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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Impact of magnetic isolation on pointing system performance in the presence of structural flexibility

The inertial pointing stability of a gimbal pointing system (AGS) was compared with a magnetic pointing/gimbal followup system (ASPS), under certain conditions of system structural flexibility and disturbance inputs from the gimbal support structure. Separate 3 degree-of-freedom (3DOF) linear models based on NASTRAN modal flexibility data for the gimbal and support structures were generated for the ASPS configurations. Using the models inertial pointing control loops providing 6dB of gain margin and 45 deg of phase margin were defined for each configuration. The pointing loop bandwidth obtained for the ASPS is more than twice the level achieved for the AGS configuration. The AGS limit is attributed to the gimbal and support structure flexibility. As a result of the higher ASPS pointing loop bandwidth and the disturbance rejection provided by the magnetic isolation ASPS pointing performane is significantly better than that of the AGS system. The low frequency peak of the ASPS transfer function from base disturbance to payload angular motion is almost 60dB lower than AGS low frequency peak.

Seller, J.↗
NASA NTRS1984

In-orbit measurements of Landsat-4 Thematic Mapper dynamic disturbances

This paper describes Landsat-4 sensors, spacecraft disturbances, and the methodology used to correct Thematic Mapper (TM) images. The discussion includes system requirements, mathematical modeling, in-orbit angular motion measurement, Fast Fourier Transformer (FFT) data analysis, and scan system correction. Emphasis is given to the cause and effect of the electromechanical disturbances beginning with the scan mirror and its interaction and sensitivity to externally and self-generated disturbances. Ground-testing results are compared with those obtained in orbit.

Sudey, J., Jr.↗
NASA NTRS1987

An overview of controls research on the NASA Langley Research Center grid

The NASA Langley Research Center has assembled a flexible grid on which control systems research can be accomplished on a two-dimensional structure that has many physically distributed sensors and actuators. The grid is a rectangular planar structure that is suspended by two cables attached to one edge so that out of plane vibrations are normal to gravity. There are six torque wheel actuators mounted to it so that torque is produced in the grid plane. Also, there are six rate gyros mounted to sense angular motion in the grid plane and eight accelerometers that measure linear acceleration normal to the grid plane. All components can be relocated to meet specific control system test requirements. Digital, analog, and hybrid control systems capability is provided in the apparatus. To date, research on this grid has been conducted in the areas of system and parameter identification, model estimation, distributed modal control, hierarchical adaptive control, and advanced redundancy management algorithms. The presentation overviews each technique and presents the most significant results generated for each area.

Montgomery, Raymond C.↗
NASA NTRS1989

Calculation of double-lunar swingby trajectories: I. Keplerian foundation

Scientific satellites may require translunar orbits aligned with the Sun-Earth line, with most of the period spent in either the sunward or antisunward direction. To maintain alignment, the orbit's line of apsides must rotate at a rate equal to mean angular motion of the Earth about the Sun. To maintain this rotation of the line of apsides by use of fuel onboard the spacecraft is prohibitively expensive. Farquhar and Dunham proposed a method for maintaining the desired alignment by gaining momentum at the expense of the Moon during a close approach (a lunar swingby) as the spacecraft passes beyond lunar orbit, then returning the momentum at the second lunar swingby as the spacecraft returns within the lunar orbit. The cycle of double-lunar swingbys may then be repeated. Dunham presented the orbit parameters necessary to achieve double-lunar swingby orbits which will maintain Sun-Earth line alignment. The details of the Keplerian approach to calculation of these parameters are presented. Methods for solution of the necessary equations for these parameters are presented.

Stalos, Stephen↗
NASA NTRS1989

Dynamic analysis of flexible multibody structures

A system composed of several interconnected elastic components that may experience large angular motion relative to each other during operation is referred to as a flexible multibody structure. Several formulations were proposed for the determination of the dynamic response of controlled flexible multibody structures. In general, these formulations consist of superposing elastic deformations of the component body onto the large rigid body motion of the component. It was shown that this particular methodology for combining linear structural deformations with nonlinear kinematics can lead to erroneous response predictions when either the beam member is very flexible or the rotational speed is high. In addition, previous formulations introduce constraint equations to define the interrelations among system components. This approach increases the number of equations that must be solved, and may result in contraint violation when numerical error accumulates during the integration process. In order to overcome the difficulties, a new approach was suggested. The approach is essentially a finite element formulation which takes advantage of the fact that many multibody structures are joint dominated. The Large Angle Transient Dynamic Analysis (LATDYN) program for clarity of documentation, ease of use, user friendliness, modeling generality, and accuracy of results was evaluated. This required gaining a working familiarity with the code and performing several case studies.

