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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

The Rome-GSFC magnetic field experiment for Helios A and B /E 3/

The Rome-GSFC magnetic field experiment utilizes a triaxial fluxgate (saturable inductor) magnetometer. The sensor unit is mounted on the end of a boom approximately four meters from the spacecraft spin axis. The three analog outputs of the magnetometer are converted into three 9 bit digital words. The experiment utilizes an automatic inflight range switch to select the optimum dynamic range out of 4 ranges. A nonmagnetic thermally oscillating actuator is used to reorient the sensor unit by 90 deg to determine all three axes zero levels. The accuracy should be approximately plus or minus 0.1 gamma. The vector measurements are made at equal intervals in time ranging from 16 per second down to 1 per second depending on the telemetry bit rate.

Scearce, C.↗
NASA NTRS1975

Radar measurements of Martian topography and surface properties - The 1971 and 1973 oppositions

The Goldstone radar system was used at a wavelength of 12.6 cm to probe the Martian surface during the 1973 opposition. Measurements of range and reflected power were made at least weekly between July 12 and November 24. Surface cells isolated by the radar system were 8 km E-W by 110 km N-S. Altitudes were calculated from signal time delays measured relative to a triaxial ellipsoid and were combined with altitudes measured during the 1971 opposition. Contours of constant altitude were calculated at 200 m intervals between latitudes -14 and -22 deg. These contours are presented in conjunction with Mars charts derived from Mariner 9 television pictures. Reflected power was measured at angles of incidence between -5 and +5 deg. These measurements were combined with those obtained during the 1971 opposition.

Downs, G. S.↗
NASA NTRS1976

Minor planets and related objects. XIX - Shape and pole orientation of /39/ Laetitia

Results are reported for analyses of UBV photoelectric photometric data and light curves of the asteroid Laetitia. The pole orientation is determined using a technique for reducing the scatter in the magnitude-phase relation. No significant variations in color are found over the surface, and the light curves are found to indicate topographic elements (peaks, scarps, or depressions) approximately 10 km in radius. It is shown that the light-curve amplitudes as well as the wide scatter in observed magnitude and phase relation can be explained by a triaxial ellipsoidal figure with a dimensional ratio of about 15:9:5. It is concluded that the size, shape, and composition of this asteroid are highly suggestive of a major collisional fragment from a substantially more massive differentiated parent body.

Sather, R. E.↗
NASA NTRS1976

Radar observations at 3.5 and 12.6 cm wavelength of asteroid 433 Eros

A study of the asteroid 433 Eros using 3.5 and 12.6 cm radar waves indicates that the surface is very much rougher than any planetary or lunar surface observed by this method. A surface completely covered with sharp edges, pits, subsurface holes, or embedded chunks with scale sizes on the order of our wavelengths seems to be indicated. A model based on a rough rotating triaxial ellipsoid having radii in the rotation equator of 18.6 and 7.9 km agrees well with our data, although a strong wobble in the apparent center frequency of the spectra as rotation progresses indicates that one side may be more reflective than the other, or more likely, that the projected axis of rotation does not equally divide the projected area.

Jurgens, R. F.↗
NASA NTRS1976

Magnetosheath lion roars

The characteristics of lion roars, which are intense packets of electromagnetic waves characteristically found in the magnetosheath, are studied. The average frequency of the emissions is 120 Hz, with over 90% occurring between 90 and 160 Hz (which is near one-half the local electron gyrofrequency); over 70% of all emissions last a mere 2 sec or less; the maximum amplitude of lion roars has an average value of 85 milligamma, over 80% being between 40 and 160 milligamma. Occurrence of lion roars is related to the level of geomagnetic activity, measured by Kp. The probability of occurrence ranges from 10% during magnetically quiet intervals to 75% during disturbed periods. Polarization and wave normal direction of lion roars, determined by variance analysis of triaxial wave forms, are righ-handed circularly polarized, with propagation essentially along the ambient magnetic field.

Smith, E. J.↗
NASA NTRS1976

Results from the GSFC fluxgate magnetometer on Pioneer 11

A high-field triaxial fluxgate magnetometer was mounted on Pioneer 11 to measure the main magnetic field of Jupiter. It is found that this planetary magnetic field is more complex than that indicated by the results of the Pioneer 10 vector helium magnetometer. At distances less than 3 Jupiter radii, the magnetic field is observed to increase more rapidly than an inverse-cubed distance law associated with any simple dipole model. Contributions from higher-order multipoles are significant, with the quadrupole and octupole being 24 and 21 percent of the dipole moment, respectively. Implications of the results for the study of trapped particles, planetary radio emission, and planetary interiors are discussed. Major conclusions are that the deviation of the main planetary magnetic field from a simple dipole leads to distortion of the L shells of the charged particles and to warping of the magnetic equator. Enhanced absorption effects associated with Amalthea and Io are predicted.

