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NASA NTRS1985

Decomposition and state variable feedback control of elastic robotic systems

Energy-efficient, lightweight robot arms for space applications have considerable structural flexibility. An approach to control of a class of flexible robotic systems is presented. A control law is derived which decouples the joint-angle motion from the flexible motion and, in addition, asymptotically decomposes the elastic dynamics into two subsystems. This allows the design of an elastic mode stabilizer independently based on lower order models representing structural flexibility. The closed-loop system is shown to be globally asymptotically stable and robust to uncertaintly in system parameters. Simulation results show that the combination of nonlinear decoupling and elastic stabilization permits rapid, accurate tracking of large joint angle commands with well damped elastic response, in spite of space vehicle motion and payload uncertainty.

Singh, S. N.↗

NASA NTRS1987

Advances and trends in computational structural mechanics

The development status and applicational range of techniques in computational structural mechanics (CSM) are evaluated with a view to advances in computational models for material behavior, discrete-element technology, quality assessment, the control of numerical simulations of structural response, hybrid analysis techniques, techniques for large-scale optimization, and the impact of new computing systems on CSM. Primary pacers of CSM development encompass prediction and analysis of novel materials for structural components, computational strategies for large-scale structural calculations, and the assessment of response prediction reliability together with its adaptive improvement.

Noor, Ahmed K.↗

NASA NTRS1987

Dynamics and control of a planar truss actuator

The concept of using an active truss actuator to control the vibration of a flexible (space) structure has been investigated. The actuator with a generic beam continuum cantilevered from it has been modeled using energy methods. A time-invariant optimal state feedback scheme was utilized for the control method. A digital simulation of the system dynamic response demonstrated the good vibration control possibilities for the (planar) truss actuator on a large flexible space structure.

Lovejoy, V. D.↗

NASA NTRS1990

Hubble space telescope six-battery test bed

A test bed for a large space power system breadboard for the Hubble Space Telescope (HST) was designed and built to test the system under simulated orbital conditions. A discussion of the data acquisition and control subsystems designed to provide for continuous 24 hr per day operation and a general overview of the test bed is presented. The data acquisition and control subsystems provided the necessary monitoring and protection to assure safe shutdown with protection of test articles in case of loss of power or equipment failure over the life of the test (up to 5 years).

Pajak, J. A.↗

NASA NTRS1992

A study of mapping exogenous knowledge representations into CONFIG

Qualitative reasoning is reasoning with a small set of qualitative values that is an abstraction of a larger and perhaps infinite set of quantitative values. The use of qualitative and quantitative reasoning together holds great promise for performance improvement in applications that suffer from large and/or imprecise knowledge domains. Included among these applications are the modeling, simulation, analysis, and fault diagnosis of physical systems. Several research groups continue to discover and experiment with new qualitative representations and reasoning techniques. However, due to the diversity of these techniques, it is difficult for the programs produced to exchange system models easily. The availability of mappings to transform knowledge from the form used by one of these programs to that used by another would open the doors for comparative analysis of these programs in areas such as completeness, correctness, and performance. A group at the Johnson Space Center (JSC) is working to develop CONFIG, a prototype qualitative modeling, simulation, and analysis tool for fault diagnosis applications in the U.S. space program. The availability of knowledge mappings from the programs produced by other research groups to CONFIG may provide savings in CONFIG's development costs and time, and may improve CONFIG's performance. The study of such mappings is the purpose of the research described in this paper. Two other research groups that have worked with the JSC group in the past are the Northwest University Group and the University of Texas at Austin Group. The former has produced a qualitative reasoning tool named SIMGEN, and the latter has produced one named QSIM. Another program produced by the Austin group is CC, a preprocessor that permits users to develop input for eventual use by QSIM, but in a more natural format. CONFIG and CC are both based on a component-connection ontology, so a mapping from CC's knowledge representation to CONFIG's knowledge representation was chosen as the focus of this study. A mapping from CC to CONFIG was developed. Due to differences between the two programs, however, the mapping transforms some of the CC knowledge to CONFIG as documentation rather than as knowledge in a form useful to computation. The study suggests that it may be worthwhile to pursue the mappings further. By implementing the mapping as a program, actual comparisons of computational efficiency and quality of results can be made between the QSIM and CONFIG programs. A secondary study may reveal that the results of the two programs augment one another, contradict one another, or differ only slightly. If the latter, the qualitative reasoning techniques may be compared in other areas, such as computational efficiency.

