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Showing papers by "Jet Propulsion Laboratory published in 1983"


Journal ArticleDOI
TL;DR: A general purpose automated planner/scheduler is described which generates parallel plans to achieve goals with imposed time con-straints and whose durations and start time windows may be specified for sets of goal conditions.
Abstract: A general purpose automated planner/scheduler is described which generates parallel plans to achieve goals with imposed time con-straints Both durations and start time windows may be specified for sets of goal conditions The parallel plans consist of not just actions but also of events (triggered by circumstances), inferences, and scheduled events (completely beyond the actor's control) Deterministic dura-tions of all such activities are explicitly modeled, and may be any com-putable function of the activity variables A start time window for each activity in the plan is updated dynamically during plan generation, in order to maintain consistency with the windows and durations of adja-cent activities and goals The plans are tailored around scheduled events The final plan network resembles a PERT chart From this a schedule of nominal start times for each activity is generated Ex-amples are drawn from the traditional blocksworld and also from a real-istic ``Spaceworld,'' in which an autonomous spacecraft photographs objects in deep space and transmits the information to Earth The author is with the Information Systems Research Section, Jet Propulsion Laboratory, Pasadena, CA 91109

423 citations


Journal ArticleDOI
TL;DR: In this paper, a least-squares fit of the parameters of the solar system model to these data limits a simple time variation in the effective Newtonian gravitational constant to (2 + or - 4) x 10 to the -12th/yr and a rate of drift of atomic clocks relative to the implicit clock of relativistic dynamics.
Abstract: Results are presented from the analysis of solar-system astrometric data, notably the range data to the Viking landers on Mars. A least-squares fit of the parameters of the solar system model to these data limits a simple time variation in the effective Newtonian gravitational constant to (2 + or - 4) x 10 to the -12th/yr and a rate of drift of atomic clocks relative to the implicit clock of relativistic dynamics to (1 + or - 8) x 10 to the -12th/yr. The error limits quoted are the result of uncertainties in the masses of the asteroids.

186 citations


Journal ArticleDOI
TL;DR: In this article, an accurate method to evaluate the ratio of the intensities of the ambiguities to that of the signal is described, and the variations of this ratio as a function of orbital latitude and attitude control error are discussed.
Abstract: Several aspects of range and azimuth (time delay and Doppler) ambiguities in spaceborne synthetic aperture radars (SARs) are examined. An accurate method to evaluate the ratio of the intensities of the ambiguities to that of the signal is described. This method has been applied to the nominal SAR system on SEASAT and the variations of this ratio as a function of orbital latitude and attitude control error are discussed. It is also shown that the detailed range migration-azimuth phase history of an ambiguity is different from that of a signal. The images of ambiguities are, therefore, dispersed. Several examples of such dispersed images observed by the SEASAT SAR are presented. These dispersions are eliminated when the processing parameters are adjusted appropriately. Finally, a method is described which uses a set of multiple pulse repetition frequencies to determine the absolute values of the Doppler centroid frequencies for SARs with high carrier frequencies and relatively poor attitude measurements.

176 citations


Journal ArticleDOI
TL;DR: In this paper, it is pointed out that the understanding of convection in large-Prandtl-number Boussinesq fluids with uniform properties and contained in simple geometries is virtually complete.
Abstract: It is pointed out that the understanding of convection in large-Prandtl-number Boussinesq fluids with uniform properties and contained in simple geometries is virtually complete. Present efforts are typically directed towards relaxing some of the original assumptions by going to lower Prandtl number, more complicated geometries, variable material properties, or introducing new dynamical processes such as the Lorentz forces. A description is given of experiments which are concerned with the effect on convection of relaxing the assumption of a uniform viscosity. The reported experiments were designed to measure both the horizontally averaged temperature as a function of depth and the heat transfer of convection over a range of viscosity variations up to 100,000.

167 citations


Journal ArticleDOI
TL;DR: Over a large class of benign and hostile environments, e.g., Gaussian IF filter, partial-band noise jamming, the differential detector offers no theoretical performance advantage over the limiter-discriminator receiver with integrate-and-dump postdetection filtering.
Abstract: The error probability performance of differential detection of narrow-band FM is determined and compared with the analogous results for limiter-discriminator detection of the same modulation. It is shown that over a large class of benign and hostile environments, e.g., Gaussian IF filter, 1 \leq BT \leq 3, h \leq 1 , AWGN, partial-band noise jamming, the differential detector offers no theoretical performance advantage over the limiter-discriminator receiver with integrate-and-dump postdetection filtering.

