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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
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NASA NTRS1976

Results from the GSFC fluxgate magnetometer on Pioneer 11

A high-field triaxial fluxgate magnetometer was mounted on Pioneer 11 to measure the main magnetic field of Jupiter. It is found that this planetary magnetic field is more complex than that indicated by the results of the Pioneer 10 vector helium magnetometer. At distances less than 3 Jupiter radii, the magnetic field is observed to increase more rapidly than an inverse-cubed distance law associated with any simple dipole model. Contributions from higher-order multipoles are significant, with the quadrupole and octupole being 24 and 21 percent of the dipole moment, respectively. Implications of the results for the study of trapped particles, planetary radio emission, and planetary interiors are discussed. Major conclusions are that the deviation of the main planetary magnetic field from a simple dipole leads to distortion of the L shells of the charged particles and to warping of the magnetic equator. Enhanced absorption effects associated with Amalthea and Io are predicted.

Acuna, M. H.↗
NASA NTRS1976

Field-aligned currents in the Jovian magnetosphere - Pioneer 10 and 11

Field-aligned currents, which are known to play an important role in the dynamics of the earth's magnetosphere, would also be expected to flow in the Jovian magnetosphere during magnetically active periods. Such currents are difficult to observe largely because of their limited spatial extent and intermittent nature, but on the Pioneer 11 inbound pass to Jupiter on day 336, 1800 GRT, near the L shell of Ganymede, the helium vector magnetometer recorded a structured perturbation with the characteristic signature of a field-aligned current. No analogous structure was found on a similar Pioneer 10 inbound pass (day 337, 1200 GRT). The perturbation could have been caused by turbulence with the wake of Ganymede through which the spacecraft was moving or the perturbation could represent the first observation of a Jovian substorm. The observations are discussed in terms of both models, and difficulties are examined.

Kivelson, M. G.↗
NASA NTRS1976

A review of the Jovian magnetosphere based upon Pioneer 10 and 11

A review and analysis are presented of data derived from the Pioneer 10 and Pioneer 11 flybys of Jupiter on the Jovian plasma, magnetic field, and energetic particles in circumjovian space. The design of the space probes is described along with the principal experiments flown. Overall features of the Jovian magnetosphere are drawn and contrasted with the earth's magnetosphere. The trajectories of the two space probes are contrasted and their data on Jupiter's plasmasphere are correlated. Isointensity contours and count rates of energetic particles are plotted, flux tubes within the Jovian magnetosphere are mapped, the ring current (plasma torus) encircling the planet is described, and possible effects of solar wind and of the moons immersed in Jupiter's magnetosphere are considered.

Trainor, J. H.↗
NASA NTRS1977

The Pioneer 11 imaging experiment of Jupiter

Pioneer 11 flew by Jupiter in December 1974 and obtained several hundred images of the planet. It is presently targeted for encounter with Saturn in 1979. The imaging photopolarimeter recorded spin-scan images with high photometric accuracy. It also recorded polarimetric and zodiacal-light data. Careful design of the instrument resulted in excellent performance in the Jovian radiation environment. Imaging data were displayed to maintain the proper shape of the planet. Color images were made by synthesizing green data from red and blue data. Pictures created from Pioneer 11 imaging data show complex detail within the Red Spot is well as indications of flow around it. Bright spots with trailing plumes are seen in the Equatorial Zone. The North Polar Region is devoid of belt structure, but numerous irregular cells are seen in red light. The Galilean satellites were imaged with a resolution of several hundred kilometers.

Swindell, W.↗
NASA NTRS1978

On the observation of a flare-generated shock wave at 9.7 AU by Pioneer 10

An apparent solar-flare-generated shock wave detected by Pioneer-10 at 9.7 AU on April 9, 1976 is discussed. The shock wave may be correlated with a radio emission burst from Jupiter not associated with Io (March 30). The fact that solar flares observed on March 20 were at the central meridian with respect to Jupiter and Pioneer-10 and the fact that solar activity was very low before March 20 contribute to the argument that a shock wave had propagated to the region of the spacecraft.

Dryer, M.↗
NASA NTRS1978

Pioneer Venus encounter will occur in December

The encounter time line and mission profile are presented for the Pioneer Venus 1 Spacecraft and for the four probes and transponder bus that comprise Pioneer Venus 2. Known facts about Venus are reviewed and the history of discoveries about the planet is related. Operations of the orbiter and multiprobe are described as well as the 30 instruments being carried and provisions for data transmission.

