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At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Space Infrared Telescope Facility/Multimission Modular Spacecraft Attitude Control System conceptual design

A control system utilizing the Multi-mission Modular Spacecraft (MMS) Attitude Control System (ACS) was developed and analyzed for the Space Infrared Telescope Facility (SIRTF) spacecraft. Alternative torquer augmentation schemes were studied to determine viable ACS approaches. A control law was developed to use a dual set of single-axis Control Moment Gyros (CMGs) for two-axis control. Flexible structural models were developed using a high fidelity, flight tested NASTRAN model of the MMS, coupled with a NASTRAN model of the SIRTF telescope. Modal significance criteria were employed to reduce the structural model. Multivariable interactive techniques were used to synthesize the control system (including the structural filters). Control system performance for the SIRTF operational modes (quiescent inertial hold, slewing, nodding, and rastering) was then determined using both single-axis and three-axis simulations). The control system described met performance requirements for all modes but the raster with the use of CMGs. The raster performance was limited by the structural flexibility.

Class, Brian F.↗
NASA NTRS1988

A high fidelity real-time simulation of a small turboshaft engine

A high-fidelity component-type model and real-time digital simulation of the General Electric T700-GE-700 turboshaft engine were developed for use with current generation real-time blade-element rotor helicopter simulations. A control system model based on the specification fuel control system used in the UH-60A Black Hawk helicopter is also presented. The modeling assumptions and real-time digital implementation methods particular to the simulation of small turboshaft engines are described. The validity of the simulation is demonstrated by comparison with analysis-oriented simulations developed by the manufacturer, available test data, and flight-test time histories.

Ballin, Mark G.↗
NASA NTRS2010

Transport Aircraft System Identification Using Roll and Yaw Oscillatory Wind Tunnel Data

Continued studies have been undertaken to investigate and develop aerodynamic models that predict aircraft response in nonlinear unsteady flight regimes for transport configurations. The models retain conventional static and dynamic terms but replace conventional acceleration terms with indicial functions. In the Subsonic Fixed Wing Project of the NASA Fundamental Aeronautics Program and the Integrated Resilient Aircraft Controls project of the NASA Aviation Safety Program one aspect of the research is to apply these current developments to transport configurations to facilitate development of advanced simulation and control design technology. This paper continues development and application of a more general modeling methodology to the NASA Langley Generic Transport Model, a sub-scale flight test vehicle. In the present study models for the lateral-directional aerodynamics are developed.

Murphy, Patrick C.↗
NASA NTRS1955

Investigation in the Langley Free-Flight Tunnel of the Low-Speed Stability and Control Characteristics of a 1/10-Scale Model Simulating the Convair F-102A Airplane

An investigation of the low-speed, power-off stability and control characteristics of a 1/10-scale model simulating the Convair F-102A airplane has been made in the Langley free-flight tunnel. The model in its basic configuration and with two modifications involving leading- edge slats and an increase in vertical-tail size was flown through a lift-coefficient range from 0.7 to the stall. Only relatively low-altitude conditions were simulated. The longitudinal stability characteristics of the model were considered satisfactory for all conditions investigated. The lateral stability characteristics were considered satisfactory for the basic configuration over the lift-coefficient range investigated, except near the stall, where large values of static directional instability caused the model to be directionally divergent. An 80-percent increase in vertical-tail area increased the angle of attack at which the model became directionally divergent. The longitudinal and lateral control characteristics were generally satisfactory. Although the adverse sideslip characteristics for the model were considered acceptable over the angle-of-attack range, analysis indicates that the adverse sideslip characteristics of the airplane may be objectionable at high angles of attack.