120 citations


Journal ArticleDOI
04 Nov 1983-Science
TL;DR: The deposition and erosion of thin deposits of bright red dust associated with global dust storms, and the removal of centimeter amounts of material in selected areas during a dust storm late in the third winter.
Abstract: The Mutch Memorial Station (Viking Lander 1) on Mars acquired imaging and meteorological data over a period of 2245 martian days (3:3 martian years). This article discusses the deposition and erosion of thin deposits (ten to hundreds of micrometers) of bright red dust associated with global dust storms, and the removal of centimeter amounts of material in selected areas during a dust storm late in the third winter. Atmospheric pressure data acquired during the period of intense erosion imply that baroclinic disturbances and strong diurnal solar tidal heating combined to produce strong winds. Erosion occurred principally in areas where soil cohesion was reduced by earlier surface sampler activities. Except for redistribution of thin layers of materials, the surface appears to be remarkably stable, perhaps because of cohesion of the undisturbed surface material.

120 citations


01 Nov 1983
TL;DR: In this article, the authors studied the characteristic properties of driver gas following a select subset of interplanetary shocks and found that the cold driver gas usually displayed a bidirectional flow of suprathermal solar wind electrons at higher energies.
Abstract: Plasma fluid parameters calculated from solar wind and magnetic field data to determine the characteristic properties of driver gas following a select subset of interplanetary shocks were studied. Of 54 shocks observed from August 1978 to February 1980, 9 contained a well defined driver gas that was clearly identifiable by a discontinuous decrease in the average proton temperature. While helium enhancements were present downstream of the shock in all 9 of these events, only about half of them contained simultaneous changes in the two quantities. Simultaneous with the drop in proton temperature the helium and electron temperature decreased abruptly. In some cases the proton temperature depression was accompanied by a moderate increase in magnetic field magnitude with an unusually low variance, by a small decrease in the variance of the bulk velocity, and by an increase in the ratio of parallel to perpendicular temperature. The cold driver gas usually displayed a bidirectional flow of suprathermal solar wind electrons at higher energies.

90 citations


Journal ArticleDOI
TL;DR: In this article, the authors derived an equality which characterizes the distribution of the modulus of a polynomial on the unit circle, and used this inequality to prove a conjecture of Boyd concerning the geometric mean of the mean of a polynomial of several variables averaged over the torus.

88 citations


Journal ArticleDOI
TL;DR: In this article, four submarine volcanoes in the southern and central Mariana arc were dredge-sampled and the recovered lavas were analyzed for major and trace-element abundances, including rare-earth elements (REE), mineral compositions, and Sr and Nd isotopic ratios.
Abstract: Four submarine volcanoes in the southern and central Mariana arc were dredge-sampled. The recovered lavas were analyzed for major- and trace-element abundances, including rare-earth elements (REE), mineral compositions, and Sr and Nd isotopic ratios. The samples exhibit a great range of chemical and mineral compositions relative to subaerial exposures in the central arc. Zealandia Bank produces high magnesium basalts (MgO = 8–9 wt %) enriched in Ni and with forsteritic olivine, as much as Fo 88 . This lava composition is probably parental to more fractionated basalts and basaltic andesites exposed on the adjacent islands of Guguan and Sarigan. The southernmost seamounts in the Mariana arc (south of lat. 15°N) produce dacitic pumice, a composition that is not common in the active arc. REE data preclude their derivation from a basaltic parent by fractional crystallization. They may be derived by direct partial mantle melting under water-saturated conditions at low pressure. Nd and Sr isotopic data ( 143 Nd/ 144 Nd = 0.5130–0.5131; 87 Sr/ 86 Sr = 0.7032–0.7035) indicate a mantle source for the Mariana arc lavas similar in isotopic characteristics to sources for ocean islands. Significant contributions to these arc magmas from subducted oceanic crust or sediment are not evident. A spatial distribution in magmatic characteristics coincides with a structural break in the arc near 16°N. South of this, submarine seamounts produce incompatible element–enriched lavas with relatively high 87 Sr/ 86 Sr (0.7034–0.7035). These lavas were produced by a relatively low degree of partial melting (5%–15%) of a shallow (spinel-bearing) mantle. To the north, Zealandia Bank and the central arc islands are characterized by lower incompatible element abundances and lower 87 Sr/ 86 Sr (0.7032–0.7033). These lavas were produced by higher degrees of partial melting (15%–25%) of a deeper (garnet-bearing) mantle.

