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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18

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NASA NTRS1991

An SSME high pressure oxidizer turbopump diagnostic system using G2(TM) real-time expert system

An expert system which diagnoses various seal leakage faults in the High Pressure Oxidizer Turbopump of the SSME was developed using G2(TM) real-time expert system. Three major functions of the software were implemented: model-based data generation, real-time expert system reasoning, and real-time input/output communication. This system is proposed as one module of a complete diagnostic system for Space Shuttle Main Engine. Diagnosis of a fault is defined as the determination of its type, severity, and likelihood. Since fault diagnosis is often accomplished through the use of heuristic human knowledge, an expert system based approach was adopted as a paradigm to develop this diagnostic system. To implement this approach, a software shell which can be easily programmed to emulate the human decision process, the G2 Real-Time Expert System, was selected. Lessons learned from this implementation are discussed.

Guo, Ten-Huei↗

NASA NTRS1991

SEDS1 mission software verification using a signal simulator

The first flight of the Small Expendable Deployer System (SEDS1) is scheduled as the secondary payload of a Delta II in late 1992. The objective of the SEDS1 mission is to collect data to validate the concept of tethered satellite systems and to verify computer simulations used to predict their behavior. A series of tests will be performed to exercise the software modules which make up the Mission Software of the SEDS Data System. These tests will be performed by using a SEDS Signal Simulator to generate signals which will simulate the inputs normally produced by sensors and circuits in the SEDS system. The SEDS Signal Simulator will be used in the debugging and in the formal verification of the SEDS1 Mission Software. The Simulator will not only emulate normal flight conditions but also exercise all modules written to handle anticipated anomalous flight conditions, conditions that would be difficult to reproduce and control with actual SEDS hardware. The simulator will help to expedite software development and to increase the confidence of the users of the Mission Software. With little modification, the Simulator should be useful in the software development of future SEDS flights.

Pierson, William E.↗

NASA NTRS1992

Evaluating human performance modeling for system assessment: Promise and problems

The development and evaluation of computational human performance models is examined. An intention is to develop models which can be used to interact with system prototypes and simulations to perform system assessment. Currently LR is working on a set of models emulating cognitive, psychomotor, auditory, and visual activity for multiple operator positions of a command and control simulation system. These models, developed in conjunction with BBN Systems and Technologies, function within the simulation environment and allow for both unmanned system assessment and manned (human-in-loop) assessment of system interface and team interactions. These are relatively generic models with built-in flexibility which allows modification of some model parameters. These models have great potential for improving the efficiency and effectiveness of system design, test, and evaluation. However, the extent of the practical utility of these models is unclear. Initial verification efforts comparing model performance within the simulation to actual human operators on a similar, independent simulation have been performed and current efforts are directed at comparing human and model performance within the same simulation environment.

Patterson, Robert W.↗

NASA NTRS1992

Kinematics of an in-parallel actuated manipulator based on the Stewart platform mechanism

This paper presents kinematic equations and solutions for an in-parallel actuated robotic mechanism based on Stewart's platform. These equations are required for inverse position and resolved rate (inverse velocity) platform control. NASA LaRC has a Vehicle Emulator System (VES) platform designed by MIT which is based on Stewart's platform. The inverse position solution is straight-forward and computationally inexpensive. Given the desired position and orientation of the moving platform with respect to the base, the lengths of the prismatic leg actuators are calculated. The forward position solution is more complicated and theoretically has 16 solutions. The position and orientation of the moving platform with respect to the base is calculated given the leg actuator lengths. Two methods are pursued in this paper to solve this problem. The resolved rate (inverse velocity) solution is derived. Given the desired Cartesian velocity of the end-effector, the required leg actuator rates are calculated. The Newton-Raphson Jacobian matrix resulting from the second forward position kinematics solution is a modified inverse Jacobian matrix. Examples and simulations are given for the VES.

Williams, Robert L., II↗

NASA NTRS1992

Improving designer productivity

Designer and design team productivity improves with skill, experience, and the tools available. The design process involves numerous trials and errors, analyses, refinements, and addition of details. Computerized tools have greatly speeded the analysis, and now new theories and methods, emerging under the label Artificial Intelligence (AI), are being used to automate skill and experience. These tools improve designer productivity by capturing experience, emulating recognized skillful designers, and making the essence of complex programs easier to grasp. This paper outlines the aircraft design process in today's technology and business climate, presenting some of the challenges ahead and some of the promising AI methods for meeting these challenges.

Hill, Gary C.↗

NASA NTRS1992

Evaluation of microwave landing system approaches in a wide-body transport simulator

The objective of this study was to determine the suitability of flying complex curved approaches using the microwave landing system (MLS) with a wide-body transport aircraft. Fifty pilots in crews of two participated in the evaluation using a fixed-base simulator that emulated an MD-11 aircraft. Five approaches, consisting of one straight-in approach and four curved approaches, were flown by the pilots using a flight director. The test variables include the following: (1) manual and autothrottles; (2) wind direction; and (3) type of navigation display. The navigation display was either a map or a horizontal situation indicator (HSI). A complex wind that changed direction and speed with altitude, and included moderate turbulence, was used. Visibility conditions were Cat 1 or better. Subjective test data included pilot responses to questionnaires and pilot comments. Objective performance data included tracking accuracy, position error at decision height, and control activity. Results of the evaluation indicate that flying curved MLS approaches with a wide-body transport aircraft is operationally acceptable, depending upon the length of the final straight segment and the complexity of the approach.

