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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Multi-limbed locomotion systems for space construction and maintenance

A well developed technology of coordination of multi-limbed locomotory systems is now available. Results from a NASA sponsored study of several years ago are presented. This was a simulation study of a three-limbed locomotion/manipulation system. Each limb had six degrees of freedom and could be used either as a locomotory grasping hand-holds, or as a manipulator. The focus of the study was kinematic coordination algorithms. The presentation will also include very recent results from the Adaptive Suspension Vehicle Project. The Adaptive Suspension Vehicle (ASV) is a legged locomotion system designed for terrestrial use which is capable of operating in completely unstructured terrain in either a teleoperated or operator-on-board mode. Future development may include autonomous operation. The ASV features a very advanced coordination and control system which could readily be adapted to operation in space. An inertial package with a vertical gyro, and rate gyros and accelerometers on three orthogonal axes provides body position information at high bandwidth. This is compared to the operator's commands, injected via a joystick to provide a commanded force system on the vehicle's body. This system is, in turn, decomposed by a coordination algorithm into force commands to those legs which are in contact with the ground.

Waldron, K. J.↗
NASA NTRS1988

Rarefied-flow pitching moment coefficient measurements of the Shuttle Orbiter

An overview of the process for obtaining the Shuttle Orbiter rarefied-flow pitching moment from flight gyro data is presented. The extraction technique involves differentiation of the output of the pitch gyro after accounting for nonaerodynamic torques, such as those produced by gravity gradient and the Orbiter's auxiliary power unit and adjusting for drift biases. The overview of the extraction technique includes examples of results from each of the steps involved in the process, using the STS-32 mission as a typical sample case. The total pitching moment and moment coefficient (Cm) for that flight are calculated and compared with preflight predictions. The flight results show the anticipated decrease in Cm with increasing altitude. However, the total moment coefficient is less than predicted using preflight estimates.

Blanchard, R. C.↗
NASA NTRS1989

Results of dynamic testing of GP-B spherical gyroscopes

Laboratory tests of the spherical electrostatically levitated cryogenically cooled coated gyroscope being developed for the Gravity Probe B (GP-B) spacecraft (Bardas et al., 1986) are reported. Spin speed and the dc components of the trapped magnetic field are measured with three orthogonal pickup loops attached to SQUID detectors as the levitated gyro is brought up to speed by an He gas jet. Data on the spin-vector time history, mass unbalance, higher rotor-shape harmonics, and spin-vector position are presented in extensive graphs and characterized in detail, and a mathematical model of the electrostatic suspension torques is derived. Prototype gyro 86-4 is found to have mass unbalance within the range required for the GP-B mission (to detect the geodetic and motional effects predicted by general relativity theory).

Keiser, G. M.↗
NASA NTRS1989

Simultaneous quaternion estimation (QUEST) and bias determination

Tests of a new method for the simultaneous estimation of spacecraft attitude and sensor biases, based on a quaternion estimation algorithm minimizing Wahba's loss function are presented. The new method is compared with a conventional batch least-squares differential correction algorithm. The estimates are based on data from strapdown gyros and star trackers, simulated with varying levels of Gaussian noise for both inertially-fixed and Earth-pointing reference attitudes. Both algorithms solve for the spacecraft attitude and the gyro drift rate biases. They converge to the same estimates at the same rate for inertially-fixed attitude, but the new algorithm converges more slowly than the differential correction for Earth-pointing attitude. The slower convergence of the new method for non-zero attitude rates is believed to be due to the use of an inadequate approximation for a partial derivative matrix. The new method requires about twice the computational effort of the differential correction. Improving the approximation for the partial derivative matrix in the new method is expected to improve its convergence at the cost of increased computational effort.

Markley, F. Landis↗
NASA NTRS1990

Spacecraft mass property identification with torque-generating control

Previous studies indicated that an applied force was necessary to perform in-flight identification of the mass and center of mass of a spacecraft. This paper shows that the mass and center of mass of a rigid spacecraft can be determined using only torque-producing actuators such as control-moment gyros or reaction wheels, and commonly available sensors, e.g., rate gyros and accelerometers. A space-station application is presented.

Bergmann, E.↗
NASA NTRS1990

Attitude determination and parameter estimation using vector observations - Application

This paper presents tests of a new method for the simultaneous estimation of spacecraft attitude and sensor biases, based on a quaternion estimation algorithm minimizing Wahba's loss function. The new method is compared with a conventional batch least-squares differential correction algorithm. The estimates are based on data from strapdown gyros and star trackers, simulated with varying levels of Gaussian noise for both inertially-fixed and earth-pointing attitudes. Both algorithms solve for the spacecraft attitude and the gyro drift rate biases. In the majority of tests performed, the two methods converge to the same estimates in the same number of iterations, but the new algorithm requires about 60 percent more computational effort. Some cases were found in which the new method converges in fewer iterations than the differential correction, and some for which the differential correction requires fewer iterations.

