Tech Briefs

Alternative Attitude Commanding and Control for Precise Spacecraft Landing

A report proposes an alternative method of control for precision landing on a remote planet. In the traditional method, the attitude of a spacecraft is required to track a commanded translational acceleration vector, which is generated at each time step by solving a two-point boundary value problem. No requirement of continuity is imposed on the acceleration. The translational acceleration does not necessarily vary smoothly. Tracking of a nonsmooth acceleration causes the vehicle attitude to exhibit undesirable transients and poor pointing stability behavior. In the alternative method, the two-point boundary value problem is not solved at each time step. A smooth reference position profile is computed. The profile is recomputed only when the control errors get sufficiently large. The nominal attitude is still required to track the smooth reference acceleration command. A steering logic is proposed that controls the position and velocity errors about the reference profile by perturbing the attitude slightly about the nominal attitude. The overall pointing behavior is therefore smooth, greatly reducing the degree of pointing instability.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Attitude control, Entry, descent, and landing, Spacecraft

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Helicity in Supercritical O2/H2 and C7H16/N2 Mixing Layers

This report describes a study of databases produced by direct numerical simulation of mixing layers developing between opposing flows of two fluids under supercritical conditions, the purpose of the study being to elucidate chemical species-specific aspects of turbulence, with emphasis on helicity. The simulations were performed for two different fluid pairs — O2/H2 and C7H16/N2 — at similar values of reduced pressure.

Posted in: Briefs, TSP, Physical Sciences, Computational fluid dynamics, Data management, Chemicals, Turbulence

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A Resonator for Low-Threshold Frequency Conversion

A nonlinear dielectric whispering-gallery resonator would be poled for quasiphase-matching. A proposed toroidal or disklike dielectric optical resonator (dielectric optical cavity) would be made of an optically nonlinear material and would be optimized for use in parametric frequency conversion by imposition of a spatially periodic permanent electric polarization. The poling (see figure) would suppress dispersions caused by both the material and the geometry of the optical cavity, thereby effecting quasi-matching of the phases of high-resonance-quality (high-Q) whispering-gallery electromagnetic modes. The quasi-phase-matching of the modes would serve to maximize the interactions among them. Such a resonator might be a prototype of a family of compact, efficient nonlinear devices for operation over a broad range of optical wavelengths.

Posted in: Briefs, TSP, Physical Sciences, Electromagnetic compatibility, Product development, Acoustics

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Solar-Powered Airplane With Cameras and WLAN

High-resolution images are sent to a ground station in nearly real time. An experimental airborne remote sensing system includes a remotely controlled, lightweight, solar-powered airplane (see figure) that carries two digital-output electronic cameras and communicates with a nearby ground control and monitoring station via a wireless local-area network (WLAN). The speed of the airplane — typically <50 km/h — is low enough to enable loitering over farm fields, disaster scenes, or other areas of interest to collect high resolution digital imagery that could be delivered to end users (e.g., farm managers or disaster-relief coordinators) in nearly real time.

Posted in: Briefs, Physical Sciences, Data exchange, Remote sensing, Surveillance, Wireless communication systems, Unmanned aerial vehicles

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Software for Automated Testing of Mission-Control Displays

MCC Display Cert Tool is a set of software tools for automated testing of computer terminal displays in spacecraft mission-control centers, including those of the space shuttle and the International Space Station. This software makes it possible to perform tests that are more thorough, take less time, and are less likely to lead to erroneous results, relative to tests performed manually.

Posted in: Briefs, Software, Computer software and hardware, Flight management systems, Displays, Ground support, Test equipment and instrumentation, Spacecraft

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WinPlot

WinPlot is a powerful desktop graphical analysis tool that allows the user to generate displays of unrestrictive amounts of data. It is designed to operate on a Windows 98/NT/2000 based desktop platform. WinPlot was developed to fulfill the need for fast and easily managed graphical displays of NASA test articles and facilities with extreme amount of test data in a desktop-computer environment. WinPlot features include seamless displays of real-time and post-test-time data with time and event synchronization of data from multiple sources. WinPlot also processes full scripting capability for automation of processes. Entire analysis procedures may be recorded and replayed with a single command. Users may record their actions within WinPlot or may write scripts using text editor. Scripts may also call and execute other scripts, providing even greater automation of tasks. WinPlot is also unique in its ability to plot large volumes of data on a desktop workstation. Up to 1,000 test data files may be opened simultaneously with plots generated containing up to 1,000 curves per plot. WinPlot also has extensive abilities in generation of “on-the-fly” calculations, reducing or eliminating the need for external programs to generate the data. Calculations may include a series of recorded parameters, constants, and math functions. WinPlot’s ability to export plots on a single mouse click can make easy work of preparing presentation material with office applications. One simply produces the plot with desired style and click of a button on the tool bar. Plots will be saved in a predefined folder with a sortable naming convention.

