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At least 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Automated ultrareliability models - A review

Analytic models are required to assess the reliability of systems designed to ultrareliability requirements. This paper reviews the capabilities and limitations of five currently available automated reliability models which are applicable to fault-tolerant flight control systems. 'System' includes sensors, computers, and actuators. A set of review criteria including validation, configuration adaptability, and resource requirements for model evaluation are described. Five models, ARIES, CARE II, CARE III, CARSRA, and CAST, are assessed against the criteria, thereby characterizing their capabilities and limitations. This review should be helpful to potential users of the models.

Bridgman, M. S.↗
NASA NTRS1985

Analytical investigation of solid rocket nozzle failure

On April 5, 1983, an Inertial Upper Stage (IUS) spacecraft experienced loss of control during the burn of the second of two solid rocket motors. The anomaly investigation showed the cause to be a malfunction of the solid rocket motor. This paper presents a description of the IUS system, a failure analysis summary, an account of the thermal testing and computer modeling done at Marshall Space Flight Center, a comparison of analysis results with thermal data obtained from motor static tests, and describes some of the design enhancement incorporated to prevent recurrence of the anomaly.

Mccoy, K. E.↗
NASA NTRS1986

Automated calibration of a flight particle spectrometer

A system for calibrating both electron and ion imaging particle spectrometers was devised to calibrate flight instruments in a large vacuum facility in the Space Science Laboratory at the Marshall Space Flight Center. An IBM-compatible computer was used to control, via an IEEE 488 buss protocol, a two-axis gimbled table, constructed to fit inside the tank. Test settings of various diagnostic voltages were also acquired via the buss. These spectrometers constructed by the author at UCSD were calibrated in an automatic procedure programmed on the small computer. Data was up-loaded to the SSL VAX where a program was developed to plot the results.

Torbert, R. B.↗
NASA NTRS1986

Applications software supporting the Spartan Attitude Control System

The native software supporting a single mission for the Spartan Attitude Control System can require up to 40,000 lines of code. Most of this must be rewritten for each mission. Control system engineers use an array of Applications Software Packages residing in ground computers to write each mission's flight software. These Applications Packages are written in the 'C' programming language and run under the UNIX Operating System. This paper discusses each of the Attitude Control Applications Software Packages, and describes the purpose and design of each.

Stone, R. W.↗
NASA NTRS1988

Integrated Displays For Helicopter Pilots

Report evaluates three similar video displays for guidance of helicopter pilots in low-level flight at night in adverse weather. Computer produces guidance information for pilot by integrating data from terrain-following radar, forward-looking infrared (FLIR) imagery, and data from such autonomous navigation instruments as inertial navigation systems and Doppler radar. FLIR imagery, information on status of helicopter, and command symbols incorporated in one head-down display.

Swenson, Harry N.↗
NASA NTRS1987

Control systems for autonomous operation of the Magellan spacecraft

The Magellan low cost interplanetary mission spacecraft, scheduled for flight in 1989, employs a computer-based Attitude and Articulation Control System (AACS) that interfaces with spacecraft sensors and actuators. The sensors include two attitude reference units, a star-scanner unit, two digital sun sensors, and a tachometer. The actuators encompass three reaction wheels, a total of 12 attitude control thrusters, eight attitude-control engines, a solar array drive assembly, and an input-output drive assembly. A detailed account is given of the AACS's onboard computer architecture.

Huang, Whittak H.↗
NASA NTRS1988

The ballistic range and aerothermodynamic testing

A renewed interest in hypervelocity vehicles requires an increase in our knowledge of aerothermodynamic phenomena. Tests conducted in our ground-based facilities can be used both to better understand the physics of hypervelocity flight, and to calibrate and validate computer codes designed to predict vehicle performance in the hypervelocity environment. This paper reviews the requirements for aerothermodynamic testing and discusses the ballistic range and its capabilities. Examples of the kinds of testing performed in typical high-performance ballistic ranges are described; we draw heavily on experience obtained in the ballistics facilities at NASA Ames. Prospects for improving the capabilities of the ballistic range by using advanced instrumentation are discussed. Finally, recent developments in gun technology and their application to extend the capability of the ballistic range are summarized.