73 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the potential of a body possessing axial symmetry can be expressed as a power series in distance, with the Legendre polynomials as coefficients, which converges slowly in the neighborhood of thin, uniform disks and rings.
Abstract: The gravitational potential of bodies possessing axial symmetry can be expressed as a power series in distance, with the Legendre polynomials as coefficients. Such series, however, converge so slowly in the neighborhood of thin, uniform disks and rings that too many series terms must be summed in order to obtain an accurate field measure. A gravitational potential expression is presently obtained in closed form, in terms of complete elliptic integrals.

73 citations


01 Sep 1983
TL;DR: In this paper, a small scale Mach 3.5 wind tunnel incorporating certain novel design features and intended for boundary-layer-transition research has been tested, and the free stream noise intensities and spectral distributions were determined throughout the test section for several values of unit Reynolds number and for nozzle boundary layer bleed on and off.
Abstract: A small scale Mach 3.5 wind tunnel incorporating certain novel design features and intended for boundary-layer-transition research has been tested. The free stream noise intensities and spectral distributions were determined throughout the test section for several values of unit Reynolds number and for nozzle boundary layer bleed on and off. The boundary layer transition location on a slender cone and the response of this to changes in the noise environment were determined. Root mean square free stream noise levels ranged from less than one tenth up to values approaching those for conventional nozzles, with the lowest values prevailing at upstream locations within the nozzle. For low noise conditions, cone transition Reynolds numbers were in the range of those for free flight; whereas for high noise conditions, they were in the range of those in conventional tunnels.

Journal ArticleDOI
01 Jul 1983-Icarus
TL;DR: In this paper, the electromagnetic and particle cascade resulting from the absorption of galactic cosmic rays in the atmosphere of Titan is shown to be an important mechanism for driving the photochemistry at pressures of 1 to 50 mbar.

Journal ArticleDOI
01 May 1983-Icarus
TL;DR: Three types of Saturnian ring spoke structure have been observed which are distinguished by their optical appearance: narrow, filamentary and extended spoke structures as mentioned in this paper, which are of irregular shape with diffuse edges, but often narrowed at large distances.

Journal ArticleDOI
01 Jan 1983-Icarus
TL;DR: The shape and orientation of Saturn's F ring and the orbits of its two shepherding satellites have been determined from Voyager images as discussed by the authors, where the data and processing are described, and orbital parameter estimates and associated uncertainties are presented.

Journal ArticleDOI
TL;DR: In this article, the authors present the results of testing nineteen different device types from six manufacturers to investigate their latchup sensitivity with argon and krypton beams and a qualitative rationale for latchup susceptibility and a latchup cross section is given for each device type.
Abstract: Complementary metal oxide semiconductor (CMOS) microcircuits are inherently latchup prone. The four layer n-p-n-p structures formed from the parasitic pnp and npn transistors comprise a silicon controlled rectifier (SCR) which, if properly biased, may be triggered "ON" by electrical transients, ionizing radiation or a single heavy ion. This latchup phenomenon might cause loss of functionality or device burnout. For space applications cosmic ray heavy ions are a significant threat and the latchup of a CMOS circuit is a major system concern because of its catastrophic nature. This paper presents the results of testing nineteen different device types from six manufacturers to investigate their latchup sensitivity with argon and krypton beams. The parasitic npnp paths have been generally identified, and a qualitative rationale for latchup susceptibility and a latchup cross section is given for each device type. The correlation between bit-flip sensitivity and latchup susceptibility is also presented.

Journal ArticleDOI
04 Aug 1983-Nature
TL;DR: A 70-day Seasat altimeter set, where altitude was determined by the delay of a radar signal before return, was high pass filtered to obtain bathymetric data on the southern ocean as mentioned in this paper.
Abstract: A 70-day Seasat altimeter set, where altitude was determined by the delay of a radar signal before return, was high pass filtered to obtain bathymetric data on the southern ocean. Variations were estimated over cross-track passages over the same points, and longer wavelength effects were removed to reveal the shorter wavelength geoid features. Edge effects near land, subtle geoid structure features at continental margins, smaller boundary seas, and lakes were preserved by the high pass filter, which involved substracting a constant height from each 6 x 6 deg square region. A volcanic origin was indicated for the nearly continuous Louisville Ridge, which had a major elongate plateau or positive gravity anomaly located just eastward and running east-west. A large Conrad Ridge was found in the Indian Ocean, compared to previous charts. The Indian Ocean was also found to contain more rises and plateaus than previously mapped.