Acuna, M. H.↗
NASA NTRS1977

The equilibrium figures of Phobos and other small bodies

Computations of figures of hydrostatic equilibrium for isolated rotating bodies are discussed. It is shown that the theoretical figure of equilibrium for Phobos is a triaxial ellipsoid whose a and b axes differ by about 25% and that this difference is less than 2% for Deimos. A density of less than 3.9 g/cu cm is estimated for Phobos. Equilibrium figures are also examined for the inner satellites of Jupiter and Saturn as well as for small asteroids.

Soter, S.↗
NASA NTRS1977

A statistical study of Pc 3 magnetic pulsations at synchronous orbit, ATS 6

Results are reported for a study designed to determine statistically the nature and variation of the polarization parameters of Pc3 magnetic pulsations at synchronous orbit. Data obtained with a triaxial flux gate magnetometer on the geosynchronous satellite ATS 6 are subjected to routine power spectral and polarization analyses, and the events examined are identified as peaks in the spectra. Coherence analysis of spectral matrices for these events indicates that Pc3 are very common at synchronous orbit and are primarily a local morning phenomenon with an occurrence peak around 1000 LT; that the pulsations occur at all frequencies in the Pc3 band, with the most common frequency at about 0.35 Hz; that the Pc3 at synchronous orbit are most often linear and generally transverse, but some have significant compressional components; and that based on azimuth angle, there are two distinct classes of Pc3 (azimuthal and radial) with different characteristics. These statistical results are compared with model predictions and ground-based observations.

Arthur, C. W.↗
NASA NTRS1977

The magnetopause at 5.2 R/E/ in August 1972 - Magnetopause motion

The paper analyzes magnetic field records from ATS 5 and Explorer 45 satellites, provided with triaxial flux gate magnetometer, during the close approach of the magnetopause to the earth. Attention is directed to a discussion of the observing arrangements, a detailed comparison of the two sets of observations, and an interpretation of the magnetopause motion and of magnetic pulsations. The pulsations appear not to be due to surface waves propagating in the magnetopause.

Cahill, L. J., Jr.↗
NASA NTRS1977

Theory of the rotation of the rigid earth

Equations of motion for a triaxial rigid earth are derived in Andoyer variables. The reference plane is the ecliptic of date which is moving as a result of planetary perturbations. By using this noninertial system, the development of the disturbing function for the sun and moon is simplified, with an additional term appearing in the Hamiltonian which, however, contributes only to precessional motion. The nutation terms derived are compared with those of Woolard.

Kinoshita, H.↗
NASA NTRS1977

Significant initial results from the environmental measurements experiment on ATS-6

The Applications Technology Satellite (ATS-6), launched into synchronous orbit on 30 May 1974, carried a set of six particle detectors and a triaxial fluxgate magnetometer. The particle detectors were able to determine the ion and electron distribution functions from 1 to greater than 10 to the 8th power eV. It was found that the magnetic field is weaker and more tilted than predicted by models which neglect internal plasma and that there is a seasonal dependence to the magnitude and tilt. ATS-6 magnetic field measurements showed the effects of field-aligned currents associated with substorms, and large fluxes of field-aligned particles were observed with the particle detectors. Encounters with the plasmasphere revealed the existence of warm plasma with temperatures up to 30 eV. A variety of correlated waves in both the particles and fields were observed: pulsation continuous oscillations, seen predominantly in the plasmasphere bulge; ultralow frequency (ULF) standing waves; ring current proton ULF waves; and low frequency waves that modulate the energetic electrons. In additon, large scale waves on the energetic-ion-trapping boundary were observed, and the intensity of energetic electrons was modulated in association with the passage of sector boundaries of the interplanetary magnetic field.

Fritz, T. A.↗
NASA NTRS1978

Compressor and fan wake characteristics

A triaxial probe and a rotating conventional probe, mounted on a traverse gear operated by two step motors were used to measure the mean velocities and turbulence quantities across a rotor wake at various radial locations and downstream stations. The data obtained was used in an analytical model developed to study how rotor flow and blade parameters and turbulence properties such as energy, velocity correlations, and length scale affect the rotor wake characteristics and its diffusion properties. The model, includes three dimensional attributes, can be used in predicting the discrete as well as broadband noise generated in a fan rotor, as well as in evaluating the aerodynamic losses, efficiency and optimum spacing between a rotor and stator in turbomachinery.

Reynolds, B.↗
NASA NTRS1977

Outline of the survey on the development of earth observation satellites

An independent earth observation system with land and sea satellites to be developed by Japan is described. Visible and infrared radiometers, microwave radiometers, microwave scattermeters, synthetic aperture radar, and laser sensors are among the instrumentation discussed. Triaxial attitude control, basic technology common to sea and land observation satellites as well as land data analytical technology developed for U.S. LANDSAT data are reviewed.