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NASA NTRS1978

Pioneer 10 and 11 mission support

Estimates of the Deep Space Network performance capability in tracking Pioneer 10 to the telecommunications limit and for Pioneer 11 Saturn encounter are discussed. Graphs of downlink performance estimates giving geocentric range, antenna elevation, and time are included.

Miller, R. B.↗
NASA NTRS1979

Pioneer to encounter Saturn on September 1

The encounter of the Pioneer 11 Spacecraft with Saturn, designed to provide information on the evolution of the Sun and its planets, is described. Photographs and measurements of Saturn, its rings, and several of its 10 satellites, including Titan, to be taken by Pioneer instruments, are emphasized. The encounter sequence and spacecraft trajectory are discussed. A description of Saturn and its atmosphere is included. Onboard instruments and experiments are also described.

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NASA NTRS1978

Measurements of the magnetic field orientation in the Jovian ionosphere deduced from Pioneer 10 and 11 scintillation observations

In this paper the S band scintillations observed during the Pioneer 10 and 11 occultation measurements of Jupiter are analyzed. It is found that while the electron density irregularities are isotropic in the collision-dominated lower ionosphere, they are anisotropic in the upper ionosphere because of alignment along the magnetic field. By using Rytov's approximation the frequency spectrum of the log-amplitude scintillations is derived for a wave propagating in an anisotropic turbulent medium. It is shown that the spectrum depends to a large extent on the direction of anisotropy and is therefore useful for measuring the orientation of the magnetic field in regions that have not yet been probed by direct measurements. This new technique is applied to the Pioneer 10 and 11 observations, and is used to deduce the first measurements of magnetic field orientation in the ionosphere of Jupiter.

Woo, R.↗
NASA NTRS1979

Retarding potential analyzer for the Pioneer-Venus Orbiter Mission

The retarding potential analyzer on the Pioneer-Venus Orbiter Mission has been designed to measure most of the thermal plasma parameters within and near the Venusian ionosphere. Parameters include total ion concentration, concentrations of the more abundant ions, ion temperatures, ion drift velocity, electron temperature, and low-energy (0-50 eV) electron distribution function. To accomplish these measurements on a spinning vehicle with a small telemetry bit rate, several functions, including decision functions not previously used in RPA's, have been developed and incorporated into this instrument. The more significant functions include automatic electrometer ranging with background current compensation; digital, quadratic retarding potential step generation for the ion and low-energy electron scans; a current sampling interval of 2 ms throughout all scans; digital logic inflection point detection and data selection; and automatic ram direction detection. Extensive numerical simulation and plasma chamber tests have been conducted to verify adequacy of the design for the Pioneer Mission.

Knudsen, W. C.↗
NASA NTRS1979

The energetics of the ionosphere of Venus - A preliminary model based on Pioneer Venus observations

A model of the energy balance of the dayside ionosphere of Venus is presented. The coupled energy equations for electrons and ions are solved numerically and the calculated temperatures are compared with temperatures measured by instruments on the Pioneer Venus Orbiter. Neutral and ion density profiles consistent with those measured by various Pioneer Venus experiments are used in the model. It was found that using standard EUV sources and thermal conductivities the calculations produce temperatures that are much lower than the measured ones. Consequently, further calculations were performed in which (1) the thermal conductivities were inhibited by means of an almost horizontal magnetic field and/or (2) heat inflow into both the electron and ion gas at the top of the ionosphere was assumed due to the solar wind interaction. It was found that the calculated and measured temperatures were in reasonably good agreement if the thermal conductivities were inhibited by a near horizontal field of about 10 gammas and if the electron and ion heat fluxes were taken to be 4 x 10 to the 9th eV/sq cm/sec and 10 to the 7th eV/sq cm/sec, respectively.

Cravens, T. E.↗
NASA NTRS1979

Pioneer Venus Star Sensor

The design predictions and orbital performance verification of the solid state star scanner used in the Onboard Attitude Control of the Pioneer Venus Orbiter and Multiprobe are presented. The star sensor extended the scanner use to active despin control, and it differs from previous sensors in solid state detection, redundant electronics for reliability, larger field of view, and large dynamic spin range. The star scanner hardware and design performance based on the ability to predict all noise sources, signal magnitudes, and expected detection probability are discussed. In-flight data collected to verify sensor ground calibration are tabulated and plotted in predicted accuracy curves. It is concluded that the Pioneer Venus Star Sensor has demonstrated predictable star calibration in the range of .1 magnitude uncertainties and usable star catalogs of 100 stars with very high probabilities of detection, which were much better than expected and well within the mission requirements.

