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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Reversionary Control Modes for the Mitigation of Failures in a Partially Turboelectric Aircraft Propulsion System

In support of emission and fuel burn reduction goals, the aviation industry is actively pursuing the advancement of electrified aircraft propulsion (EAP) technology. This includes turboelectric and hybrid electric propulsion designs that combine gas turbine engine and electrical system hardware. Such architectures exhibit a high degree of coupling between subsystems. This drives the need for system-level control strategies to ensure the safe, coordinated, and efficient operation of all subsystems. The design and certification of any aircraft propulsion system requires that all potential subsystem failures are identified, and the hazards posed by these failures are appropriately mitigated. This requirement is particularly challenging for EAP systems due to their integrated nature. One approach to assist in EAP failure mitigation is the inclusion of automated reconfiguration capabilities within the propulsion control system. Such control modes, referred to as reversionary control modes, are designed to automatically detect failures and activate backup control modes upon failure detection. This paper covers the design and evaluation of reversionary control mode logic developed for a partially turboelectric propulsion concept. Test results from a real-time hardware-in-the-loop evaluation of the concept are also presented and discussed. The results show that the developed reversionary control logic can successfully detect and mitigate subsystem failures in a representative environment that includes actual electrical system hardware.

Electrified Aircraft Propulsion↗
NASA NTRSDate not supplied

Reversionary Control Modes for the Mitigation of Failures in a Partially Turboelectric Aircraft Propulsion System

In support of emission and fuel burn reduction goals, the aviation industry is actively pursuing the advancement of electrified aircraft propulsion (EAP) technology. This includes turboelectric and hybrid electric propulsion designs that combine gas turbine engine and electrical system hardware. Such architectures exhibit a high degree of coupling between subsystems. This drives the need for system-level control strategies to ensure the safe, coordinated, and efficient operation of all subsystems. The design and certification of any aircraft propulsion system requires that all potential subsystem failures are identified, and the hazards posed by these failures are appropriately mitigated. This requirement is particularly challenging for EAP systems due to their integrated nature. One approach to assist in EAP failure mitigation is the inclusion of automated reconfiguration capabilities within the propulsion control system. Such control modes, referred to as reversionary control modes, are designed to automatically detect failures and activate backup control modes upon failure detection. This paper covers the design and evaluation of reversionary control mode logic developed for a partially turboelectric propulsion concept. Test results from a real-time hardware-in-the-loop evaluation of the concept are also presented and discussed. The results show that the developed reversionary control logic can successfully detect and mitigate subsystem failures in a representative environment that includes actual electrical system hardware.

Electrified Aircraft Propulsion↗
NASA NTRS2024

Reversionary Control Modes for the Mitigation of Failures in a Partially Turboelectric Aircraft Propulsion System

In support of emission and fuel burn reduction goals, the aviation industry is actively pursuing the advancement of electrified aircraft propulsion (EAP) technology. This includes turboelectric and hybrid electric propulsion designs that combine gas turbine engine and electrical system hardware. Such architectures exhibit a high degree of coupling between subsystems. This drives the need for system-level control strategies to ensure the safe, coordinated, and efficient operation of all subsystems. The design and certification of any aircraft propulsion system requires that all potential subsystem failures are identified, and the hazards posed by these failures are appropriately mitigated. This requirement is particularly challenging for EAP systems due to their integrated nature. One approach to assist in EAP failure mitigation is the inclusion of automated reconfiguration capabilities within the propulsion control system. Such control modes, referred to as reversionary control modes, are designed to automatically detect failures and activate backup control modes upon failure detection. This paper covers the design and evaluation of reversionary control mode logic developed for a partially turboelectric propulsion concept. Test results from a real-time hardware-in-the-loop evaluation of the concept are also presented and discussed. The results show that the developed reversionary control logic can successfully detect and mitigate subsystem failures in a representative environment that includes actual electrical system hardware.

