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At least 271 records · Page 15

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NASA NTRS2007

Proceedings of the 20th International Symposium on Space Flight Dynamics

Topics include: Measuring Image Navigation and Registration Performance at the 3-Sigma Level Using Platinum Quality Landmarks; Flight Dynamics Performances of the MetOp A Satellite during the First Months of Operations; Visual Navigation - SARE Mission; Determining a Method of Enabling and Disabling the Integral Torque in the SDO Science and Inertial Mode Controllers; Guaranteeing Pointing Performance of the SDO Sun-Pointing Controllers in Light of Nonlinear Effects; SDO Delta H Mode Design and Analysis; Observing Mode Attitude Controller for the Lunar Reconnaissance Orbiter; Broken-Plane Maneuver Applications for Earth to Mars Trajectories; ExoMars Mission Analysis and Design - Launch, Cruise and Arrival Analyses; Mars Reconnaissance Orbiter Aerobraking Daily Operations and Collision Avoidance; Mars Reconnaissance Orbiter Interplanetary Cruise Navigation; Motion Parameters Determination of the SC and Phobos in the Project Phobos-Grunt; GRAS NRT Precise Orbit Determination: Operational Experience; Orbit Determination of LEO Satellites for a Single Pass through a Radar: Comparison of Methods; Orbit Determination System for Low Earth Orbit Satellites; Precise Orbit Determination for ALOS; Anti-Collision Function Design and Performances of the CNES Formation Flying Experiment on the PRISMA Mission; CNES Approaching Guidance Experiment within FFIORD; Maneuver Recovery Analysis for the Magnetospheric Multiscale Mission; SIMBOL-X: A Formation Flying Mission on HEO for Exploring the Universe; Spaceborne Autonomous and Ground Based Relative Orbit Control for the TerraSAR-X/TanDEM-X Formation; First In-Orbit Experience of TerraSAR-X Flight Dynamics Operations; Automated Target Planning for FUSE Using the SOVA Algorithm; Space Technology 5 Post-Launch Ground Attitude Estimation Experience; Standardizing Navigation Data: A Status Update; and A Study into the Method of Precise Orbit Determination of a HEO Orbiter by GPS and Accelerometer.

Woodard, Mark↗

NASA NTRS1989

An acoustic experimental and theoretical investigation of single disc propellers

An experimental study of the acoustic field associated with two, three, and four blade propeller configurations with a blade root angle of 50 deg was performed in the Texas A&M University 5 ft. x 6 ft. acoustically-insulated subsonic wind tunnel. A waveform analysis package was utilized to obtain experimental acoustic time histories, frequency spectra, and overall sound pressure level (OASPL) and served as a basis for comparison to the theoretical acoustic compact source theory of Succi (1979). Valid for subsonic tip speeds, the acoustic analysis replaced each blade by an array of spiraling point sources which exhibited a unique force vector and volume. The computer analysis of Succi was modified to include a propeller performance strip analysis which used a NACA 4-digit series airfoil data bank to calculate lift and drag for each blade segment given the geometry and motion of the propeller. Theoretical OASPL predictions were found to moderately overpredict experimental values for all operating conditions and propeller configurations studied.

Bumann, Elizabeth A.↗

NASA NTRS1963

The autotrack system

The autotrack system accurately senses the direction of arrival, at the horn-reflector antenna, of the microwave beacon signal from the communications satellite. When this direction does not coincide with the horn-reflector pointing direction, error correcting voltages are automatically generated to enable the antenna direction system to steer the antenna toward the satellite. This paper presents a simple analysis of error voltage generation, a description of the system, and a brief discussion of system performance. Measurements at Andover, Maine, have shown that an angular pointing error of less than 0.005 degree is maintained by the antenna when using the autotrack system to follow the Telstar communications satellite.

SATELLITE COMMUNICATION↗

NASA NTRS2018

Image Guider Subsystem Analysis for the GHAPS Project

The Gondola for High-Altitude Planetary Science (GHAPS) project is a balloon-borne astronomical observatory designed operate in the UV, Visible, and near-mid IR spectral region. The GHAPS Optical Telescope Assembly (OTA) is designed around a one meter aperture narrow field-of-view telescope with near diffraction limited performance. GHAPS will utilize Wallops Arc-Second Pointing System (WASP) for pointing the OTA with an accuracy of 1 arc second or better. WASP relies heavily on a self-contained star tracker assembly to determine the OTA line of sight. Preliminary structural analysis indicated that potential misalignments could be present between the OTA line of sight and the star tracker FOV center during the expected flight conditions that could compromise GHAPS pointing accuracy. An analysis is presented that estimates the worst case long-term (or bias) pointing misalignments for the GHAPS opto-mechanical configuration, examines the need for additional hardware to correct pointing errors, and determines the best hardware and software implementation to do so. The analysis includes the development of a photometric model to predict the limiting magnitude of a GHAPS Facility Guide System (FGS) for a variety of image sensor technologies from visible to mid IR. FGS system performance is estimated using star magnitude and spectral data from actual star catalogs for more realistic predictions. Based on expected performance and other factors, such as size, weight, power, and cost, a final recommendation is made for the GHAPS configuration.