Boisseau, Peter C.↗
NASA NTRSDate not supplied

Evaluation of Performance, Fatigue and Workload During Real-time, Reactive Telerobotic Mission Control Operations

Real-time, reactive telerobotic mission control operations require personnel to actively operate and manage remotely controlled vehicles or robots in real time. Due to the physical separation of the vehicle from the operator, such operations present many additional factors that can influence fatigue (i.e., degraded mental performance) and workload (i.e., mental and physical cost of task requirements), making it difficult to assess how long an individual can safely and accurately conduct operations. The upcoming Volatiles Investigating Polar Exploration Rover (VIPER) mission involves remotely controlling a lunar vehicle from an Earth-based mission control station. METHODS: In order to determine how long personnel could successfully maintain alertness and performance while operating a rover, we studied seven trained operators (i.e., 5 drivers, 2 real-time scientists) in a simulated mission control environment. We further assessed workload in order to determine whether perceived workload levels would change relative to time on task and by time of day. Operators completed two five-hour simulations in a randomized order, beginning at noon and at midnight. Performance was evaluated every 30 minutes using the psychomotor vigilance task (PVT), Karolinska Sleepiness Scale (KSS), and NASA Task Load Index (NASA-TLX). RESULTS: On average, participants rated themselves as sleepier (5.06 ± 2.28) on the night drives compared to the day drives (3.12 ± 1.44; P < .0001). Workload was rated higher during the day drives (37.93 ± 20.09) compared to night (32.09 ± 21.74; P < .01). Lastly, participants had no change in average reaction time between the two drives. CONCLUSIONS: From the analysis, we observed performance began to degrade after approximately three hours of driving. Our findings suggest that rotating drivers at least every three hours would be prudent to allow for breaks, and to minimize performance degradation, particularly during night shifts.

fatigue↗
NASA NTRS2005

A Unifying Multibody Dynamics Algorithm Development Workbench

The development of new and efficient algorithms for multibody dynamics has been an important research area. These algorithms are used for modeling, simulation, and control of systems such as spacecraft, robotic systems, automotive applications, the human body, manufacturing operations, and micro-electromechanical systems (MEMS). At JPL's Dynamics and Real Time Simulation (DARTS) Laboratory we have developed software that serves as a computational workbench for these algorithms. This software utilizes the mathematical perspective of the spatial operator algebra, which allows the development of dynamics algorithms and new insights into multibody dynamics.

Ziegler, John L.↗
NASA NTRS1990

Advanced control schemes and kinematic analysis for a kinematically redundant 7 DOF manipulator

The kinematic analysis and control of a kinematically redundant manipulator is addressed. The manipulator is the slave arm of a telerobot system recently built at Goddard Space Flight Center (GSFC) to serve as a testbed for investigating research issues in telerobotics. A forward kinematic transformation is developed in its most simplified form, suitable for real-time control applications, and the manipulator Jacobian is derived using the vector cross product method. Using the developed forward kinematic transformation and quaternion representation of orientation matrices, we perform computer simulation to evaluate the efficiency of the Jacobian in converting joint velocities into Cartesian velocities and to investigate the accuracy of Jacobian pseudo-inverse for various sampling times. The equivalence between Cartesian velocities and quaternion is also verified using computer simulation. Three control schemes are proposed and discussed for controlling the motion of the slave arm end-effector.

Nguyen, Charles C.↗
NASA NTRS1989

Autonomous spacecraft attitude control using magnetic torquing only

Magnetic torquing of spacecraft has been an important mechanism for attitude control since the earliest satellites were launched. Typically a magnetic control system has been used for precession/nutation damping for gravity-gradient stabilized satellites, momentum dumping for systems equipped with reaction wheels, or momentum-axis pointing for spinning and momentum-biased spacecraft. Although within the small satellite community there has always been interest in expensive, light-weight, and low-power attitude control systems, completely magnetic control systems have not been used for autonomous three-axis stabilized spacecraft due to the large computational requirements involved. As increasingly more powerful microprocessors have become available, this has become less of an impediment. These facts have motivated consideration of the all-magnetic attitude control system presented here. The problem of controlling spacecraft attitude using only magnetic torquing is cast into the form of the Linear Quadratic Regulator (LQR), resulting in a linear feedback control law. Since the geomagnetic field along a satellite trajectory is not constant, the system equations are time varying. As a result, the optimal feedback gains are time-varying. Orbit geometry is exploited to treat feedback gains as a function of position rather than time, making feasible the onboard solution of the optimal control problem. In simulations performed to date, the control laws have shown themselves to be fairly robust and a good candidate for an onboard attitude control system.