Book ChapterDOI
TL;DR: In this article, a review of interplanetary shock observations since the prior Solar Terrestrial Physics Symposium in 1978 is presented, focusing on shocks associated with transient solar phenomena, including coronal transients and eruptive prominences as well as flares.
Abstract: Interplanetary shock observations since the prior Solar Terrestrial Physics Symposium in 1978 are reviewed. Since the interval coincides with the recent solar maximum, emphasis is placed on shocks associated with transient solar phenomena, including coronal transients and eruptive prominences as well as flares. A good correlation between shocks and Storm Sudden Commencements has persisted into the recent maximum. Shocks have been identified that are associated with disappearing filaments and coronal transients rather than with flares. Significant progress has been made in the indirect observation of shocks near the Sun as a result of radio wave measurements in interplanetary space and measurement of the scintillation and spectral broadening of spacecraft radio transmissions. Preliminary results regarding the thickness of interplanetary shocks have appeared. Several quasi-parallel shocks propagating more nearly along, rather than across, the magnetic field have been identified. The plasma drivers accompanying interplanetary shocks have received increased attention and distinctive features have been found in electron, ion and magnetic field data.

Journal ArticleDOI
TL;DR: In this article, the energy-efficient capacity of the noiseless optical PPM channel was examined and it was shown that although the capacity per photon can be made to increase without bound, the capacity for best energy efficiency is always less than 2 nats and approaches 2nats/symbol as the bandwidth expansion factor goes to infinity.
Abstract: The energy-efficient capacity of the noiseless optical PPM channel is examined. It is shown that, although the capacity per photon can be made to increase without bound, the capacity per channel use (for best energy efficiency) is always less than 2 nats and approaches 2 nats/symbol as the bandwidth expansion factor goes to infinity.

Proceedings ArticleDOI
01 May 1983
TL;DR: A prototype system that integrates geophysical data and its metadata from both satellite and in situ sources is described, using a relational general-purpose DBMS to manage the catalog and observational data, and a video optical disk to archive images.
Abstract: This paper presents the characteristics of scientific remotely-sensed databases that are relevant to --- and pose unique challenges for --- general-purpose database management systems (DBMSs). We describe a prototype system that integrates geophysical data and its metadata from both satellite and in situ sources, using a relational general-purpose DBMS to manage the catalog and observational data, and a video optical disk to archive images. Based upon our experience with this application, we suggest augmentations to DBMSs that would facilitate their use not only for scientific databases, but also for engineering, document, and even commercial database applications.

Journal ArticleDOI
TL;DR: In this article, the design and performance of an 800 X 800 pixel charge-coupled device (CCD) imager are described using a three-phase, three-level polysilicon gate process.
Abstract: The design and performance of an 800 X 800 pixel charge-coupled device (CCD) imager are described. This device is fabricated utilizing a three-phase, three-level polysilicon gate process. The chip is thinned to 8 um and is employed in the rear illumination mode. Detailed measurements of the device performance, including dark current as a function of temperature, linearity, and noise, are presented. The device is coated with an ultraviolet (UV) downconverting phosphor which allows imaging with the same device over an extremely wide optical bandwidth.

