Showing papers by "Jet Propulsion Laboratory published in 1977"

New upper bounds on the rate of a code via the Delsarte-MacWilliams inequalities

Abstract: With the Delsarte-MacWilliams inequalities as a starting point, an upper bound is obtained on the rate of a binary code as a function of its minimum distance. This upper bound is asymptotically less than Levenshtein's bound, and so also Elias's.

The navigation system of the JPL robot

Abstract: The control structure of the JPL research robot and the operations of the navigation subsystem are discussed The robot functions as a network of interacting concurrent processes distributed among several computers and coordinated by a central executive The results of scene analysis are used to create a segmented terrain model in which surface regions are classified by traversibility The model is used by a path-planning algorithm, PATH, which uses tree search methods to find the optimal path to a goal In PATH, the search space is defined dynamically as a consequence of node testing Maze-solving and the use of an associative data base for context-dependent node generation are also discussed Execution of a planned path is accomplished by a feedback guidance process with automatic error recovery

Ultraviolet spectrometer experiment for the Voyager mission

Abstract: The Voyager Ultraviolet Spectrometer (UVS) is an objective grating spectrometer covering the wavelength range of 500–1700 A with 10 A resolution. Its primary goal is the determination of the composition and structure of the atmospheres of Jupiter, Saturn, Uranus and several of their satellites. The capability for two very different observational modes have been combined in a single instrument. Observations in the airglow mode measure radiation from the atmosphere due to resonant scattering of the solar flux or energetic particle bombardment, and the occultation mode provides measurements of the atmospheric extinction of solar or stellar radiation as the spacecraft enters the shadow zone behind the target. In addition to the primary goal of the solar system atmospheric measurements, the UVS is expected to make valuable contributions to stellar astronomy at wavelengths below 1000 A.

Noncoherent Pseudonoise Code Tracking Performance of Spread Spectrum Receivers

Abstract: The optimum design and performance of two noncoherent PN tracking loop configurations, namely, the delay-locked loop and tau-dither loop, are described. In particular, the bandlimiting effects of the bandpass arm filters are considered by demonstrating that for a fixed data rate and data signal-to-noise ratio, there exists an optimum filter bandwidth in the sense of minimizing the loop's tracking jitter. Both the linear and nonlinear loop analyses are presented and the region of validity of the former relative to the latter is indicated. In addition, numerical results are given for several filter types. For example, assuming ideal bandpass arm filters, it is shown that the tau-dither loop requires approximately 1 dB more signal-to-noise ratio than the delay-locked loop for equal rms tracking jitters.

Control of Cavity Noise

Abstract: Experiments have been conducted on axisymmetric shallow cavity flows with the aim of investigating methods to modify cavity shear flows such that cavity noise may be reduced. The experiments indicate the presence of large gross lateral motion of the shear layer close to the downstream cavity corner which, on interaction with it, results in production of cavity flow noise. Results also show that the continuous injection of a fluid mass at the base of the cavity has a stabilizing effect on cavity shear flows. This stability is believed to have been achieved by supplying the mass required for cavity shear layer entrainment externally. This was also accompanied by a delay in large periodic lateral motion of the cavity shear layer close to the downstream cavity corner as observed without the mass injection. Thus the addition of a continuous fluid mass appears to be an effective means of suppressing cavity flow noise.

The Aristarchus-Harbinger region of the moon: Surface geology and history from recent remote-sensing observations

Abstract: The region including the Aristarchus Plateau and Montes Harbinger is probably the most diverse, geologically, of any area of comparble size on the Moon. This part of the northwest quadrant of the lunar near side includes unique dark mantling material; both the densest concentration and the largest of the sinuous rilles; apparent volcanic vents, sinks, and domes; mare materials of various ages and colors; one of the freshest large craters (Aristarchus) with ejecta having unique colors and albedos; and three other large craters in different states of flooding and degradation (krieger, Herodotus, and Prinz). The three best-authenticated lunar transient phenomena were also observed here. This study is based principally on photographic and remote sensing observations made from Earth and Apollo orbiting space craft. Results include (1) delineation of geologic map units and their stratigraphic relationships; (2) discussion of the complex interrelationships between materials of volcanic and impact origin, including the effects of excavation, redistribution and mixing of previously deposited materials by younger impact craters; (3) deduction of physical and chemical properties of certain of the geologic units, based on both the remote-sensing information and on extrapolation of Apollo data to this area; and (4) development of a detailed geologic history of the region, outlining the probable sequence of events that resulted in its present appearance. A primary concern of the investigation has been anomalous red dark mantle on the Plateau. Based on an integration of Earth- and lunar orbit-based data, this layer seems to consist of fine-grained, block-free material containing a relatively large fraction of orange glass. It is probably of pyroclastic origin, laid down at some time during the Imbrian period of mare flooding.

