Analog Computer Needed!

Science and technology advance neither steadily nor continuously. Concepts deemed obsolete and confined to oblivion find their niche in new developments. Discarded old methods revive as the key ingredients to new designs. Analog computing was the birthplace of two important technologies: Computer simulation, as applied to system design, was founded. The operational amplifier, to become the basis for modern linear circuitry, was perfected. Valuable as it was, analog simulation's quasi-hardware approach to analysis aggravated users as much as it aided them. When digital simulation languages arrived, simulation engineers readily adopted them. When the microprocessor transformed digital computers into inexpensive circuit components (more like gates, flip-flops, amplifiers, etc. than computers,) there arose unlimited prospects for digital control. But, the discrete digital and continuous analog worlds are not compatible. Timing discontinuities and variable resolution limitations create problems. Control system designs, especially microprocessor based ones, need laboratory development. For hands-on testing, the analog computer is as handy an instrument as a controls engineer could have. Its two unique and valuable functions are: Simulator of Systems to be Controlled... The electrical analogs or physical models, analog computer simulations offer predictable yet realistic representations of mechanisms and processes to be controlled. Programmable Linear Circuits Manifold... The terminal points for high quality, linear circuit devices, analog computer patch panels offer the only formal means of programing linear signal processing, interface and control circuits. This paper offers a discussion of these two analog computing uses.     

Minitact gyroscope-the low cost alternative

The allure of the solid state optical gyros is being challenged by the invention of a new spinning mass device, providing superior low noise drift performance, high reliability at a very low cost. The Minitact is a unique two axis gyroscope advancing the technology of spinning mass devices to set new low cost standards. Minitact provides all the low noise performance benefits of tuned rotor gyroscopes without the vagaries of fixture suspension systems. The Minitact design integrates together the advantages of a spherical hydrodynamic gas bearing and a three axis permanent magnet DC commutated, motor and torquer, into miniature two aids gyroscope with a dynamic range of greater than 10^-7. The design is described and performance data presented illustrating the capability of this low cost next generation rate gyroscope. The Minitact is the result of Integrated Product Development (IPD) and Design to Unit Production Cost (DTUPC) design processes and is expected to become the tactical performance benchmark     

On the Derivation and Numerical Evaluation of the Weibull-Rician Distribution

The Weibull-Rician distribution and density functions are derived by a method based on conditional probability. The derivation is much simpler than the usual Rician approach, giving both the distribution and density as single integrals that are easy to evaluate numerically.     

Comet West 1976 VI: Photopolarimetry by the Helios 2 Zodiacal Light Experiment

Shortly after it passed through perihelion on February 25, 1976 Comet West was observed by the Helios Zodiacal Light Experiment. Broadband photopolarimetric measurements of the head and of the tail were performed in three wavelength bands (U, B, V). The phase angles encountered range from 67° to 85°. The polarization measurements indicated wavelength independent linear polarization. The maximum degree of polarization in the visual channel was found to be .28 at a phase angle of 83°.     

A cost effective critical space systems design approach

NASA-ISC requires avionics platforms capable of serving a wide range of applications in a cost-effective manner. In part, making the avionics platform cost effective means adhering to open standards and supporting the integration of COTS products with custom products. Inherently, operation in space requires low power, mass, and volume while retaining high performance, reconfigurability, scalability, and upgradability. The Universal Mini-Controller (UMC) project is based on a modified PC/104-Plus architecture while maintaining full compatibility with standard COTS PC/104 products. The architecture consists of a library of stackable building block modules, which can be mixed and matched to meet a specific application. A set of NASA developed core building blocks, (e.g. processor card, analog input/output card, high level analog card, and a Mil-Std-1553 card) were constructed to meet critical functions and unique interfaces     

Assessment and improvement of the capabilities of a window correlator to model GPS multipath phase errors

The potential of output from a window correlator to mitigate GPS phase multipath is reviewed and assessed based on the analysis of data collected in controlled multipath environments under both static and kinematic conditions. Previous findings that the method is suboptimal for reflectors leading to additional path lengths of less than about 7m are confirmed, and methods for combining this output with two other multipath indicators: time series of signal-to-noise ratios (SNRs) and estimates of code multipath from dual frequency code and phase combinations, are investigated. A new method to combine all three indicators has been found and its application is shown to improve the quality of GPS static phase data by between 10% and 20% depending on the length of the additional path travelled by the reflected signal. The method can be applied completely automatically as it uses just the three multipath indicators; no knowledge of the surrounding environment is required. The paper concludes with some suggested practical applications.     

High resolution measurements of nightside ion troughs at venus: Evidence of electrodynamic perturbations

The Bennett rf ion mass spectrometer (OIMS) on the Pioneer Venus Orbiter was particularly designed to provide variable temporal resolution for measurements of thermal ion composition and density. An Explore-Adapt mode is used to obtain priority for measurement of most prominent ion species, and in a 2/16 configuration, the two dominant ions within the available range of 16 species are selectively sampled at the highest rate of 0.2 sec/sample. The high resolution measurements are combined with independent observations from the magnetic field (OMAG), neutral mass spectrometer (ONMS), and electron temperature (OETP) experiments to investigate sharply structured troughs in the low altitude nightside ion concentrations. The results indicate a close correlation between the structure in the ion distributions and the structured configuration of the magnetic field which is draped about the planet. In the regions of the ion depletions, sharp fluctuations in electron temperature and anomalous increases in the density of neutral gases indicate that the ion depletion may be associated either with dynamic perturbation in the ion and neutral flows, and/or local joule heating. The configuration of the ion flow/magnetic field draping and consequent electric fields for these events must be analyzed in detail to understand the relationships.     

Direct evidence for chromospheric evaporation in a well-observed compact flare

We have observed the flare of 1980 May 7 1456 UT with several Solar Maximum Mission instruments, in coordination with the Sacramento Peak Observatory Vacuum Tower Telescope. From the X-ray data we determine the total amount of plasma at T > 2 × 10⁶ K, commonly attributed to chromospheric evaporation. From Hα we have determined the amount of plasma that has been evaporated from the chromosphere. We find that enough material has been evaporated from the chromosphere to account for the X-ray plasma. Taken together, the Hα, soft and hard X-ray images suggest that chromospheric evaporation is driven both by flare accelerated electrons, during the impulsive phase, and conduction, during the thermal phase.     

Fluctuating Target Detection in Clutter Using Sidelobe Blanking Logic

In an earlier paper, Maisel [6] considered two-channel detection systems using a sidelobe blanking logic when a nonfluctuating target was present. This paper is an extension of the earlier work to include fluctuating targets. The Swerling I, II, III, and IV models are considered when single-pulse detection is of interest. An adaptive threshold procedure is also briefly discussed whereby the probability of false alarm at any given resolution cell is maintained constant, even though the input clutter level may vary from cell to cell or from beam position to beam position. Useful data are presented for detection probabilities in the range 0.5 to 0.9, for false alarm probabilities in the range 104 to 10-8, and for a false detection probability of 0.1 for a sidelobe target yielding an apparent signal to total noise power density ratio of 13.0 dB in the main beam receiver.