Telescope Guider↗

NASA NTRS1993

Evaluation of CSI enhancements for jitter reduction on the EOS AM-1 observatory

A collaborative study between the Goddard Space Flight Center and the Langley Research Center is now underway to investigate the application of Control-Structure Integration (CSI) technologies to the EOS AM-1 spacecraft. Preliminary GN&C pointing studies of EOS AM-1, performed in 1991 and 1992, have indicated the potential for low pointing jitter and stability margins. Hence, a detailed baseline and CSI enhanced jitter assessment has been undertaken. This paper describes the spacecraft jitter pointing requirements, finite element models, and on-board disturbances. The jitter assessment approach being used by the NASA LaRC and various tools developed for efficient simulation and analysis of jitter are presented. In addition, preliminary results are given to show the potential need of CSI technologies for improving pointing performance of the spacecraft.

Belvin, W. K.↗

NASA NTRS2010

Analysis of Anechoic Chamber Testing of the Hurricane Imaging Radiometer

The Hurricane Imaging Radiometer System (HIRAD) is a new airborne passive microwave remote sensor developed to observe hurricanes. HIRAD incorporates synthetic thinned array radiometry technology, which use Fourier synthesis to reconstruct images from an array of correlated antenna elements. The HIRAD system response to a point emitter has been measured in an anechoic chamber. With this data, a Fourier inversion image reconstruction algorithm has been developed. Performance analysis of the apparatus is presented, along with an overview of the image reconstruction algorithm

Fenigstein, David↗

NASA NTRS2007

International Space Station Remote Sensing Pointing Analysis

This paper analyzes the geometric and disturbance aspects of utilizing the International Space Station for remote sensing of earth targets. The proposed instrument (in prototype development) is SHORE (Station High-Performance Ocean Research Experiment), a multiband optical spectrometer with 15 m pixel resolution. The analysis investigates the contribution of the error effects to the quality of data collected by the instrument. This analysis supported the preliminary studies to determine feasibility of utilizing the International Space Station as an observing platform for a SHORE type of instrument. Rigorous analyses will be performed if a SHORE flight program is initiated. The analysis begins with the discussion of the coordinate systems involved and then conversion from the target coordinate system to the instrument coordinate system. Next the geometry of remote observations from the Space Station is investigated including the effects of the instrument location in Space Station and the effects of the line of sight to the target. The disturbance and error environment on Space Station is discussed covering factors contributing to drift and jitter, accuracy of pointing data and target and instrument accuracies.

Jacobson, Craig A.↗

NASA NTRS2007

Flutter Analysis of the Shuttle Tile Overlay Repair Concept

The Space Shuttle tile overlay repair concept, developed at the NASA Johnson Space Center, is designed for on-orbit installation over an area of damaged tile to permit safe re-entry. The thin flexible plate is placed over the damaged area and secured to tile at discreet points around its perimeter. A series of flutter analyses were performed to determine if the onset of flutter met the required safety margins. Normal vibration modes of the panel, obtained from a simplified structural analysis of the installed concept, were combined with a series of aerodynamic analyses of increasing levels of fidelity in terms of modeling the flow physics to determine the onset of flutter. Results from these analyses indicate that it is unlikely that the overlay installed at body point 1800 will flutter during re-entry.

Bey, Kim S.↗

NASA NTRS1975

Spectrum analysis of acoustic emissions from boron-aluminum composites

Acoustic emissions were monitored from unidirectional tension specimens of boron-aluminum composites. It is shown that a sudden increase in count rate presages final failure. This sudden increase, however, occurs at a variable point relative to final failure load. Spectrum analysis in the range from 1 to 100 kHz was performed on the emissions with the result that no immediately obvious recognition pattern exists to distinguish between types of failure mechanisms. It is suggested that either acoustic emissions cannot be used to distinguish different failure modes in boron-aluminum composites in the frequency range studied or the specimens used had only one failure mode operating with sufficient energy release to be detected. The spectrum analysis did show, however, that the acoustic emissions had frequency components much higher than the frequencies for the fundamental modes of natural vibration of the specimen.

