Showing papers by "Jet Propulsion Laboratory published in 1978"

The ISEE-1 and ISEE-2 Plasma Wave Investigation

Abstract: The ISEE-1 and ISEE-2 plasma wave investigation is designed to provide basic information on wave-particle interactions in the earth's magnetosphere and in the solar wind. The ISEE-1 plasma wave instrument uses three electric dipole antennas with lengths of 215, 73.5, and 0.61 m for electric-field measurements, and a triaxial search coil antenna for magnetic-field measurements. The ISEE-2 plasma wave instrument uses two electric dipoles with lengths of 30 and 0.61 m for electric-field measurements, and a single-axis search coil antenna for magnetic-field measurements. The ISEE-1 plasma wave instrumentation provides a comprehensive determination of wave characteristics over a broad frequency range, including high-frequency resolution spectrum scans, simultaneous high-time resolution electric- and magnetic-frequency-spectrum measurements, wave normal and Poynting flux measurements, and wide-band waveform measurements. The basic frequency range of the ISEE-1 measurements is 5.62 Hz-311 kHz, although wide-band waveform measurements can be made in selected frequency ranges up to 2.0 MHz using a special long baseline interferometer mode of operation. The ISEE-2 plasma wave instrumentation consists of a 16-channel spectrum analyzer covering the frequency range from 5.62 Hz to 31.1 kHz and a wide-band waveform receiver with the capability of making waveform measurements in selected frequency ranges up to 2.0 MHz.

In-flight performance of the IUE

Abstract: A report on the initial performance of the IUE satellite, launched in January, 1978, is given. Attention is given to optical performance, camera performance, background corrections, photometric performance, and data reduction. Samples of high-dispersion and low-dispersion spectra are shown. A remaining problem of proper separation of high dispersion orders in data reduction is discussed.

Filtering and error analysis via the UDU^{T} covariance factorization

Abstract: Kalman filter algorithms based on the UDUTcovariance factorization are discussed, with special attention given to algorithm implementation efficiency. A U-D factored covariance error analysis algorithm is formulated, and its efficiency and numerical stability are demonstrated in a representative orbit determination problem. The numerical results are compared with those obtained using covariance error analysis formulae, and the comparison highlights the numerical superiority of our algorithm A by-product of the U-D analysis is a new, highly efficient algorithm mechanization of the arbitrary gain covariance update formula.

Nonlinear and linear bottom interaction effects in shallow water

Abstract: Spectral wave transformation in shallow water is investigated by examining nonlinear and linear bottom interaction effects. The effect of nonlinear wave-wave interaction in shallow water is investigated by including the depth dependent dispersion relationship in the nonlinear calculations. Dissipative mechanisms examined are bottom friction, percolation within the sand layer, and wave motion in the mud layer induced by hydrodynamic forces acting at the mud line. Comparisons with observations suggest that bottom motion can be one order of magnitude more pronounced than friction or percolation when soft mud occupies the top layer such as found in the Gulf of Mexico. In the North Sea (JONSWAP area) coarse sand with mean grain diameter ≥ 0.3 mm is found in the top sediment layer. Here swell energy dissipation can be explained by the linear percolation mechanism. When bottom sand is fine (mean grain diameter ≤ 0.4 mm), such as found offshore of Panama City and Marine-land, Florida, nonlinear bottom friction is found to explain swell dissipation adequately. A nonlinear bottom scattering mechanism was investigated by Long (1973) who found the effect to be possibly important in the JONSWAP area but required detailed directional wave measurements to derive conclusive results. This paper examines five different data sets on wave transformation in shallow water and offers explanations in terms of bottom interaction mechanisms.

Double-sided solar cell package

Abstract: In a solar cell array of terrestrial use, an improved double-sided solar cell package consisting of a photovoltaic cell having a metallized P-contact strip and an N-contact grid provided on opposite faces of the cell, a transparent tubular body forming an enclosure for the cell, a pedestal supporting the cell from within the enclosure comprising an electrical conductor connected with the P-contact strip provided for each face of the cell, and a reflector having an elongated reflective surface disposed in substantially opposed relation with one face of the cell for redirecting light to impinge thereon whereby the cell is subjected to incident radiation at each of its opposite faces.

