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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 217 records · Page 12
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NASA NTRS1992

Aspects of parking orbit selection in a manned Mars mission

For any round-trip Mars mission, the selection of a parking orbit at Mars must consider the precession caused by the oblateness of the planet. This precession will affect the departure condition for Earth return and, therefore, the initial mass required in low Earth orbit (LEO). In this investigation, which considers precession effects, minimum initial LEO masses were obtained for parking orbits characterized by having near-equatorial inclinations, high eccentricities, and three-dimensional departure burns (i.e., a burn with an in-plane and an out-of-plane velocity increment component). However, because near-equatorial inclination orbits have poor planetary coverage characteristics, they are not desirable from a science viewpoint. To enhance the potential for satisfying science requirements along with landing site accessibility, a penalty in the initial LEO mass is required. This study shows that there are a set of orbits characterized by low to moderate essentricities (e = 0.2 to 0.5) and nonequatorial inclinations (i = 70 to 140 deg) that reduce this initial LEO mass penalty. Therefore, careful selection of a parking orbit at Mars can enhance the potential for satisfying science requirements with minimal mass penalties.

Desai, Prasun N.↗
NASA NTRS1992

Annual, orbital, and enigmatic variations in tropical oceanography recorded by the Equatorial Atlantic amplifier

Equatorial Atlantic surface waters respond directly to changes in zonal and meridional lower tropospheric winds forced by annual insolation. This mechanism has its maximum effect along the equatorial wave guide centered on 10 deg W. The result is to amplify even subtle tropical climate changes such that they are recorded by marked amplitude changes in the proxy signals. Model realizations, NCAR AGCM and OGCM for 0 Ka and 126 Ka (January and July), and paleoceanographic proxy data show that these winds are also forced by insolation changes at the orbital periods of precession and obliquity. Perhelion in boreal summer produces a strengthened monsoon, e.g., increase meridional and decrease zonal wind stress. This reduces oceanic Ekman divergence and thermocline/nutricline shallowing. The result, in the equatorial Atlantic, is reduced primary productivity and higher euphotic zone temperatures; vice versa for perihelion in boreal winter. Perihelion is controlled by precession. Thus, the dominant period in spectra from a stacked SST record (0-252 Ka BP) at the site of the equatorial Atlantic amplifier is 23 Ky (53 percent of the total variance). This precessional period is coherent (k = 0.920) and in phase with boreal summer insolation. Oscillations of shorter period are present in records from cores sited beneath the amplifier region. These occur between 12.5 and 74.5 Ka BP, when eccentricity modulation of precession is at a minimum. Within this time interval there are 21 cycles with mean periods of 3.0 plus or minus 0.5 Ky. Similar periods have been documented from high latitude regions, e.g., Greenland ice cores from Camp Century. The Camp Century signal in this same time interval contains 21 cycles. A subjective correlation was made between the Camp Century and the equatorial records; the signals were statistically similar, r = 0.722 and k = 0.960.

Mcintyre, Andrew↗
NASA NTRS1993

SCATHA mission termination report

The SCATHA (Spacecraft Charging at High Altitudes) satellite was operated from the Consolidated Space Test Center in Sunnyvale, California from February 1979 to May 1991. It was a spin stabilized vehicle in a highly eccentric orbit that collected data on spacecraft charging. The purpose of such data gathering was to predict and/or model the effects of the Earth's magnetic field on synchronous and near synchronous satellites. During the majority of its lifetime, attitude precession maneuvers were done every 10-15 days to maintain solar panel orientation. Maneuver planning was difficult due to the structural characteristics of SCATHA. It is cylindrically shaped and has seven booms ranging in length from 2 to 50 meters. These precession maneuvers induced predictable nutation that damped out after a few days. Eventually fuel began running low due to these frequent maneuvers. Experiments that had required the spin axis be in the orbit plane had already been turned off or had collected all their data. To increase the vehicle lifetime, the spin axis was moved to ecliptic normal. While this stopped the need for frequent attitude maneuvering (only two per year required now), this movement of the spin axis caused nutation that would not damp out for the remainder of the mission. This phase of the mission, with the ecliptic normal orientation, lasted for approximately three years. Although nutation never damped, data gathering was uninterrupted. In late 1990, when SCATHA's transmitter became seriously degraded, the Air Force decided to turn SCATHA off. This would only be done after the satellite was made 'safe'. The most difficult part of making the vehicle safe was quickly purging the fuel. Several plans were considered. The selected plan was to perform a series of 20 degree attitude precession maneuvers (3 days apart to allow for the worst nutation to damp) until the fuel was depleted. Although this sounded simple, the actual execution proved difficult. This was due to a nearly complete lack of available telemetry data, large undamped motion of the long booms, inadequacies in attitude determination software, and an error in the fuel level calculation software. This paper discusses the various proposed termination plans and execution of the selected one. Attitude determination methodologies, nutation from maneuvers, and effects of the flexible booms on the termination mission are presented and analyzed from a satellite analyst point of view.

