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At least 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Shuttle relative navigation of a tethered satellite mission with current on board software

A Shuttle mission planned in 1991 will test the feasibility of tethers in space. This mission, a joint effort between Italy and the United States, will connect a satellite (built by the Italians) to the Shuttle with a 20 km long tether. This mission poses unique navigation problems. The flight software on the Shuttle was never designed to account for the low level acceleration that is generated by the gravity gradient. IMUs on the Shuttle was never designed to account for the low level acceleration that is generated by the gravity gradient. Inertial Maneuvering Units on the shuttle will sense the acceleration of the tether but it turns out that incorporating the continuous accelerometer noise also generates large error growth. Relative navigation is another important issue since the majority of the mission will be conducted while the satellite is out of the visual range of the crew. Some kind of feedback on the motion of the satellite will be desirable. Feedback of the satellite motion can be generated by using the rendezvous radar. To process the radar measurements, the flight software uses a 13 state Kalman Filter, but unfortunately with the filter currently tuned as it is, valid measurements tend to be ignored. This is due to the constraint of the tether on the satellite, which is an unmodeled force. Analysis shows that with proper tuning, relative navigation is possible.

Lee, Kevin A.↗
NASA NTRS1989

Analytical derivation and verification of zero-gyro control for the IUE satellite

The International Ultraviolet Explorer (IUE) satellite was launched January 26, 1978 into a geosynchronous orbit over South America. From its stationary position, the telescope maintains continuous communication with the control centers at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and at the European Space Agency's (ESA's) Villagranca del Castillo Satellite Tracking Station in Spain. Since its launch in 1978, the satellite has gradually lost four of the original six gyroscopes in the Inertial Reference Assembly (IRA). In August 1985, the fourth of the original six gyros failed and a two-gyro system developed by NASA-GSFC was uplinked to the satellite and is currently in use. A one-gyro system also developed by NASA-GSFC is ready for use in case of another gyro failure. In the event that the sixth gyro should also fail, a zero-gyro system is being developed. The goal of this system is to provide interial target pointing without the use of gyroscopes. The satellite has sun sensors to provide attitude information about two of the three axes. It relies upon the exchange of reaction wheel momenta to determine angular position and rate of the third axis.

Bowles, Tiffany↗
NASA NTRS1988

Compendium of meteorological space programs, satellites, and experiments

This compendium includes plans and events known to the authors through January 1987. Compilation of the information began in 1967. This document is intended: (1) as a historical record of all satellites and instrumentation that has been useful for meteorological research or operational uses; and (2) as a working document to be used to assist meteorologists in identifying meteorological satellites, locating data from these satellites, and understanding experiment operation which is related to satellite data that may be of interest to them. A summary of all known launched satellites for all countries and their experiments, which were concerned with meteorological operations or research, are included. Programs covered include AEM, Apollo, ATS, Bhaskara, Cosmos, Discoverer, DMSP, DOD, DODGE, EOLE, ERBE, ESSA, Explorer, Gemini, GMS, GOES/SMS, INSAT, IRS, LANDSAT, Mercury, Meteor 1 and 2, Meteosat, Molniya, MOS, Nimbus, NOAA (1-5)/ITOS, NOAA (6,7,D)/TIROS-N, NOAA (8-10, H-J)/ATN, Salyut, Seasat, Shuttle 1, Shuttle 2: Spacelab, Skylab, Soyuz, TIROS, TOPEX, Vanguard, Voskhod, Vostok, and Zond.

Dubach, Leland L.↗
NASA NTRS1989

An Earth Orbiting Satellite Service and Repair Facility

A conceptual design was produced for the Geosynchronous Satellite Servicing Platform (GSSP), an orbital facility capable of repairing and servicing satellites in geosynchronous orbit. The GSSP is a man-tended platform, which consists of a habitation module, operations module, service bay and truss assembly. This design review includes an analysis of life support systems, thermal and power requirements, robotic and automated systems, control methods and navigation, and communications systems. The GSSP will utilize existing technology available at the time of construction, focusing mainly on modifying and integrating existing systems. The entire facility, along with two satellite retrieval vehicles (SRV), will be placed in geosynchronous orbit by the Advanced Launch System. The SRV will be used to ferry satellites to and from the GSSP. Technicians will be transferred from Earth to the GSSP and back in an Apollo-derived Crew Transfer Capsule (CTC). These missions will use advanced telerobotic equipment to inspect and service satellites. Four of these missions are tentatively scheduled per year. At this rate, the GSSP will service over 650 satelites during the projected 25 year lifespan.

