SEARCH · Engineering Papers

Results for “spin models”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20

All sources NASA NTRS DOE OSTI

NASA NTRS2024

SOLES XII. The Aligned Orbit of TOI-2533 b, a Transiting Brown Dwarf Orbiting an F8-type Star

Brown dwarfs occupy a middle ground in mass space between gaseous giant planets and ultracool dwarf stars, and the characterisation of their orbital orientations may shed light on how these neighbouring objects form. We present an analysis of the Rossiter–McLaughlin effect across the transit of TOI-2533 b, a brown dwarf on a moderately eccentric (e b = 0.2476 ± 0.0090) and wide-separation (a b /R ⋆ = 13.34 ± 0.30) orbit around an F8-type star, using data from the NEID/WIYN spectrograph in combination with archival photometry and radial velocity observations. Spin-orbit analyses of brown dwarfs are relatively rare, and TOI-2533 stands out as the fifth brown dwarf system with a measured spin–orbit constraint. We derive a sky-projected stellar obliquity of λ = −7° ± 14° for TOI-2533 b, finding that the brown dwarf is consistent with spin–orbit alignment. Our joint model also indicates that TOI-2533 b falls near the lower bound of the hydrogen-burning minimum mass range (M b = 74.9 ± 5.3 M Jup ). Ultimately, we find that TOI-2533 b is consistent with formation from disc fragmentation in a primordially spin–orbit aligned orientation, although we cannot rule out the possibility that the system has been tidally realigned during its lifetime.

Thiago Ferreira dos Santos↗

NASA NTRS1992

Dynamics and stability of a tethered centrifuge in low earth orbit

The three-dimensional attitude dynamics of a spaceborne tethered centrifuge for artificial gravity experiments in low earth orbit is analyzed using two different methods. First, the tethered centrifuge is modeled as a dumbbell with a straight viscoelastic tether, point tip-masses, and sophisticated environmental models such as nonspherical gravity, thermal perturbations, and a dynamic atmospheric model. The motion of the centrifuge during spin-up, de-spin, and steady-rotation is then simulated. Second, a continuum model of the tether is developed for analyzing the stability of lateral tether oscillations. Results indicate that the maximum fluctuation about the 1-g radial acceleration level is less than 0.001 g; the time required for spin-up and de-spin is less than one orbit; and lateral oscillations are stable for any practical values of the system parameters.

Quadrelli, B. M.↗

NASA NTRS2018

A NICER Spectrum of MAXI J1535-571: Near-Maximal Black Hole Spin and Potential Disk Warping

We report on a Neutron star Interior Composition Explorer (NICER) observation of the Galactic X-ray binary and stellar-mass black hole candidate, MAXI J1535−571. The source was likely observed in an "intermediate" or "very high" state, with important contributions from both an accretion disk and hard X-ray corona. The 2.3-10 keV spectrum shows clear hallmarks of relativistic disk reflection. Fits with a suitable model strongly indicate a nearmaximal spin parameter of a = cJ/GM(exp 2) = 0.994(2) and a disk that extends close to the innermost stable circular orbit, r/r(sub ISCO) = 1.08(8) (1σ statistical errors). In addition to the relativistic spectrum from the innermost disk, a relatively narrow Fe K emission line is also required. The resolution of NICER reveals that the narrow line may be asymmetric, indicating a specific range of emission radii. Fits with a relativistic line model suggest an inner radius of r = 144 +140/-60 GM/c(exp 2) for the putative second reflection geometry; full reflection models suggest that radii a few times larger are possible. The origin of the narrow line is uncertain, but a warp likely provides the most physically plausible explanation. We discuss our results in terms of the potential for NICER to reveal new features of the inner and intermediate accretion disk around black holes.

Miller, J. M.↗

NASA NTRS2015

Secluded WIMPs, Dark QED with Massive Photons, and the Galactic Center Gamma-Ray Excess

We discuss a particular secluded WIMP dark matter model consisting of neutral fermions as the dark matter candidate and a Proca-Wentzel (PW) field as a mediator. In the model that we consider here, dark matter WIMPs interact with standard model (SM) particles only through the PW field of approximately MeV-multi-GeV mass particles. The interactions occur via a U(1)' mediator, V'(sub mu), which couples to the SM by kinetic mixing with U(1) hypercharge bosons, B'(sub mu). One important difference between our model and other such models in the literature is the absence of an extra singlet scalar, so that the parameter with dimension of mass M(sup 2, sub V) is not related to a spontaneous symmetry breaking. This QED based model is also renormalizable. The mass scale of the mediator and the absence of the singlet scalar can lead to interesting astrophysical signatures. The dominant annihilation channels are different from those usually considered in previous work. We show that the GeV energy gamma-ray excess in the galactic center region, as derived from Fermi-LAT Gamma-ray Space Telescope data, can be attributed to such secluded dark matter WIMPs, given parameters of the model that are consistent with both the cosmological dark matter density and the upper limits on WIMP spin-independent elastic scattering. Secluded WIMP models are also consistent with suggested upper limits on a DM contribution to the cosmic-ray antiproton flux.

