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NASA NTRS1984

Landsat thematic mapper attitude data processing

The Landsat 4 and 5 satellites carry a new, high resolution, seven band thematic mapper imaging instrument. The spacecraft also carry two types of attitude sensors: a gyroscopic internal reference unit (IRU) which senses angular rate from dc to about 2 Hz, and an AC-coupled angular displacement sensor (ADS) measuring angular deviation above 2 Hz. A description of the derivation of the crossover network used to combine and equalize the IRU and ADS data is made. Also described are the digital data processing algorithms which produce the time history of the satellites' attitude motion including the finite impulse response (FIR) implementation of G and F filters; the resampling (interpolation/decimation) and synchronization of the IRU and ADS data; and the axis rotations required as a result of the on-board sensor locations on three orthogonal axes.

Sehn, G. J.↗

NASA NTRS1986

Physical interpretations from the motions of comets Halley and Giacobini-Zinner

For comets Halley and Giacobini-Zinner (GZ), the model of the rocket-like, outgassing forces affecting the comet motion is shown to be consistent with the vaporization of water ice from the comet nuclei. For comet GZ, the dramatic time dependence of the outgassing forces suggests that this comet's spin axis passed through the orbit plane in the mid 1960's. Modeling of Halley's motion over two millennia indicates that the comet is rotating in a direct sense, with no obvious long-term time dependence in the average outgassing forces. The precession of the spin pole axis is not apparent. Secular changes in the comet's angular elements show no evidence for a ring of comet-like material beyond the orbit of Neptune. An obvious 1986 postperihelion bias in comet Halley's observation residuals is modeled by assuming a radial center-of-light/center-of-mass offset.

Yeomans, D. K.↗

NASA NTRS1992

Rotating-unbalanced-mass devices and methods for scanning balloon-borne-experiments, free-flying spacecraft, and space shuttle/space station attached experiments

A method and apparatus for scanning balloon-borne experiments, free-flying spacecraft, or gimballed experiments mounted on a space shuttle or space station, makes use of one or more rotating unbalanced mass devices for selectively generating circular, line, or raster scan patterns for the experiment line of sight. An auxiliary control system may also be used in combination with the rotating unbalanced mass device, for target acquisition, keeping the scan centered on the target, or for producing complementary motion for raster scanning. The rotating unbalanced mass makes use of a mass associated with a drive shaft, such mass having a center of gravity which is displaced from the drive shaft rotation axis. The drive shaft is driven with a substantially constant angular velocity, thereby resulting in relatively low power requirements since no acceleration or deceleration of the mass is generally involved during steady state operations. The resulting centrifugal force of the rotating unbalanced mass is used to generate desired reaction forces on the experiment or spacecraft to create a desired scan pattern for the experiment line of sight.

Polites, Michael E.↗

NASA NTRS1996

Fluid Physics in a Fluctuating Acceleration Environment

We summarize several aspects of an ongoing investigation of the effects that stochastic residual accelerations (g-jitter) onboard spacecraft can have on experiments conducted in a microgravity environment. The residual acceleration field is modeled as a narrow band noise, characterized by three independent parameters: intensity (g(exp 2)), dominant angular frequency Omega, and characteristic correlation time tau. Realistic values for these parameters are obtained from an analysis of acceleration data corresponding to the SL-J mission, as recorded by the SAMS instruments. We then use the model to address the random motion of a solid particle suspended in an incompressible fluid subjected to such random accelerations. As an extension, the effect of jitter on coarsening of a solid-liquid mixture is briefly discussed, and corrections to diffusion controlled coarsening evaluated. We conclude that jitter will not be significant in the experiment 'Coarsening of solid-liquid mixtures' to be conducted in microgravity. Finally, modifications to the location of onset of instability in systems driven by a random force are discussed by extending the standard reduction to the center manifold to the stochastic case. Results pertaining to time-modulated oscillatory convection are briefly discussed.

Thomson, J. Ross↗

NASA NTRS1994

Occultation Predictions Using CCD Strip-Scanning Astrometry

We are developing the method of CCD strip-scanning astrometry for the purpose of deriving reliable advance predictions for occultations involving small objects in the outer solar system. We are using a camera system based on a Ford/Loral 2Kx2K CCD with the Crossley telescope at Lick Observatory for this work. The columns of die CCD are aligned East-West, the telescope drive is stopped, and the CCD is clocked at the same rate that the stars drift across it. In this way we obtain arbitrary length strip images 20 arcmin wide with 0.58" pixels. Since planets move mainly in RA, it is possible to obtain images of the planet and star to be occulted on the same strip well before the occultation occurs. The strip-to-strip precision (i.e. reproducibility) of positions is limited by atmospheric image motion to about 0.1" rms per strip. However, for objects that are nearby in R.A., the image motion is highly correlated and their relative positions are good to 0.02" rms per strip. We will show that the effects of atmospheric image motion on a given strip can be removed if a sufficient number of strips of a given area have been obtained. Thus, it is possible to reach an rms precision of 0.02" per strip, corresponding to about 0.3 of Pluto or Triton's angular radius. The ultimate accuracy of a prediction based on strip-scanning astrometry is currently limited by the accuracy of the positions of the stars in the astrometric network used and by systematic errors most likely due to the optical system. We will show the results of . the prediction of some recent occultations as examples of the current capabilities and limitations of this technique.

