Showing papers by "Jet Propulsion Laboratory published in 1981"

Advanced automation for space missions

Abstract: A NASA/ASEE Summer Study conducted at the University of Santa Clara in 1980 examined the feasibility of using advanced artificial intelligence and automation technologies in future NASA space missions. Four candidate applications missions were considered. (1) An intelligent Earth-sensing information system, (2) an autonomous space exploration system, (3) an automated space manufacturing facility, and (4) a self-replicating, growing lunar factory. The study assessed the various AI and machine technologies which must be developed if such sophisticated missions are to become feasible by century's end.

The long-term motion of comet Halley

Abstract: The orbital motion of comet Halley is numerically integrated back to 1404 BC. Starting with an orbit based on the 1759, 1682, and 1607 observations of the comet, the integration was run back in time with full planetary perturbations and nongravitational forces taken into account at each 0.5 day time-step. Small empirical corrections were made to the computed perihelion passage time in 837 and to the osculating orbital eccentricity in 800. In nine cases, the perihelion passage times calculated by Kiang (1971) from Chinese observations have been redetermined, and osculating orbital elements are given at each apparition from 1910 back to 1404 BC.

Transformation from proper time on Earth to coordinate time in solar system barycentric space-time frame of reference

Abstract: In order to obtain accurate computed values of Earth-based range and Doppler observables of a beep space probe, an expression is required for the time differencet−τ, wheret is coordinate time in the solar system barycentric space-time frame of reference and τ is proper time recorded on a fixed atomic clock on earth. This paper is part 1 of a two-part article which obtains an expression fort−τ which is suitable for use in obtaining computed values of observations of a spacecraft or celestial body located anywhere in the solar system. The expression can also be used in the computation of Very Long Baseline Interferometry data types. Part 1 obtains an expression fort−τ which is a function of position and velocity vectors of the major celestial bodies of the solar system and the atomic clock on Earth which reads τ. In Part 2, this expression will be transformed to a function of time and the Earth-fixed coordinates of the atomic clock.

Evaluation of sommerfeld integrals for lossy half-space problems

Abstract: This paper reviews some of the recent techniques investigated by the authors for numerical, asymptotic and approximate evaluations of the Somraerfeld integrals. Only the summaries of the final formulations are given and their numerical characteristics are illustrated using representative numerical data. Due to space limitations, the discussion in this paper is limited to the cases where both the source and the observation points are above the lossy half-space.

Orbits of the Small Satellites of Saturn

Abstract: Orbital parameter values and associated uncertainties determined from Voyager 1 imaging data for the satellites 1980S1, 1980S3, 1980S6, 1980S26, 1980S27, and 1980S28 are presented.

Coherent Detection of Frequency-Hopped Quadrature Modulations in the Presence of Jamming--Part I: QPSK and QASK Modulations

Abstract: This paper examines the performance of coherent QPSK and QASK systems combined with FH or FH/PN spread spectrum techniques in the presence of partial-band multitone or noise jamming. The worst-case jammer and worst-case performance are determined as functions of the signal-to-background noise ratio (SNR) and signal-to-jammer power ratio (SJR). Asymptotic results for high SNR are shown to have a linear dependence between the jammer's optimal power allocation and the system error probability performance.

AFGL trace gas compilation: 1980 version.

Abstract: A new edition of the AFGL trace gas compilation is now available. Absorption line parameters of positions, intensities, and half-widths are given for the major bands of thirteen gases covering the spectral region from 0 to 10,000/cm. In addition to updating the original gases (NO, SO2, NO2, and NH3), the molecules HNO3, OH, HF, HCl, HBr, HI, ClO, OCS, and H2CO have been added to the compilation. The sources for the additions and modifications are described.