Electrified Aircraft Propulsion↗
NASA NTRS1996

Dynamic control of photosynthetic photon flux for lettuce production in CELSS

A new dynamic control of photosynthetic photon flux (PPF) was tested using lettuce canopies growing in the Minitron II plant-growth/canopy gas-exchange system. Canopy photosynthetic rates (Pn) were measured in real time and fedback for further environment control. Pn can be manipulated by changing PPF, which is a good environmental parameter for dynamic control of crop production in a Controlled Ecological Life-Support Systems CELSS. Decision making that combines empirical mathematical models with rule sets developed from recent experimental data was tested. With comparable yield indices and potential for energy savings, dynamic control strategies will contribute greatly to the sustainability of space-deployed CELSS.

NASA Discipline Life Support Systems↗
NASA NTRS1991

Formulation of a strategy for monitoring control integrity in critical digital control systems

Advanced aircraft will require flight critical computer systems for stability augmentation as well as guidance and control that must perform reliably in adverse, as well as nominal, operating environments. Digital system upset is a functional error mode that can occur in electromagnetically harsh environments, involves no component damage, can occur simultaneously in all channels of a redundant control computer, and is software dependent. A strategy is presented for dynamic upset detection to be used in the evaluation of critical digital controllers during the design and/or validation phases of development. Critical controllers must be able to be used in adverse environments that result from disturbances caused by an electromagnetic source such as lightning, high intensity radiated field (HIRF), and nuclear electromagnetic pulses (NEMP). The upset detection strategy presented provides dynamic monitoring of a given control computer for degraded functional integrity that can result from redundancy management errors and control command calculation error that could occur in an electromagnetically harsh operating environment. The use is discussed of Kalman filtering, data fusion, and decision theory in monitoring a given digital controller for control calculation errors, redundancy management errors, and control effectiveness.

Belcastro, Celeste M.↗
NASA NTRS1990

Evolution and advanced technology

The NASREM architecture with its standard interfaces permits development and evolution of the Flight Telerobotic Servicer to greater autonomy. Technologies in control strategies for an arm with seven DOF, including a safety system containing skin sensors for obstacle avoidance, are being developed. Planning and robotic execution software includes symbolic task planning, world model data bases, and path planning algorithms. Research over the last five years has led to the development of laser scanning and ranging systems, which use coherent semiconductor laser diodes for short range sensing. The possibility of using a robot to autonomously assemble space structures is being investigated. A control framework compatible with NASREM is being developed that allows direct global control of the manipulator. Researchers are developing systems that permit an operator to quickly reconfigure the telerobot to do new tasks safely.

Ollendorf, Stanford↗
NASA NTRS2019

Meteoroid Impact Detection for Exploration of Asteroids (MIDEA)

Asteroids contain a wealth of resources including water and precious metals that can be extracted. These resources could be applied to in-space manufacture of products that depend less on material launched from Earth's surface. The Meteoroid Impact Detection for Exploration of Asteroids (MIDEA) concept addresses the challenge of characterizing an asteroid surface using a small satellite with a constellation of free-flying plasma sensors to assess the asteroid’s viability for in situ resource utilization (ISRU). The plasma sensors detect ions ejected from the surface of an asteroid by meteoroid impacts, enabling the surface composition to be inferred. The objective of this NIAC Phase I study was to demonstrate feasibility of the MIDEA architecture in the context of proximity operations around an asteroid target and to develop the design of an orbital geometry and attitude control strategy for the ultralight plasma sensors. This was undertaken through a simulation framework to identify and characterize a favorable orbit for the MIDEA sensor constellation, and developing a sensor geometry that is consistent with maintaining the pointing requirements necessary to operate with sufficient power generation. Our study showed that a polar orbit aligned along the asteroid terminator provided sufficient stability for the sensors in the low gravitational environment under the influence of substantial solar radiation pressure. Reflector vanes using controlled reflectivity devices implemented with liquid crystal technology are capable of maintaining the sensor attitude so that it consistently points its solar panels in the sun direction and the sensor electrode at the asteroid surface. Finally, the reduction in meteoroid impact detection due to visibility constraints from the proposed orbit does not substantially extend the expected mission duration. These results indicate that the MIDEA concept can be achievable using a 10–20 kg spacecraft, which would be able to characterize the surface composition of an asteroid within 30–50 days of proximity operations. This architecture, implemented in parallel to multiple asteroid targets, would enable widespread exploration of near-Earth asteroids at low cost.

Asteroids↗
NASA NTRS1972

On simultaneous choice of dynamic control and measurement strategies for stochastic systems.