Musser, Keith L.↗
NASA NTRS1993

Low bandwidth robust controllers for flight

Through throttle manipulations, engine thrust can be used for emergency flight control for multi-engine aircraft. Previous study by NASA Dryden has shown the use of throttles for emergency flight control to be very difficult. In general, manual fly-by-throttle is extremely difficult - with landing almost impossible, but control augmentation makes runway landings feasible. Flight path control using throttles-only to achieve safe emergency landing for a large jet transport airplane, Boeing 720, was investigated using Quantitative Feedback Theory (QFT). Results were compared to an augmented control developed in a previous simulation study. The control augmentation corrected the unsatisfactory open-loop characteristics by increasing system bandwidth and damping, but increasing the control bandwidth substantially proved very difficult. The augmented pitch control is robust under no or moderate turbulence. The augmented roll control is sensitive to configuration changes.

Biezad, Daniel J.↗
NASA NTRS1994

On the use of controls for subsonic transport performance improvement: Overview and future directions

Increasing competition among airline manufacturers and operators has highlighted the issue of aircraft efficiency. Fewer aircraft orders have led to an all-out efficiency improvement effort among the manufacturers to maintain if not increase their share of the shrinking number of aircraft sales. Aircraft efficiency is important in airline profitability and is key if fuel prices increase from their current low. In a continuing effort to improve aircraft efficiency and develop an optimal performance technology base, NASA Dryden Flight Research Center developed and flight tested an adaptive performance seeking control system to optimize the quasi-steady-state performance of the F-15 aircraft. The demonstrated technology is equally applicable to transport aircraft although with less improvement. NASA Dryden, in transitioning this technology to transport aircraft, is specifically exploring the feasibility of applying adaptive optimal control techniques to performance optimization of redundant control effectors. A simulation evaluation of a preliminary control law optimizes wing-aileron camber for minimum net aircraft drag. Two submodes are evaluated: one to minimize fuel and the other to maximize velocity. This paper covers the status of performance optimization of the current fleet of subsonic transports. Available integrated controls technologies are reviewed to define approaches using active controls. A candidate control law for adaptive performance optimization is presented along with examples of algorithm operation.

Gilyard, Glenn↗
NASA NTRS1994

The selective use of functional optical variables in the control of forward speed

Previous work on the perception and control of simulated vehicle speed has examined the contributions of optical flow rate (angular visual speed) and texture, or edge rate (frequency of passing terrain objects or markings) on the perception and control of forward speed. However, these studies have not examined the ability to selectively use edge rate or flow rate. The two studies presented here show that this ability is far greater for pilots than non-pilots, as would be expected since pilots must control vehicular speed over a variety of altitudes where flow rates change independently of forward speed. These studies also show that this ability to selectively use these variables is linked to the visual contextual information about the relative validity (linkage with speed) of the two variables. Subjective judgment data also indicated that awareness of altitude and ground texture density did not mediate ground speed awareness.

Johnson, Walter W.↗
NASA NTRS1993

Low Bandwidth Robust Controllers for Flight

Through throttle manipulations, engine thrust can be used for emergency flight control for multi-engine aircraft. Previous study by NASA Dryden has shown the use of throttles for emergency flight control to be very difficult. In general, manual fly-by-throttle is extremely difficult - with landing almost impossible, but control augmentation makes runway landings feasible. Flight path control using throttles-only to achieve safe emergency landing for a large jet transport airplane, Boeing 720, was investigated using Quantitative Feedback Theory (QFT). Results were compared to an augmented control developed in a previous simulation study. The control augmentation corrected the unsatisfactory open-loop characteristics by increasing system bandwidth and damping, but increasing the control bandwidth substantially proved very difficult. The augmented pitch control is robust under no or moderate turbulence. The augmented roll control is sensitive to configuration changes.