Berndt, Andrew↗
NASA NTRS1990

Comparison of satellite based cloud retrieval methods for cirrus and stratocumulus

One difficulty in using satellite remote sensing data is the spatial variability of cloud properties on scales smaller than most meteorological satellite fields of view (approx. 4 to 8 km). The variation is examined of satellite derived cloud cover as a function of the satellite sensor spatial resolution for seven cloud cover retrieval methods: (1) Reflectance threshold; (2) Temperature threshold; (3) ISCCP; (4) HBTM (Hybrid Bispectral Threshold Method); (5) NCLE; (6) Spatial coherence; and (7) Functional Box Counting. The first two methods are simple single spectral thresholds which specify a satellite pixel as cloud filled if the measured reflectance is greater than the threshold, or if the measured equivalent blackbody temperature is less than the threshold. The next three methods are bispectral, using one visible wavelength window channel and one thermal infrared wavelength window. The final two algorithms rely on the spatial variability within the cloud field to determine cloud cover. Spatial coherence assumes only that the cloud field occurs in a single layer and that the clouds are optically thick in the infrared window. LANDSAT Thematic Mapper (TM) data is used to test the spatial resolution dependence of the cloud algorithms. The ISCCP bispectral threshold applied to the full resolution data is used as the reference or truth cloud cover, after which the retrieval methods are applied to the spatial resolutions. Studies of the fraction of pixels in the scene at cloud edge, and of the profile of reflectance and temperature near cloud edges indicate an uncertainty in the reference cloud fraction of 1 to 5 percent.

Parker, Lindsay↗
NASA NTRS1990

Satellite-derived cloud fields during the FIRE cirrus IFO case study

The First ISCCP Regional Experiment (FIRE) Cirrus Intensive Field Observation (IFO) program measured cirrus cloud properties with a variety of instruments from the surface, aircraft, and satellites. Surface and aircraft observations provide a small scale point and line measurements of different micro- and macro-physical properties of advecting and evolving cloud systems. Satellite radiance data may be used to measure the areal variations of the bulk cloud characteristics over meso- and large scales. Ideally, the detailed cloud properties derived from the small scale measurements should be tied to the bulk cloud properties typically derived from the satellite data. Full linkage of these data sets for a comprehensive description of a given cloud field, one of the goals of FIRE, should lead to significant progress in understanding, measuring, and modeling cirrus cloud systems. The relationships derived from intercomparisons of lidar and satellite data by Minnis et al. are exploited in a mesoscale analysis of the satellite data taken over Wisconsin during the Cirrus IFO case study.

Heck, Patrick W.↗
NASA NTRS1990

An aeronautical mobile satellite experiment

The various activities and findings of a NASA/FAA/COMSAT/INMARSAT collaborative aeronautical mobile satellite experiment are detailed. The primary objective of the experiment was to demonstrate and evaluate an advanced digital mobile satellite terminal developed at the Jet Propulsion Laboratory under the NASA Mobile Satellite Program. The experiment was a significant milestone for NASA/JPL, since it was the first test of the mobile terminal in a true mobile satellite environment. The results were also of interest to the general mobile satellite community because of the advanced nature of the technologies employed in the terminal.

Jedrey, T. C.↗
NASA NTRS1989

Satellite-map position estimation for the Mars rover

A method for locating the Mars rover using an elevation map generated from satellite data is described. In exploring its environment, the rover is assumed to generate a local rover-centered elevation map that can be used to extract information about the relative position and orientation of landmarks corresponding to local maxima. These landmarks are integrated into a stochastic map which is then matched with the satellite map to obtain an estimate of the robot's current location. The landmarks are not explicitly represented in the satellite map. The results of the matching algorithm correspond to a probabilistic assessment of whether or not the robot is located within a given region of the satellite map. By assigning a probabilistic interpretation to the information stored in the satellite map, researchers are able to provide a precise characterization of the results computed by the matching algorithm.