Summers, L. G.↗

NASA NTRS1992

Integrated control-structure design of the JPL phase B testbed

Structure and damper optimization problems driven by control objective metrics are developed for the optimal design of a testbed structure emulating a spaceborne interferometer. The structure optimization problem uses a multiobjective criterion to generate a family of optimized design that allows trades to be made between the competing objectives of minimizing structural mass and maximizing disturbance attenuation. The damper optimization problems focus on the placement and tuning of viscous elements to maximally damp selected modes of the testbed structure. The optimization techniques are verified on a large model of the testbed.

Milman, M.↗

NASA NTRS1990

Suppression of biodynamic interference in head-tracked teleoperation

Results are reported from an experimental simulation study examining improvements achievable in pointing and tracking precision using dynamic display shifting in helmet-mounted displays. The experiment was conducted in a 6-deg-of-freedom motion base simulator with an emulated helmet-mounted sight. It is shown that, for tracking tasks involving continuously moving targets, improvements of up to 70 percent can be achieved in percent on-target dwelling time and of up to 35 percent in rms tracking error, with the adaptive plus low-pass filter configuration. The results with the same filter configuration for the task of capturing randomly positioned, stationary targets show an increase of up to 340 percent in the number of targets captured and an improvement of up to 24 percent in the average capture time. The adaptive plus low-pass filter combination is considered to exhibit the best overall display dynamics by each of the subjects.

Lifshitz, S.↗

NASA NTRS1990

Real time data acquisition for expert systems in Unix workstations at Space Shuttle Mission Control

A distributed system of proprietary engineering-class workstations is incorporated into NASA's Space Shuttle Mission-Control Center to increase the automation of mission control. The Real-Time Data System (RTDS) allows the operator to utilize expert knowledge in the display program for system modeling and evaluation. RTDS applications are reviewed including: (1) telemetry-animated communications schematics; (2) workstation displays of systems such as the Space Shuttle remote manipulator; and (3) a workstation emulation of shuttle flight instrumentation. The hard and soft real-time constraints are described including computer data acquisition, and the support techniques for the real-time expert systems include major frame buffers for logging and distribution as well as noise filtering. The incorporation of the workstations allows smaller programming teams to implement real-time telemetry systems that can improve operations and flight testing.

Muratore, John F.↗

NASA NTRS1992

The simulated features of heliospheric cosmic-ray modulation with a time-dependent drift model. II - On the energy dependence of the onset of new modulation in 1987

Time-dependent heliospheric cosmic-ray modulation for the period 1985-1989 is simulated by means of a time-dependent axially symmetric drift model with an emulated wavy heliospheric neutral sheet (HNS). The model is used to extend previous calculations to other energies in order to study a possible energy-dependence of the onset of new modulation at various radial distances in 1987. The model, with the outward propagating changes of the HNS as the only time-dependent parameters, is found to predict essentially no energy-dependence in the time when new modulation started in the simulated 1987. When a more practical approach in defining 'constant' modulation in 1987 is followed, the present calculations can be interpreted to indicate that the end of the recovery period in 1987 happened progressively earlier and the onset of new modulation progressively later the higher the rigidity of the cosmic rays. This period of relatively unchanged modulation is predicted to last longer with increasing radial distance.

Le Roux, J. A.↗

NASA NTRS1992

Onboard configuration and operation of the TDRSS onboard navigation system (TONS)

This paper presents an overview of onboard navigation via TDRSS for both the EP/EUVE (Explorer Platform/Extreme Ultraviolet Explorer) experiment and for future users of TONS. System goals and objectives are discussed, and the operations concept for the three stages of TONS development is presented. A description is given of the first stage of the TONS development, the experiment implementation on EP, including the hardware characteristics, signal acquisition process, onboard data acquisition, and ground data processing in the flight emulation environment of the TONS Ground Support System (TGSS). Evaluation of the experiment implementation is presented and improvements described in terms of the second development stage, a full TONS I system, which uses Doppler data derived from scheduled forward-link S-band services to provide onboard orbit and frequency determination. A method for onboard time maintenance commensurate with TONS I is also presented. TONS II, the third stage, will use Doppler and pseudorange data derived from a continuous, nonscheduled forward-link S-band beacon service to provide onboard orbit, time, and frequency determination.

Gramling, Cheryl J.↗

NASA NTRS1992

The simulated features of heliospheric cosmic-ray modulation with a time-dependent drift model. III - General energy dependence

The time-dependent cosmic-ray transport equation is solved numerically in an axially symmetric heliosphere. Gradient and curvature drifts are incorporated, together with an emulated wavy neutral sheet. This model is used to simulate heliospheric cosmic-ray modulation for the period 1985-1989 during which drifts are considered to be important. The general energy dependence of the modulation of Galactic protons is studied as predicted by the model for the energy range 1 MeV to 10 GeV. The corresponding instantaneous radial and latitudinal gradients are calculated, and it is found that, whereas the latitudinal gradients follow the trends in the waviness of the neutral sheet to a large extent for all energies, the radial gradients below about 200 MeV deviate from this general pattern. In particular, these gradients increase when the waviness decreases for the simulated period 1985-1987.3, after which they again follow the neutral sheet by increasing rapidly.