Mayfield, Blayne E.↗

NASA NTRS2000

MHD-Based Specification of Magnetotail Plasma and Fields: Possibilities and Limitations

Magnetohydrodynamics (MHD) constitutes the simplest comprehensive and self-consistent formulation of the properties of space plasmas. As such, it has been applied with large success to the dynamics of solar system plasmas. For the nightside region of the Earth, the magnetotail, MHD simulations have led to new understanding of the structure and dynamics of the plasmas, in response to both changes in boundary conditions as well as internal dynamical processes. As a result, substantial knowledge of the structure and dynamics of the nightside region have been accumulated. In basic MHD conservation laws on magnetospheric structure, as well as the role of non-MHD processes in the initiation and evolution of dynamical processes of the magnetotail. This presentation will consist of three parts, the first of which addresses the basic constraints on magnetotail structure as well as their consequences for magnetotail specification and forecasting. We will then review some examples of magnetotail structural changes brought about by solar-wind-like boundary conditions. Last, we consider the role of non-MHD processes in magnetotail specification and forecasting. The emphasis here will be on inclusion of these processes into MHD models, and their impact on the overall structure and dynamics.

Hesse, M.↗

NASA NTRS2000

Modeling Separate and Combined Atmospheres in BIO-Plex

We modeled BIO-Plex designs with separate or combined atmospheres and then simulated controlling the atmosphere composition. The BIO-Plex is the Bioregenerative Planetary Life Support Systems Test Complex, a large regenerative life support test facility under development at NASA Johnson Space Center. Although plants grow better at above-normal carbon dioxide levels, humans can tolerate even higher carbon dioxide levels. Incinerator exhaust has very high levels of carbon dioxide. An elaborate BIO-Plex design would maintain different atmospheres in the crew and plant chambers and isolate the incinerator exhaust in the airlock. This design easily controls the crew and plant carbon dioxide levels but it uses many gas processors, buffers, and controllers. If all the crew's food is grown inside BIO-Plex, all the carbon dioxide required by the plants is supplied by crew respiration and the incineration of plant and food waste. Because the oxygen mass flow must balance in a closed loop, the plants supply all the oxygen required by the crew and the incinerator. Using plants for air revitalization allows using fewer gas processors, buffers, and controllers. In the simplest design, a single combined atmosphere was used for the crew, the plant chamber, and the incinerator. All gas processors, buffers, and controllers were eliminated. The carbon dioxide levels were necessarily similar for the crew and plants. If most of the food is grown, carbon dioxide can be controlled at the desired level by scheduling incineration. An intermediate design uses one atmosphere for the crew and incinerator chambers and a second for the plant chamber. This allows different carbon dioxide levels for the crew and plants. Better control of the atmosphere is obtained by varying the incineration rate. Less gas processing storage and control is needed if more food is grown.

