Information Science

Maximum-Likelihood Scheme for Tracking an Optical Source

Subpixel resolution should be possible, even in a high-disturbance environment. A fine-pointing scheme that involves correlation of images and maximum-likelihood estimation has been proposed to enable tracking of optical sources. This scheme is intended for implementation in the pointing-control system of an imaging instrument (e.g., a telescope equipped with an image detector) to provide a capability for highly stable and accurate pointing to a specific area within a moving target, even under conditions that ordinarily give rise to pointing jitters. Such conditions include motion of the target relative to the instrument, instability of the platform that supports the instrument-aiming mechanism, and turbulence in the atmosphere or other optical medium. In the original intended application, the scheme would be implemented in a ground station for tracking a laser that would be part of an optical communication aboard a distant spacecraft. Other potential applications include stabilization of images for video cameras and precise pointing of lasers in military, industrial, and surgical settings. This scheme is expected to make it possible to achieve subpixel resolution in a high-disturbance environment.

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Digital Library of NACA Reports

Aging paper NACA documents are scanned, then disseminated in electronic form. The NACA Technical Report Server (NACATRS) is both a node in the NASA Technical Report Server and a stand-alone World Wide Web (WWW) site. The NACATRS is dedicated to the preservation and dissemination of reports produced by the National Advisory Committee for Aeronautics (NACA).

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A Method for Designing Low-Pass FIR Digital Filters

Time-domain filters are first constructed in the frequency domain, using special window functions. A class of finite-impulse-response (FIR) digital filters has been developed to perform certain frequency-limiting, decimation, and differentiation (with respect to time) functions on a time series of data samples. The method is implemented by use of design equations that contain parameters that can be adjusted to obtain the desired functionality while limiting such undesired effects as aliasing and gain ripple. The original application is processing of a time series of raw range data from the proposed Gravity Recovery and Climate Experiment (GRACE), in which microwave phase tracking between two small spacecraft orbiting the Earth would yield the time-tagged raw range data, which would be processed to extract information on the structure of the gravitational field of the Earth. The method is general enough to be applicable in other situations that involve similar signal-processing requirements.

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Ex — Software for Numerical Computation in Native Oberon

“Ex” is the name of a library of software modules from which one can rapidly develop prototype or production versions of efficient numerical-computation application programs in the Native Oberon programming environment. Mathematical constructs that can be represented and processed by use of Ex modules include both integer and non-integer rational, real, and complex numbers; vectors; matrices; and the arithmetic, algebra, and calculus of the aforementioned quantities.

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Software for Analyzing Root Causes of Process Anomalies

Root Cause Analysis (RoCA) is a computer program that assists analysts in understanding the root causes of process anomalies. As used here, “process anomalies” includes incidents that have caused, or that can potentially cause, injuries to personnel, damage to facilities, abnormal costs, or delays in processing. RoCA could be used, for example, in industry to investigate anomalies in production and by government agencies and airlines in investigating airplane accidents. Older software developed to aid such investigations offers limited capabilities for mapping the contribution of each root cause to a given process anomaly. Unlike the prior software, RoCA not only identifies root causes of process anomalies but also supports the identification of trends over multiple anomalies.

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Accumulate-Repeat-Accumulate-Accumulate Codes

Fast, high-performance coders and decoders could be designed. Accumulate-repeat- accumulate-accumulate (ARAA) codes have been proposed, inspired by the recently proposed accumulate- repeat-accumulate (ARA) codes. These are error-correcting codes suitable for use in a variety of wireless data-communication systems that include noisy channels. ARAA codes can be regarded as serial turbolike codes or as a subclass of low-density parity- check (LDPC) codes, and, like ARA codes they have projected graph or protograph representations; these characteristics make it possible to design high-speed iterative decoders that utilize belief-propagation algorithms. The objective in proposing ARAA codes as a subclass of ARA codes was to enhance the error-floor performance of ARA codes while maintaining simple encoding structures and low maximum variable node degree.

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State-Estimation Algorithm Based on Computer Vision

Available data are utilized optimally without incurring an excessive computational burden. An algorithm and software to implement the algorithm are being developed as means to estimate the state (that is, the position and velocity) of an autonomous vehicle, relative to a visible nearby target object, to provide guidance for maneuvering the vehicle. In the original intended application, the autonomous vehicle would be a spacecraft and the nearby object would be a small astronomical body (typically, a comet or asteroid) to be explored by the spacecraft. The algorithm could also be used on Earth in analogous applications — for example, for guiding underwater robots near such objects of interest as sunken ships, mineral deposits, or submerged mines.

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