Potgieter, M. S.↗

NASA NTRS1990

On the use of distributed sensing in control of large flexible spacecraft

Distributed processing technology is being developed to process signals from distributed sensors using distributed computations. Thiw work presents a scheme for calculating the operators required to emulate a conventional Kalman filter and regulator using such a computer. The scheme makes use of conventional Kalman theory as applied to the control of large flexible structures. The required computation of the distributed operators given the conventional Kalman filter and regulator is explained. A straightforward application of this scheme may lead to nonsmooth operators whose convergence is not apparent. This is illustrated by application to the Mini-Mast, a large flexible truss at the Langley Research Center used for research in structural dynamics and control. Techniques for developing smooth operators are presented. These involve spatial filtering as well as adjusting the design constants in the Kalman theory. Results are presented that illustrate the degree of smoothness achieved.

Montgomery, Raymond C.↗

NASA NTRS1992

Improving designer productivity

Hill, Gary C.↗

NASA NTRS1984

Spacecraft Control Laboratory Experiment: Status report

The Spacecraft Control Laboratory Experiment (SCOLE) will allow direct experimental comparison of competing control schemes for large flexible spacecraft structures. The experiment was designed to emulate the essential characteristics of a mathematical model design challenge which represents a Space Shuttle with a flexible mast and antenna attached. This experiment represents the third in a series of three flexible structure control experiments used by the Flight Dynamics and Control Division at LaRC. The key problem addressed by the facility is that flexible motion of the mast and antenna must be considered in the slewing and pointing control problems.

Williams, J. P.↗

NASA NTRS1993

Surgical Force-Measuring Probe

Aerodynamic balance adapted to medical use. Electromechanical probe measures forces and moments applied to human tissue during surgery. Measurements used to document optimum forces and moments for surgical research and training. In neurosurgical research, measurements correlated with monitored responses of nerves. In training, students learn procedures by emulating forces used by experienced surgeons. Lightweight, pen-shaped probe easily held by surgeon. Cable feeds output signals to processing circuitry.

Tcheng, Ping↗

NASA NTRS1992

Autonomous power system brassboard

The Autonomous Power System (APS) brassboard is a 20 kHz power distribution system which has been developed at NASA Lewis Research Center, Cleveland, Ohio. The brassboard exists to provide a realistic hardware platform capable of testing artificially intelligent (AI) software. The brassboard's power circuit topology is based upon a Power Distribution Control Unit (PDCU), which is a subset of an advanced development 20 kHz electrical power system (EPS) testbed, originally designed for Space Station Freedom (SSF). The APS program is designed to demonstrate the application of intelligent software as a fault detection, isolation, and recovery methodology for space power systems. This report discusses both the hardware and software elements used to construct the present configuration of the brassboard. The brassboard power components are described. These include the solid-state switches (herein referred to as switchgear), transformers, sources, and loads. Closely linked to this power portion of the brassboard is the first level of embedded control. Hardware used to implement this control and its associated software is discussed. An Ada software program, developed by Lewis Research Center's Space Station Freedom Directorate for their 20 kHz testbed, is used to control the brassboard's switchgear, as well as monitor key brassboard parameters through sensors located within these switches. The Ada code is downloaded from a PC/AT, and is resident within the 8086 microprocessor-based embedded controllers. The PC/AT is also used for smart terminal emulation, capable of controlling the switchgear as well as displaying data from them. Intelligent control is provided through use of a T1 Explorer and the Autonomous Power Expert (APEX) LISP software. Real-time load scheduling is implemented through use of a 'C' program-based scheduling engine. The methods of communication between these computers and the brassboard are explored. In order to evaluate the features of both the brassboard hardware and intelligent controlling software, fault circuits have been developed and integrated as part of the brassboard. A description of these fault circuits and their function is included. The brassboard has become an extremely useful test facility, promoting artificial intelligence (AI) applications for power distribution systems. However, there are elements of the brassboard which could be enhanced, thus improving system performance. Modifications and enhancements to improve the brassboard's operation are discussed.

Merolla, Anthony↗

NASA NTRS1991

Vehicle/payload interface specification for the reusable reentry satellite

This document describes the common interface requirements between the Vehicle Segment and the Payload Segment of the Reusable Reentry Satellite (RRS) system. The system consists of a single transport vehicle design that provides a uniform, unidirectional payload gravitational environment which is selectable during on-orbit operations over the range of 10(exp -5) (microgravity) to 1.5 g's. The initial Reusable Reentry Vehicle/Payload Module (RRV/PM) integration and checkout will occur at the launch base unless otherwise agreed to in a mission-unique addendum to this specification. Pre-integration interface qualification shall be done using emulators as described.

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