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At least 505 records · Page 28

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NASA NTRS1985

On the determination of laminar flame speeds from stretched flames

The effects of stretch on the determination of the laminar flame speed are experimentally studied by using the positively-stretched stagnation flame and negatively-stretched bunsen flame, and by using lean and rich mixtures of methane, propane, butane, and hydrogen with air whose effective Lewis numbers are either greater or less than unity. Results demonstrate that flame speed determination can be influenced by stretch through two factors: (1) Preferential diffusion which tends to increase or decrease the flame temperature and burning rate depending on the effective Lewis number, and (2) Flow divergence which causes the flame speed to assume higher values when evaluated at the upstream boundary of the preheat zone instead of the reaction zone. Recent data on flame speed including the present ones are then examined from the unified viewpoint of flame stretch, leading to satisfactory resolution of the discrepancies between them. The present study also proposes a methodology of determining the laminar flame speeds by using the stagnation flame and linearly extrapolating the data to zero stretch rate.

Wu, C. K.↗

NASA NTRS1986

A terrain-dependent reference atmosphere determination method for available potential energy calculations

An iterative technique that determines the reference atmosphere which incorporates the effects of uneven surface topography is presented. This method has been successfully applied in several available potential energy studies. An alternative method due to Taylor is also evaluated. While Taylor presented excellent continuous formulations of the available potential energy that include topography, his method for determining the reference atmosphere distributions failed to provide the accuracy needed to produce reliable available potential energy estimates. Since topography has a significant influence on the general circulation, it is important to employ techniques that incorporate its effects in the determination of available potential energy.

Koehler, T. L.↗

NASA NTRS1986

Orbit determination for the Mariner Mark II Comet Rendezvous/Asteroid Flyby mission - The orbiting phase

The Comet Rendezvous/Asteroid Flyby (CRAF) mission is the first of the Mariner Mark II mission set, designed to explore the outer solar system. Major objectives of orbit determination will be determine the positions and masses of the comet and asteroid and the relative position of the spacecraft, which is important to accurate pointing of the scan platform on which the narrow angle camera and scientific instruments are positioned. Position prediction is also important, since continuous commuication with the spacecraft will not be possible. The small gravitational attractions and poorly known ephemerides of the comet and asteroid, and the small, slow spacecraft orbit about the comet, pose significant new problems for orbit determination. Results of simulations studying the effectiveness of key data types, the accuracies of estimates, and prediction capabilities, are presented.

Weeks, C. J.↗

NASA NTRS1986

Differential GPS approaches to orbit determination of high-altitude earth satellites

Orbit determination of earth satellites using conventional (up-looking) differential GPS is limited to lower altitudes due to the finite antenna beamwidth and altitude of GPS satellites. Higher user satellites suffer from having short GPS view period; at sufficiently high altitudes, up-looking GPS visibility becomes so poor that no differential measurements are possible. For such higher user satellites, two alternative differential GPS approaches are suggested. A covariance analysis is performed investigating the capabilities of these approaches at various user satellite altitudes. Best differential GPS data types are identified for satellites within different altitude ranges. Error sources and other factors affecting the orbit determination accuracy are examined. Relative merits of these approaches are compared. When applied to QUASAT, the proposed earth orbiting radio telescope with an elliptical orbit, a sub-meter orbit determination accuracy is expected.

Wu, S.-C.↗

NASA NTRS1986

Orbit determination for the Voyager II Uranus encounter

The Voyager II flyby of Uranus in January 1986 was the most distant planetary encounter ever attempted, and presented unique challenges to the process of orbit determination. Long light-times and spacecraft receiver difficulties hampered the collection of two-way radiometric data and helped bring about the maturation of a Very Long Baseline Interferometry navigational data type during the long cruise from Saturn. Planet and satellite ephemeris uncertainties necessitated the use of the onboard spacecraft optical system for Uranus-relative navigation. During the close approach phase, these optical data were combined with radiometric data to drive the Uranus system-relative uncertainties down to the level of a few tens of kilometers. This paper contains qualitative and quantitative results and conclusions based on orbit determination experience during Uranus cruise and encounter. Topics include an overview of the navigation-related mission events and requirements, and a review of the salient orbit determination results.