Posted in: Briefs, Software, Computer software and hardware, Human machine interface (HMI), Displays

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Software for Autonomous Spacecraft Maneuvers

The AutoCon computer programs facilitate and accelerate the planning and execution of orbital control maneuvers of spacecraft while analyzing and resolving mission constraints. AutoCon-F is executed aboard spacecraft, enabling the spacecraft to plan and execute maneuvers autonomously; AutoCon-G is designed for use on the ground. The AutoCon programs utilize advanced techniques of artificial intelligence, including those of fuzzy logic and natural language scripting, to resolve multiple conflicting constraints and automatically plan maneuvers. These programs can be used to satisfy requirements for missions that involve orbits around the Earth, the Moon, or any planet, and are especially useful for missions in which there are requirements for frequent maneuvers and for resolution of complex conflicting constraints. During operations, the software targets new trajectories, places and sizes maneuvers, and controls spacecraft burns. AutoCon-G provides a user friendly graphical interface, and can be used effectively by an analyst with minimal training. AutoCon-F reduces latency and supports multiple-spacecraft and formation-flying missions. The AutoCon architecture supports distributive processing, which can be critical for formation-control missions. AutoCon is completely object-oriented and can easily be enhanced by adding new objects and events. AutoCon-F was flight demonstrated onboard GSFC’s EO-1 spacecraft flying in formation with Landsat-7.

Posted in: Briefs, TSP, Software, Artificial intelligence, Computer software and hardware, Spacecraft guidance, Unmanned aerial vehicles

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Software Assists in Responding to Anomalous Conditions

Fault Induced Document Retrieval Officer (FIDO) is a computer program that reduces the need for a large and costly team of engineers and/or technicians to monitor the state of a spacecraft and associated ground systems and respond to anomalies. FIDO includes artificial-intelligence components that imitate the reasoning of human experts with reference to a knowledge base of rules that represent failure modes and to a database of engineering documentation. These components act together to give an unskilled operator instantaneous expert assistance and access to information that can enable resolution of most anomalies, without the need for highly paid experts. FIDO provides a system state summary (a configurable engineering summary) and documentation for diagnosis of a potentially failing component that might have caused a given error message or anomaly.

Posted in: Briefs, TSP, Software, Adaptive control, Artificial intelligence, Computer software and hardware, Human machine interface (HMI), Spacecraft

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Program Analyzes Radar Altimeter Data

A computer program has been written to perform several analyses of radar altimeter data. The program was designed to improve on previous methods of analysis of altimeter engineering data by (1) facilitating and accelerating the analysis of large amounts of data in a more direct manner and (2) improving the ability to estimate performance of radar-altimeter instrumentation and provide data corrections. The data in question are openly available to the international scientific community and can be downloaded from anonymous file-transfer-protocol (FTP) locations that are accessible via links from altimetry Web sites. The software estimates noise in range measurements, estimates corrections for electromagnetic bias, and performs statistical analyses on various parameters for comparison of different altimeters. Whereas prior techniques used to perform similar analyses of altimeter range noise require comparison of data from repetitions of satellite ground tracks, the present software uses a high-pass filtering technique to obtain similar results from single satellite passes. Elimination of the requirement for repeat-track analysis facilitates the analysis of large amounts of satellite data to assess subtle variations in range noise.

Posted in: Briefs, Software, Altimeters, Computer software and hardware, Data exchange, Radar, Satellite communications, Noise

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Format for Interchange and Display of 3D Terrain Data

Visible Scalable Terrain (ViSTa) is a software format for production, interchange, and display of three-dimensional (3D) terrain data acquired by stereoscopic cameras of robotic vision systems. ViSTa is designed to support scalability of data, accuracy of displayed terrain images, and optimal utilization of computational resources. In a ViSTa file, an area of terrain is represented, at one or more levels of detail, by coordinates of isolated points and/or vertices of triangles derived from a texture map that, in turn, is derived from original terrain images. Unlike prior terrain-image software formats, ViSTa includes provisions to ensure accuracy of texture coordinates.

Posted in: Briefs, TSP, Software, Cartography, Computer software and hardware, Data exchange, Terrain, Displays

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