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Soft Real-Time PID Control on a VME Computer

microPID (μPID) is a computer program for real-time proportional + integral + derivative (PID) control of a translation stage in a Fourier-transform ultraviolet spectrometer. μPID implements a PID control loop over a position profile at sampling rate of 8 kHz (sampling period 125 μs). The software runs in a stripped-down Linux operating system on a VersaModule Eurocard (VME) computer operating in real-time priority queue using an embedded controller, a 16-bit digital-to-analog converter (D/A) board, and a laser-positioning board (LPB).

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Analyzing Radio-Frequency Coverage for the ISS

The Interactive Coverage Analysis Tool (iCAT) is an interactive desktopcomputer program serving to (1) support planning of coverage, and management of usage of frequencies, of current and proposed radio communication systems on and near the International Space Station (ISS) and (2) enable definition of requirements for development of future such systems. The iCAT can also be used in design trade studies for other (both outerspace and terrestrial) communication systems.

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Payload Operations Support Team Tools

Payload Operations Support Team Tools is a software system that assists in (1) development and testing of software for payloads to be flown aboard the space shuttles and (2) training of payload customers, flight controllers, and flight crews in payload operations. POST Tools includes the following subsystems:

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Displaying and Analyzing Antenna Radiation Patterns

Radiant Energy Display and Analysis Software Package (REDAP) is a computer program for processing antenna-radiation- pattern data that have been preprocessed by a data-collection program and stored in a spherical-coordinate format. REDAP is designed specifically for application to data generated in testing of antennas in an anechoic chamber at Johnson Space Center; parts of REDAP may be reusable for processing antennatest data collected elsewhere. REDAP provides a graphical user interface (GUI) and executes mathematical and plotting routines on a personal computer. The routines include statistical calculations (e.g., maximum, minimum, 3-dB-falloff points, and percent coverage); addition and subtraction of offsets; multiplication and division by scaling factors; and computation of circular-polarization characteristics from linear-polarization measurement data.

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Programs for Testing an SSME-Monitoring System

A suite of computer programs has been developed for special test equipment (STE) that is used in verification testing of the Health Management Computer Integrated Rack Assembly (HMC-IRA), a ground- based system of analog and digital electronic hardware and software for “flight-like” testing for development of components of an advanced health- management system for the space shuttle main engine (SSME). HMC-IRA units are designed to be integrated into a test facility wherein they enable additional engine monitoring during SSME hot-fire tests. Running on a control processor that is part of the STE, the STE software enables the STE to simulate the SSME Controller, the SSME itself, and interfaces between the SSME and the HMC-IRA.

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Analysis of Complex Valve and Feed Systems

A numerical framework for analysis of complex valve systems supports testing of propulsive systems by simulating key valve and control system components in the test loop. In particular, it is designed to enhance the analysis capability in terms of identifying system transients and quantifying the valve response to these transients. This system has analysis capability for simulating valve motion in complex systems operating in diverse flow regimes ranging from compressible gases to cryogenic liquids. A key feature is the hybrid, unstructured framework with sub-models for grid movement and phase change including cryogenic cavitations.

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Solving Equations of Multibody Dynamics

Darts++ is a computer program for solving the equations of motion of a multibody system or of a multibody model of a dynamic system. It is intended especially for use in dynamical simulations performed in designing and analyzing, and developing software for the control of, complex mechanical systems. Darts++ is based on the Spatial- Operator- Algebra formulation for multibody dynamics. This software reads a description of a multibody system from a model data file, then constructs and implements an efficient algorithm that solves the dynamical equations of the system. The efficiency and, hence, the computational speed is sufficient to make Darts++ suitable for use in real-time closed-loop simulations. Darts++ features an objectoriented software architecture that enables reconfiguration of system topology at run time; in contrast, in related prior software, system topology is fixed during initialization. Darts++ provides an interface to scripting languages, including Tcl and Python, that enable the user to configure and interact with simulation objects at run time.

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