Taylor, T. H.↗

NASA NTRS1986

Summary of longitudinal stability and control parameters as determined from space shuttle Columbia flight test data

Extensive wind tunnel tests were conducted to establish the preflight aerodynamics of the Shuttle vehicle. This paper presents the longitudinal, short-period aerodynamics of the space shuttle Columbia as determined from flight test data. These flight-determined results are compared with the preflight predictions, and areas of agreement or disagreement are noted. In addition to the short-period aerodynamics, the pitch RCS effectiveness was determined.

Suit, W. T.↗

NASA NTRS1986

Determination of U, V, and W from single station Doppler radar radial velocities

The ST/MST (stratosphere troposphere/mesosphere stratosphere troposphere) clear air Doppler radar, or wind profiler, is an important tool in observational meteorology because of its capability to remote observe dynamic parameters of the atmosphere. There are difficulties in transforming the observed radial velocities into meteorological wind components. How this problem has been treated in the past is reviewed, and some of the analysis is recast to a form more suited to the high diagnostic abilities of a number of fixed beam configurations with reference to a linear wind field. The results, in conjunction with other works which treats problems such as the effects of finite sample volumes in the presence of nonhomogeneous atmospheric reflectivity, have implications important to the design of both individual MST/ST radars and MST/ST radar networks. The key parameters to uncoupling terms in the scaling equations are w sub x and w sub y. Whenever the stratiform condition, which states that these two parameters are negligible, is satisfied, a five beam ST radar may determine unbiased values of u, v, and w for sample volumes directly above the radar. The divergence and partial deformation of the flow may also be determined. Three beam systems can determine w and w sub z, but are unable to obtain u and v wind components uncontaminated by vertical sheer terms, even when the stratiform condition is satisfied.

Clark, W. L.↗

NASA NTRS1987

The calibration of photographic and spectroscopic films. The utilization of the digital image processor in the determination of aging of the surf clam (Spisula solidissima)

The age of the surf clam (Spisula solidissima) can be determined with the use of the Digital Image Processor. This technique is used in conjunction with a modified method for aging, refined by John Ropes of the Woods Hole Laboratory, Massachusetts. This method utilizes a thinned sectioned chondrophore of the surf clam which contains annual rings. The rings of the chondrophore are then counted to determine age. By digitizing the chondrophore, the Digital Image Processor is clearly able to separate these annual rings more accurately. This technique produces an easier and more efficient way to count annual rings to determine the age of the surf clam.

Peters, Kevin A.↗

NASA NTRS1987

Galilean satellite tour orbit determination assessment

Results are given which demonstrate the ability of the orbit determination system to satisfy accuracy requirements in support of the Galileo Project's planned tour of Jupiter's satellites. The results are derived through the application of mission operation strategies and assumptions. It is shown that the achievement of the requisite orbit determination accuracies is predicated on the availability of optical navigation data. It is further demonstrated that the unavailability of tour optical navigation data yields not only degraded orbit determination accuracies which fail to meet propellant budget and science instrument pointing requirements, but also produces, for the planned 200 km flyby of Europa, an approximate 0.02 risk of having the spacecraft collide with the satellite.

Moultrie, B.↗

NASA NTRS1986

Precise orbit determination of a geosynchronous satellite with differential very-long-baseline interferometry

The use of differential VLBI (DVLBI) to determine the orbit of a U.S. geosynchronous satellite with a position accuracy of a few meters is examined. DVLBI was employed to track the geosynchronous satellite DSCS-II; two observation channels with 2 MHz bandwidth each in a 2 GHz band were used to receive the telemetry signal of the satellite and quasar radio signals. The random observation, delay, station location, and quasar position errors are discussed. The correlation processing of the quasar and satellite signals is described. The accuracy of the estimated satellite position is evaluated using a covariance analysis. It is determined that the satellite position was estimated with an accuracy of about 4 m at the center of the observation arc. It is noted that the modeling error of the solar radiation pressure factor, ionospheric correction error, and observation error need to be corrected in order to provide more accurate orbit determinations.