Consideration of stochastic optimal control problems in which the measurement equation contains a control variable. Conditions under which it is possible to separately optimize the dynamic and measurement controls are studied, with particular emphasis on showing (by counterexample) that certain results already available for the linear-Gaussian-quadratic case do not extend to more general problems. Conditions under which the extension is possible are discussed.

Kramer, L. C.↗
NASA NTRS2004

The Precision Formation Flying Integrated Analysis Tool (PFFIAT)

Several space missions presently in the concept phase (e.g. Stellar Imager, Submillimeter Probe of Evolutionary Cosmic Structure, Terrestrial Planet Finder) plan to use multiple spacecraft flying in precise formation to synthesize unprecedently large aperture optical systems. These architectures present challenges to the attitude and position determination and control system; optical performance is directly coupled to spacecraft pointing with typical control requirements being on the scale of milliarcseconds and nanometers. To investigate control strategies, rejection of environmental disturbances, and sensor and actuator requirements, a capability is needed to model both the dynamical and optical behavior of such a distributed telescope system. This paper describes work ongoing at NASA Goddard Space Flight Center toward the integration of a set of optical analysis tools (Optical System Characterization and Analysis Research software, or OSCAR) with the Formation Flying Test Bed (FFTB). The resulting system is called the Precision Formation Flying Integrated Analysis Tool (PFFIAT), and it provides the capability to simulate closed-loop control of optical systems composed of elements mounted on multiple spacecraft. The attitude and translation spacecraft dynamics are simulated in the FFTB, including effects of the space environment (e.g. solar radiation pressure, differential orbital motion). The resulting optical configuration is then processed by OSCAR to determine an optical image. From this image, wavefront sensing (e.g. phase retrieval) techniques are being developed to derive attitude and position errors. These error signals will be fed back to the spacecraft control systems, completing the control loop. A simple case study is presented to demonstrate the present capabilities of the tool.

Stoneking, Eric↗
NASA NTRS2004

The Precision Formation Flying Integrated Analysis Tool (PFFIAT)

Several space missions presently in the concept phase (e.g. Stellar Imager, Sub- millimeter Probe of Evolutionary Cosmic Structure, Terrestrial Planet Finder) plan to use multiple spacecraft flying in precise formation to synthesize unprecedently large aperture optical systems. These architectures present challenges to the attitude and position determination and control system; optical performance is directly coupled to spacecraft pointing with typical control requirements being on the scale of milliarcseconds and nanometers. To investigate control strategies, rejection of environmental disturbances, and sensor and actuator requirements, a capability is needed to model both the dynamical and optical behavior of such a distributed telescope system. This paper describes work ongoing at NASA Goddard Space Flight Center toward the integration of a set of optical analysis tools (Optical System Characterization and Analysis Research software, or OSCAR) with the Formation J?lying Test Bed (FFTB). The resulting system is called the Precision Formation Flying Integrated Analysis Tool (PFFIAT), and it provides the capability to simulate closed-loop control of optical systems composed of elements mounted on multiple spacecraft. The attitude and translation spacecraft dynamics are simulated in the FFTB, including effects of the space environment (e.g. solar radiation pressure, differential orbital motion). The resulting optical configuration is then processed by OSCAR to determine an optical image. From this image, wavefront sensing (e.g. phase retrieval) techniques are being developed to derive attitude and position errors. These error signals will be fed back to the spacecraft control systems, completing the control loop. A simple case study is presented to demonstrate the present capabilities of the tool.

Stoneking, Eric↗
NASA NTRS1986

Physical and numerical sources of computational inefficiency in integration of chemical kinetic rate equations: Etiology, treatment and prognosis

The design of a very fast, automatic black-box code for homogeneous, gas-phase chemical kinetics problems requires an understanding of the physical and numerical sources of computational inefficiency. Some major sources reviewed in this report are stiffness of the governing ordinary differential equations (ODE's) and its detection, choice of appropriate method (i.e., integration algorithm plus step-size control strategy), nonphysical initial conditions, and too frequent evaluation of thermochemical and kinetic properties. Specific techniques are recommended (and some advised against) for improving or overcoming the identified problem areas. It is argued that, because reactive species increase exponentially with time during induction, and all species exhibit asymptotic, exponential decay with time during equilibration, exponential-fitted integration algorithms are inherently more accurate for kinetics modeling than classical, polynomial-interpolant methods for the same computational work. But current codes using the exponential-fitted method lack the sophisticated stepsize-control logic of existing black-box ODE solver codes, such as EPISODE and LSODE. The ultimate chemical kinetics code does not exist yet, but the general characteristics of such a code are becoming apparent.