Hernried, Alan G.↗
NASA NTRS1991

Passive dynamic controllers for nonlinear mechanical systems

A methodology for model-independant controller design for controlling large angular motion of multi-body dynamic systems is outlined. The controlled system may consist of rigid and flexible components that undergo large rigid body motion and small elastic deformations. Control forces/torques are applied to drive the system and at the same time suppress the vibration due to flexibility of the components. The proposed controller consists of passive second-order systems which may be designed with little knowledge of the system parameter, even if the controlled system is nonlinear. Under rather general assumptions, the passive design assures that the closed loop system has guaranteed stability properties. Unlike positive real controller design, stabilization can be accomplished without direct velocity feedback. In addition, the second-order passive design allows dynamic feedback controllers with considerable freedom to tune for desired system response, and to avoid actuator saturation. After developing the basic mathematical formulation of the design methodology, simulation results are presented to illustrate the proposed approach to a flexible six-degree-of-freedom manipulator.

Juang, Jer-Nan↗
NASA NTRS1991

Large Angle Transient Dynamics (LATDYN) demonstration problem manual

LATDYN is a computer code for modeling the Large Angle Transient Dynamics of structures. The objective in developing the code was to investigate new techniques for analyzing flexible deformation and control/structure interaction problems associated with large angular motions of spacecraft. Such motions may consist of pointing the entire spacecraft or articulation of individual components, events which occur frequently during construction, operation, and maintenance of large spacecraft. This type of analysis is beyond the routine capability of conventional analytical tools without simplifying assumptions. In some instances, the motion may be sufficiently slow and the spacecraft (or component) sufficiently rigid to simplify the analysis of dynamics and controls by making pseudo-static and/or rigid body assumptions. LATDYN introduces a new approach to the problem by combining finite element structural analysis, multi-body dynamics, and control system analysis in a single tool. It includes a new type of finite element that can deform and rotate through large angles at the same time, and which can be connected to other finite elements either rigidly or through mechanical joints. LATDYN also provides symbolic capabilities for modeling control systems which are interfaced directly with the finite element structural model. Thus, the nonlinear equations representing the structural model are integrated along with the equations representing sensors, processing, and controls as a coupled system.

Wu, Shih-Chin↗
NASA NTRS1991

Large Angle Transient Dynamics (LATDYN) user's manual

A computer code for modeling the large angle transient dynamics (LATDYN) of structures was developed to investigate techniques for analyzing flexible deformation and control/structure interaction problems associated with large angular motions of spacecraft. This type of analysis is beyond the routine capability of conventional analytical tools without simplifying assumptions. In some instances, the motion may be sufficiently slow and the spacecraft (or component) sufficiently rigid to simplify analyses of dynamics and controls by making pseudo-static and/or rigid body assumptions. The LATDYN introduces a new approach to the problem by combining finite element structural analysis, multi-body dynamics, and control system analysis in a single tool. It includes a type of finite element that can deform and rotate through large angles at the same time, and which can be connected to other finite elements either rigidly or through mechanical joints. The LATDYN also provides symbolic capabilities for modeling control systems which are interfaced directly with the finite element structural model. Thus, the nonlinear equations representing the structural model are integrated along with the equations representing sensors, processing, and controls as a coupled system.

Abrahamson, A. Louis↗
NASA NTRS1991

Passive dynamic controllers for non-linear mechanical systems

A methodology for model-independent controller design for controlling large angular motion of multi-body dynamic systems is outlined.The controlled system may consist of rigid and flexible components that undergo large rigid body motion and small elastic deformations. Control forces/torques are applied to drive the system, and at the same time suppress the vibrations due to flexibility of the components. The proposed controller consists of passive second-order systems which may be designed with little knowledge of the system parameters, even if the controlled system is non-linear. Under rather general assumptions, the passive design assures that the closed loop system has guaranteed stability properties. Unlike positive real controller design, stabilization can be accomplished without direct velocity feedback. In addition, the second-order passive design allows dynamic feedback controllers with considerable freedom to tune for desired system response, and to avoid actuator saturation. After developing the basic mathematical formulation of the design methodology, simulation results are presented to illustrate the proposed approach applied to a flexible six-degree-of-freedom manipulator.