Experimental results of large-scale structures in jet flows and their relation to jet noise production

Abstract: Experiments have been performed to determine the role of large-scale turbulent structures in the production of jet noise. Axisymmetric turbulent jet flows at ambient stagnation temperature have been observed with the aid of flow visualization techniques. Jet Mach numbers at the nozzle exit ranged between 0.1 and 0.9, and the Reynolds number, based on nozzle exit diameter, was approximately 10 to the 6th. Large organized turbulent structures existed as far downstream of the nozzle exit as 7 diameters. High-speed schlieren motion pictures synchronized with near-field pressure measurements of an excited jet indicated that strong instantaneous peaks in the pressure signal occurred whenever a merging process between two large-scale organized structures occurred. This pressure pulse propagated at a speed which was somewhat larger than the velocity of the jet at the nozzle exit.

Microwave remote sensing of sea ice in the AIDJEX Main Experiment

Abstract: A microwave remote sensing program of sea ice in the Beaufort Sea was conducted during the Arctic Ice Dynamics Joint Experiment (AIDJEX). Several types of both passive and active sensors were used to perform surface and aircraft measurements during all seasons of the year. In situ observations were made of physical properties (salinity, temperature, density, surface roughness), dielectric properties, and passive microwave measurements were made of first-year, multiyear, and first-year/multiyear mixtures. Airborne passive microwave measurements were performed with the electronically scanning microwave radiometer while airborne active microwave measurements were performed by synthetic aperture radar, X- and L-band radar, and a scatterometer.

Interferometric locating system

Abstract: A system for determining the position of a vehicle or other target that emits radio waves, which is of the type that senses the difference in time of arrival at spaced ground stations of signals from the vehicle to locate the vehicle on a set of intersecting hyperbolas. A network of four ground stations detects the radio emissions from the vehicle, and by means of cross correlation derives the relative signal delay at the ground stations from which the vehicle position is deduced. Because the signal detection is by cross correlation, no knowledge of the emission is needed, which makes even unintentional radio noise emissions usable as a locator beacon. By positioning one of the four ground stations at an elevation significantly above the plane of the other three stations, a three dimensional fix on the vehicle is possible.

IUE observations of extragalactic objects

Abstract: During the commissioning phase of IUE several extragalactic objects were observed spectrally at low dispersion in the UV range lambda lambda 1150-3200: the Seyfert galaxies NGC4151 and NGC1068, the QSO 3C273, the BL Lacertae object B2 1101+38, the giant elliptical galaxy M87 and the spiral galaxy M81. The results obtained are presented and a preliminary analysis given for all six objects, discussing the continuous spectrum, extinction, emission line spectrum and absorption line spectrum, where possible for each case. Several new or confirmatory astrophysical results are obtained.

Photocatalytic oxidation of organic compounds on Mars

Abstract: Ultraviolet-stimulated catalytic oxidation is proposed as a mechanism for the destruction of organic compounds on Mars. The process involves the presence of gaseous oxygen, UV radiation, and a catalyst (titanium dioxide), and all three of these have been found to be present in the Martian environment. Therefore it seems plausible that UV-stimulated oxidation of organics is responsible for degrading organic molecules into inorganic end products.

Radar observations of hurricane wave directions

Abstract: This paper presents an analysis of data collected in a hurricane wave research program. The data were collected with a synthetic aperture radar (SAR) during five aircraft flights into hurricanes in August and September, 1976. These data are the first collected on the directional distributions of waves throughout the region of active generation. The wave patterns in all of the storms are similar and show a marked radially asymmetry. The dominant waves propagate ahead of the storm in a broad arc that has an apparent center in a region of confused sea to the right and rear of the hurricane eye. The asymmetry in the wave patterns is attributed to the forward motion of the storms. The wave directions throughout the storms do not show a sensitive dependence on the forward speed of the storms or on their maximum wavespeeds. However, there is an increase in peak wavelength with increasing windspeed and forward velocity.