Pratt, D. T.↗
NASA NTRS2003

Boundary-Layer Separation Control under Low-Pressure Turbine Airfoil Conditions using Glow-Discharge Plasma Actuators

Modem low-pressure turbines, in general, utilize highly loaded airfoils in an effort to improve efficiency and to lower the number of airfoils needed. Typically, the airfoil boundary layers are turbulent and fully attached at takeoff conditions, whereas a substantial fraction of the boundary layers on the airfoils may be transitional at cruise conditions due to the change of density with altitude. The strong adverse pressure gradients on the suction side of these airfoils can lead to boundary-layer separation at the latter low Reynolds number conditions. Large separation bubbles, particularly those which fail to reattach, cause a significant degradation of engine efficiency. A component efficiency drop of the order 2% may occur between takeoff and cruise conditions for large commercial transport engines and could be as large as 7% for smaller engines at higher altitude. An efficient means of of separation elimination/reduction is, therefore, crucial to improved turbine design. Because the large change in the Reynolds number from takeoff to cruise leads to a distinct change in the airfoil flow physics, a separation control strategy intended for cruise conditions will need to be carefully constructed so as to incur minimum impact/penalty at takeoff. A complicating factor, but also a potential advantage in the quest for an efficient strategy, is the intricate interplay between separation and transition for the situation at hand. Volino gives a comprehensive discussion of several recent studies on transition and separation under low-pressure-turbine conditions, among them one in the present facility. Transition may begin before or after separation, depending on the Reynolds number and other flow conditions. If the transition occurs early in the boundary layer then separation may be reduced or completely eliminated. Transition in the shear layer of a separation bubble can lead to rapid reattachment. This suggests using control mechanisms to trigger and enhance early transition. Gad-el-Hak provides a review of various techniques for flow control in general and Volino discusses recent studies on separation control under low-pressure-turbine conditions utilizing passive as well as active devices. As pointed out by Volino, passive devices optimized for separation control at low Reynolds numbers tend to increase losses at high Reynolds numbers, Active devices have the attractive feature that they can be utilized only in operational regimes where they are needed and when turned off would not affect the flow. The focus in the present paper is an experimental Separation is induced on a flat plate installed in a closed-circuit wind tunnel by a shaped insert on the opposite wall. The flow conditions represent flow over the suction surface of a modem low-pressure-turbine airfoil ('Pak-B'). The Reynolds number, based on wetted plate length and nominal exit velocity, is varied from 50,000 to 300,000, covering cruise to takeoff conditions. Low (0.2%) and high (2.5%) Gee-stream turbulence intensities are set using passive grids. A spanwise-oriented phased-plasma-array actuator, fabricated on a printed circuit board, is surface- flush-mounted upstream of the separation point and can provide forcing in a wide frequency range. Static surface pressure measurements and hot-wire anemometry of the base and controlled flows are performed and indicate that the glow-discharge plasma actuator is an effective device for separation control. of active separation control using glow discharge plasma actuators.

Hultgren, Lennart S.↗
NASA NTRS2004

Microgravity Investigation of Crew Reactions in 0-G (MICRO-G)