Strawa, A. W.↗
NASA NTRS1988

A research study for the preliminary definition of an aerophysics free-flight laboratory facility

A renewed interest in hypervelocity vehicles requires an increase in the knowledge of aerodynamic phenomena. Tests conducted with ground-based facilities can be used both to better understand the physics of hypervelocity flight, and to calibrate and validate computer codes designed to predict vehicle performance in the hypervelocity environment. This research reviews the requirements for aerothermodynamic testing and discusses the ballistic range and its capabilities. Examples of the kinds of testing performed in typical high performance ballistic ranges are described. We draw heavily on experience obtained in the ballistics facilities at NASA Ames Research Center, Moffett Field, California. Prospects for improving the capabilities of the ballistic range by using advanced instrumentation are discussed. Finally, recent developments in gun technology and their application to extend the capability of the ballistic range are summarized.

Canning, Thomas N.↗
NASA NTRS1987

Microwave emission from steady and moving sunspots

Force-free extrapolations of photospheric magnetic field observations from Marshall Space Flight Center have been used to compute the total intensity and circular polarizaton of sunspot associated emission from active region 2502 in the period June 13 to 15, 1980. The computed maps were compared to high resolution observations of the same active region obtained with the Westerbork Synthesis Radio Telescope. The most interesting aspect of the active region was the development of a new spot between the preceding and the following spots on June 14, which subsequently merged with the preceding with the preceding spot. The new spot was associated with enhanced microwave emission with a peak brightness temperature in excess of 4 x 10 to the 6th K. It is shown that unrealistic values of the conductive flux are required for the interpretation of the emission of the new sunspot in terms of thermal processes. It is suggested that this source is due to gyrosynchrotron radiation from mildly relativistic electrons accelerated by resistive instabilities in the evolving magnetic field.

Alissandrakis, C. E.↗
NASA NTRS1989

Validation of NSSC-I software for the Hubble Space Telescope

This paper describes the simulation and test methods used to ensure that the NASA Standard Spacecraft Computer, Model 1, (NSSC-I) flight software for the Hubble Space Telescope properly carries out its requirements for control of scientific observations and for monitoring the health and safety of the payload. The hardware and software test environment is discussed. The different kinds of tests (unit, special real time, and stress tests) that are performed before the software is incorporated into the flight system are described, and the kinds of errors that each test category is best suited to find are listed. Finally, the limitations of the tests are discussed, and current plans for enhancing the test environment are outlined.

Foley, Glenn↗
NASA NTRS1991

Computer Simulation Of A Small Turboshaft Engine

Component-type mathematical model of small turboshaft engine developed for use in real-time computer simulations of dynamics of helicopter flight. Yields shaft speeds, torques, fuel-consumption rates, and other operating parameters with sufficient accuracy for use in real-time simulation of maneuvers involving large transients in power and/or severe accelerations.

Ballin, Mark G.↗
NASA NTRS1990

Parallelized reliability estimation of reconfigurable computer networks

A parallelized system, ASSURE, for computing the reliability of embedded avionics flight control systems which are able to reconfigure themselves in the event of failure is described. ASSURE accepts a grammar that describes a reliability semi-Markov state-space. From this it creates a parallel program that simultaneously generates and analyzes the state-space, placing upper and lower bounds on the probability of system failure. ASSURE is implemented on a 32-node Intel iPSC/860, and has achieved high processor efficiencies on real problems. Through a combination of improved algorithms, exploitation of parallelism, and use of an advanced microprocessor architecture, ASSURE has reduced the execution time on substantial problems by a factor of one thousand over previous workstation implementations. Furthermore, ASSURE's parallel execution rate on the iPSC/860 is an order of magnitude faster than its serial execution rate on a Cray-2 supercomputer. While dynamic load balancing is necessary for ASSURE's good performance, it is needed only infrequently; the particular method of load balancing used does not substantially affect performance.