Shiomi, Tadashi↗

NASA NTRS1987

A demonstration of high precision GPS orbit determination for geodetic applications

High precision orbit determination of Global Positioning System (GPS) satellites is a key requirement for GPS-based precise geodetic measurements and precise low-earth orbiter tracking, currently under study at JPL. Different strategies for orbit determination have been explored at JPL with data from a 1985 GPS field experiment. The most successful strategy uses multi-day arcs for orbit determination and includes fine tuning of spacecraft solar pressure coefficients and station zenith tropospheric delays using the GPS data. Average rms orbit repeatability values for 5 of the GPS satellites are 1.0, 1.2, and 1.7 m in altitude, cross-track, and down-track componenets when two independent 5-day fits are compared. Orbit predictions up to 24 hours outside the multi-day arcs agree within 4 m of independent solutions obtained with well tracked satellites in the prediction interval. Baseline repeatability improves with multi-day as compared to single-day arc orbit solutions. When tropospheric delay fluctuations are modeled with process noise, significant additional improvement in baseline repeatability is achieved. For a 246-km baseline, with 6-day arc solutions for GPS orbits, baseline repeatability is 2 parts in 100 million (0.4-0.6 cm) for east, north, and length components and 8 parts in 100 million for the vertical component. For 1314 and 1509 km baselines with the same orbits, baseline repeatability is 2 parts in 100 million for the north components (2-3 cm) and 4 parts in 100 million or better for east, length, and vertical components.

Lichten, S. M.↗

NASA NTRS1987

Determination of Earth rotation by the combination of data from different space geodetic systems

Formerly, Earth Rotation Parameters (ERP), i.e., polar motion and UTI-UTC values, have been determined using data from only one observational system at a time, or by the combination of parameters previously obtained in such determinations. The question arises as to whether a simultaneous solution using data from several sources would provide an improved determination of such parameters. To pursue this reasoning, fifteen days of observations have been simulated using realistic networks of Lunar Laser Ranging (LLR), Satellite Laser Ranging (SLR) to Lageos, and Very Long Baseline Interferometry (VLBI) stations. A comparison has been done of the accuracy and precision of the ERP obtained from: (1) the individual system solutions, (2) the weighted means of those values, (3) all of the data by means of the combination of the normal equations obtained in 1, and (4) a grand solution with all the data. These simulations show that solutions done by the normal equation combination and grand solution methods provide the best or nearly the best ERP for all the periods considered, but that weighted mean solutions provide nearly the same accuracy and precision. VLBI solutions also provide similar accuracies.

Archinal, Brent Allen↗

NASA NTRS1988

Method for determining artillery position

A method is disclosed for determining the position of cannon from measurement sites whose distance from each other lies in the same order of magnitude as the distance between the cannons -- that distance being in the kilometer range -- with the help of the travel time evaluation of muzzle blasts received at the measurement sites. There are at least two measurement sites, consisting of a cruciform of four microphones each positioned so that one axis is oriented to an arbitrarily chosen reference direction with the microphones spaced closely together. In this arrangement of diametrically opposed microphones, the respective travel times are determined and placed in a relationship whose arctangent is a radio bearing to the reference direction in which radio bearings are determined with consideration of their position and their opposing distance from the cannon position.

Fischer, Johannes↗

NASA NTRS1988

Experimental Determination of Aerodynamic Damping in a Three-Stage Transonic Axial-Flow Compressor

Rotor blade aerodynamic damping is experimentally determined in a three-stage transonic axial flow compressor having design aerodynamic performance goals of 4.5:1 pressure ratio and 65.5 lbm/sec weight flow. The combined damping associated with each mode is determined by a least squares fit of a single degree of freedom system transfer function to the nonsynchronous portion of the rotor blade strain gauge output power spectra. The combined damping consists of aerodynamic and structural and mechanical damping. The aerodynamic damping varies linearly with the inlet total pressure for a given equivalent speed, equivalent mass flow, and pressure ratio while structural and mechanical damping are assumed to be constant. The combined damping is determined at three inlet total pressure levels to obtain the aerodynamic damping. The third stage rotor blade aerodynamic damping is presented and discussed for 70, 80, 90, and 100 percent design equivalent speed. The compressor overall performance and experimental Campbell diagrams for the third stage rotor blade row are also presented.