Biezad, Daniel J.↗
NASA NTRS1994

Selective Use of Optical Variables to Control Forward Speed

Previous work on the perception and control of simulated vehicle speed has examined the contributions of optical flow rate (angular visual speed) and texture, or edge rate (frequency of passing terrain objects or markings) on the perception and control of forward speed. However, these studies have not examined the ability to selectively use edge rate or flow rate. The two studies reported here show that subjects found it very difficult to arbitrarily direct attention to one or the other of these variables; but that the ability to selectively use these variables is linked to the visual contextual information about the relative validity (linkage with speed) of the two variables. The selectivity also resulted in different velocity adaptation levels for events in which flow rate and edge rate specified forward speed. Finally, the role of visual context in directing attention was further buttressed by the finding that the incorrect perception of changes in ground texture density tended to be coupled with incorrect perceptions of changes in forward speed.

Johnson, Walter W.↗
NASA NTRS2004

Environmental Test Program for the Mars Exploration Rover Project

On June 10 and July 7, 2003 the National Aeronautics and Space Administration (NASA) launched two spacecraft from Cape Canaveral, Florida for a six (6) months flight to the Red Planet, Mars. The two Mars Exploration Rover spacecraft landed safely on the planet in January 2004. Prior to the successful launch, both of the spacecraft were involved in a comprehensive test campaign that included development, qualification, and protoflight test programs. Testing was performed to simulate the environments associated with launch, inter-planetary cruise, landing on the planet and Mars surface operations. Unique test requirements included operating the spacecraft while the chamber pressure was controlled to simulate the decent to the planet from deep space, high impact landing loads and rover operations on the surface of the planet at 8 Torr and -130 C. This paper will present an overview of the test program that included vibration, pyro-shock, landing loads, acoustic noise, thermal vacuum and solar simulation testing at the Jet Propulsion Laboratory (JPL) Environmental Test Laboratory facilities in Pasadena, California.

Fisher, Terry C.↗
NASA NTRS2019

Gravity as a Continuum: Effects of Altered Gravity on Drosophila Melanogaster Immunity

The impact of spaceflight on immune function is undoubtedly a critical focus in the area of space biology and human health research. Heat shock proteins (Hsp) are an evolutionarily conserved family of proteins that are expressed in response to cellular and physiological stressors, experienced during radiation exposure, confinement, circadian rhythm disruption, and altered gravity (hypergravity experienced at launch/landing and microgravity experienced in-flight). In particular, Hsp70 aids in the folding of proteins, facilitates the movement of proteins across the membranes during signal transductions and can stimulate innate immunity. Since Hsp70 is induced during cellular stress, and can act as a stimulator for innate immunity, we sought to address how a loss of Hsp70 affects immunity, under the stress-inducing model of acute and chronic hypergravity. Moreover, the effects of gravity as a continuum on the induction of Hsps and key immune genes were also assessed to determine if increased cellular stress, via increased gravity (g)-force, contributes to immune dysfunctions. For this, wildtype (W1118) and Hsp70 deficient (Hsp70null) Drosophila melanogaster were subjected to simulated hypergravity at increasing levels of g-force (1.2g, 3g, and 5g) for acute (1hr) and chronic (7-day) timepoints and were compared to 0g 'non-hypergravity' controls. Following simulation, whole bodies were sex-segregated, RNA was isolated and quantitative (q)PCR was performed to determine differential immune gene expression profiles. Further, functional output of hemocytes were assessed by a phagocytosis assay. Collectively, these studies evaluated the effects of Hsp70 in the context of immunity during acute and chronic hypergravity. Indeed, relevance for this work can directly translate to acute effects of launch/landing gravitational forces upon liftoff (~1.7g) and entry (~3.4g) that astronauts experience. In addition, the effects of chronic cellular stress is directly relevant to the immune health of astronauts on long duration missions, as well. Thus, as we approach the goal of returning to the Moon and landing the first humans on Mars, an evaluation of gravity as a continuum and the stress-inducing effects of altered gravity experienced during spaceflight on astronaut immunity and health are necessary.

Olivieri, Joe↗