There is a need for a human factors, technology-based bioastronautics research effort to develop an integrated system that reduces risk and provides scientific knowledge of astronaut-induced loads and motions during long-duration missions on the International Space Station (ISS), which will lead to appropriate countermeasures. The primary objectives of the Microgravity Investigation of Crew Reactions in 0-G (MICRO-GI research effort are to quantify astronaut adaptation and movement as well as to model motor strategies for differing gravity environments. The overall goal of this research program is to improve astronaut performance and efficiency through the use of rigorous quantitative dynamic analysis, simulation and experimentation. The MICRO-G research effort provides a modular, kinetic and kinematic capability for the ISS. The collection and evaluation of kinematics (whole-body motion) and dynamics (reacting forces and torques) of astronauts within the ISS will allow for quantification of human motion and performance in weightlessness, gathering fundamental human factors information for design, scientific investigation in the field of dynamics and motor control, technological assessment of microgravity disturbances, and the design of miniaturized, real-time space systems. The proposed research effort builds on a strong foundation of successful microgravity experiments, namely, the EDLS (Enhanced Dynamics Load Sensors) flown aboard the Russian Mir space station (19961998) and the DLS (Dynamic Load Sensors) flown on Space Shuttle Mission STS-62. In addition, previously funded NASA ground-based research into sensor technology development and development of algorithms to produce three-dimensional (3-0) kinematics from video images have come to fruition and these efforts culminate in the proposed collaborative MICRO-G flight experiment. The required technology and hardware capitalize on previous sensor design, fabrication, and testing and can be flight qualified for a fraction of the cost of an initial spaceflight experiment. Four dynamic load sensors/restraints are envisioned for measurement of astronaut forces and torques. Two standard ISS video cameras record typical astronaut operations and prescribed IVA motions for 3-D kinematics. Forces and kinematics are combined for dynamic analysis of astronaut motion, exploiting the results of the detailed dynamic modeling effort for the quantitative verification of astronaut IVA performance, induced-loads, and adaptive control strategies for crewmember whole-body motion in microgravity. This comprehensive effort, provides an enhanced human factors approach based on physics-based modeling to identify adaptive performance during long-duration spaceflight, which is critically important for astronaut training as well as providing a spaceflight database to drive countermeasure design.

Newman, Dava↗
NASA NTRS1985

Control of a free-flying robot manipulator system

The goal of the research is to develop and test control strategies for a self-contained, free flying space robot. Such a robot would perform operations in space similar to those currently handled by astronauts during extravehicular activity (EVA). The focus of the work is to develop and carry out a program of research with a series of physical Satellite Robot Simulator Vehicles (SRSV's), two-dimensionally freely mobile laboratory models of autonomous free-flying space robots such as might perform extravehicular functions associated with operation of a space station or repair of orbiting satellites. The development of the SRSV and of some of the controller subsystems are discribed. The two-link arm was fitted to the SRSV base, and researchers explored the open-loop characteristics of the arm and thruster actuators. Work began on building the software foundation necessary for use of the on-board computer, as well as hardware and software for a local vision system for target identification and tracking.

Alexander, H.↗
NASA NTRS1987

Heuristic control of the Utah/MIT dextrous robot hand

Basic hand grips and sensor interactions that a dextrous robot hand will need as part of the operation of an EVA Retriever are analyzed. What is to be done with a dextrous robot hand is examined along with how such a complex machine might be controlled. It was assumed throughout that an anthropomorphic robot hand should perform tasks just as a human would; i.e., the most efficient approach to developing control strategies for the hand would be to model actual hand actions and do the same tasks in the same ways. Therefore, basic hand grips that human hands perform, as well as hand grip action were analyzed. It was also important to examine what is termed sensor fusion. This is the integration of various disparate sensor feedback paths. These feedback paths can be spatially and temporally separated, as well as, of different sensor types. Neural networks are seen as a means of integrating these varied sensor inputs and types. Basic heuristics of hand actions and grips were developed. These heuristics offer promise of control dextrous robot hands in a more natural and efficient way.