Gamma-Rays↗

NASA NTRS1990

Diabatic forcing and initialization with assimilation of cloud and rain water in a forecast model: Methodology

The focus of this part of the investigation is to find one or more general modeling techniques that will help reduce the time taken by numerical forecast models to initiate or spin-up precipitation processes and enhance storm intensity. If the conventional data base could explain the atmospheric mesoscale flow in detail, then much of our problem would be eliminated. But the data base is primarily synoptic scale, requiring that a solution must be sought either in nonconventional data, in methods to initialize mesoscale circulations, or in ways of retaining between forecasts the model generated mesoscale dynamics and precipitation fields. All three methods are investigated. The initialization and assimilation of explicit cloud and rainwater quantities computed from conservation equations in a mesoscale regional model are examined. The physical processes include condensation, evaporation, autoconversion, accretion, and the removal of rainwater by fallout. The question of how to initialize the explicit liquid water calculations in numerical models and how to retain information about precipitation processes during the 4-D assimilation cycle are important issues that are addressed. The explicit cloud calculations were purposely kept simple so that different initialization techniques can be easily and economically tested. Precipitation spin-up processes associated with three different types of weather phenomena are examined. Our findings show that diabatic initialization, or diabatic initialization in combination with a new diabatic forcing procedure, work effectively to enhance the spin-up of precipitation in a mesoscale numerical weather prediction forecast. Also, the retention of cloud and rain water during the analysis phase of the 4-D data assimilation procedure is shown to be valuable. Without detailed observations, the vertical placement of the diabatic heating remains a critical problem.

Raymond, William H.↗

NASA NTRS1994

Spin glasses and error-correcting codes

In this article, we study a model for error-correcting codes that comes from spin glass theory and leads to both new codes and a new decoding technique. Using the theory of spin glasses, it has been proven that a simple construction yields a family of binary codes whose performance asymptotically approaches the Shannon bound for the Gaussian channel. The limit is approached as the number of information bits per codeword approaches infinity while the rate of the code approaches zero. Thus, the codes rapidly become impractical. We present simulation results that show the performance of a few manageable examples of these codes. In the correspondence that exists between spin glasses and error-correcting codes, the concept of a thermal average leads to a method of decoding that differs from the standard method of finding the most likely information sequence for a given received codeword. Whereas the standard method corresponds to calculating the thermal average at temperature zero, calculating the thermal average at a certain optimum temperature results instead in the sequence of most likely information bits. Since linear block codes and convolutional codes can be viewed as examples of spin glasses, this new decoding method can be used to decode these codes in a way that minimizes the bit error rate instead of the codeword error rate. We present simulation results that show a small improvement in bit error rate by using the thermal average technique.

Belongie, M. L.↗

NASA NTRS1975

Mass center estimation of a drag-free satellite

The mass center location of a spinning drag-free satellite can be estimated because there is control required to accelerate the mass center along the axis of spin as long as there is some nutation in the spinning motion. Linear and nonlinear models are compared and observability discussed. Online estimation fails when nutation is damped so an offline mechanization is proposed. A new sensor has been designed to permit greater relative motion than was possible on the drag-free satellite flown in 1972 (JH-1). Experimental laboratory results using a spinning vehicle with the new sensor mounted 30 cm from a spherical air bearing support are presented which confirm earlier simulation results.

Sanz Fernandez De Cordova, S.↗

NASA NTRS2004

Parameter Estimation of Spacecraft Fuel Slosh Model

Fuel slosh in the upper stages of a spinning spacecraft during launch has been a long standing concern for the success of a space mission. Energy loss through the movement of the liquid fuel in the fuel tank affects the gyroscopic stability of the spacecraft and leads to nutation (wobble) which can cause devastating control issues. The rate at which nutation develops (defined by Nutation Time Constant (NTC can be tedious to calculate and largely inaccurate if done during the early stages of spacecraft design. Pure analytical means of predicting the influence of onboard liquids have generally failed. A strong need exists to identify and model the conditions of resonance between nutation motion and liquid modes and to understand the general characteristics of the liquid motion that causes the problem in spinning spacecraft. A 3-D computerized model of the fuel slosh that accounts for any resonant modes found in the experimental testing will allow for increased accuracy in the overall modeling process. Development of a more accurate model of the fuel slosh currently lies in a more generalized 3-D computerized model incorporating masses, springs and dampers. Parameters describing the model include the inertia tensor of the fuel, spring constants, and damper coefficients. Refinement and understanding the effects of these parameters allow for a more accurate simulation of fuel slosh. The current research will focus on developing models of different complexity and estimating the model parameters that will ultimately provide a more realistic prediction of Nutation Time Constant obtained through simulation.