Markley, F. Landis↗
NASA NTRS1990

A preliminary look at techniques used to obtain airdata from flight at high angles of attack

Flight research at high angles of attack has posed new problems for airdata measurements. New sensors and techniques for measuring the standard airdata quantities of static pressure, dynamic pressure, angle of attack, and angle of sideslip were subsequently developed. The ongoing airdata research supporting NASA's F-18 high alpha research program is updated. Included are the techniques used and the preliminary results. The F-18 aircraft was flown with three research airdata systems: a standard airdata probe on the right wingtip, a self-aligning airdata probe on the left wingtip, and a flush airdata system on the nose cone. The primary research goal was to obtain steady-state calibrations for each airdata system up to an angle of attack of 50 deg. This goal was accomplished and preliminary accuracies of the three airdata systems were assessed and are presented. An effort to improve the fidelity of the airdata measurements during dynamic maneuvering is also discussed. This involved enhancement of the aerodynamic data with data obtained from linear accelerometers, rate gyros, and attitude gyros. Preliminary results of this technique are presented.

Moes, Timothy R.↗
NASA NTRS1990

Accuracy of the ERBS definitive attitude determination system in the presence of propagation noise

Definitive attitude solutions are supposed to be the most accurate possible. For the Earth Radiation Budget Satellite (ERBS), this has been accomplished by using gyro rates to transform many nonsimultaneous observations to a common time point and then averaging to reduce the effects of observation noise. Rate quality is critical to realizing improved accuracy with this method. Gyro deterioration, which shows up as large observation residuals and discontinuities between contiguous batch solutions, now discourages using the batch approach for ERBS. To address this problem, a simple Kalman filter is tried in place of the batch estimator. The filter works well as long as the attitude is completely observable. During periods without Sun coverage, however, the extrapolated yaw may diverge and then change abruptly when the Sun returns to the sensor field of view. Causes of this behavior are discussed, and some solutions are tried that address the observability aspect of the problem.

Chu, D.↗
NASA NTRS1990

The accuracy of dynamic attitude propagation

Propagating attitude by integrating Euler's equation for rigid body motion has long been suggested for the Earth Radiation Budget Satellite (ERBS) but until now has not been implemented. Because of limited Sun visibility, propagation is necessary for yaw determination. With the deterioration of the gyros, dynamic propagation has become more attractive. Angular rates are derived from integrating Euler's equation with a stepsize of 1 second, using torques computed from telemetered control system data. The environmental torque model was quite basic. It included gravity gradient and unshadowed aerodynamic torques. Knowledge of control torques is critical to the accuracy of dynamic modeling. Due to their coarseness and sparsity, control actuator telemetry were smoothed before integration. The dynamic model was incorporated into existing ERBS attitude determination software. Modeled rates were then used for attitude propagation in the standard ERBS fine-attitude algorithm. In spite of the simplicity of the approach, the dynamically propagated attitude matched the attitude propagated with good gyros well for roll and yaw but diverged up to 3 degrees for pitch because of the very low resolution in pitch momentum wheel telemetry. When control anomalies significantly perturb the nominal attitude, the effect of telemetry granularity is reduced and the dynamically propagated attitudes are accurate on all three axes.

Harvie, E.↗
NASA NTRS1991

Preliminary results from an airdata enhancement algorithm with application to high-angle-of-attack flight

A technique was developed to improve the fidelity of airdata measurements during dynamic maneuvering. This technique is particularly useful for airdata measured during flight at high angular rates and high angles of attack. To support this research, flight tests using the F-18 high alpha research vehicle (HARV) were conducted at NASA Ames Research Center, Dryden Flight Research Facility. A Kalman filter was used to combine information from research airdata, linear accelerometers, angular rate gyros, and attitude gyros to determine better estimates of airdata quantities such as angle of attack, angle of sideslip, airspeed, and altitude. The state and observation equations used by the Kalman filter are briefly developed and it is shown how the state and measurement covariance matrices were determined from flight data. Flight data are used to show the results of the technique and these results are compared to an independent measurement source. This technique is applicable to both postflight and real-time processing of data.