The fast decoding of Reed-Solomon codes using Fermat theoretic transforms and continued fractions

Abstract: It is shown that Reed-Solomon (RS) codes can be decoded by using a fast Fourier transform (FFT) algorithm over finite fields GF(F_{n}) , where F_{n} is a Fermat prime, and continued fractions. This new transform decoding method is simpler than the standard method for RS codes. The computing time of this new decoding algorithm in software can be faster than the standard decoding method for RS codes.

Module failure isolation circuit for paralleled inverters

Abstract: A module failure isolation circuit for paralleled inverters senses and averages the collector current of each inverter power transistor and compares the collector current of each power transistor with the average collector current of all power transistors to determine when the sensed collector current of a power transistor in any one inverter falls below a predetermined ratio of the average collector current The module associated with any transistor that fails to maintain a current level above the predetermined ratio of the average collector current is then shut off A separate circuit detects when there is no load, or a light load, to inhibit operation of the isolation circuit during no load or light load conditions

The ISEE-C Plasma Wave Investigation

Abstract: The ISEE-C plasma wave investigation is designed to provide comprehensive information on interplanetary wave-particle interactions. Three spectrum analyzers with a total of 19 bandpass channels cover the frequency range 0.3 Hz to 100 kHz. The main analyzer, which uses 16 continuously active amplifiers, gives two complete spectral scans per second in each of 16 filter channels. The instrument sensors include a high-sensitivity magnetic search coil, and electric antennas with effective lengths of 0.6 and 45 m.

Tracking Performance of Costas Loops with Hard-Limited In-Phase Channel

Abstract: It is becoming increasingly popular in the design of suppressed carrier receivers, which employ Costas loops for earrier reconstruction, to hard-limit the output of the in-phase channel. Doing so allows replacement of the analog multiplier, which forms the loop error signal, with a chopper-type device which typically exhibits much less dc offset. The false lock behavior of such a hard-limited loop was recently investigated and shown to be quite different from that of the conventional Costas loop without the hard limiter. This paper presents the companion, analysis of the tracking performance of the hard-limited loop and assesses the penalty, if indeed it is a penalty rather than an improvement, in this performance relative to the conventional Costas loop with an analog third multiplier. In particular, for the case of RC arm filters and NRZ data, the squaring loss (or equivalently the linear loop tracking jitter) is evaluated and illustrated as a function of the ratio of arm filter bandwidth to data rate and data signal-to-noise ratio. Superimposed on these numerical results will be the corresponding ones for the conventional Costas loop. As a finale, the equivalence in operation of the Costas loop with hard-limited in-phase channel and a baseband modulation carrier reconstruction loop referred to as a demod/ remod loop is discussed.

Images of Io's Sodium Cloud

Abstract: The first direct images of Io's sodium cloud are reported and analyzed. The observed cloud extends for more than 100,000 kilometers along Io's orbit and is a somewhat 'banana-shaped' partial toroid. More sodium atoms precede Io than follow it. A model based on the escape of sodium from a specific localized area on Io provides a reasonable fit to the observed intensity distribution whereas isotropic escape does not.

Delay-Lock-Loop Mean Time to Lose Lock

Abstract: A solution to the mean time to lose lock for a first order, pseudo-noise, code tracking loop is derived for both the fulltime delay-lock loop and the time-shared delay lock loop, with both utilizing an early-late gate size of 1/2 chip, and assuming ideal bandpass filters. The result allows a spread spectrum system designer to assess the slip time performance of his code tracking loop by a simple calculation and then a reading of a curve presented in this paper. The results presented here are actually very general and apply to other code loop spacings and types. It also applies to carrier tracking loops and agrees with the carrier loop result of Viterbi [3].