Control Theoretic Models of Human Drivers in Car Following

Abstract: This paper is concerned with mathematical models of the control behavior of human drivers while following another vehicle in single lane traffic The emphasis is on the representation of the individual driver, rather than on such abstract parameters of multi-lane traffic as average density or average velocity Three basic types of approaches to representing the driver's control strategy are reviewed First is a classical control structure in which assumptions concerning the stimulus-response characteristics of the driver are included, and a form for his control strategy algorithm is assumed The second class of models is based on optimal control theory The major feature of this class of models is that an assumed performance index is explicitly included in the formulation, so that the driver's control strategy arises as a result of his attempts to minimize this index or criterion The third class of models reviewed in the paper are heuristic models, which arise from control theory The first of these, ter

System for near real-time crustal deformation monitoring

Abstract: A system for use in detecting earth crustal deformation using an RF interferometer technique for such purposes as earthquake predictive research and eventual operational predictions. A lunar based RF transmission or transmissions from earth orbiting satellites are received at two locations on Earth, and a precise time dependent phase measurement is made of the RF signal as received at the two locations to determine two or three spatial parameters of the antenna relative positions. The received data are precisely time tagged and land-line routed to a central station for real-time phase comparison and analysis. By monitoring the antenna relative positions over an extended period of months or years, crustal deformation of the earth can be detected.

Voyager imaging experiment

Abstract: The overall objective of this experiment is exploratory reconnaissance of Jupiter, Saturn, their satellites, and Saturn's rings. Such reconnaissance, at resolutions and phase angles unobtainable from Earth, can be expected to provide much new data relevant to the atmospheric and/or surface properties of these bodies. The experiment also has the following specific objectives:

Matrix Perturbation for Structural Dynamic Analysis

Abstract: The objective of the effort was to investigate methodologies to reduce the cost of evaluating changes in dynamic loads when small modifications are made in the structure. A matrix perturbation technique has been developed to calculate the dynamic responses of a structural system that has been modified from the original design. The calculation is based on the results of the original design and the assumption that the structural modification is small. The advantage of the method is an update of the dynamic response due to design changes without performing an entire analysis. This procedure can be used in a design load analysis cycle in which the structural design is subject to frequent changes. A sample problem is given to demonstrate the validity of the technique.

Sun tracking solar energy collector

Abstract: A parabolic reflector is supported so that it can track the sun The support for this reflector comprises an azimuth frame supported on two wheels and a central pivotal point which are positioned in a substantially triangular configuration The two wheels rotate on tracks On top of the azimuth frame, there is provided an elevation frame The elevation frame includes curved rails which define a portion of an arc and extend vertically The reflector rides on wheels captured within the curved rails The wheels of the azimuth frame are driven by an azimuth actuator The reflector structure is counterbalanced about its elevation axis by a pendulum cable system which is driven by a motor to change elevation At the focal point of the parabolic reflector, a heat engine or receiver is mounted independently on the reflector Suitable means are provided for moving the reflector about its two axes in order to track the sun

Solar energy collection system

Abstract: A fixed, linear, ground-based primary reflector having an extended curved sawtooth-contoured surface covered with a metalized polymeric reflecting material, reflects solar energy to a movably supported collector that is kept at the concentrated line focus of the reflector primary. The primary reflector may be constructed by a process utilizing well-known freeway paving machinery. The solar energy absorber is preferably a fluid-transporting pipe. Efficient utilization leading to high temperatures from the reflected solar energy is obtained by cylindrical shaped secondary reflectors that direct off-angle energy to the absorber pipe. To obtain higher temperature levels, refocusing secondary reflectors, that cause a series of discrete spots of highly concentrated solar energy to fall on the fluid-transporting pipe, are utilized. A seriatim arrangement of cylindrical secondary reflector stages and spot-forming reflector stages produces a high temperature solar energy collection system of greater efficiency.