Moes, Timothy R.↗
NASA NTRS1991

Buffet induced structural/flight-control system interaction of the X-29A aircraft

High angle-of-attack flight regime research is currently being conducted for modern fighter aircraft at the NASA Ames Research Center's Dryden Flight Research Facility. This flight regime provides enhanced maneuverability to fighter pilots in combat situations. Flight research data are being acquired to compare and validate advanced computational fluid dynamic solutions and wind-tunnel models. High angle-of-attack flight creates unique aerodynamic phenomena including wing rock and buffet on the airframe. These phenomena increase the level of excitation of the structural modes, especially on the vertical and horizontal stabilizers. With high gain digital flight-control systems, this structural response may result in an aeroservoelastic interaction. A structural interaction on the X-29A aircraft was observed during high angle-of-attack flight testing. The roll and yaw rate gyros sensed the aircraft's structural modes at 11, 13, and 16 Hz. The rate gyro output signals were then amplified through the flight-control laws and sent as commands to the flaperons and rudder. The flight data indicated that as the angle of attack increased, the amplitude of the buffet on the vertical stabilizer increased, which resulted in more excitation to the structural modes. The flight-control system sensors and command signals showed this increase in modal power at the structural frequencies up to a 30 degree angle-of-attack. Beyond a 30 degree angle-of-attack, the vertical stabilizer response, the feedback sensor amplitude, and control surface command signal amplitude remained relatively constant. Data are presented that show the increased modal power in the aircraft structural accelerometers, the feedback sensors, and the command signals as a function of angle of attack. This structural interaction is traced from the aerodynamic buffet to the flight-control surfaces.

Voracek, David F.↗
NASA NTRS1990

Attitude determination error analysis - General model and specific application

This paper presents a comprehensive approach to filter and dynamics modeling for attitude determination error analysis. The discussion includes models for both batch least-squares and sequential estimators, a specific dynamic model for attitude determination error analysis of a three-axis stabilized spacecraft equipped with strapdown gyros, and the incorporation of general attitude sensor observations. An analyst using this approach to perform an error analysis chooses a subset of the spacecraft parameters to be 'solve-for' parameters, which are to be estimated, and another subset to be 'consider' parameters, which are assumed to have errors but not to be estimated. The result of the error analysis is an indication of overall uncertainties in the 'solve-for' parameters, as well as the contributions of the various error sources to these uncertainties, including those of errors in the a priori 'solve-for' estimates, of measurement noise, of dynamic noise (also known as process noise or plant noise), and of 'consider' parameter uncertainties. The analysis of attitude, star tracker alignment, and gyro bias uncertainties for the Gamma Ray Observatory spacecraft provide a specific example of the use of a general-purpose software package incorporating these models.

Markley, F. Landis↗
NASA NTRS1991

Preliminary results from an airdata enhancement algorithm with application to high-angle-of-attack flight

A technique has been developed to improve the fidelity of airdata measurements during dynamic maneuvering. This technique is particularly useful for airdata measured during flight at high angular rates and high angles of attack. To support this research, flight tests using the F-18 high alpha research vehicle were conducted at the NASA Ames Research Center Dryden Flight Research Facility. A Kalman filter was used to combine information from research airdata, linear accelerometers, angular rate gyros, and attitude gyros to determine better estimates of airdata quantities such as angle of attack, angle of sideslip, airspeed, and altitude. This paper briefly develops the state and observation equations used by the Kalman filter and shows how the state and measurement covariance matrices were determined from flight data.

Moes, Timothy R.↗
NASA NTRS1990

Design and performance of a fiber optic gyroscope using integrated optics

Navigation grade fiber optic rotation sensors (FORS) are being developed as an alternative to spinning mass gyro's for unmanned planetary exploration spacecraft. FORS is attractive because of its many advantages such as long life, low weight, low power, and low cost as compared to its mechanical counterparts. FORS incorporates an advanced integrated optics circuit. The advanced eight-component integrated optics circuit performs all the key signal processing functions and in addition incorporates a unique optical beat detection circuit thereby providing an output in the form of pulses proportional to incremental angular position similar to a ring laser gyro (RLG) but without the inherent lock-in problem RLG's possess.

Youmans, B. R.↗
NASA NTRS1992

Payload isolation and stabilization by a Suspended Experiment Mount (SEM)

Many Space Shuttle and Space Station payloads can benefit from isolation from crew or attitude control system disturbances. Preliminary studies have been performed for a Suspended Experiment Mount (SEM) system that will provide isolation from accelerations and stabilize the viewing direction of a payload. The concept consists of a flexible suspension system and payload-mounted control moment gyros. The suspension system, which is rigidly locked for ascent and descent, isolates the payload from high frequency disturbances. The control moment gyros stabilize the payload orientation. The SEM will be useful for payloads that require a lower-g environment than a manned vehicle can provide, such as materials processing, and for payloads that require stabilization of pointing direction, but not large angle slewing, such as nadir-viewing earth observation or solar viewing payloads.

