a comprehensive study of the general problem of how planets, including Earth, generate their magnetic fields, and a determination of the detailed geometry of their inner magnetospheres. Principal investigator: Mario H. Acuna Goddard Space Flight Center, NASA, Greenbelt, Maryland Coinvestigator: Norman F. Hess Goddard Space Flight Center, NASA The instrument, mounted on the main body of the spacecraft, used two magnetic ring cores that were driven to saturation by associated oscillators at a frequency of 8 kHz. The presence of an external magnetic field created an imbalance in the sensors which was detected by four coil windings; the coil windings were oriented perpendicular to each other. The instrument had a single dynamic range with a compressed response that provided a maximum field measurement capability of +10 gauss (0.001 tesla) and a resolution of +0.05 gauss for external fields of less than 2 gauss. Interplanetary Solar Wind and Heliosphere The solar wind consists of streams of protons, electrons, and some helium nuclei emitted by the Sun in all directions. Particles in the solar wind affect electrical and communication systems on Earth and may give rise to long-term weather cycles. This wind was unknown until spacecraft began to explore space beyond Earth's magnetosphere less than 20 years ago. Some of the charged particles of the solar wind become trapped in radiation belts by Earth's magnetic field. They also account for the aurora borealis, the aurora australis, and other phenomena that baffled scientists until the radiation belts were discovered by experiments carried out by Earth satellites. The behavior of the solar wind at great distances from the Sun could only be conjectured before the flight of Pioneer 10 to the outer planets. Until the Pioneer 10 mission, instruments on spacecraft had measured the wind only as far as the orbit of Mars. And virtually nothing was known of the interaction of the solar wind with Jupiter and Saturn or about the effects of Saturn's rings on the wind. Principal investigator: John H. Wolfe (Jupiter/Saturn) Ames Research Center, NASA, Moffett Field, California Aaron Barnes (Post-Saturn) Ames Research Center, NASA, Moffett Field, California Coinvestigators: John Mihalov, H. Collard, and D. D. McKibbin Ames Research Center, NASA Louis A. Frank University of Iowa, Iowa City Reimar Lust Max Planck Institut fur Physik und Astrophysik, Garching, Germany Devrie Intriligator University of Southern California, Los Angeles William C. Feldman Los Alamos Scientific Laboratory, New Mexico The Pioneer spacecraft each carried a plasma analyzer to evaluate the solar wind. It looked toward the Sun through a hole in each spacecraft's large dish-shaped antenna. The solar wind particles entered the plasma analyzer's apertures between two quadraspherical plates where the direction of arrival, the energy (speed), and the number of ions and electrons making up the solar wind were measured. [See Plasma Analyzer: A lasma analyzer was aimed toward the Sun through a hole in the large dish antenna of each Pioneer spacecraft; its purpose was to map the density and energy of the solar wind. (a) Diagram of the plasma analyzer. (b) Plasma analyzer ready for installation in the spacecraft.] A voltage was applied across the quadraspherical plates in a maximum of 64 steps, at a rate of one step/revolution of the spacecraft, to count particles in discrete energy ranges. The direction of particle travel was determined from instrument orientation and by knowing which of the detector targets the particle struck. The instrument had a high resolution analyzer and a medium-resolution analyzer to detect particles of different energy levels. The high-resolution analyzer had 26 continuous channel multipliers (CCM) to measure the number of ions per second with energies from 100 to 8000 eV. The medium-resolution analyzer had 5 electrometers to count ions in the energy range from 100 to 18,000 eV and electrons from 1 to 500 eV. Charged Particle Composition The charged particle detector had four measuring systems: two particle telescopes that operated in interplanetary space and two that measured the trapped electrons and protons inside the radiation belts of Jupiter and Saturn. Principal investigator: John A. Simpson University of Chicago Coinvestigators: Joseph J. O'Gallagher University of Chicago Anthony J. Tuzzolino and R. Bruce McKibben University of Chicago During the interplanetary phase of the mission, before and after encounter with Jupiter and Saturn, this experiment sought to identify the chemical elements hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, and oxygen, and to separate hydrogen, deuterium, helium-3, and helium in an attempt to differentiate between particles emanating from the Sun and those from the Galaxy. The instrument was also used to determine how streams of high-energy particles from the Sun travel through interplanetary space. The main telescope of seven solid-state detectors measured the composition of cosmic rays from 1 to 500 MeV, and a three-element, low-energy telescope measured 0.4- to 10-MeV protons and helium nuclei. Two new types of sensors were developed to cope with the extremely high intensities of trapped particles in the Jovian magnetosphere. A solid-state electron current detector, operating below -40 C (-40 F), detected those electrons above 3.3 MeV that generate the decimetric radio waves emitted by Jupiter and similar electrons in the radiation environment of Saturn. A trapped proton detector contained a foil of thorium, the atoms of which underwent nuclear fission when hit by protons with energies above 35 MeV; the foil was insensitive to electrons. Energy Spectra of Cosmic Rays The cosmic ray telescope used for this experiment was designed to monitor solar and galactic cosmic ray particles and to track the high-energy particles from the Sun. The instrument could determine which nuclei of the 10 lightest elements are the cosmic ray particles. Before saturation by radiation when near Jupiter and Saturn, the cosmic ray telescope measured high-energy particles in the radiation belts of these planets. Principal investigator: Frank B. McDonald Goddard Space Flight Center, NASA, Greenbelt, Maryland Coinvestigators: Kenneth G. McCracken Minerals Research Laboratory, North Ryde, Australia William R. Webber and Edmond C. Roelof University of New Hampsture, Durham Bonnard J. Teegarden and James H. Trainor Goddard Space Flight Center, NASA The instrument consisted of three three-element solid-state telescopes. The high-energy telescope measured the flux of protons between 56 and 800 MeV. The medium-energy telescope measured protons with energies between 3 and 22 MeV and identified the 10 elements from hydrogen to neon. The low-energy telescope measured the flux of electrons between 0.05 and 1 MeV and of protons between 0.05 and 20 MeV.