Dunham, Edward W.↗

NASA NTRS2020

HD 191939: Three Sub-Neptunes Transiting a Sun-like Star Only 54 pc Away

We present the discovery of three sub-Neptune-sized planets transiting the nearby and bright Sun-like star HD 191939 (TIC 269701147, TOI 1339), a Ks = 7.18 mag G8 V dwarf at a distance of only 54 pc. We validate the planetary nature of the transit signals by combining 5 months of data from the Transiting Exoplanet Survey Satellite with follow-up ground-based photometry, archival optical images, radial velocities, and high angular resolution observations. The three sub-Neptunes have similar radii (R(b)=3.42(+0.11,-0.11), R(c)=3.23(+0.11,-0.11), and R(d)=3.16(+0.11,-0.11 Rꚛ), and their orbits are consistent with a stable, circular, and coplanar architecture near mean-motion resonances of 1:3 and 3:4 (P(b) = 8.88, P(c) = 28.58, and P(d) = 38.35 days). The HD 191939 system is an excellent candidate for precise mass determinations of the planets with high-resolution spectroscopy due to the host star's brightness and low chromospheric activity. Moreover, the system's compact and near-resonant nature can provide an independent way to measure planetary masses via transit timing variations while also enabling dynamical and evolutionary studies. Finally, as a promising target for multiwavelength transmission spectroscopy of all three planets' atmospheres, HD 191939 can offer valuable insight into multiple sub-Neptunes born from a protoplanetary disk that may have resembled that of the early Sun.

Mariona Badenas-Agusti↗

NASA NTRS2005

Exposure to a Rotating Virtual Environment During Treadmill Locomotion Causes Adaptation in Heading Direction

The goal of the present study was to investigate the adaptive effects of variation in the direction of optic flow, experienced during linear treadmill walking, on modifying locomotor trajectory. Subjects (n = 30) walked on a motorized linear treadmill at 4.0 km/h for 24 minutes while viewing the interior of a 3D virtual scene projected onto a screen 1.5 m in front of them. The virtual scene depicted constant self-motion equivalent to either 1) walking around the perimeter of a room to one s left (Rotating Room group) 2) walking down the center of a hallway (Infinite Hallway group). The scene was static for the first 4 minutes, and then constant rate self-motion was simulated for the remaining 20 minutes. Before and after the treadmill locomotion adaptation period, subjects performed five stepping trials where in each trial they marched in place to the beat of a metronome at 90 steps/min while blindfolded in a quiet room. The subject s final heading direction (deg), final X (for-aft, cm) and final Y (medio-lateral, cm) positions were measured for each trial. During the treadmill locomotion adaptation period subject s 3D torso position was measured. We found that subjects in the Rotating Room group as compared to the Infinite Hallway group: 1) showed significantly greater deviation during post exposure testing in the heading direction and Y position opposite to the direction of optic flow experienced during treadmill walking 2) showed a significant monotonically increasing torso yaw angular rotation bias in the direction of optic flow during the treadmill adaptation exposure period. Subjects in both groups showed greater forward translation (in the +X direction) during the post treadmill stepping task that differed significantly from their pre exposure performance. Subjects in both groups reported no perceptual deviation in position during the stepping tasks. We infer that 3 viewing simulated rotary self-motion during treadmill locomotion causes adaptive modification of sensory-motor integration in the control of position and trajectory during locomotion which functionally reflects adaptive changes in the integration of visual, vestibular, and proprioceptive cues. Such an adaptation in the control of position and heading direction during locomotion due to the congruence of sensory information demonstrates the potential for adaptive transfer between sensorimotor systems and suggests a common neural site for the processing and self-motion perception and concurrent adaptation in motor output. This will result in lack of subjects perception of deviation of position and trajectory during the post treadmill step test while blind folded.

Mulavara, A. P.↗

DOE OSTI2024

Theory, analysis, and testing of an angular resonator for wave energy generation

This article describes the theory, analysis, and initial bench-top testing of a minimally invasive, rotational resonator designed to produce small amounts of electrical energy for use in oceanic observation buoys. Here, this work details the systems of equations that govern such a resonator, its potential power production, and its predicted effects on the modified motion of the buoy. Finally, a bench-top test apparatus is designed and experimented upon to identify the system and verify the system of equations empirically.