Bailey, Wayne L.↗
NASA NTRS1991

Fiber optic and laser sensors VIII; Proceedings of the Meeting, San Jose, CA, Sept. 17-19, 1990

This issue presents topics on the advances in fiber-optic sensor technology, fiber-optic gyroscope, fiber-optic position and pressure sensors, fiber-optic magnetic and temperature sensors, and generic fiber-optic sensors. Papers included are on a novel analog phase tracker for interferometric fiber-optic sensor applications, recent development status of fiber-optic sensors in China, the magnetic-field sensitivity of depolarized fiber-optic gyros, a depolarized fiber-optic gyro for future tactical applications, fiber-optic position transducers for aircraft controls, and a metal embedded optical-fiber pressure sensor. Attention is also given to a fiber-optic magnetic field sensor using spectral modulation encoding, a bare-fiber temperature sensor, an interferometric fiber-optic accelerometer, improvement of specular reflection pyrometer, a theoretical analysis of two-mode elliptical-core optical fiber sensors, and a fiber probe for ring pattern.

Depaula, Ramon P.↗
NASA NTRS1993

Investigation of a geodesy coexperiment to the Gravity Probe B relativity gyroscope program

Geodesy is the science of measuring the gravitational field of and positions on the Earth. Estimation of the gravitational field via gravitation gradiometry, the measurement of variations in the direction and magnitude of gravitation with respect to position, is this dissertation's focus. Gravity Probe B (GP-B) is a Stanford satellite experiment in gravitational physics. GP-B will measure the precession the rotating Earth causes on the space time around it by observing the precessions of four gyroscopes in a circular, polar, drag-free orbit at 650 km altitude. The gyroscopes are nearly perfect niobium-coated spheres of quartz, operating at 1.8 K to permit observations with extremely low thermal noise. The permissible gyroscope drift rate is miniscule, so the torques on the gyros must be tiny. A drag-free control system, by canceling accelerations caused by nongravitational forces, minimizes the support forces and hence torques. The GP-B system offers two main possibilities for geodesy. One is as a drag-free satellite to be used in trajectory-based estimates of the Earth's gravity field. We described calculations involving that approach in our previous reports, including comparison of laser only, GPS only, and combined tracking and a preliminary estimate of the possibility of estimating relativistic effects on the orbit. The second possibility is gradiometry. This technique has received a more cursory examination in previous reports, so we concentrate on it here. We explore the feasibility of using the residual suspension forces centering the GP-B gyros as gradiometer signals for geodesy. The objective of this work is a statistical prediction of the formal uncertainty in an estimate of the Earth's gravitation field using data from GP-B. We perform an instrument analysis and apply two mathematical techniques to predict uncertainty. One is an analytical approach using a flat-Earth approximation to predict geopotential information quality as a function of spatial wavelength. The second estimates the covariance matrix arising in a least-squares estimate of a spherical harmonic representation of the geopotential using GP-B gradiometer data. The results show that the GP-B data set can be used to create a consistent estimate of the geopotential up to spherical harmonic degree and order 60. The formal uncertainty of all coefficients between degrees 5 and 50 is reduced by factors of up to 30 over current satellite-only estimates and up to 7 over estimates which include surface data. The primary conclusion resulting from this study is that the gravitation gradiometer geodesy coexperiment to GP-B is both feasible and attractive.

Everitt, C. W. F.↗
NASA NTRS1993

Fiber optic and laser sensors X; Proceedings of the Meeting, Boston, MA, Sept. 8-11, 1992

Topics addressed include acoustic and pressure sensors; fiber optic gyros; electric and magnetic field sensors; bend, strain, and temperature sensors; industrial applications of sensors; and processing techniques. Particular attention is given to fiber optic interferometric acoustic sensors for wind tunnel applications, polished coupler and resonator fabrication, second-harmonic detection for rotation sensing in fiber optic gyros, simplified control theory in closed-loop fiber optic gyroscopes, and a Fabry-Perot sensor with digital signal processing for the measurement of magnetostriction. Also discussed are a Bragg fiber laser sensor, commercialization of fiber optic strain gauge systems, thermal ignition in hazardous environments due to stray light from optical fibers, a system for absolute measurements by interferometric sensors, and high-performance interferometric demodulation techniques.

Udd, Eric↗