Stakkestad, Kjell↗
NASA NTRS1993

On the origin of the Z-shaped narrow-line region in the Seyfert galaxy NGC 3516

A kinematic study has been carried out of the line-emitting gas in the Seyfert galaxy NGC 3516. The existence of two curved filaments in the central 2.5 kpc of this galaxy, which give Z-shaped appearance to its NLR. A precessing twin-jet model in which the line-emitting material is entrained by a precessing radio jet and kept ionized by the nuclear ionization field can explain the kinematic data of the brightest emission rather well. If this model is valid, this would make NGC 3516 the least luminous known active galaxy with a precessing jet. An alternative scenario assumes that the curved inner filaments represent gas entrained by a radio jet which is deflected by ram pressure from the rotation interstellar medium of the galaxy.

Veilleux, Sylvain↗
NASA NTRS1993

The warped disk of Centaurus A in the near-infrared

We present infrared images of Cen A (NGC 5128) in the J, H, and K bands. The infrared morphology is primarily determined by the presence of a thin absorptive warped disk. By integrating the light of the underlying prolate galaxy through such a disk, we construct models which we compare with infrared and X-ray data. The geometry of the warped disk needed to fit the IR data is consistent with a warped disk which has evolved as a result of differential precession in a prolate potential. The disk has an inclination, with respect to the principal axis of the underlying elliptical galaxy, that is higher at larger radii than in the inner region. A scenario is proposed where a small gas-rich galaxy infalling under the force of dynamical friction is tidally stripped. Stripping occurs at different times during its infall. The orientation of the resulting gas disk depends upon the angular momentum of the infalling galaxy. We find that the resulting precession angle of the disk is well described by the precession model, but that the inclination angle may vary as a function of radius. We propose an orbit for the infalling galaxy that is consistent with the geometry of the warped disk needed to fit our infrared data, and rotation observed in the outer part of the galaxy.

Quillen, A. C.↗
NASA NTRS1993

Compressibility effects on rotor forces in the leakage path between a shrouded pump impeller and its housing

A modified approach to Childs' previous work on fluid-structure interaction forces in the leakage path between an impeller shroud and its housing is presented in this paper. Three governing equations consisting of continuity, path-momentum, and circumferential-momentum equations were developed to describe the leakage path inside a pump impeller. Radial displacement perturbations were used to solve for radial and circumferential force coefficients. In addition, impeller-discharge pressure disturbances were used to obtain pressure oscillation responses due to precessing impeller pressure wave pattern. Childs' model was modified from an incompressible model to a compressible barotropic-fluid model (the density of the working fluid is a function of the pressure and a constant temperature only). Results obtained from this model yielded interaction forces for radial and circumferential force coefficients. Radial and circumferential forces define reaction forces within the impeller leakage path. An acoustic model for the same leakage path was also developed. The convective, Coriolis, and centrifugal acceleration terms are removed from the compressible model to obtain the acoustics model. A solution due to impeller discharge pressure disturbances model was also developed for the compressible and acoustics models. The results from these modifications are used to determine what effects additional perturbation terms in the compressible model have on the acoustic model. The results show that the additional fluid mechanics terms in the compressible model cause resonances (peaks) in the force coefficient response curves. However, these peaks only occurred at high values of inlet circumferential velocity ratios greater than 0.7. The peak pressure oscillation was shown to occur at the wearing ring seal. Introduction of impeller discharge disturbances with n = 11 diametral nodes showed that maximum peak pressure oscillations occurred at nondimensional precession frequencies of f = 6.4 and f = 7.8 for this particular pump. Bolleter's results suggest that for peak pressure oscillations to occur at the wearing ring seal, the nondimensional excitation frequency should be on the order of f = 2.182 for n = 11. The resonances found in this research do not match the excitation frequencies predicted by Bolleter. At the predicted peak excitation frequencies given by Bolleter, the compressible model shows an attenuation of the pressure oscillations at the seal exit. The compressibility of the fluid does not have a significant influence on the model at low values of nondimensional excitation frequency. At high values of nondimensional frequency, the effects of compressibility become more significant. For the acoustic analysis, the convective, Coriolis, and centrifugal acceleration terms do affect the results to a limited extent for precession excitation and to a large extent for a pressure excitation when the fluid operates at relatively high Mach numbers.