Jones, Harry↗

NASA NTRS2000

Modeling Separate and Combined Atmospheres in BIO-Plex

We modeled BIO-Plex designs with separate or combined atmospheres and then simulated controlling the atmosphere composition. The BIO-Plex is the Bioregenerative Planetary Life Support Systems Test Complex, a large regenerative life support test facility under development at NASA Johnson Space Center. Although plants grow better at above-normal carbon dioxide levels, humans can tolerate even higher carbon dioxide levels. incinerator exhaust has very high levels of carbon dioxide. An elaborate BIO-Plex design would maintain different atmospheres in the crew and plant chambers and isolate the incinerator exhaust in the airlock. This design easily controls the crew and plant carbon dioxide levels but it uses many gas processors, buffers, and controllers. If all the crew's food is grown inside BIO-Plex, all the carbon dioxide required by the plants is supplied by crew respiration and the incineration of plant and food waste. Because the oxygen mass flow must balance in a closed loop, the plants supply all the oxygen required by the crew and the incinerator. Using plants for air revitalization allows using fewer gas processors, buffers, and controllers. In the simplest design, a single combined atmosphere was used for the crew, the plant chamber, and the incinerator. All gas processors, buffers, and controllers were eliminated. The carbon dioxide levels were necessarily similar for the crew and plants. If most of the food is grown, carbon dioxide can be controlled at the desired level by scheduling incineration. An intermediate design uses one atmosphere for the crew and incinerator chambers and a second for the plant chamber. This allows different carbon dioxide levels for the crew and plants. Better control of the atmosphere is obtained by varying the incineration rate. Less gas processing, storage, and control is needed if more food is grown.

Jones, Harry↗

NASA NTRS2016

UAS in the NAS Project: Large-Scale Communication Architecture Simulations with NASA GRC Gen5 Radio Model

This report provides a description and performance characterization of the large-scale, Relay architecture, UAS communications simulation capability developed for the NASA GRC, UAS in the NAS Project. The system uses a validated model of the GRC Gen5 CNPC, Flight-Test Radio model. Contained in the report is a description of the simulation system and its model components, recent changes made to the system to improve performance, descriptions and objectives of sample simulations used for test and verification, and a sampling and observations of results and performance data.

avionics↗

NASA NTRSDate not supplied

Parahydrogen Properties Version 05 Database Release for Nuclear Thermal Propulsion Applications

Consistent modeling assumptions across any large project are crucial to minimize errors between different approaches. Use of consistent material and fluid properties across a large project supports consistent interpretation and application within modeling and simulation results as well as their relevancy to operational systems. NASA’s Space Nuclear Propulsion program dedicates extensive resources towards establishing consistent and, to the extent possible, accurate property databases for its internal staff and all external partners. This work highlights the extensive research performed to modernize the fluid property database of hydrogen which is the leading propellant option for in-space nuclear propelled spacecraft. Specifically, the parahydrogen spin state is of interest since the propellant is stored in a near normal boiling point liquid state which results in it consisting almost entirely of the parahydrogen spin isomer. This database tool has taken recent NASA work and modernized it into a python-based package for easy usage across all modeling entities. The package allows users to provide temperature and pressure pairs along with their desired output properties to yield results accounting for both real-gas and equilibrium dissociation effects while also sharing the default thermodynamic reference state provided by the National Institute of Standards and Technology (NIST) Standard Database 23. The suite also includes advanced capabilities to increase usability, such as on-the-fly interpolation and multidimensional plotting.

Nuclear Thermal Propulsion↗

NASA NTRSDate not supplied

Parahydrogen Properties Version 05 Database Release for NTP Applications

Nuclear Thermal Propulsion↗

NASA NTRS1988

Development of a verification program for deployable truss advanced technology

Use of large deployable space structures to satisfy the growth demands of space systems is contingent upon reducing the associated risks that pervade many related technical disciplines. The overall objectives of this program was to develop a detailed plan to verify deployable truss advanced technology applicable to future large space structures and to develop a preliminary design of a deployable truss reflector/beam structure for use a a technology demonstration test article. The planning is based on a Shuttle flight experiment program using deployable 5 and 15 meter aperture tetrahedral truss reflections and a 20 m long deployable truss beam structure. The plan addresses validation of analytical methods, the degree to which ground testing adequately simulates flight and in-space testing requirements for large precision antenna designs. Based on an assessment of future NASA and DOD space system requirements, the program was developed to verify four critical technology areas: deployment, shape accuracy and control, pointing and alignment, and articulation and maneuvers. The flight experiment technology verification objectives can be met using two shuttle flights with the total experiment integrated on a single Shuttle Test Experiment Platform (STEP) and a Mission Peculiar Experiment Support Structure (MPESS). First flight of the experiment can be achieved 60 months after go-ahead with a total program duration of 90 months.