Effect of zinc impurity on silicon solar-cell efficiency

Abstract: Zinc is a major residue impurity in the preparation of solar-grade silicon material by the zinc vapor reduction of silicon tetrachloride. This paper projects that in order to get a 17-percent AM1 cell efficiency for the Block IV module of the Low-Cost Solar Array Project,1the concentration of the zinc recombination centers in the base region of silicon solar cells must be less than 4 × 1011Zn/cm3in the p-base n+/p/p+ cell and 7 × 1011Zn/cm3in the n-Base p+/n/n+ cell for a base dopant impurity concentration of 5 × 1014atoms/cm3. If the base dopant impurity concentration is increased by a factor of 10 to 5 × 1015atoms/cm3, then the maximum allowable zinc concentration is increased by a factor of about two for a 17-percent AM1 efficiency. The thermal equilibrium electron and hole recombination and generation rates at the double-acceptor zinc centers are obtained from previous high-field measurements as well as new measurements at zero field described in this paper. These rates are used in the exact dc-circuit model to compute the projections.

Iue Detection Of Bursts Of H Ly-alpha Emission From Saturn

Abstract: A new investigation is reported of the potential sources of Ly-alpha emission in a series of observations of the Saturnian system carried out between January and July 1980 using the short wavelength spectrograph of the IUE Observatory. It is noted that north-south maps of the Ly-alpha emission across the planet disk show pronounced spatial asymmetries in emission brightness. These asymmetries vary to a marked extent on a time scale of days and are interpreted as bursts of Ly-alpha emission of as much as 1 kR brightness averaged over a 6 x 10 arcsec area, above a constant planetary emission level of 700-800 R. In fact, the Ly-alpha emission peaks manifest themselves as essentially point source features in these data; it is pointed out that if the emitting region is smaller than the 6 x 10 arcsec instrumental resolution, the surface brightness must be proportionally higher.

Formation of organic molecules on Titan

Abstract: A mechanism is proposed for the formation of complex organic nitrogen compounds in the dense lower atmosphere of Titan. The mechanism is based on three-body association reactions with HCNH(+) ions formed by the reaction of N(+) with CH4, which lead to the production of ethyl cyanide, vinyl cyanide and cyanoacetylene. Calculations for a model atmosphere consistent with the preliminary interpretation of Voyager 1 data for the region of maximum cosmic ray activated chemistry, corresponding to a temperature between 150 and 160 K and a pressure of 20 mbar, are presented which show substantial organic nitrile and hydrogen cyanide production rates. Based on these production rates, it is expected that significant equilibrium concentrations of these compounds will be found on Titan.

Anomalous wind estimates from the Seasat scatterometer

Abstract: The Seasat-A Satellite Scatterometer (SASS) measured the radar backscatter intensity from the sea surface using a four-beam microwave antenna. Estimates of wind speed and direction derived from these data agree well with surface measurements made during the Joint Air-Sea Interaction experiment, but there are occasions (3 out of 23 satellite passes) when the results are anomalous. One such occasion when the satellite measurements differed substantially from those at the surface of the sea has been studied, and it has been concluded that the interpretation of the SASS measurements may have been vitiated by a mid-level convective system deep enough to produce thunderstorms and lightning.

Virtual Phase Imager For Galileo

Abstract: A CCD imaging array with a new virtual-phase technology that has been developed for use in a slow-scan imaging system for NASA's Galileo mission to Jupiter is described. Among its features are an absence of interlevel shorts, simplicity of fabrication, low dark current (less than 0.4 nA/sq cm), high full well, high quantum efficiency in the front side illumination mode, large dynamic range (greater than 5000), good charge transfer efficiency (0.99997), excellent linearity (0.2%), uniform pixel response (1%), and improved radiation hardness. It is noted that its operating voltages must be constrained to narrow windows to maintain good charge transfer efficiency and avoid the production of spurious and leakage charge.