Radiometric measurement of stratospheric HCl

Abstract: On March 17, 1976, the atmospheric absorption of solar infrared radiation at sunset was measured by a balloon-borne pressure modulator, whose major feature was a cell containing gaseous HCl, through which the incoming radiation passed. The side-band:wide-band ratio which is related to the amount of atmospheric HCl in the path between the instrument and the sun, was also measured. The vertical mixing ratio profile for gaseous HCl for the altitude range 16-39 km, was derived from the data by using a computer model. The shape of the profile implies that the major source of HCl in the stratosphere is around 32 km. The importance of this profile in determining the effects of man-made chlorine compounds on atmospheric ozone is stressed.

On Szebehely's equation for the potential of a prescribed family of orbits

Abstract: In the present note we first give a simple proof of the Dainelli formulas for the force field generating a given family of orbits. We also show that the Szebehely partial differential equation for the potential can be derived from the Dainelli formulas if the energy integral is assumed. The Szebehely equation can be solved directly with the method of characteristics or indirectly with the Joukovsky formulas. Several examples are briefly described in the article. In particular we find some rather general potential functions corresponding to circular motion.

A generalized |ω|-filter for 3-D reconstruction

Abstract: The 3-D reconstruction of a density function is based on a direct convolution algorithm developed first by Ramachandran and Lakshiminarayanan. Their method adopts a particular choice of weighting function or filter which is called here an |ω|-filter. In some cases this choice of filter had an undesirable oscillatory response. To remedy this problem Shepp and Logan found a weighting function which produced a better reconstruction of a head section. The filter functions of Ramachandran and Lakshminarayanan and Shepp and Logan are only two of many choices for an |ω|-filter. Shepp and Logan's filter was the best for the early tomographic machines. Their filter function provided both a damped response to the cut-off frequency and a low sensitivity to noise. For the new tomographic machines, however, it is desirable to find filters that are not sensitive to counting noise, sample size and sample spacing as the previous filters. Here a study and generalization is made of the previous |ω|-filters. It extends the important filters of Ramachandran and Lakshiminarayanan, and Shepp and Logan to a class of generalized |ω|-filters. A generalized |ω|-filter can be chosen to have both good accuracy and a flexibility to cope with noise. A detailed comparison is made among the different possible filter shapes with respect to their responses to simulated data and noise. Finally in this paper it is demonstrated that a substantial reduction in the x-ray exposure time can be accomplished by choosing the appropriate generalized |ω|-filter.

Optimal policy for batch operations: backup, checkpointing, reorganization, and updating

Abstract: Many database maintenance operations are performed periodically in batches, even in realtime systems. The purpose of this paper is to present a general model for determining the optimal frequency of these batch operations. Specifically, optimal backup, checkpointing, batch updating, and reorganization policies are derived. The approach used exploits inventory parallels by seeking the optimal number of items—rather than a time interval—to trigger a batch. The Renewal Reward Theorem is used to find the average long run costs for backup, recovery, and item storage, per unit time, which is then minimized to find the optimal backup policy. This approach permits far less restrictive assumptions about the update arrival process than did previous models, as well as inclusion of storage costs for the updates. The optimal checkpointing, batch updating, and reorganization policies are shown to be special cases of this optimal backup policy. The derivation of previous results as special cases of this model, and an example, demonstrate the generality of the methodology developed.

Chemical bioinduction of rubber in guayule plant.

Abstract: The treatment of young guayule plants with 2-(3,4-dichlorophenoxy)-triethylamine stimulated the accumulation of polyisoprenoid rubber in the stem and root tissues. This finding suggests that rubber productivity can be improved by the use of chemical agents on guayule and other rubber-forming plants.

System for plotting subsoil structure and method therefor

Abstract: Data for use in producing a tomograph of subsoil structure between boreholes is derived by placing spaced geophones in one borehole, and if desired also on the earth surface, and by producing a sequence of shots at spaced apart locations in the other borehole. The signals, detected by each of the geophones from the various shots, are processed either on a time of arrival basis, or on the basis of signal amplitude, to provide information of the characteristics of a large number of incremental areas (pixels) between the boreholes. Such information is useable to produce a tomograph of the subsoil structure between the boreholes. By processing signals of relatively high frequencies, e.g., up to 1000 Hz, and by closely spacing the geophones, a high resolution tomograph can be produced.