Hayashi, Akira↗
NASA NTRS1990

Satellite altimeter calibration techniques

This paper examines calibration techniques which can most effectively satisfy the requirements of future satellites carrying high-accuracy radar altimeters, such as the ESA ERS-1 and the NASA/CNES Topex/Poseidon satellites scheduled for launch during the next five years. The calibration accuracies and the advantages and disadvantages of the four currently proposed calibration techniques for over-water calibration are discussed: (1) a tide gauge on a tower at-sea and a nearby laser, (2) a laser and a tide gauge on an island with an offshore satellite pass and a geoid tie between the satellite ground track and the laser, (3) a tide gauge on a tower at-sea with satellite positioning from multiple lasers and a GPS, and (4) a laser and a tide gauge on a tower at-sea. Error budgets for these techniques, developed on the basis of state-of-the-art tracking systems, were found to have one sigma height uncertainties in the 2.8 to 4.9 cm range.

Kolenkiewicz, R.↗
NASA NTRS1990

Use of non-geostationary orbits for a Ka-band Personal Access Satellite system

This paper discusses the use of satellites in circular orbits at altitudes high enough for continental U.S. (CONUS) visibility. This enables one satellite to relay signals between geographically separated earth stations within CONUS at any one time and thus bypasses the need for intersatellite links. System performance is examined for three circular satellite orbits at altitudes of 20,182 km, 10,353 km, and 5143 km. Inclination angles between the satellite orbit plane and the equatorial plane of 0, 45, and 90 deg are considered. The number of satellites required to provide continuous CONUS coverage is calculated.

Estabrook, Polly↗
NASA NTRS1990

Mobile satellite system propagation measurements at L-band using Marecs-B2

A mobile satellite system (MSS) propagation experiment at 1.5 GHz was performed near the east coast of the United States in central Maryland during December 1987 using the Marecs-B2 satellite as a transmitter platform. A receiving system in a vehicle measured signal fades caused by shadowing and multipath from roadside trees and utility poles. The propagation degradations were characterized for a system of three roads previously examined using a helicopter as the transmitter platform. The objectives of the Marecs-B2 MSS tests were to: (1) establish cumulative fade distributions for the particular satellite geometry for both rural and suburban roads; (2) validate the consistency of previous roadside tree measurements which employed a helicopter as the transmitter platform for the same system of roads; (3) obtain an additional set of fade levels at a lower angle hitherto not measured in central Maryland; and (4) combine the satellite-acquired data set with previous helicopter results and establish an analytic, empirically derived function describing the cumulative fade distributions for a family of path angles. An analysis of the satellite data has demonstrated the successful achievement of these objectives.

Vogel, Wolfhard J.↗
NASA NTRS1990

Satellite formation in capillary jet breakup

Computations of finite-amplitude, spatially periodic wave growth on a cylindrical jet have been carried out using a boundary integral method. The initial wave growth is in agreement with Rayleigh's linear theory. When followed to completion these waves pinch off large drops separated by smaller satellite drops (spherules) that decrease in size with decreasing wavelength. The computed sizes of both drops and satellites agree with experiment. It is found that satellites will form for all unstable wave numbers. The small satellites that are computed at wave numbers near the critical wave number were not predicted by near-linear analysis but are observed in experimental photographs of jet breakup. Computation of the collapse of elongated satellites shows short waves propagating on their surfaces.

Mansour, Nagi N.↗
NASA NTRS1990

The role of technology in influencing future civil communications satellites

Technology, both as an enabler and as a driver of new and improved communication satellites, is discussed. A brief look at the beginnings and evolution of satellite communications is given to reveal the continuing influence of technology over the past 25 years. An assessment of the current state of the art which serves as a benchmark representing how far technology has come and as a basis for comparison for future possibilities is presented. A short tutorial on communications satellite basics is presented, followed by an assessment of technologies used for satellite antennas and signal amplification and routing. A discussion of future service requirements follows, and emerging technologies are identified along with possible improved communications capabilities that can result from them. The outlook for the role of technology for future communication satellites is summarized.