The False Lock Performance of Costas Loops with Hard-Limited In-Phase Channel

Abstract: The ability of a Costas loop to false lock on a data sideband is a problem which must be dealt with in the design of suppressedcarrier receivers which employ such loops for carrier reconstruction. For conventional Costas loops wherein the error signal is formed from the product of two analog signals, the false lock problem has recently been investigated by the author and others and is now well understood. For implementation reasons associated with the reduction of dc offsets, it is often desirable to hard limit the output of the in-phase channel and replace the analog multiplier which forms the above product with a chopper-type device. The false lock behavior of such a Costas loop with hard-limited in-phase channel is quite different from that of the conventional Costas loop and is the subject of investigation in this paper. Results are also presented for a modified version of the Costas loop wherein the quadrature arm filter is removed. This configuration has recently been suggested as a means of improving the false lock performance of the Costas loop with hard-limited in-phase channel.

Optimum Receiver structures for Phase-Multiplexed Modulations

Abstract: The problem of deriving "optimum" receiver structures for synchronization of BPSK, QPSK, and unbalanced QPSK (UQPSK) modulations has been addressed by many authors starting with the wellknown maximum a posteriori (MAP) estimation technique as motivation. In general, the closed loop structures which result from application of this theory are impractical because of the difficulty of implementing the hyperbolic tangent nonlinearity which is suggested by using the gradient of the likelihood function as an error control signal in the loop. To arrive at practical realizations, one ordinarily approximates this nonlinearity with simpler, more easily implementable functions. This paper reexamines some of these approximations and the optimum structures which result. Using a slightly more sophisticated approximation of the nonlinearity, new and interesting structures are presented which overcome some of the deficiencies posed by MAP receiver structures for QPSK and UQPSK suggested by authors in the past. The equivalence of the QPSK structure with the well-known quadriphase Costas loop is discussed. Furthermore, it is argued that the new UQPSK structure allows carrier reconstruction at all ratios of data rates and powers in the two channels even in the limit of balanced QPSK.

Microwave power transmission beam safety system

Abstract: A system in which the characteristics of a microwave power transmission beam are controlled in accordance with power distribution profiles altered due to the detected presence or entrance of an object into the beam which causes changes that are perceived in various received, reflected and scattered power distribution profiles resulting over various receiving elements of the system An analysis of these changes is made, the results of which are used to reshape, dim or douse the power beam in accordance with predetermined criteria Additionally, a "FAIL SAFE" condition is obtained by employing a beam penetration tester, whose function is to repeatedly test the correct performance of the beam intrusion detecting scheme by presenting a minimal threshold scattering or absorbing cross section while crossing the power beam If the beam penetration tester is undetected by the beam safety system, then the beam control is preconditioned to turn off the power beam Conversely, if the beam penetration tester is successfully detected, then the power beam is allowed to remain on The system comprises a microwave power beam radiator array, a microwave power beam receiving antenna array, the radiator array in one embodiment being located on an orbiting spacecraft and the receiving array being located at a ground station Another embodiment provides a ground based transmitting array and a receiving array aboard an aircraft or airship

Radio frequency arraying method for receivers

Abstract: A method and apparatus for increasing the signal-to-noise ratio of a receiving facility for coherent frequency reception by arraying receiving systems using separate antennas for each, or one antenna for all systems. One system is operated with a carrier tracking loop to provide a first local oscillator frequency for the first and all other systems arrayed, with individual tracking loops in all other systems operated at IF for tracking out any phase differences due to separate group delays using an adjustable phase shifter for a second reference (REF. 2) to compensate for different group delays in the antenna and low-noise amplifier of each of the other systems. The second IF output of all systems are summed into the first system. This technique may also be used when two systems are arrayed to an antenna designed for circular or linear polarization diversity reception to effectively provide the same signal-to-noise ratio for both polarized signal transmission channels that would result from matched polarization. An arrangement adapted to high rate telemetry reception is disclosed. With additional components, the same arrangement is adapted to provide low rate telemetry reception as well.

Primary reflector for solar energy collection systems

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.