Journal ArticleDOI
07 Oct 1983-Science
TL;DR: Comparison of the measured transmission of the ringlet at radio, visible, and ultraviolet wavelengths indicates that about half of the total extinction is due to particles smaller than 1 centimeter in radius, in contrast even with nearby regions of the C ring.
Abstract: The Voyager spacecraft observed a narrow, eccentric ringlet in the Maxwell gap (1.45 Saturn radii) in Saturn's rings. Intercomparison of the Voyager imaging, photopolarimeter, ultraviolet spectrometer, and radio science observations yields results not available from individual observations. The width of the ringlet varies from about 30 to about 100 kilometers, its edges are sharp on a radial scale < 1 kilometer, and its opacity exhibits a double peak near the center. The shape and width of the ringlet are consistent with a set of uniformly precessing, confocal ellipses with foci at Saturn's center of mass. The ringlet precesses as a unit at a rate consistent with the known dynamical oblateness of Saturn; the lack of differential precession across the ringlet yields a ringlet mass of about 5 x 10^(18) grams. The ratio of surface mass density to particle cross-sectional area is about five times smaller than values obtained elsewhere in the Saturn ring system, indicating a relatively larger fraction of small particles. Also, comparison of the measured transmission of the ringlet at radio, visible, and ultraviolet wavelengths indicates that about half of the total extinction is due to particles smaller than 1 centimeter in radius, in contrast even with nearby regions of the C ring. However, the color and brightness of the ringlet material are not measurably different from those of nearby C ring particles. We find this ringlet is similar to several of the rings of Uranus.

Journal ArticleDOI
TL;DR: A new planetary protection policy, with the following key features, is proposed: deemphasizing the use of mathematical models and quantitative analyses and simplification of the remaining compliance procedures.

Journal ArticleDOI
01 Jan 1983-Icarus
TL;DR: The presence of a temperature inversion in the lower stratospheres of both Uranus and Neptune is confirmed by the 20-micron photometric data presented in this article, which suggests that these temperature inversions may be understood as a consequence of heating through CH4 and aerosol absorption of sunlight.

Journal ArticleDOI
01 Sep 1983-Icarus
TL;DR: In this paper, it was suggested that the Kreutz group of sun-grazing comets may have collided with another body, probably a comet, at large heliocentric distance, but the probability of such an event is extremely small.

Journal ArticleDOI
07 Jan 1983-Science
TL;DR: By use of a new, very sensitive interferometric system, a faint, compact radio source has been detected near the center of the galaxy that acts as the main part of a gravitational lens.
Abstract: By use of a new, very sensitive interferometric system, a faint, compact radio source has been detected near the center of the galaxy that acts as the main part of a gravitational lens. This lens forms two previously discovered images of the quasar Q0957+561, which lies in the direction of the constellation Ursa Major. The newly detected source has a core smaller than 0.002 arc second in diameter with a flux density of 0.6 + or - 0.1 millijansky at the 13-centimeter wavelength of the radio observations. This source could be the predicted third image of the transparent gravitational lens, the central core of the galaxy, or some combination of the two. It is not yet possible to choose reliably between these alternatives.

Journal ArticleDOI
08 Sep 1983-Nature
TL;DR: In this article, the rotation rate of the northern hemisphere dipole of Venus was investigated using the Pioneer Venus Orbiter, and the relationship of the periodicity of the dipole and its long-term variation to the circulation of the cloud top atmosphere was discussed.
Abstract: Orbiter Infrared Radiometer images of the northern hemisphere dipole of Venus made at 11.5 microns aboard the Pioneer Venus Orbiter are used to investigate the detailed rotation of the dipole. The rotation rate is observed to change steadily over the 72-day data set, and there is some evidence for oscillatory variations superimposed on this trend. The relationship of the periodicity of the dipole and its long-term variation to the circulation of the cloud top atmosphere is discussed. The steady deceleration of the dipole is shown to be accompanied by a slow drift in the thermal structure of the polar atmosphere.

Journal ArticleDOI
TL;DR: In this article, the rate coefficients and product-ion distributions have been measured at near-thermal energies for reactions of CN + and C 2 N + with a number of neutral molecules using the ICR technique.

Journal ArticleDOI
TL;DR: In this article, the electrical properties of pitch-based fibers heat treated to 2500, 2750 and 3000 °C and then intercalated are reported. But the electrical resistivity both above and below room temperature, the tensile strength, and Young's modulus are not reported.

Journal ArticleDOI
TL;DR: In this paper, a minor isotope of the element of interest is implanted directly into the analytical sample to be utilized as a standard, and the hydrogen content determined by reference to the implanted deuterium standard was compared to a nuclear reaction analysis of the same sample.

Journal ArticleDOI
01 Dec 1983-Icarus
TL;DR: The spectral reflectance of a column of liquid sulfur has been measured at several temperatures between the melting point (approximately 118 C) and 173 C, and it is concluded that liquid sulfur at any temperature on Io's surface would be classified as a 'black area' according to the standards used by the Voyager imaging team in their spectrophotometric analysis as mentioned in this paper.