Cao, Nhai The↗
NASA NTRS2003

What is the Time Scale for Orbital Forcing of the Martian Water Cycle?

Calculation of the periodic variations in the martian orbital parameters by Ward and subsequent refinements to the theory have inspired numerous models of variation of the martian water cycle. Most of these models have focused on variations in planetary obliquity on a both a short-term (110 kyr) time scale as well as larger oscillations occuring over millions of years. To a lesser extent, variations in planetary eccentricity have also been considered. The third and fastest mode of variation, the precession of the longitude of perihelion, has generally been deemphasized because, among the three parameters, it is the only one that does not change the integrated annual insolation. But as a result of this precession, the asymmetry in peak summer insolation between the poles exceeds 50%, with the maximum cycling between poles every 25.5 kyrs. The relative contribution of these different elements to orbital forcing of climate takes on particular importance in the context of apparently recent waterrelated features such as gullies or polar layered deposits (PLD). Christensen, for example, recently indentified mantling of heavily gullied crater walls as residual dust-covered snow deposits that were responsible for the formation of the gullies in a previous epoch. Christensen assumed that the snow was originally deposited at a period of high obliquity which was stabilized against sublimation by a lag deposit of dust. It is suggested here that not obliquity, but the shortterm oscillations associated with precession of the perihelion may play the dominant role in the formation of gullies, major strata in the polar layered deposits (PLD), and other water-related features.

M H Hecht↗
NASA NTRS2004

Fine-Tuning the Accretion Disk Clock in Hercules X-1

RXTE ASM count rates from the X-ray pulsar Her X-1 began falling consistently during the late months of 2003. The source is undergoing another state transition similar to the anomalous low state of 1999. This new event has triggered observations from both space and ground-based observatories. In order to aid data interpretation and telescope scheduling, and to facilitate the phase-connection of cycles before and after the state transition, we have re-calculated the precession ephemeris using cycles over the last 3.5 years. We report that the source has displayed a different precession period since the last anomalous event. Additional archival data from CGRO suggests that each low state is accompanied by a change in precession period and that the subsequent period is correlated with accretion flux. Consequently our analysis reveals long-term accretion disk behaviour which is predicted by theoretical models of radiation-driven warping.

Still, M.↗
NASA NTRS2004

Measurement of Gravitational Spin-Orbit Coupling in a Binary Pulsar System

In relativistic gravity, a spinning pulsar will precess as it orbits a compact companion star. We have measured the effect of such precession on the average shape and polarization of the radiation from PSR B1534+12. We have also detected, with limited precision, special-relativistic aberration of the revolving pulsar beam due to orbital motion. Our observations fix the system geometry, including the misalignment between the spin and orbital angular momenta, and yield a measurement of the precession timescale consistent with the predictions of General Relativity.