Electrical, magnetic, and optical properties of the tetrathiafulvalene /TTF/ pseudohalides, /TTF/12/SCN/7 and /TTF/12/SeCN/7

Abstract: The electrical, magnetic, and optical properties of charge-transfer salts containing tetrathiafulvalene (TTF) and the pseudohalides, thiocyanate (SCN) and selenocyanate (SeCN), have been investigated. These salts are quasi-one-dimensional compounds containing cation radicals only, in contrast to a cation-radical-anion-radical system, such as tetrathiafulvalene tetracyanoquinodimethane (TTF) (TCNQ). Measurements of electrical conductivity, thermoelectric power, and optical reflectivity of single crystals of the nonstoichiometric salts (TTF)12(SCN)7 and (TTF)12(SeCN)7 show metal-like characteristics above 200 K (high-temperature region). The conductivities at room temperature are approximately 750 mho/cm comparable to those found in (TTF) (TCNQ), and increase with decreasing temperature down to approximately 200 K. The thermoelectric power at room temperature is small and positive (approximately 9 microvolts/deg K), and decreases linearly with decreasing temperature in this region (as expected for metal-like hole conduction along the TTF chains). The ESR intensity, however, decreases with decreasing temperature above 200 K. At 170 K a metal-nonmetal transition occurs, and the transport and magnetic properties below this temperature are characteristic of a semiconducting state.

Are striations on Phobos evidence for tidal stress

Abstract: A series of striations or grooves over a great part of the surface of Phobos, the inner satellite of Mars, can be observed on Viking orbiter photographs. It is suggested that some of these features are related to a readjustment of the satellite's figure with increasing tidal stress as the orbit evolves inwards under the action of tidal friction. If the width of the grooves is in fact due to tidal readjustments of the figure of Phobos, then the older craters should be systematically deformed from their initial nearly circular shapes.

Radio structure of 3C147 determined by multi-element very long baseline interferometry

Abstract: The radio structure of the quasar 3C147 has been determined from multi-baseline VLBI data at 609 MHz using both a conventional method and a technique which uses the 'closure' phase information to produce a good approximation to a synthesis map of the source. The structure is similar to the central part of M87, with a bright core and a linear 'jet' of a projected length of about 1.5 kpc which is concentrated in bright 'knots'.

Solar photolysis of water

Abstract: Hydrogen is produced by the solar photolysis of water in a first photo-oxidation vessel with a transparent wall in the presence of a water soluble photo-oxidizable reagent and an insoluble hydrogen recombination catalyst Simultaneously oxygen is produced in a second photo-reduction reactor with a transparent wall in the presence of an insoluble photo-reduction reagent catalyst When spent, the solution from the first reactor is fed into the second reactor A reaction occurs in the dark in which the redox reagents are regenerated, and the regenerated photo-oxidation reagent solution is recycled to the first reactor The photo-oxidation reagent is preferably a europium salt, and the first reactor also contains a hydrogen recombination catalyst such as platinum supported on glass beads The photo-reduction catalyst is a bifunctional reagent catalyst including a transition metal salt such as a manganese oxychloride salt covalently bonded to the surface of a high area support such as glass fibers, together with a hydroxyl or chlorohydroxyl decomposition catalyst of high area

The origin of the grooves on Phobos

Abstract: Various theories for the long, linear depressions on the surface of Phobos are reviewed. Imagery from Viking Orbiters is used to map the surface distribution of the grooves, study their morphology, and date them by means of the density of superimposed impact craters. Data is presented which tends to support the hypothesis that the deep-seated fracturing was caused by a large, nearly catastrophic cratering event. It is suggested that the grooves were produced during the creation of the Stickney crater, rather than as the result of tidal stresses induced by Mars or by drag forces during the hypothetical capture of the satellite by Mars.

Solar array strip and a method for forming the same

Abstract: Providing printed circuitry in a sandwiched relation with a pair of flexible layers of non-conductive material, depositing solder pads on the printed circuitry and storing the resulting substrate on a drum, withdrawing the substrate from the drum and incrementally advancing it along a linear path, serially transporting solderless solar cells into engagement with the pads and thereafter heating the pads for thus attaching the cells to the circuitry, cleaning excess flux from the solar cells, encapsulating the cells in a protective coating and thereafter spirally winding the resulting array on a drum.

Dual membrane, hollow fiber fuel cell and method of operating same

Abstract: A gaseous fuel cell is described which includes a pair of electrodes formed by open-ended, ion-exchange hollow fibers, each having a layer of metal catalyst deposited on the inner surface thereof and large surface area current collectors such as braided metal mesh in contact with the metal catalyst layer. A fuel cell results when the electrodes are immersed in electrolyte and electrically connected. As hydrogen and oxygen flow through the bore of the fibers oxidation and reduction reactions develop an electrical potential. Since the hollow fiber configuration provides large electrode area per unit volume and intimate contact between fuel and oxidizer at the interface, and due to the low internal resistance of the electrolyte, high power densities can be obtained.