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Goal-Based Fault Tolerance for Spacecraft Systems

A report discusses the concept of goal-based fault tolerance as implemented in NASA’s Mission Data System (MDS), which is a developmental architecture for unified flight, test, and ground software that is intended to be adaptable to a variety of next-generation deep-space missions. In goal-based fault tolerance, unlike in prior approaches to fault tolerance, it is not assumed that faults that necessitate deviations from prescribed sequences of commands will occur infrequently; instead, it is assumed that unpredictable conditions, including faults, can arise at any time, and fault tolerance is incorporated as an intrinsic feature of every aspect of system design in a unified approach to ensuring robust system behavior.

Posted in: Information Sciences, Briefs

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Quantum Superluminal Transmission of Random Messages

Messages that would not convey information could be useful for deception. In a proposed communication scheme, quantum entanglement and quantum nonlocality would be utilized to effect instantaneous transmission of randomly chosen messages to remote locations. Although the messages would not convey any information, they might nevertheless be of some value under circumstances in which deception and secrecy are of more importance than are the specific contents of the messages.

Posted in: Information Sciences, Briefs

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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.

Posted in: Information Sciences, Briefs

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Direct Methanol Fuel Cells With Aerosol Feed

Relative to liquid feed, aerosol feed would result in less methanol crossover. Direct methanol fuel cells that would function with aerosol feed (instead of all-gas or all-liquid feed) have been proposed. As explained below, aerosol feed would afford the advantages of liquid feed, while reducing or eliminating some of the disadvantageous effects of liquid feed.

Posted in: Physical Sciences, Briefs

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Long-Life Stratospheric Balloon System With Altitude Control

There would be no venting of helium or dropping of ballast. A proposed improved balloon system for carrying scientific instruments in the stratosphere would include a lightweight, ambient-pressure helium balloon and a vented infrared Montgolfiere (see figure). [An infrared Montgolfiere is an ambient-pressure warm-air balloon, named after the familiar fire-heated hot-air balloons invented by the Montgolfier brothers. An infrared Montgolfiere is heated primarily by the Sun during the day, and/or by infrared radiation from relatively warm surface of the Earth at night.] The system would feature controllability of altitude for taking scientific data, landing, or taking advantage of favorable winds for relocation. The system would be designed for long life, but would weigh less (and therefore cost less) than do previously developed long-life balloon systems.

Posted in: Physical Sciences, Briefs

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Seed-Wing Flyers for Exploration

Scientific instruments would be dispersed from aloft by use of miniature autogyros. Small instrumented, free-flying (unpowered) rotary aircraft have been proposed for use in gathering scientific data from hazardous or inaccessible terrain on remote planets as well as on Earth. These aircraft are called “seed-wing flyers” because they would resemble winged seeds (e.g., maple seeds) in both appearance and aerodynamic behavior.

Posted in: Physical Sciences, Briefs

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Boundary Conditions for Computing Flows of Real Gas Mixtures

It is possible to suppress errors that arise in a simplistic formulation. An improved formulation of equations of flow of a general gas mixture includes consistent boundary conditions that are applicable to real gases. An analysis of prior formulations, with focus on boundary conditions, led to the conclusion that boundary conditions based on ideal mixtures and/or perfect gases can lead to errors in computed flows of real gases. The improved formulation makes it possible to achieve greater accuracy in computation of flows of real (including chemically reactive) gas mixtures, and is expected to be especially beneficial in computing flows of supercritical fluids like those in diesel engines, gas turbine engines, rocket engines, supercritical-fluid extraction processes, and crude oil under high pressure.

Posted in: Physical Sciences, Briefs

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