Stairs, I. H.↗
NASA NTRS1996

Classical Spin-Orbit Coupling and Periastron Advance in a Binary Pulsar

We report on radio timing observations of PSR J0045-7319, and eccentric pulsar/B star 51-day binary in the Small Magellanic Cloud. Significant deviations from a simple Keplerian orbit, observed as precessions of the periastron longitude and orbital plane, are identified with classical spin-orbit coupling and apsidal advance, for the fist time in a binary pulsar. Both precessions result from the B star's rotationally-induced gravitational quadropole moment, however, the orbital plane precession requires the B star's spin axis to be inclined with respect to the orbital angular momentum. We constrain this inclination angle (theta) to be 25(deg) <(theta)<41(deg). Under the conventional assumption that the pre-supernova angular momenta were aligned, our observations provide the most direct evidence yet for an asymmetric supernova.

radio timing psr j0045-7319 pulsars binary pulsars↗
NASA NTRS1995

Spin-Orbit Interaction in Neutron Star/Main Sequence Binaries and Implications for Pulsar Timing

The spin-induced quadrupole moment of a rapidly rotating star changes the orbital dynamics in a binary system, giving rise to advance (or regression) of periastron and precession of the orbital plane. We show that these effects are important in the recently discovered radio pulsar/mail sequence star binary system PSR J0045-7319, and reliably account for the observed peculiar timing residuals. Precise measurements of the apsidal motion and orbital plane precession can yield valuable information on the internal structure and rotation of the star. The detection of orbital precession implies that the spin of the companion star is not aligned with the orbital angular momentum, and suggests that the supernova gave the pulsar a kick out of the original orbital plane. Excitations of g-mode oscillations near periastron (the dynamical tide) can induce measurable changes in the orbital period and eccentricity at each passage for this system. We also discuss the spin-orbit coupling effects for the accreting X-ray pulsars and the other know radio pulsar/main sequence binary, PSR B1259-63.

neutron stars↗
NASA NTRS2010

Reducing Field Distortion in Magnetic Resonance Imaging

A concept for a magnetic resonance imaging (MRI) system that would utilize a relatively weak magnetic field provides for several design features that differ significantly from the corresponding features of conventional MRI systems. Notable among these features are a magnetic-field configuration that reduces (relative to the conventional configuration) distortion and blurring of the image, the use of a superconducting quantum interference device (SQUID) magnetometer as the detector, and an imaging procedure suited for the unconventional field configuration and sensor. In a typical application of MRI, a radio-frequency pulse is used to excite precession of the magnetic moments of protons in an applied magnetic field, and the decaying precession is detected for a short time following the pulse. The precession occurs at a resonance frequency proportional to the strengths of the magnetic field and the proton magnetic moment. The magnetic field is configured to vary with position in a known way; hence, by virtue of the aforesaid proportionality, the resonance frequency varies with position in a known way. In other words, position is encoded as resonance frequency. MRI using magnetic fields weaker than those of conventional MRI offers several advantages, including cheaper and smaller equipment, greater compatibility with metallic objects, and higher image quality because of low susceptibility distortion and enhanced spin-lattice-relaxation- time contrast. SQUID MRI is being developed into a practical MRI method for applied magnetic flux densities of the order of only 100 T

Eom, Byeong Ho↗
NASA NTRS2010

EPR Imaging at a Few Megahertz Using SQUID Detectors

An apparatus being developed for electron paramagnetic resonance (EPR) imaging operates in the resonance-frequency range of about 1 to 2 MHz well below the microwave frequencies used in conventional EPR. Until now, in order to obtain sufficient signal-to-noise radios (SNRs) in conventional EPR, it has been necessary to place both detectors and objects to be imaged inside resonant microwave cavities. EPR imaging has much in common with magnetic resonance imaging (MRI), which is described briefly in the immediately preceding article. In EPR imaging as in MRI, one applies a magnetic pulse to make magnetic moments (in this case, of electrons) precess in an applied magnetic field having a known gradient. The magnetic moments precess at a resonance frequency proportional to the strength of the local magnetic field. One detects the decaying resonance-frequency magnetic- field component associated with the precession. Position is encoded by use of the known relationship between the resonance frequency and the position dependence of the magnetic field. EPR imaging has recently been recognized as an important tool for non-invasive, in vivo imaging of free radicals and reduction/oxidization metabolism. However, for in vivo EPR imaging of humans and large animals, the conventional approach is not suitable because (1) it is difficult to design and construct resonant cavities large enough and having the required shapes; (2) motion, including respiration and heartbeat, can alter the resonance frequency; and (3) most microwave energy is absorbed in the first few centimeters of tissue depth, thereby potentially endangering the subject and making it impossible to obtain adequate signal strength for imaging at greater depth. To obtain greater penetration depth, prevent injury to the subject, and avoid the difficulties associated with resonant cavities, it is necessary to use lower resonance frequencies. An additional advantage of using lower resonance frequencies is that one can use weaker applied magnetic fields: For example, for a resonance frequency of 1.4 MHz, one needs a magnetic flux density of 0.5 Gauss approximately the flux density of the natural magnetic field of the Earth.