Juang, Jer-Nan↗
NASA NTRS1992

Pressure vessel flex joint

An airtight, flexible joint is disclosed for the interfacing of two pressure vessels such as between the Space Station docking tunnel and the Space Shuttle Orbiter bulkhead adapter. The joint provides for flexibility while still retaining a structural link between the two vessels required due to the loading created by the internal/external pressure differential. The joint design provides for limiting the axial load carried across the joint to a specific value, a function returned in the Orbiter/Station tunnel interface. The flex joint comprises a floating structural segment which is permanently attached to one of the pressure vessels through the use of an inflatable seal. The geometric configuration of the joint causes the tension between the vessels created by the internal gas pressure to compress the inflatable seal. The inflation pressure of the seal is kept at a value above the internal/external pressure differential of the vessels in order to maintain a controlled distance between the floating segment and pressure vessel. The inflatable seal consists of either a hollow torus-shaped flexible bladder or two rolling convoluted diaphragm seals which may be reinforced by a system of straps or fabric anchored to the hard structures. The joint acts as a flexible link to allow both angular motion and lateral displacement while it still contains the internal pressure and holds the axial tension between the vessels.

Kahn, Jon B.↗
NASA NTRS1990

Indexing system for optical beam steering

This paper describes the design and testing of an indexing system for optical-beam steering. The cryogenic beam-steering mechanism is a 360-degree rotation device capable of discrete, high-precision alignment positions. It uses low-precision components for its rough alignment and kinematic design to meet its stringent repeatability and stability requirements (of about 5 arcsec). The principal advantages of this design include a decoupling of the low-precision, large angular motion from the high-precision alignment, and a power-off alignment position that potentially extends the life or hold time of cryogenic systems. An alternate design, which takes advantage of these attributes while reducing overall motion, is also presented. Preliminary test results show the kinematic mount capable of sub-arc second repeatability.

Sullivan, Mark T.↗
NASA NTRS1992

Neural processing of gravity information

The goal of this project was to use the linear acceleration capabilities of the NASA Vestibular Research Facility (VRF) at Ames Research Center to directly examine encoding of linear accelerations in the vestibular system of the cat. Most previous studies, including my own, have utilized tilt stimuli, which at very low frequencies (e.g., 'static tilt') can be considered a reasonably pure linear acceleration (e.g., 'down'); however, higher frequencies of tilt, necessary for understanding the dynamic processing of linear acceleration information, necessarily involves rotations which can stimulate the semicircular canals. The VRF, particularly the Long Linear Sled, has promise to provide controlled pure linear accelerations at a variety of stimulus frequencies, with no confounding angular motion.

Schor, Robert H.↗
NASA NTRS1992

On the origin of interplanetary dust within recorded history

The possibility of an abrupt origin of interplanetary dust as a result of a collision between asteroids or an extraordinary comet is considered. If all interplanetary dust were produced in one event within recorded history, it would have been visible from the Earth with the unaided eye. The rate, surface area, and brightness of asteroid collision remnants are derived. Ancient Chinese records are searched for extraordinary comets aand bright pointlike objects with small angular motion and concentration to the ecliptic.

Reach, William T.↗
NASA NTRS1929

Mechanical control of airplanes

Before undertaking a detailed description of an automatic-control mechanism, I will state briefly the fundamental conditions for such devices. These are: 1) it must be sensitive at one or more reference values; 2) it must stop the angular motions of the airplane not produced by the pilot; and 3) it must be possible to switch it off and on by a simple hand lever.

AUTOMATIC PILOTS - BOYKOW↗
NASA NTRS1996

The Role of Linear Acceleration in Visual-Vestibular Interactions and Implications in Aircraft Operations