16 TIDAL AND WAVE POWER↗

DOE OSTI2023

On the circularly polarized luminescence of individual triplet sublevels

Here, we discuss the possibility of using circularly polarized luminescence (CPL) as a tool to probe individual triplet spin sublevels that are populated nonadiabatically following photoexcitation. This study is motivated by a mechanism proposed for chirality-induced spin selectivity in which coupled electronic-nuclear dynamics may lead to a non-statistical population of the three triplet sublevels in chiral systems. We find that low-temperature CPL should aid in quantifying the exact spin state/s populated through coupled electronic-nuclear motion in chiral molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Quantum quenches of an SO(5) pseudospin reveal Higgs bosons

A controlled dynamical probe measurement of complex order parameter fluctuations of a system may reveal its massive collective excitations. Here, we design dynamical quench protocols to excite independently all ten midgap Higgs bosons in the isotropic Balian-Werthamer state of a spinful p -wave superfluid or superconductor. The analysis is based on microscopic equations of motion of an SO(5) pseudospin, an extension of the usual Bloch equation to a five-dimensional space. Key to these protocols is the realization of quenches that break the rotational symmetry of the kinetic energy and exploit the irreducible representation of the angular momentum J = 2. For perturbative quenches, we find ( nondecaying ) periodic oscillations in time of these Higgs modes. Finally, we present experimental protocols for superconductors (superfluids), with the intention of unveiling the nature of their order parameters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1972

A VTOL translational rate control system study on a six degrees-of-freedom motion simulator

A linearized translational rate system for near hover flight was optimized on a large motion simulator under the constraints of no disturbances and limited control power. Both lateral and longitudinal modes were considered with the primary variables of investigation being control sensitivity and response stiffness and secondarily system damping. Yaw and height control characteristics were represented by an angular rate and acceleration system, respectively. General regions of desired sensitivity and stiffness for the longitudinal and lateral modes were determined under VFR conditions for both the rapid maneuver task and the station keeping/mild maneuver task.

Corliss, L. D.↗

NASA NTRS1983

Discovery of a quasar with a wide angle radio tail in a distant cluster of galaxies

Radio, optical, and X-ray observations of two extended radio sources separated by 99 arc sec (4C 08.66) are reported. Both sources are identified with quasars: z = 0.6227 for the northern source, and z = 0.2282 for the southern. A faint cluster of galaxies is found near the northern source, and the radio structure of this source is interpreted as providing evidence for relative motion between the quasar and the cluster gas, just as Hintzen et al. (1981) interpreted their quasar-cluster association, 3C 275.1. Physical parameters for the core and the extended emission of the northern quasar are estimated. Limits on the magnetic field strength and angular diameter are derived from the radio spectrum of the core and the magnetic field direction in the jet is found from polarization measurements. The morphology of the X-ray source is consistent with inverse-Compton emission from relic radio lobes, but an origin from the quasar itself or cluster gas cannot be ruled out.

Harris, D. E.↗

DOE OSTI2021

Cross-correlation analysis of X-ray photon correlation spectroscopy to extract rotational diffusion coefficients

Coefficients for translational and rotational diffusion characterize the Brownian motion of particles. Emerging X-ray photon correlation spectroscopy (XPCS) experiments probe a broad range of length scales and time scales and are well-suited for investigation of Brownian motion. While methods for estimating the translational diffusion coefficients from XPCS are well-developed, there are no algorithms for measuring the rotational diffusion coefficients based on XPCS, even though the required raw data are accessible from such experiments. In this paper, we propose angular-temporal cross-correlation analysis of XPCS data and show that this information can be used to design a numerical algorithm (Multi-Tiered Estimation for Correlation Spectroscopy [MTECS]) for predicting the rotational diffusion coefficient utilizing the cross-correlation: This approach is applicable to other wavelengths beyond this regime. We verify the accuracy of this algorithmic approach across a range of simulated data.

97 MATHEMATICS AND COMPUTING↗

NASA NTRS1981

Application of unsteady airfoil theory to rotary wings

A clarification is presented on recent work concerning the application of unsteady airfoil theory to rotary wings. The application of this theory may be seen as consisting of four steps: (1) the selection of an appropriate unsteady airfoil theory; (2) the resolution of that velocity which is the resultant of aerodynamic and dynamic velocities at a point on the elastic axis into radial, tangential and perpendicular components, and the angular velocity of a blade section about the deformed axis; (3) the expression of lift and pitching moments in terms of the three components; and (4) the derivation of explicit expressions for the components in terms of flight velocity, induced flow, rotor rotational speed, blade motion variables, etc.