Henneke, E. G., II↗

NASA NTRS1976

Comparison of modal test results - Multipoint sine versus single-point random

The Mariner Jupiter/Saturn (MJS) spacecraft was subjected to the traditional multipoint sine dwell (MPSD) modal test using 111 accelerometer channels, and also to single-point random (SPR) testing using 26 accelerometer channels, and the two methods are compared according to cost, schedule, and technical criteria. A measure of comparison between the systems was devised in terms of the cumulative difference in the kinetic energy distribution of the common accelerometers. The SPR and MPSD method show acceptable agreement with respect to frequencies and mode damping. The merit of the SPR method is that the excitation points are minimized and the test article can be committed to other uses while data analysis is performed. The MPSD approach allows validity of the data to be determined as the test progresses. Costs are about the same for the two methods.

Leppert, E. L.↗

NASA NTRS1987

Proof-mass actuator placement strategies for regulation of flexure during the SCOLE slew

An analysis was performed in order to find the best placement for proof-mass actuators and to determine the importance of placement, i.e., what is the sensitivity of beam flexure to actuator placement. The analysis was performed by using the NASTRAN finite element model for a flexible beam with 21 grid points on beam, by using the nonlinear DISCOS simulation of 20 deg slew and the use of a closed-loop linear quadratic regulator (lqr). Some conclusions reached are: (1) proof-mass actuators can reduce flexure amplitude and damp oscillations; (2) amplitude of deformations during slew is relatively insensitive to placement of actuators; (3) damping factor of oscillations is sensitive to actuator placement; and (4) the degree of controllability method indicates most effective placement for actuators.

Fisher, Shalom (mike)↗

NASA NTRS2007

Observing Mode Attitude Controller for the Lunar Reconnaissance Orbiter

The Lunar Reconnaissance Orbiter (LRO) mission is the first of a series of lunar robotic spacecraft scheduled for launch in Fall 2008. LRO will spend at least one year in a low altitude polar orbit around the Moon, collecting lunar environment science and mapping data to enable future human exploration. The LRO employs a 3-axis stabilized attitude control system (ACS) whose primary control mode, the "Observing mode", provides Lunar Nadir, off-Nadir, and Inertial fine pointing for the science data collection and instrument calibration. The controller combines the capability of fine pointing with that of on-demand large angle full-sky attitude reorientation into a single ACS mode, providing simplicity of spacecraft operation as well as maximum flexibility for science data collection. A conventional suite of ACS components is employed in this mode to meet the pointing and control objectives. This paper describes the design and analysis of the primary LRO fine pointing and attitude re-orientation controller function, known as the "Observing mode" of the ACS subsystem. The control design utilizes quaternion feedback, augmented with a unique algorithm that ensures accurate Nadir tracking during large angle yaw maneuvers in the presence of high system momentum and/or maneuver rates. Results of system stability analysis and Monte Carlo simulations demonstrate that the observing mode controller can meet fine pointing and maneuver performance requirements.

Calhourn, Philip C.↗

NASA NTRS2007

Observing Mode Attitude Controller for the Lunar Reconnaissance Orbiter

Calhoun, Philip C.↗

NASA NTRS2013

Reducing Earth Topography Resolution for SMAP Mission Ground Tracks Using K-Means Clustering

The K-means clustering algorithm is used to reduce Earth topography resolution for the SMAP mission ground tracks. As SMAP propagates in orbit, knowledge of the radar antenna footprints on Earth is required for the antenna misalignment calibration. Each antenna footprint contains a latitude and longitude location pair on the Earth surface. There are 400 pairs in one data set for the calibration model. It is computationally expensive to calculate corresponding Earth elevation for these data pairs. Thus, the antenna footprint resolution is reduced. Similar topographical data pairs are grouped together with the K-means clustering algorithm. The resolution is reduced to the mean of each topographical cluster called the cluster centroid. The corresponding Earth elevation for each cluster centroid is assigned to the entire group. Results show that 400 data points are reduced to 60 while still maintaining algorithm performance and computational efficiency. In this work, sensitivity analysis is also performed to show a trade-off between algorithm performance versus computational efficiency as the number of cluster centroids and algorithm iterations are increased.

ground tracks↗

NASA NTRSDate not supplied

Use of Beacon Satellites for Efficient Uplink Transmission for Free-Space Quantum Entanglement Distribution

Efficient transmission of optical beams from ground to space is important for free-space entanglement distribution in a dual-uplink architecture in which photons from entanglement sources at two ground locations interact in an optical Bell-state measurement implemented on a satellite. Efficient transmission requires large transmitting apertures to minimize diffraction losses and high-performance adaptive optics to overcome the effects of atmospheric turbulence. Achieving good atmospheric compensation for beams transmitted to satellites is challenging because the need to point ahead of the satellite introduces anisoplanatism error that limits the effectiveness of the adaptive optics. An attractive approach for solving the point-ahead problem is to position a separate small satellite at the point-ahead location to provide a beacon source for the adaptive optics. This paper presents analysis of the requirements for the beacon source(s) for a dual-uplink entanglement-distribution demonstration. A relative performance metric is defined and evaluated for multiple beacon configurations, from a single, fixed beacon serving both ground sites to a dedicated beacon for each site continually adjusted to be at the correct point-ahead distance from the target satellite.