Bass, Andrew H., Jr.↗
NASA NTRS2005

Integrated Locomotor Function Tests for Countermeasure Evaluation

Following spaceflight crewmembers experience locomotor dysfunction due to inflight adaptive alterations in sensorimotor function. Countermeasures designed to mitigate these postflight gait alterations need to be assessed with a new generation of tests that evaluate the interaction of various sensorimotor sub-systems central to locomotor control. The goal of the present study was to develop new functional tests of locomotor control that could be used to test the efficacy of countermeasures. These tests were designed to simultaneously examine the function of multiple sensorimotor systems underlying the control of locomotion and be operationally relevant to the astronaut population. Traditionally, gaze stabilization has been studied almost exclusively in seated subjects performing target acquisition tasks requiring only the involvement of coordinated eye-head movements. However, activities like walking involve full-body movement and require coordination between lower limbs and the eye-head-trunk complex to achieve stabilized gaze during locomotion. Therefore the first goal of this study was to determine how the multiple, interdependent, full-body sensorimotor gaze stabilization subsystems are functionally coordinated during locomotion. In an earlier study we investigated how alteration in gaze tasking changes full-body locomotor control strategies. Subjects walked on a treadmill and either focused on a central point target or read numeral characters. We measured: temporal parameters of gait, full body sagittal plane segmental kinematics of the head, trunk, thigh, shank and foot, accelerations along the vertical axis at the head and the shank, and the vertical forces acting on the support surface. In comparison to the point target fixation condition, the results of the number reading task showed that compensatory head pitch movements increased, peak head acceleration was reduced and knee flexion at heel-strike was increased. In a more recent study we investigated the adaptive remodeling of the full-body gaze control systems following exposure to visual-vestibular conflict. Subjects walked on a treadmill before and after a 30- minute exposure to 0.5X minifying during which self-generated sinusoidal vertical head rotations were performed while seated. Following exposure to visual-vestibular conflict subjects showed a restriction in compensatory head movements, increased knee and ankle flexion after heel-strike and a decrease in the rate of body loading during the rapid weight transfer phase after the heel strike event. Taken together, results from both studies provide evidence that the full body contributes to gaze stabilization during locomotion, and that different functional elements are responsive to changes in visual task constraints and are subject to adaptive alterations following exposure to visual-vestibular conflict. This information provides the basis for the design of a new generation of integrative tests that incorporate the evaluation of multiple neural control systems relevant to astronaut operational performance.

Bloomberg, J. J.↗
NASA NTRS2009

Integrated Traffic Flow Management Decision Making

A generalized approach is proposed to support integrated traffic flow management decision making studies at both the U.S. national and regional levels. It can consider tradeoffs between alternative optimization and heuristic based models, strategic versus tactical flight controls, and system versus fleet preferences. Preliminary testing was accomplished by implementing thirteen unique traffic flow management models, which included all of the key components of the system and conducting 85, six-hour fast-time simulation experiments. These experiments considered variations in the strategic planning look-ahead times, the replanning intervals, and the types of traffic flow management control strategies. Initial testing indicates that longer strategic planning look-ahead times and re-planning intervals result in steadily decreasing levels of sector congestion for a fixed delay level. This applies when accurate estimates of the air traffic demand, airport capacities and airspace capacities are available. In general, the distribution of the delays amongst the users was found to be most equitable when scheduling flights using a heuristic scheduling algorithm, such as ration-by-distance. On the other hand, equity was the worst when using scheduling algorithms that took into account the number of seats aboard each flight. Though the scheduling algorithms were effective at alleviating sector congestion, the tactical rerouting algorithm was the primary control for avoiding en route weather hazards. Finally, the modeled levels of sector congestion, the number of weather incursions, and the total system delays, were found to be in fair agreement with the values that were operationally observed on both good and bad weather days.

Grabbe, Shon R.↗
NASA NTRS2003

Coupled Attitude and Orbit Dynamics and Control in Formation Flying Systems

Formation flying systems can range from global constellations offering extended service coverage to clusters of highly coordinated vehicles that perform distributed sensing. Recently, the use of groups of micro-satellites in the areas of near Earth explorations, deep space explorations, and military applications has received considerable attention by researchers and practitioners. To date, most proposed control strategies are based on linear models (e.g., Hill-Clohessy-Wiltshire equations) or nonlinear models that are restricted to circular reference orbits. Also, all models in the literature are uncoupled between relative position and relative attitude. In this paper, a generalized dynamic model is proposed. The reference orbit is not restricted to the circular case. In this formulation, the leader or follower satellite can be in either a circular or an elliptic orbit. In addition to maintaining a specified relative position, the satellites are also required to maintain specified relative attitudes. Thus the model presented couples vehicle attitude and orbit requirements. Orbit perturbations are also included. In particular, the J(sub 2) effects are accounted in the model. Finally, a sliding mode controller is developed and used to control the relative attitude of the formation and the simulation results are presented.

Yunjun Xu↗