Hahn, Inseob↗
NASA NTRS2011

Measuring Parameters of Massive Black Hole Binaries with Partially Aligned Spins

The future space-based gravitational wave detector LISA will be able to measure parameters of coalescing massive black hole binaries, often to extremely high accuracy. Previous work has demonstrated that the black hole spins can have a strong impact on the accuracy of parameter measurement. Relativistic spin-induced precession modulates the waveform in a manner which can break degeneracies between parameters, in principle significantly improving how well they are measured. Recent studies have indicated, however, that spin precession may be weak for an important subset of astrophysical binary black holes: those in which the spins are aligned due to interactions with gas. In this paper, we examine how well a binary's parameters can be measured when its spins are partially aligned and compare results using waveforms that include higher post-Newtonian harmonics to those that are truncated at leading quadrupole order. We find that the weakened precession can substantially degrade parameter estimation, particularly for the "extrinsic" parameters sky position and distance. Absent higher harmonics, LISA typically localizes the sky position of a nearly aligned binary about an order of magnitude less accurately than one for which the spin orientations are random. Our knowledge of a source's sky position will thus be worst for the gas-rich systems which are most likely to produce electromagnetic counterparts. Fortunately, higher harmonics of the waveform can make up for this degradation. By including harmonics beyond the quadrupole in our waveform model, we find that the accuracy with which most of the binary's parameters are measured can be substantially improved. In some cases, the improvement is such that they are measured almost as well as when the binary spins are randomly aligned.

Lang, Ryan N.↗
NASA NTRSDate not supplied

Perturbations, TTVs & the (Un)reliability of Ephemerides of Kepler Planets

Fractional uncertainties quoted for orbital periods of the vast majority of planet candidates listed in recent Kepler catalogs are $<10^{-5}$, with values $\sim 10^{-6}$ (corresponding to 2 minutes per 4 years) being typical. These small uncertainties suggest ephemeris predictions for most Kepler planets are robust for decades to come. Tabulated periods list formal uncertainties in the mean times between midpoints of successive transits during the time interval in which transits were observed. However, transit timing variations (TTVs) produce errors in estimates of some planets’ orbital periods that need to be accounted for in certain dynamical investigations and ephemeris predictions. Periodic TTVs with timescales short compared to the interval of Kepler observations largely average out and do not produce significant errors in estimates of orbital periods. TTVs with timescales comparable to the interval of Kepler observations have been fit for dozens of Kepler planet candidates to estimate long-term average orbital periods (Holczer et al. 2016, ApJS 225, 9), and more detailed dynamical models have been used to estimate long-term average periods of a small number of well-studied planets. Most Kepler planets that show large TTVs are near mean-motion orbital resonances with other planets. The largest effect for planets moderately close to two-body resonances are due to rotation of the forced eccentricity vector by resonant perturbations; the timescale for this precession is typically short, so the variations tend to average out. Libration of planets locked in resonances typically occurs on timescales longer than the Kepler baseline, but few Kepler planets appear to be resonantly-locked. The more general but smaller (during the era of Kepler observations) effect is caused by secular precession of the planets' free eccentricities usually has a period much longer than the baseline of the Kepler observations, so it is not accounted for in estimates of mean periods or uncertainties. This precession causes a discrepancy between Kepler era mean orbital period and long-term mean orbital period can exist even for planets having TTVs that are too small to be observable during the epoch of Kepler observations.