Dyer, Jack E.↗

NASA NTRS1986

Material damping of simple structures in a simulated space environment

The need for accurate, quantitative knowledge of the vibration dissipation of large space structures is explained. The sources of experimental error in vibrational measurements are detailed. A new method for such testing based on the use of a miniature telemetry system is presented, which allows the testing of structures in a simulated space environment consisting of free-fall inside of a vacuum chamber. Theoretical relations are given for the damping ratios of metals and composites. Measured damping ratios for both aluminum and composite beams and plates, and aluminum planar trusses, are presented. Experimental results are used to evaluate the theoretical damping relations.

Edberg, D. L.↗

NASA NTRS1994

Spacecraft Data Simulator for the test of level zero processing systems

The Microelectronic Systems Branch (MSB) at Goddard Space Flight Center (GSFC) has developed a Spacecraft Data Simulator (SDS) to support the development, test, and verification of prototype and production Level Zero Processing (LZP) systems. Based on a disk array system, the SDS is capable of generating large test data sets up to 5 Gigabytes and outputting serial test data at rates up to 80 Mbps. The SDS supports data formats including NASA Communication (Nascom) blocks, Consultative Committee for Space Data System (CCSDS) Version 1 & 2 frames and packets, and all the Advanced Orbiting Systems (AOS) services. The capability to simulate both sequential and non-sequential time-ordered downlink data streams with errors and gaps is crucial to test LZP systems. This paper describes the system architecture, hardware and software designs, and test data designs. Examples of test data designs are included to illustrate the application of the SDS.

Shi, Jeff↗

NASA NTRS1993

An Arctic source for the Great Salinity Anomaly - A simulation of the Arctic ice-ocean system for 1955-1975

The paper employs a fully prognostic Arctic ice-ocean model to study the interannual variability of sea ice during the period 1955-1975 and to explain the large variability of the ice extent in the Greenland and Iceland seas during the late 1960s. The model is used to test the contention of Aagaard and Carmack (1989) that the Great Salinity Anomaly (GSA) was a consequence of the anomalously large ice export in 1968. The high-latitude ice-ocean circulation changes due to wind field changes are explored. The ice export event of 1968 was the largest in the simulation, being about twice as large as the average and corresponding to 1600 cu km of excess fresh water. The simulations suggest that, besides the above average ice export to the Greenland Sea, there was also fresh water export to support the larger than average ice cover. The model results show the origin of the GSA to be in the Arctic, and support the view that the Arctic may play an active role in climate change.

Hakkinen, Sirpa↗

NASA NTRS2002

A Data Management System for International Space Station Simulation Tools

Groups associated with the design, operational, and training aspects of the International Space Station make extensive use of modeling and simulation tools. Users of these tools often need to access and manipulate large quantities of data associated with the station, ranging from design documents to wiring diagrams. Retrieving and manipulating this data directly within the simulation and modeling environment can provide substantial benefit to users. An approach for providing these kinds of data management services, including a database schema and class structure, is presented. Implementation details are also provided as a data management system is integrated into the Intelligent Virtual Station, a modeling and simulation tool developed by the NASA Ames Smart Systems Research Laboratory. One use of the Intelligent Virtual Station is generating station-related training procedures in a virtual environment, The data management component allows users to quickly and easily retrieve information related to objects on the station, enhancing their ability to generate accurate procedures. Users can associate new information with objects and have that information stored in a database.