Bagwell, James W.↗
NASA NTRS1990

Evidence for asymmetric inertial instability in the FIRE satellite dataset

One of the main goals of the First ISCCP Regional Experiment (FIRE) is obtaining the basic knowledge to better interpret satellite image of clouds on regional and smaller scales. An analysis of a mesoscale circulation phenomenon as observed in hourly FIRE satellite images is presented. Specifically, the phenomenon of interest appeared on satellite images as a group of propagating cloud wavelets located on the edge of a cirrus canopy on the anticylonic side of a strong, upper-level subtropical jet. These wavelets, which were observed between 1300 and 2200 GMT on 25 February 1987, are seen most distinctly in the GOES-West infrared satellite picture at 1800 GMT. The purpose is to document that these wavelets were a manifestation of asymmetric inertial instability. During their lifetime, the wavelets were located over the North American synoptic sounding network, so that the meteorological conditions surrounding their occurrence could be examined. A particular emphasis of the analysis is on the jet streak in which the wavelets were imbedded. The characteristics of the wavelets are examined using hourly satellite imagery. The hypothesis that inertial instability is the dynamical mechanism responsible for generating the observed cloud wavelets was examined. To further substantiate this contention, the observed characteristics of the wavelets are compared to, and found to be consistent with, a theoretical model of inertia instability by Stevens and Ciesielski.

Stevens, Duane E.↗
NASA NTRS1990

Stationary orbits of satellites of disk galaxies

The satellite of an S-galaxy will experience opposing dynamical-friction forces from the stars of the disk and the halo. If these forces are in balance, the satellite may travel in a stable, near-circular orbit whose radius, for a wide range of physical parameters, should be limited to a zone 1.2 to 1.4 times the disk radius, much as is observed. The idea is very simple. The dynamical friction acting on a small satellite, moving through a stellar galactic halo, makes this satellite slow down. On the other hand, a stellar disk, rotating faster than a satellite, makes it speed up. But the density distributions in radius for disk's and halo's stars in real flat galaxies are quite different (respectively, exponential and power-law). Moreover, the observational data show that the exponential profile for disk's surface density drops abruptly at some radius (r sub d). So it is natural to expect that a stationary orbit could be near the edge of a disk (where two effects are mutually compensated).

Polyachenko, Valerij L.↗
NASA NTRS1991

Advanced Satellite Research Project: SCAR Research Database. Bibliographic analysis

The literature search was provided to locate and analyze the most recent literature that was relevant to the research. This was done by cross-relating books, articles, monographs, and journals that relate to the following topics: (1) Experimental Systems - Advanced Communications Technology Satellite (ACTS), and (2) Integrated System Digital Network (ISDN) and Advance Communication Techniques (ISDN and satellites, ISDN standards, broadband ISDN, flame relay and switching, computer networks and satellites, satellite orbits and technology, satellite transmission quality, and network configuration). Bibliographic essay on literature citations and articles reviewed during the literature search task is provided.

Pelton, Joseph N.↗
NASA NTRS1991

Outer planet satellites

Recent findings on the outer-planet satellites are presented, with special consideration given to data on the rheologic properties of ice on icy satellites, the satellite surfaces and exogenic processes, cratering on dead cratered satellites, volcanism, and the interiors of outer-planet satellites. Particular attention is given to the state of Titan's surface and the properties of Triton, Pluto, and Charon.

Schenk, Paul M.↗
NASA NTRS1991

Tidal evolution of planetary satellites

Early in the history of the Solar System, Europa and Ganymede may have evolved through a 3:1 mean-motion commensurability, which would have been encountered prior to the establishment of the current Laplace resonance involving Io, Europa, and Ganymede. If Europa and Ganymede passed through the 3:1 mean-motion commensurability, the orbital eccentricities of both satellites may have increased to large values during a phase of chaotic behavior, after which the satellites would have escaped from the resonance. In spite of the relatively large J sub 2 of Jupiter, Europa, and Ganymede are sufficiently massive and distant from the planet that resonances at the 3:1 mean-motion commensurability interact strongly, leading to chaotic behavior via the same kinds of dynamical mechanisms present at resonances among the Uranian satellites. As a result of the large eccentricity increases possible during the evolution of Europa and Ganymede through the 3:1 mean-motion commensurability, tidal heating may have melted water ice in the mantles of both satellites, and stresses on the lithosphere of both satellites due to tidal deformation may have been sufficient to cause extensive fracturing, making resurfacing possible. This may account for the post-heavy bombardment geological activity on both Europa and Ganymede. In addition, the effects of resonance passage on Ganymede may provide an explanation of the Ganymede-Callisto dichotomy by providing Ganymede with an intense source of internal heat and lithospheric stress not present in Callisto. Further possibilities of this evolution are presented.

Tittemore, William C.↗