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At least 523 records · Page 29

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NASA NTRS1979

Multiple scene attitude estimator performance for LANDSAT-1

Initial results are presented to demonstrate the performance of a linear sequential estimator (Kalman Filter) used to estimate a LANDSAT 1 spacecraft attitude time series defined for four scenes. With the revised estimator a GCP poor scene - a scene with no usable geodetic control points (GCPs) - can be rectified to higher accuracies than otherwise based on the use of GCPs in adjacent scenes. Attitude estimation errors was determined by the use of GCPs located in the GCP-poor test scene, but which are not used to update the Kalman filter. Initial results achieved indicate that errors of 500m (rms) can be attained for the GCP-poor scenes. Operational factors are related to various scenarios.

Rifman, S. S.↗

NASA NTRS1979

Modal Interpolation Program, L 215 (INTERP): Supplemental System Design and Maintenance Document - Volume 2

The design, structure, and usage of the modal interpolation program L215 are presented. The program uses modal data sets of arrays containing interpolation coefficients. The interpolation arrays are used to determine displacements at various aerodynamic control points. The displacements consist of translations normal to the aerodynamic surface and surface slopes that are parallel and perpendicular to the free stream direction. Five different interpolation methods are available.

Hirayama, M. Y.↗

NASA NTRS1979

Mapping of sea ice and measurement of its drift using aircraft synthetic aperture radar images

Side-looking radar images of Arctic sea ice were obtained as part of the Arctic Ice Dynamics Joint Experiment. Repetitive coverages of a test site in the Arctic were used to measure sea ice drift, employing single images and blocks of overlapping radar image strips; the images were used in conjunction with data from the aircraft inertial navigation and altimeter. Also, independently measured, accurate positions of a number of ground control points were available. Initial tests of the method were carried out with repeated coverages of a land area on the Alaska coast (Prudhoe). Absolute accuracies achieved were essentially limited by the accuracy of the inertial navigation data. Errors of drift measurements were found to be about + or - 2.5 km. Relative accuracy is higher; its limits are set by the radar image geometry and the definition of identical features in sequential images. The drift of adjacent ice features with respect to one another could be determined with errors of less than + or - 0.2 km.

Leberl, F.↗

NASA NTRS1979

New determinations of far-side lunar radii from Apollo photography

Determinations of far side lunar radii based on the reduction of photogrammetric measurements derived from Apollo 16 photographs obtained during the trans-earth phase of the spacecraft trajectory are presented. Reduction is accomplished by determining the Apollo 16 metric camera orientation relative to control points on the lunar surface whose coordinates are known exactly, than charting the surface on the basis of data coverage. The positions of 66 surface features in the area between longitudes 90 and 130 deg E and 10 and 60 deg N relative to the center of mass of the moon, with a relative accuracy of 500 km, are presented. A topographical map which can resolve basin-sized features has been derived from radius determinations. It is found that the craters Fabry, Riemann and Szilard comprise a topographically depressed region about 500 km in diameter with a floor 2.4 to 3.4 km below the 1730.0 km reference sphere and 4.8 to 5.8 km below the northern rim of the unfilled basin.

Mohan, S. N.↗

NASA NTRS1979

Voyager 1 encounter with the Jovian system

An overview of the Voyager 1 encounter with Jupiter is presented. Voyager conducted close range measurements of the atmosphere, satellites and magnetosphere of Jupiter from January 6, 1979 to April 13, 1979, coming as close as 348,890 km to the planet. The three-axis stabilized spacecraft carries radioisotope thermoelectric generators providing 445 W of power to the instruments and transmitters and makes use of an X-band telemetry rate of up to 115.2 kbit/sec, a scan platform providing pointing control of 0.15 deg/axis for the instruments carried on it, and three interconnected computer systems. The trajectory of Voyager through the Galilean satellites is illustrated, noting that the trajectory allows for periods of sun and earth occultation, south polar passage by Io, close encounters with Ganymede and Callisto and earth-Jupiter communications distances supporting 21 to 22 h of maximum data rates daily. Highlights of the results of the investigations are presented.