Betts, Bradley J.↗

NASA NTRS2015

Conflict Alerts for Aircraft Conducting Visual Approaches

It is common for aircraft to conduct visual and instrument final approaches to a single runway or multiple parallel runways. Useful, nonexcessive safety alerts on aircraft conducting visual approaches are helpful to air traffic controllers, though pilots are responsible for separation with the preceding aircraft. A variety of visual approaches to various runway configurations are studied, and a set of safety alert thresholds is proposed. Fast-time simulations with recorded real-world air traffic data of mostly visual approach flights are performed on a prototype tactical separation assurance system for terminal airspace. Alerts are generated -- with both the standard separation thresholds and the proposed safety alert thresholds -- and compared with those from the Conflict Alert (CA) functionality in the Standard Terminal Automation Replacement System (STARS). The results show that the number of Mode-C Intruder alerts generated was reduced 76% as compared to STARS CA. The nuisance alerts generated by assuming visual to be instrument approaches was reduced by 92% when the proposed safety alert thresholds were used and visual approaches were assumed.A set of safety alert thresholds, which allow safety alerts to be provided to the controllers for aircraft conductingvisual approaches to a single runway or multiple parallel runways, has been proposed based on input from SubjectMatter Experts as well as visual approach procedures and common practices. The goal is to maximize the thresholdswithin the guidance of the procedures and common practices and to minimize the number of nuisance alerts and totalnumber of alerts with the support of flight intent information. Tests have been performed using a recently developedprototype tactical separation assurance system for terminal airspace, called Terminal Tactical Separation-AssuredFlight Environment (T-TSAFE). The input was a full day of air traffic data from Dallas/Fort Worth (DFW) TRACONwith most arriving flights conducting visual approaches. The results compare favorably with those of the ConflictAlert (CA) functionality of the Standard Terminal Automation Replacement System (STARS).When fast-time simulation experiment was performed using T-TSAFE with all arriving flights assumed to conductinstrument approaches, the expected large number of separation alerts were observed. When compared with STARSCA, the conflict pairs common to both T-TSAFE and STARS CA was only 21% of the total STARS CA alerts. As aresult, the nuisance-alert rate for STARS CA was estimated to be about 70%, which is comparable to a similar previously estimation of 80% nuisance-alert rate for CARTS (Common Automated Radar Terminal System) CA. The Mode-CIntruder (MCI) alerts were also reduced by 76% as compared to STARS CA.Examination of the common conflict pairs between T-TSAFE and STARS CA shows that they are valid separationconflicts with good alert lead times for T-TSAFE. However, many of them would still be considered nuisance alertsif the aircraft were conducting visual approaches. This was confirmed by another visual approach fast-time simulationT-TSAFE experiment, in which all DFW arriving flights were assumed to be on visual approaches and our proposedsafety alert thresholds were used and tested. The result of the experiment showed that the number of non-MCI alertswas less by 92% as compared to the number when all DFW arrivals were assumed to be conducting instrumentapproaches. The common conflict pairs involving aircraft conducting visual approaches to parallel runways werereduced by 93% as well. Thus, the flight intent information and the safety alert thresholds are effective in reducingnuisance alerts.T-TSAFE can thus provide separation and safety conflict alerts seamlessly in the real-world environment of mixedterminal operations with arriving flights of both visual and instrument approaches. Compared with STARS CA, TTSAFEhas fewer false alerts, larger alert lead time, and larger alert thresholds. While the nuisance alerts are reducedsignificantly with the safety alert thresholds, further work is needed to study if the alert lead time for safety alerts issufficient.

Tang, Huabin↗

NASA NTRS1999

A One Dimensional, Time Dependent Inlet/Engine Numerical Simulation for Aircraft Propulsion Systems

The NASA Lewis Research Center (LeRC) and the Arnold Engineering Development Center (AEDC) have developed a closely coupled computer simulation system that provides a one dimensional, high frequency inlet/engine numerical simulation for aircraft propulsion systems. The simulation system, operating under the LeRC-developed Application Portable Parallel Library (APPL), closely coupled a supersonic inlet with a gas turbine engine. The supersonic inlet was modeled using the Large Perturbation Inlet (LAPIN) computer code, and the gas turbine engine was modeled using the Aerodynamic Turbine Engine Code (ATEC). Both LAPIN and ATEC provide a one dimensional, compressible, time dependent flow solution by solving the one dimensional Euler equations for the conservation of mass, momentum, and energy. Source terms are used to model features such as bleed flows, turbomachinery component characteristics, and inlet subsonic spillage while unstarted. High frequency events, such as compressor surge and inlet unstart, can be simulated with a high degree of fidelity. The simulation system was exercised using a supersonic inlet with sixty percent of the supersonic area contraction occurring internally, and a GE J85-13 turbojet engine.

Doug Garrard↗