Spacecraft-Doppler gravity-wave detection. I. Theory

Abstract: It is the purpose of this paper to produce a self-contained summary of the methods which may be used to analyze data in the newly developing field of spacecraft-Doppler gravity-wave detection. Three algorithms are developed. The first is a near-optimal matched filter which produces a $\sqrt{2}$ improvement in signal-to-noise ratio for purposes of detecting short bursts of gravitational radiation. The second two methods are to be used in the search for the cosmic background, the one concentrating on the spectrum of the Doppler data and the other concentrating on the autocorrelation function. It is shown that these two methods are theoretically equivalent, although the autocorrelation method may be somewhat easier to use. The gain of these algorithms is shown to be $\ensuremath{\propto}\sqrt{n}$ where $n$ is the number of data points in the Doppler record.

Extended plausible inference

Abstract: A generalized theory of plausible inference has been developed. extended to arbitrary expressions of propositional calculus from Shortliffe and Buchanan's original MYCIN formulation. The theory represents uncertainty of belief, and invokes four rules of inference, instead of the two of standard logic. Areas of application include diagnostic problems and deciding between alternative hypotheses. The theory has been implemented in the PI system. The intended area of application for PI is the trouble-shooting of a failed spacecraft, and the solution to a simplified problem drawn from this area is described.

Spacecraft-Doppler gravity-wave detection. II - Results

Abstract: A description is presented of the results of experiments conducted to detect very-low-frequency (VLF)-band gravitational radiation. The experiments are based on Doppler tracking of the Voyager I spacecraft. There were basically two kinds of experiments performed. The first was concerned with the detection of solitary bursts of gravitational radiation such as might emanate from a single violent astrophysical event. There were no positive results of the search for such burst events at a level of 3 x 10 to the -14th, nearly two orders of magnitude away from the required sensitivity. The second kind of experiment performed was related to an attempt to detect the isotropic background of cosmic gravitational radiation. The negative results fail by a little over an order of magnitude to limit radiation below the existing limits due to cosmic evolution. In summary, there was no detection of gravitational radiation at an amplitude of 3 x 10 to the -14th for VLF waves of frequency around 0.001 Hz.

On the application of a fast polynomial transform and the Chinese remainder theorem to compute a two-dimensional convolution

Abstract: In this paper, a fast algorithm is developed to compute two-dimensional convolutions of an array of d 1 × d 2 complex number points where d 2 =2mand d 1 =2m-r+1for some 1\leq r \leq m . This new algorithm requires fewer multiplications and about the same number of additions as the conventional FFT method for computing the two-dimensional convolution. It also has the advantage that the operation of transposing the matrix of data can be avoided.

Non‐parametric identification of a class of non‐linear close‐coupled dynamic systems

Abstract: A non-parametric identification technique for the identification of arbitrary memoryless non-linearities has been presented for a class of close-coupled dynamic systems which are commonly met with in mechanical and structural engineering. The method is essentially a regression technique and expresses the non-linearities as series expansions in terms of orthogonal functions. Whereas no limitation on the type of test signals is imposed, the method requires the monitoring of the response of each of the masses in the system. The computational efficiency of the method, its easy implementation on analogue and digital machines and its relative insensitivity to measurement noise make it an attractive approach to the non-parametric identification problem.

Analysis Techniques in AC/DC Power Systems

Abstract: Many present-day industrial power systems have combined ac/dc power distribution systems. A typical example is a coal mine power system, where ac is used for running the mining equipment and dc is used for track haulage, etc. Also, the topology of the dc network is constantly changing due to the movement of locomotives along the track. Methods are described that can be used to carry out load-flow and short-circuit analyses of such a system.

Overview of Containerless Processing Technologies

Abstract: In the near future, a large segment of the scientific community will have an opportunity to perform materials processing experiments on the Space Shuttle in the reduced gravity environment of space. Many of these experiments will require containerless processing techniques that provide manipulation and control of weightless (molten) materials without physical contact with container walls or other holding devices. A variety of containerless processing technologies are now being developed for space and ground-based materials processing facilities. The utilization of air jets or high intensity acoustic, electromagnetic or electrostatic fields can produce forces that support and manipulate materials. Most of the present containerless research is directed toward the development of high temperature systems capable of melting and resolidifying materials. This paper will review the materials processing capabilities and level of developmental progress of each technique. An introduction to available NASA test facilities will also be given.