While considerable attention has been given to visual-vestibular interaction (VVI) during angular motion of the head as might occur during an aircraft spin, much less attention has been given to VVI during linear motion of the head. Such interaction might occur, for example, while viewing a stationary or moving display during vertical take-off and landing operations Research into linear VVI, particularly during prolonged periods of linear acceleration, has been hampered by the unavailability of a programmable translator capable of large excursions We collaborated with Otis Elevator Co. and used their research tower and elevator, whose motion could be digitally programmed, to vertically translate human subjects over a distance of 92.3 meters with a peak linear acceleration of 2 meters/sec(exp 2) During pulsatile or sinusoidal translation, the subjects viewed moving stripes (optokinetic stimulus) or a fixed point source (light emitting diode, led, display), respectively and it was generally found that. The direction of linear acceleration relative to the cardinal head axes and the direction of the slow component of optokinetic nystagmus (OKN) determined the extent of VVI during concomitant stripe motion and linear acceleration. Acceleration along the z head axis (A(sub z)) produced the largest VVI, particularly when the slow component of OKN was in the same direction as eye movements produced by the linear acceleration and Eye movements produced by linear acceleration are suppressed by viewing a fixed target at frequencies below 10 Hz But, above this frequency the suppression produced by VVI is removed. Finally, as demonstrated in non-human primates, vergence of the eyes appears to modulate the vertical eye movement response to linear acceleration in humans.

Correia, Manning J.↗
NASA NTRS1959

A Weight Comparison of Several Attitude Controls for Satellites

A brief theoretical study has been made for the purpose for estimating and comparing the weight of three different types of controls that can be used to change the attitude of a satellite. The three types of controls are jet reaction, inertia wheel, and a magnetic bar which interacts with the magnetic field of the earth. An idealized task which imposed severe requirements on the angular motion of the satellite was used as the basis for comparison. The results showed that a control for one axis can be devised which will weigh less than 1 percent of the total weight of the satellite. The inertia-wheel system offers weight-saving possibilities if a large number of cycles of operation are required, whereas the jet system would be preferred if a limited number of cycles are required. The magnetic-bar control requires such a large magnet that it is impractical for the example application but might be of value for supplying small trimming moments about certain axes.

Adams, James J.↗
NASA NTRS1960

Aerodynamic and Landing Measurements Obtained During the First Powered Flight of the North American X-15 Research Airplane

During the first powered flight of the North American X-15 research airplane on September 17, 1959, a Mach number of 2.1 and an altitude of 52,000 feet were attained. Static and dynamic maneuvers were performed to evaluate the characteristics of the airplane at subsonic and supersonic speeds. Data from these maneuvers as well as from the launch and landing phases are presented, discussed, and compared with predicted values. The rate of separation of the X-15 from the B-52 carrier airplane at launch was less than that predicted by wind-tunnel studies and was less rapid than in the lightweight condition of the initial glide flight. In addition, the angular motions and bank angle attained following the launch were of lesser magnitude than in the glide flight. Stable longitudinal-stability trends were apparent during the acceleration to maximum speed, and the pilot reported experiencing little or no transonic trim excursions. An inexplicable high-frequency vibration, which occurred at Mach numbers above 1.4, is being investigated further. Essentially linear lift and stability characteristics were indicated within the limited ranges of angle of attack and angle of sideslip investigated. The dynamic longitudinal and lateral-directional stability and control-effectiveness characteristics appeared satisfactory to the pilot. Although the longitudinal- and lateral-directional-damping ratios showed no significant change from subsonic to supersonic speeds, on the basis of time to damp, the damping characteristics at supersonic speeds appeared to the pilot to be somewhat improved over those at subsonic speeds.

Source record↗
NASA NTRS1998

Operational Data Reduction Procedure for Determining Density and Vertical Structure of the Martian Upper Atmosphere from Mars Global Surveyor Accelerometer Measurements

The success of aerobraking by the Mars Global Surveyor (MGS) spacecraft was partly due to the analysis of MGS accelerometer data. Accelerometer data was used to determine the effect of the atmosphere on each orbit, to characterize the nature of the atmosphere, and to predict the atmosphere for future orbits. To interpret the accelerometer data, a data reduction procedure was developed to produce density estimations utilizing inputs from the spacecraft, the Navigation Team, and pre-mission aerothermodynamic studies. This data reduction procedure was based on the calculation of aerodynamic forces from the accelerometer data by considering acceleration due to gravity gradient, solar pressure, angular motion of the MGS, instrument bias, thruster activity, and a vibration component due to the motion of the damaged solar array. Methods were developed to calculate all of the acceleration components including a 4 degree of freedom dynamics model used to gain a greater understanding of the damaged solar array. The total error inherent to the data reduction procedure was calculated as a function of altitude and density considering contributions from ephemeris errors, errors in force coefficient, and instrument errors due to bias and digitization. Comparing the results from this procedure to the data of other MGS Teams has demonstrated that this procedure can quickly and accurately describe the density and vertical structure of the Martian upper atmosphere.

Cancro, George J.↗