Stone, E. C.↗

NASA NTRS1979

A 1.2 meter balloon-borne telescope for a submillimeter wave sky survey

A balloon-borne, 1.2 meter Cassegrain telescope designed for diffraction-limited imagery at 100 microns is being developed for a survey of the Galactic plane at submillimeter wavelengths. The telescope pointing system is servocontrolled using a gyroscope for the primary stabilization reference. Extensive use is made of microprocessors for flight sequencing, pointing control and stabilization, and telemetry formatting. A description of the telescope, helium-cooled detectors, and the orientation subsystems are presented together with a brief discussion of the proposed astronomical observations.

Silverberg, R. F.↗

NASA NTRS1979

Orbit/attitude estimation with Landsat-1 and -2 landmark data

The accuracy of spacecraft orbit and attitude determination is investigated using Landsat-1 and -2 picture data. The data consists of ground control points, of known geodetic coordinates, which are identified on a series of Landsat pictures. Both sequential (extended Kalman filter) and batch (nonlinear Bayesian weighted least-squares) estimation techniques have been implemented in two software systems. Discussion of these systems includes a system overview, mathematical formulation, and sample numerical results. Particular emphasis is given to the application of a spectral analysis technique to derive spacecraft attitude models.

Hall, D. L.↗

NASA NTRS1979

An improved Woodward's panel method for calculating leading-edge and side-edge suction forces at subsonic and supersonic speeds

Woodward's panel method for subsonic and supersonic flow was improved by employing control points determined by exactly matching two-dimensional pressure at a finite number of points. The results show great improvement in the predicted pressure distribution of a flapped airfoil. With the paneling scheme of cosine law in both chordwise and spanwise directions, the method is shown to accurately predict leading edge and side edge suction forces of various configurations in subsonic and supersonic flow.

Lan, C. E.↗

NASA NTRS1980

USSAERO computer program development, versions B and C

Versions B and C of the unified subsonic and supersonic aerodynamic analysis program, USSAERO, are described. Version B incorporates a new symmetrical singularity method to provide improved surface pressure distributions on wings in subsonic flow. Version C extends the range of application of the program to include the analysis of multiple engine nacelles or finned external stores. In addition, nonlinear compressibility effects in high subsonic and supersonic flows are approximated using a correction based on the local Mach number at panel control points. Several examples are presented comparing the results of these programs with other panel methods and experimental data.

Woodward, F. A.↗

NASA NTRS1980

The influence of topographic structures on night-time surface temperatures: Evaluation of a satellite thermal image of the upper Rhine plain and the surrounding highlands

The author has identified the following significant results. Satellite data supplied the same information as aerial IR registrations with corresponding averaging for all studies requiring a survey of the thermal pattern within an area measuring 10 km x 10 km ore more, provided that sufficiently precise control points could be established for the purpose of geometric rectification in the surroundings of the area observed. Satellite thermal data are more comprehensive than aircraft data for studies on a regional, rather than a local scale, since airborne images often obscure the basic correlation in thermal patterns because of a variety of irrelevant topographical detail. The satellite data demonstrate the dependence of surface temperature on relief more clearly than comparable airborne imagery.

Gossmann, H.↗

NASA NTRS1979

A history of Mars atmospheric opacity in the southern hemisphere during the Viking extended mission

A history of developing opacity in the Mars southern hemisphere during the Viking extended mission has been compiled using orbiter images obtained at high altitude. Observations of changing contrasts under similar viewing conditions have been modeled by multiple-scattering intensity transfer equations that have produced a temporal description of changes in optical depth and particle-scattering properties within a network of control points. The results are presented in the form of Mercator and perspective plots for various dates.

Thorpe, T. E.↗

NASA NTRS1979

Landsat-D data acquisition and processing

The Landsat-D system, in which S-band and X-band data links will provide real-time direct transmission of sensor data, is described. System performance objectives include input data quantity of 200 MSS scenes/day and 100 TM scenes/day by the Domestic Communication Satellite, and processing capability, in a pipeline mode, of 2.6 x 10 to the 11th input bits of sensor data per 16-hour day. Data processing techniques, including automated cloudcover assessment, control point library build system, radiometric calibration, and geometric correction are discussed.