Kaza, K. R. V.↗

NASA NTRS1990

Effect of the Great Attractor on the cosmic microwave background radiation

A map is presented of the anisotropy Delta T/T in cosmic microwave background (CMB) temperature of our region of the universe as viewed by a distant observer, predicted on the basis of the gravitational potential field. This field is calculated in the vicinity of the Local Group of galaxies from the observed peculiar velocities of galaxies under the assumption that the peculiar motions are induced by gravity. If the cosmological density parameter Omega is one, the gravitational potential field of the Great Attractor and surrounding regions produces a maximum Sachs-Wolfe anisotropy of Delta T/T = (1.7 + or - 0.3) x 10 to the -5th on an angular scale of 1 deg. Doppler and adiabatic contributions to this anisotropy are expected to be somewhat larger. If similar fluctuations in the gravitational potential are present elsewhere in the universe, the anisotropy present when the CMB was last scattered should be visible from the earth and should be detectable in current experiments.

Bertschinger, Edmund↗

NASA NTRS1993

Atmospheric holes and small comets

Global images of Earth's UV dayglow as gained with an imaging photometer on board Dynamics Explorer 1 exhibit transient decreases, or atmospheric holes, in the dayglow intensities over areas with diameters about 50 km. Features of these atmospheric holes include (1) preferential motion in the east-to-west direction across the sunlit face of Earth, (2) similar diurnal variations in occurrence rates as those for radar meteors, (3) correlation of the occurrence rates with the nonshower rates as determined with forward scatter radar, and (4) larger angular diameters for these atmospheric holes when the spacecraft approaches Earth during its perigee passes. These atmospheric holes are interpreted in terms of obscuration of the dayglow by water clouds from the disruption and subsequent vaporization of small comets at low altitudes above the atmosphere. Supporting evidence for the existence of these small comets is given by their telescopic sighting at greater altitudes before disruption and the detection of water bursts in Earth's upper atmosphere. The small-comet hypothesis and its relationship to geophysical, lunar, and interplanetary phenomena are discussed.

Frank, L. A.↗

NASA NTRS1994

Numerical simulation of three-dimensional self-gravitating flow

The three-dimensional flow of a self-gravitating fluid is numerically simulated using a Fourier pseudospectral method with a logarithmic variable formulation. Two cases with zero total angular momentum are studied in detail, a 32(exp 3) simulation (Run A) and a 64(exp 3) simulation (Run B). Other than the grid size, the primary differences between the two cases are that Run A modeled atomic hydrogen and had considerably more compressible motion initially than Run B, which modeled molecular hydrogen. ('Compressible motion' is that part of the velocity which has zero curl, but non-zero divergence). The numerical results indicate that gravitational collapse can proceed in a variety of ways. In Run A, collapse led to an elongated tube-like structure, while in Run B, collapse led to a flatter, disk-like structure.

Shebalin, J. V.↗

NASA NTRS2003

The Effect of Surface Topography on the Nonlinear Dynamics of Rossby Waves

Boussinesq convection in rotating systems attracts a sustained attention of the fluid dynamics community, because it has intricate non-linear dynamics (Cross & Hohenberg 1993) and plays an important role in geophysical and astrophysical applications, such as the motion of the liquid outer core of Earth, the Red Spot in Jupiter, the giant cells in the Sun etc. (Alridge et al. 1990). A fundamental distinction between the real geo- and astrophysical problems and the idealized laboratory studies is that natural systems are inhomogeneous (Alridge et al. 1990). Heterogeneities modulate the flow and influence significantly the dynamics of convective patterns (Alridge et al. 1990; Hide 1971). The effect of modulations on pattern formation and transition to turbulence in Boussinesq convection is far from being completely understood (Cross & Hohenberg 1993; Aranson & Kramer 2002). It is generally accepted that in the liquid outer core of the Earth the transport of the angular momentum and internal heat occurs via thermal Rossby waves (Zhang et al. 2001; Kuang & Bloxham 1999). These waves been visualized in laboratory experiments in rotating liquid-filled spheres and concentric spherical shells (Zhang et al. 2001; Kuang & Bloxham 1999). The basic dynamical features of Rossby waves have been reproduced in a cylindrical annulus, a system much simpler than the spherical ones (Busse & Or 1986; Or & Busse 1987). For convection in a cylindrical annulus, the fluid motion is two-dimensional, and gravity is replaced by a centrifugal force, (Busse & Or 1986; Or & Busse 1987). Hide (1971) has suggested that the momentum and heat transport in the core might be influenced significantly by so-called bumps, which are heterogeneities on the mantle-core boundary. To model the effect of surface topography on the transport of momentum and energy in the liquid outer core of the Earth, Bell & Soward (1996), Herrmann & Busse (1998) and Westerburg & Busse (2001) have studied the nonlinear dynamics of thermal Rossby waves in a cylindrical annulus with azimuthally modulated height.

Abarzhi, S. I.↗