quantum↗

NASA NTRS2002

[High Pressure Gas Tanks]

Four high-pressure gas tanks, the basis of this study, were especially made by a private contractor and tested before being delivered to NASA Kennedy Space Center. In order to insure 100% reliability of each individual tank the staff at KSC decided to again submit the four tanks under more rigorous tests. These tests were conducted during a period from April 10 through May 8 at KSC. This application further validates the predictive safety model for accident prevention and system failure in the testing of four high-pressure gas tanks at Kennedy Space Center, called Continuous Hazard Tracking and Failure Prediction Methodology (CHTFPM). It is apparent from the variety of barriers available for a hazard control that some barriers will be more successful than others in providing protection. In order to complete the Barrier Analysis of the system, a Task Analysis and a Biomechanical Study were performed to establish the relationship between the degree of biomechanical non-conformities and the anomalies found within the system on particular joints of the body. This relationship was possible to obtain by conducting a Regression Analysis to the previously generated data. From the information derived the body segment with the lowest percentage of non-conformities was the neck flexion with 46.7%. Intense analysis of the system was conducted including Preliminary Hazard Analysis (PHA), Failure Mode and Effect Analysis (FMEA), and Barrier Analysis. These analyses resulted in the identification of occurrences of conditions, which may be becoming hazardous in the given system. These conditions, known as dendritics, may become hazards and could result in an accident, system malfunction, or unacceptable risk conditions. A total of 56 possible dendritics were identified. Work sampling was performed to observe the occurrence each dendritic. The out of control points generated from a Weighted c control chart along with a Pareto analysis indicate that the dendritics "Personnel not Wearing Proper Protective and Hose/tubing located in high-traffic area" which account for 59.18% of total dendritic frequency need to be addressed to reduce the chance of a hazard from occurring. However, the occurrences of some dendritics are more important than others. As a result immediate, from a Weighted c perspective, corrective action should be taken to ameliorate the cause of the Class A dendritic "Personnel located under suspended or moving loads" rather than just the most commonly occurring dendritics. In any case the vast majority of data obtained indicates that testing operations possess a relatively high degree of safety.

Quintana, Rolando↗

NASA NTRS2018

Initial Jitter Analysis of Lynx, A Proposed Future Large Astrophysics Facility

Lynx, formerly known as the X-Ray surveyor, is one of the large strategic mission concepts being studied for input into the 2020 Astrophysics Decadal Survey. Lynx is the first future X-ray mission concept planning to match Chandra's angular-resolution and will combine this with very high throughput, large field of view, and high-resolution spectroscopy for point-like and extended sources. These ambitious performance requirements clearly merit early detailed engineering to demonstrate feasibility. An on-going structural dynamic analysis is being performed on the Lynx structural design to predict dynamic responses, jitter, to expected on-board vibrational disturbances. Applicable disturbance sources include a cryogenic pump, and six reaction wheels. The structural design, disturbances, analysis, and results are presented. Ultimately, responses will be compared to Lynx performance requirements as they relate to a system error budget.

Knight, J. Brent↗

NASA NTRS1993

Prediction of incidence and surface roughness effects on turbine performance

The results of a Navier-Stokes analysis for predicting the change in turbine efficiency due to a change in either incidence or surface roughness is discussed. It was experimentally determined by Boynton, Tabibzadeh, and Hudson that polishing the SSME high pressure fuel turbine blades improved turbine efficiency by about 2 points over a wide range of operating conditions. These conditions encompassed the range of incidence seen by the turbine blading during flight. It is also necessary to be able to predict turbine performance at various operating points for future rocket turbopump applications. The code RVCQ3D, developed by Rod Chima, was used to determine the effects of changes in incidence angle on turbine blade row efficiency. The midspan Navier-Stokes results were used in conjunction with an inviscid flow analysis code to predict the efficiency of the two stage SSME over a wide range of operating conditions for smooth and rough turbine blades. The use of the Navier-Stokes analysis to predict changes in turbine efficiency due to variation in incidence angles was found to be superior to other incidence loss correlations available in the literature. The sensitivity of the Navier-Stokes results to grid parameters is discussed. The effects of the surface roughness were accounted for using the Cebeci-Chang rough wall turbulence model. This model was implemented in the code RVCQ3D. The implementation of this model for predicting the change in efficiency is also discussed.

Boyle, R. J.↗