Newman, Frederick A.↗

NASA NTRS1988

Determination of the Venus flyby orbits of the Soviet Vega probes using VLBI techniques

In December 1984, the Soviet Union launched two identical Vega spacecraft with the dual objective of exploring Venus and continuing to rendezvous with the comet Halley. The two Vega spacecraft encountered Venus in mid-June 1985 and successfully deployed entry probes and wind-measuring balloons into the Venus atmosphere. An objective of the Venus Balloon experiment was to measure the Venus winds using differential VLBI from the balloon and the flyby bus. NASA's Deep Space 64 meter subnet was part of a world wide network organized to collect data from the Vega probes and balloons. A critical element of this experiment was an accurate determination of the Venus relative flyby orbits of the Vega spacecraft during the 46 hour balloon lifetime. Venus flyby solutions were independently determined by the Soviets using two-way range and Doppler from Soviet stations and by JPL using one-way Doppler and VLBI data collected from the DSN. The Vega flyby solutions determined by the Soviets using a sparse two-way tracking strategy with JPL solutions using the DSN VLBI data to complement the Soviet data and with solutions using only one-way data collected by the DSN were compared.

Ellis, J.↗

NASA NTRS1988

Experiments for the determination of convective diffusion heat/mass transfer to burner rig test targets comparable in size to jet stream diameter

The application of a recently formulated vapor transport theory to predict deposition rates of corrosive salts from alkali-seeded combustion gases of a small-capacity, high-velocity, atmospheric-pressure burner rig was hampered by the relatively large dimensions of the cylindrical deposit collector compared to the diameter of the combustion gas stream. The relative dimensions lead to a highly nonadiabatic combustion gas flow around the collector and necessitate two series of experiments. In the first series, mass transfer coefficients are determined by utilizing the naphthalene sublimation technique. The second series of experiments determines the dilution effect on the sodium species concentrations due to the entrainment of ambient air. This second series involves the measurement of the temperature variation along the surface of the collector under steady state conditions. Vapor deposition rates are determined exploiting this information and the results are found to compare favorably with experimentally obtained rates.

Santoro, G. J.↗

NASA NTRS1988

Attitude determination and control subsystem for the TOPEX satellite

The Ocean Topography Experiment satellite will carry a modular Attitude Determination and Control Subsystem (ADCS) which contains all equipment required for attitude determination, stabilization, and control, as well as hydrazine thruster firing control, during all mission phases. Attention is presently given to the ADCS's architecture, constituent hardware components, performance requirements, and predicted on-orbit performance compliance, with emphasis on the design and analysis of the Normal Mission Mode control algorithm furnishing the primary scientific data-acquisition operational mode. This mode's attitude determination and control of on-orbit performance is predicted to better than 43 arcsec.

Dennehy, C. J.↗

NASA NTRS1988

The effects of geopotential resonance on orbit determination for Landsat-4

Analysis is presented demonstrating improved performance for Landsat-4 orbit determination using the Goddard Trajectory Determination System with an adjusted Goddard Earth Model-9 (GEM-9) for geopotential coefficients of the 15th degree and order. The orbital state is estimated along with the sine and cosine coefficients of degree and order 15, (C, S) sub 15,15. The estimates are made for two 5-day intervals of range and doppler data, primarily from the Tracking and Data Relay Satellite, during a period of low solar activity in January 1987. The average values of the estimated coefficients (C, S) sub 15,15 are used to modify the GEM-9 model, and orbit determination performance is tested on 17 consecutive 34-hour operational tracking data arcs in January 1987. Significant reductions in the mean values and standard deviations of the along-track position difference and the drag model scaling parameter from solution to solution are observed. The approach is guided by the shallow resonance theory of geopotential orbit perturbations.

Hoge, S. L.↗