Nicol, David M.↗
NASA NTRS1990

Some far-field acoustics characteristics of the XV-15 tilt-rotor aircraft

Far-field acoustics tests have been conducted on an instrumented XV-15 tilt-rotor aircraft. The purpose of these acoustic measurements was to create an encompassing, high confidence (90 percent), and accurate (-1.4/ +1/8 dB theoretical confidence interval) far-field acoustics data base to validate ROTONET and other current rotorcraft noise prediction computer codes. This paper describes the flight techniques used, with emphasis on the care taken to obtain high-quality far-field acoustic data. The quality and extensiveness of the data base collected are shown by presentation of ground acoustic contours for level flyovers for the airplane flight mode and for several forward velocities and nacelle tilts for the transition mode and helicopter flight mode. Acoustic pressure time-histories and fully analyzed ensemble averaged far-field data results (spectra) are shown for each of the ground contour cases.

Golub, Robert A.↗
NASA NTRS1991

Numerical prediction of the unsteady flowfield around the F-18 aircraft at large incidence

This paper describes a numerical method capable of solving the steady and unsteady viscous flow around complete aircraft configurations at high angles of attack. This method is used to simulate the external flow around the F-18 aircraft, including deflected control surfaces. The current technique employs a generalized overset zonal grid scheme to decompose the computational space around the aircraft. The grid around various components of the aircraft are created numerically using a three-dimensional hyperbolic grid generation procedure. The Reynolds-averaged Navier-Stokes equations are integrated using a time-accurate, implicit procedure. Results for the turbulent flow around the F-18 aircraft at 30 degrees angle of attack show the details of the flowfield structure, including the unsteadiness created by the vortex burst and the resulting fluctuating airloads exerted on the vertical tail. The computed results agree fairly well with flight data for surface pressure, surface flow pattern, vortex burst location, and the dominant frequency for tail load fluctuations.

Rizk, Yehia M.↗
NASA NTRS1990

Fault analysis of multichannel spacecraft power systems

The NASA Marshall Space Flight Center proposes to implement computer-controlled fault injection into an electrical power system breadboard to study the reactions of the various control elements of this breadboard. Elements under study include the remote power controllers, the algorithms in the control computers, and the artificially intelligent control programs resident in this breadboard. To this end, a study of electrical power system faults is being performed to yield a list of the most common power system faults. The results of this study will be applied to a multichannel high-voltage DC spacecraft power system called the large autonomous spacecraft electrical power system (LASEPS) breadboard. The results of the power system fault study and the planned implementation of these faults into the LASEPS breadboard are described.

Dugal-Whitehead, Norma R.↗
NASA NTRS1992

Synchronization Of Parallel Discrete Event Simulations

Adaptive, parallel, discrete-event-simulation-synchronization algorithm, Breathing Time Buckets, developed in Synchronous Parallel Environment for Emulation and Discrete Event Simulation (SPEEDES) operating system. Algorithm allows parallel simulations to process events optimistically in fluctuating time cycles that naturally adapt while simulation in progress. Combines best of optimistic and conservative synchronization strategies while avoiding major disadvantages. Algorithm processes events optimistically in time cycles adapting while simulation in progress. Well suited for modeling communication networks, for large-scale war games, for simulated flights of aircraft, for simulations of computer equipment, for mathematical modeling, for interactive engineering simulations, and for depictions of flows of information.

Steinman, Jeffrey S.↗
NASA NTRS1992

Numerical simulation of STOL operations using thrust-vectoring

The flow field about a delta wing equipped with thrust reverser jets in slow speed flight near the ground has been computed. Results include the prediction of the flow about the delta wing at four fixed heights above the ground, and a simulated landing, in which the delta wing descends towards the ground. Comparison of computed and experimental lift coefficients indicates that the simulations can capture at least the qualitative trends in lift-loss encountered by thrust-vectoring aircraft operating in ground effect.

Chawla, Kalpana↗
NASA NTRS1933

Application of practical hydrodynamics to airship design

The purpose of the first two parts of this report is to present in concise format all the formulas required for computation of the hydrodynamic forces, so that they can be easily computed for either straight or curvilinear flight. Improved approximations are also introduced having a high degree of accuracy throughout the entire range of practical proportions. The remaining two parts of the report are devoted respectively to stability and skin friction, as functions of the same hydrodynamic forces.

Upson, Ralph H↗