Smith, P. L., Jr.↗

NASA NTRS1980

Rocket instrument for far-UV spectrophotometry of faint astronomical objects

A sensitive sounding rocket instrument for moderate (about 10-A) resolution far-UV (1160-1750-A) spectrophotometry of faint astronomical objects has been developed. The instrument employes a photon-counting microchannel plate imaging detector and a concave grating spectrograph behind a 40-cm Dall-Kirkham telescope. A unique remote-control pointing system, incorporating an SIT vidicon aspect camera, two star trackers, and a tone-encoded command telemetry link, permits the telescope to be oriented to within 5 arc sec of any target for which suitable guide stars can be found. The design, construction, calibration, and flight performance of the instrument are discussed.

Hartig, G. F.↗

NASA NTRS1980

Planetary spacecraft - SEPS interface design

The interactions between a spacecraft which would rendezvous with the comet Tempel II, the stage, and the mission design are summarized along with solar electric propulsion system design issues. Attention is given to data communication, the spacecraft pointing control system, spacecraft power, plasma interactions, the release of a probe to study the comet Halley, and thruster usage. It was concluded that for a planetary mission design using a low-thrust stage, the control of the mission should reside in the payload spacecraft and that the power should be provided by the stage; the NASA standard 28 VDC bus is recommended.

Pless, L. C.↗

NASA NTRS1980

Interplanetary optical navigation using Charge Coupled Devices

Charge Coupled Devices (CCD) will be used as optical navigation image detectors in space missions planned for the 1980's. This paper presents analyses directed at assessing the performance of an imaging system employing a CCD (i.e., a solid state imager (SSI)), for a Jovian satellite tour environment. CCD operating principles are summarized and methods of calculating theoretical dynamic range presented. Methods of analyzing the SSI's ability to perform the fundamental optical navigation function of imaging a target body and one or more stars, are presented. This capability is expressed as a function of SSI optical and electronic parameters and of astrophysical parameters. The influence of these factors and pointing control errors on navigation picture budgets is analyzed. The effect of the sun's glare is analyzed from the standpoint of its reduction of SSI dynamic range and increase of navigation picture budget. Radiation effects on SSI navigation imaging performance are discussed and a method of analyzing probabilities of distinguishing real from false stars presented.

Davis, R. P.↗

NASA NTRS1980

A new look at Togo through the eyes of a SLAR

Imaging of Togo in 1977 with SLAR provided the data required for the production of map controlled radar mosaics at a scale of 1:200,000 with 95 percent of all control points at that scale within + or - 4.0 millimeters of true positions. The moasics served as the base for the generation of a revised geologic map of Togo. Aided by two looks, numerous revisions resulted, not only with the addition of previously unknown structural features, a revision of age relationships, and the refinement of unit boundaries, but also with the repositioning of rock units and the reorientation of major faults.

Dellwig, L. F.↗

NASA NTRS1980

Image processing of HCMM-satellite thermal images for superposition with other satellite imagery and topographic and thematic maps

The southwestern part of Central Europe between Basal and Frankfurt was used in a study to determine the accuracy with which a regionally bounded HCMM scene could be rectified with respect to a preassigned coordinate system. The scale to which excerpts from HCMM data can be sensibly enlarged and the question of how large natural structures must be in order to be identified in a satellite thermal image with the given resolution were also examined. Relief and forest and population distribution maps and a land use map derived from LANDSAT data were digitalized and adapted to a common reference system and then combined in a single multichannel data system. The control points for geometrical rectification were determined using the coordinates of the reference system. The multichannel scene was evaluated in several different manners such as the correlation of surface temperature and relief, surface temperature and land use, or surface temperature and built up areas.

Gossmann, H.↗

NASA NTRS1980

Influence of rotor blade tip shape on tip vortex shedding - An unsteady, inviscid analysis

An unsteady potential flow panel method is described based on a time-stepping procedure and using planar quadrilateral panels to represent the surface of thick blades. Each panel has a constant source and doublet distribution and a central control point where an internal Dirichlet boundary condition is applied. The method includes detail paneling around the tip edge and offers the facility of prescribing a tip-edge separation. Preliminary results are shown for four blade tip shapes which are treated as semi-span wings oscillating in pitch about a mean angle of attack of 6 deg. Further work is planned for the wake model before proceeding to higher angles of attack.

Maskew, B.↗