Gutshall, R. L.↗
NASA NTRS1978

Cosmic ray intensity gradients in the outer solar system measured by Pioneer 10 and 11

Earlier results are extended to include data from Pioneer 10 to a radial range of 11.3 AU, and from Pioneer 11 inward from 5 AU to 3.75 AU after Jupiter encounter, and to a maximum heliographic latitude of 17 deg. The data include the period from March 1972 through October 1976, during which time the neutron monitor cosmic ray intensity was, except for a few significant excursions, near solar minimum level. It is shown that the radial gradients of all particle species considered are small and positive throughout the period of study. On a shorter time scale, the data indicate transient decreases in the value of the differential gradient associated with major decreases in the cosmic ray intensity in the inner solar system. The observations are consistent with a modulating region whose radius is large compared to 11 AU. The 'anomalous' helium component, present since 1972 at earth orbit, is observed continuously at all radial distances.

Mckibben, R. B.↗
NASA NTRS1979

Polar clearing in the Venus clouds observed from the Pioneer Orbiter

High data rate, high resolution observations made by the Pioneer Venus 1 Orbiter of Venus clouds in the polar region are reported. Data obtained by the Pioneer IR radiometer reveal the presence of a localized, very warm (260 K) feature at about 80 deg N, 359 deg E, indicating a cloud height differential of about 15 km between the depressed, but not totally absent, cloud level indicated by the temperature peak and the surrounding cold zones. The observations are considered to constitute new evidence for the presence of strong atmospheric subsidence near the poles, fitting a model of vortex-type polar circulation. Implications of the observations for the single cell model of the Venus stratosphere are noted.

Taylor, F. W.↗
NASA NTRS1979

Nature of the ultraviolet absorber in the Venus clouds - Inferences based on Pioneer Venus data

Several photometric measurements of Venus made from the Pioneer Venus orbiter and probes indicate that solar near-ultraviolet radiation is being absorbed throughout much of the main cloud region, but little above the clouds or within the first one or two optical depths. Radiative transfer calculations were carried out to simulate both Pioneer Venus and ground-based data for a number of proposed cloud compositions. This comparison rules out models invoking nitrogen dioxide, meteoritic material, and volatile metals as the source of the ultraviolet absorption. Models involving either small (approximately 1 micrometer) or large (approximately 10 micrometers) sulfur particles have same serious difficulties, while ones invoking sulfur dioxide gas appear to be promising.

Pollack, J. B.↗
NASA NTRS1979

Measurements of turbulence in the Venus atmosphere deduced from Pioneer Venus multiprobe radio scintillations

The 2.3-GHz log-amplitude fluctuations observed in the radio links of the Pioneer Venus entry probes during Venus encounter have been used to study turbulence in the Venus atmosphere. The deduced estimates of the upper bound of the structure constant of the refractive index fluctuations (less than approximately 4 x 10 to the -8th/cu root cm) are inconsistent with similar entry probe measurements by Veneras 4 to 8 but are consistent with the radio occultation measurements by flyby (Mariners 5 and 10) and orbiting (Venera 9) spacecraft. The Pioneer Venus measurements therefore provide a resolution of the long-standing order of magnitude discrepancy between these earlier measurements of the structure constant.

Woo, R.↗
NASA NTRS1979

Gamma-ray burst observations by Pioneer Venus Orbiter

The Pioneer Venus Orbiter gamma burst detector is an astrophysics experiment for monitoring cosmic gamma-ray bursts. It is included in this planetary mission to provide a long baseline for accurately locating the sources of these bursts in order to identify them with specific astronomical objects. Responses to 14 gamma-ray burst events were examined; these events were verified from data acquired by other systems. Preliminary locations are proposed for three events, based on data from the Pioneer Venus Orbiter, ISEE C, and Vela spacecraft. These locations will be improved, and additional locations will be determined by including in the analyses data from Helios B and the Russian Venera 11, Venera 12, and Prognoz 7 spacecraft.

Evans, W. D.↗
NASA NTRS1979

Pioneer Saturn Encounter

The Pioneer Saturn Spacecraft, which began its journey as Pioneer 11, provided the first close view of the rings of Saturn as well as its system of moons. Its payload of 11 operating instruments obtained or confirmed data about the mass, temperature, composition, radiation belts, and atmosphere of the planet and its larger satellite, Titan. It made photometric and polarization measurements of lapetus, Rhea, Dione, and Tethys, as well as discovered additional rings. Scientific highlights of the mission are summarized. Color imagery provided by the photopolarimeter is included along with illustrations of the planet's magnetic field and radiation belts.

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