Kepler↗
DOE OSTI2025

The Juno mission as a probe of long-range new physics

Orbits of celestial objects, especially the geocentric and heliocentric ones, have been well explored to constrain new long-range forces beyond the Standard Model (SM), often referred to as fifth forces. In this paper, for the first time, we apply the motion of a spacecraft around Jupiter to probe fifth forces that don’t violate the equivalence principle. The spacecraft is the Juno orbiter, and ten of its early orbits already allow a precise determination of the Jovian gravitational field. We use the shift in the precession angle as a proxy to test non-gravitational interactions between Juno and Jupiter. Requiring that the contribution from the fifth force does not exceed the uncertainty of the precession shift inferred from data, we find that a new parameter space with the mass of the fifth-force mediator around 10 −14 eV is excluded at 95% C.L.

new light particles↗
DOE OSTI2024

Evanescent and inertial-like waves in rigidly rotating odd viscous liquids

Three-dimensional non-rotating odd viscous liquids give rise to Taylor columns and support axisymmetric inertial-like waves ( J. Fluid Mech ., vol. 973, 2023, A30). When an odd viscous liquid is subjected to rigid-body rotation however, there arise in addition a plethora of other phenomena that need to be clarified. In this paper, we show that three-dimensional incompressible or two-dimensional compressible odd viscous liquids, rotating rigidly with angular velocity 𝛺, give rise to both oscillatory and evanescent inertial-like waves or a combination thereof (which we call of mixed type) that can be non-axisymmetric. By evanescent, we mean that along the radial direction, typically when moving away from a solid boundary, the velocity field decreases exponentially. These waves precess in a prograde or retrograde manner with respect to the rotating frame. The oscillatory and evanescent waves resemble respectively the body and wall-modes observed in (non-odd) rotating Rayleigh–Bénard convection ( J. Fluid Mech ., vol. 248, 1993, pp. 583–604). We show that the three types of waves (wall, body or mixed) can be classified with respect to pairs of planar wavenumbers 𝜅 which are complex, real or a combination, respectively. Experimentally, by observing the precession rate of the patterns, it would be possible to determine the largely unknown values of the odd viscosity coefficients. This formulation recovers as special cases recent studies of equatorial or topological waves in two-dimensional odd viscous liquids which provided examples of the bulk–interface correspondence at frequencies 𝜔 < 2⁢𝛺. We finally point out that the two- and three-dimensional problems are formally equivalent. Their difference then lies in the way data propagate along characteristic rays in three dimensions, which we demonstrate by classifying the resulting Poincaré–Cartan equations.

Mechanics↗
DOE OSTI2025

Gas and dust dynamics in γ Cephei-type disks

Context. Giant planets are observed orbiting the primary stars of close binary systems. Such planets may have formed in compact circumprimary disks, which once surrounded these stars, under conditions much different than those encountered around single stars. Aims. In order to quantify the effects of the strong gravitational perturbations exerted on circumprimary disk material, the three-dimensional (3D) dynamics of gas and dust in orbit around the primary star of a compact and eccentric binary system was modeled by applying the stellar and orbital parameters of γ Cephei, a well-known system that can be representative of a class of close binaries. Methods. Circumprimary gas was approximated as an Eulerian viscous and compressible fluid and modeled by means of 3D hydrodynamical simulations, assuming locally isothermal conditions in the medium around the primary star. Dust grains were modeled as Lagrangean particles, subjected to gravity and aerodynamic drag forces. Models that include a giant planet were also considered. Results. Models indicate that spiral density waves excited around pericenter passage propagate toward the inner boundary of the disk, through at least a few pressure scale-heights from the mid-plane, inducing radial and vertical mixing in the gas. However, perturbations imparted to gas, both in terms of eccentricity and precession, are far weaker than previously estimated by two-dimensional (2D) simulations. Models predict small eccentricities, ≲0.03, and slow retrograde precession. The addition of a giant planet does not change the low eccentricity state of the disk. The parameters applied to the disk would lead to the formation of a massive planet, many times the mass of Jupiter, in agreement with some observations. Micron to mm-size dust grains are well coupled to the gas, resulting in similar dynamics and statistically similar distributions of orbital elements. The planet only affects the dust distributions locally. In agreement with outcomes of recent 2D models, the lifetime of an isolated circumprimary disk would be brief, ~10 5 years, because of its compact nature, requiring a long-term external supply of mass to allow for the in situ formation of a giant planet.

79 ASTRONOMY AND ASTROPHYSICS↗