Source record↗
NASA NTRS1977

The MJS-77 magnetometer actuator

A two-position (0 deg and 180 deg) actuating mechanism (flipper) driven by alternately-heated wax motors (pellets) used to rotate the low field triaxial fluxgate magnetometer experiment on the 1977 Mariner Jupiter-Saturn spacecraft to its 0 deg and 180 deg positions is described. The magnetic field, power requirements, weight and volume of this device are discussed. The problems encountered in design and development of this mechanism are presented.

Stange, W. C.↗
NASA NTRS1978

Mars synthetic topographic mapping

Topographic contour maps of Mars are compiled by synthesizing data acquired from various scientific experiments of the Mariner 9 mission, including S-band radio occultation, the UV spectrometer, the IR radiometer, the IR interferometer spectrometer, and television imagery, as well as earth-based radar information. The entire planet is mapped at scales of 1:25,000,000 and 1:5,000,000 using Mercator, Lambert, and polar stereographic map projections. For the computation of map projections, a biaxial spheroid figure is adopted. The semimajor and semiminor axes are 3393.4 and 3375.7 km, respectively, with a polar flattening of 0.0052. For the computation of elevations, a topographic datum is defined by a gravity field described in terms of spherical harmonics of fourth order and fourth degree combined with a 6.1-mbar occultation pressure surface. This areoid can be approximated by a triaxial ellipsoid with semimajor axes of A = 3394.6 km and B = 3393.3 km and a semiminor axis of C = 3376.3 km. The semimajor axis A intersects the Martian surface at longitude 105 deg W. The dynamic flattening of Mars is 0.00525. The contour interval of the maps is 1 km. For some prominent features where overlapping pictures from Mariner 9 are available, local contour maps at relatively larger scales were also compiled by photogrammetric methods on stereo plotters.

Wu, S. S. C.↗
NASA NTRS1978

On the rotation of elliptical galaxies

The tensor virial theorem is applied to models of early-type galaxies. First the theorem is applied to rotating elliptical galaxies whose constant-density surfaces are similar ellipsoids. A relationship is obtained between the observed rotations and the forms of generally triaxial galaxies. By applying the results of Robert (1962) to the evaluation of the components of the Chandrasekhar tensor which occurs in this relationship, it is found that the form of a galaxy that lacks global velocity anisotropy uniquely determines the ratio of its rotational and random kinetic energies independently of the radial density profile of that galaxy. A distribution of three-dimensional prolate spheroids is derived which accounts for the observed distribution of ellipticities reported by Sandage, Freeman, and Stokes (1970). This is then used to derive curves giving the expected frequency of occurrence of galaxies of given rotational velocities for each of a number of different apparent elongations on the sky. It is found that if elliptical galaxies are prolate, there should be little correlation between apparent ellipticity and rotation velocity.

Binney, J.↗
NASA NTRS1978

Twisted and warped disks as consequences of heavy halos

Observationally testable consequences of the hypothesis that galactic disks are confined less by their self-gravity than that of some hot stellar component are sought. Theoretical and observational studies are reviewed which suggest that elliptical galaxies are typically triaxial in form. It is argued that any hot stellar component is likely to be similarly spherical. The motion of a galactic disk about such a population is calculated. Within the plane the flow is to first order along similar concentric ellipses and without of the plane, provided that certain conditions on the background field are met, an oscillation may be excited which can cause isolated galaxies to become warped. The circular motion of matter in such disks will manifest itself in the misalignment of the apparent minor axis and the H I zero-velocity contour. Such an effect may be present in a number of recent H I surveys, although the data presently available do not allow definite conclusions. Alternative explanations of galactic warps are reviewed and their relation to the present proposal discussed.

Binney, J.↗
NASA NTRS1978

Characteristics of the near wake of a compressor or fan rotor blade

Research reported in this paper covers an experimental investigation of the rotor wake. The experimental investigation included a study of the mean velocity, turbulence intensity, and Reynolds stress variations across the wake of a lightly loaded rotor blade at various axial and radial locations. Only the mean velocity data and their interpretation is presented in this paper. Measurements were carried out with a triaxial probe; rotating with the rotor and stationary behind the rotor. Also, measurements were made with a spherical head static pressure probe rotating with the rotor. Wakes were measured at various incidences to discern the effect of blade loading on the rotor wake. The wake is found to be three dimensional in nature with appreciable radial velocity. The measurements close to the blade trailing edge indicate that the decay of the wake is rapid in this region. The wake data is correlated to derive expressions for the profile and decay of all the components.

Reynolds, B.↗