Gangadharan, Sathya↗

NASA NTRS1985

Generalized math model for simulation of high-altitude balloon systems

Balloon systems have proved to be a cost-effective means for conducting research experiments (e.g., infrared astronomy) in the earth's atmosphere. The purpose of this paper is to present a generalized mathematical model that can be used to simulate the motion of these systems once they have attained float altitude. The resulting form of the model is such that the pendulation and spin motions of the system are uncoupled and can be analyzed independently. The model is evaluated by comparing the simulation results with data obtained from an actual balloon system flown by NASA.

Nigro, N. J.↗

NASA NTRS1973

Observations of disk-shaped bodies in free flight at terminal velocity

Ten disk-shaped models of a proposed nuclear heat source module were released from an aircraft and observed by radar. The initial launch attitude, spin rate, and mass of the models were varied. Significant differences were observed in the mode of flight and terminal velocity among models of different mass and launch attitudes. The data were analyzed to yield lift and drag coefficients as a function of Reynolds number. The total sea-level velocity of the models was found to be well correlated as a function of mass per unit frontal area. The demonstrated terminal velocity of the modular disk heat source, about 27 m/sec for this specific design, is only 33% of that of existing heat source designs.

Vorreiter, J. W.↗

NASA NTRS1995

Telemetry down-link Doppler as an attitude sensor for spin stabilized spacecraft

The communications antenna on a spin stabilized spacecraft is seldom located on the spin axis, hence, the antenna is in motion relative to the center of mass of the spacecraft. The Doppler shift observed at the ground or space relay communications receivers will include oscillations whose frequency and amplitude are functions of the motion of the antenna and the attitude of the spacecraft relative to the line of sight (LOS). This functional dependence creates the possibility of estimating attitude parameters from Doppler measurements. This paper presents mathematical models of Doppler oscillations from spinning spacecraft, including the effects of nutation. Algorithms for estimating spin rate, attitude and nutation angle are described. Results of analysis of Doppler tracking of GOES-8 and WIND are also discussed.

Hendry, S. D.↗

NASA NTRS1982

Gravitational spin precession in binary systems

The precessional behavior of a binary system is modeled along the lines of one orbital angular and two spin angular non-dissipatively coupled momenta. It is found that the precessional behavior consists of a periodic nutation superimposed on an overall precession of the system about the axis of total angular momentum. A periodic nutation, superimposed on an overall precession of the system about the axis of total angular momentum, is found to characterize system behavior. It is also shown that the nutation associated with precession in such compact object-containing binaries as the PSR 1913+16 pulsar and the Martin and Rees (1979) model of SS 433 will generally be too small to be observable.

Hamilton, A. J. S.↗

NASA NTRS1982

Current perspectives on emergency spin-recovery systems

The requirements generated by the loss-of-control problems of contemporary and future aircraft are discussed in connection with the development of rocket and parachute technology for spin-recovery systems used in current aircraft. Recovery rockets must be designed to provide the thrust (not impulse) levels required by the specific application, because insufficient thrust will not effect a recovery regardless of its duration. The need for long firing times and a restart capability make liquid rocket systems preferable. Alternatives to the current tail-mounted method of implementing parachute systems include: nose chutes, wing-tip parachutes, dual-bridle and rigid towline systems. Comparative test results for these and the conventional system are given along with the latest dynamic model test technique for spin-recovery rockets.

Whipple, R. D.↗

NASA NTRS1994

On the energetics and number of gamma-ray pulsars

We examine a nearly aligned pulsar model with polar cap acceleration in order to explain the energetics and number of the known gamma-ray pulsars. In this model, the efficiency of converting spin-down luminosity to gamma-ray luminosity increases with decreasing spin-down luminosity, a trend recently emphasized by Ulmer. The predicted gamma-ray flux is proportional to dot P(exp 3/4)/P(exp 5/4) d(exp 2), where P is the period, dot P is the period derivative, and d is the distance to the pulsar. For initial spin periods between approximately equals 10 and 30 ms and neutron star polar magnetic fields between approximately equals 1 and 4 TG, this model accounts for the number and age distribution of the five pulsars which have been observed to emit gamma rays at energies greater than 100 MeV. Implications for pulsar studies are considered.

Dermer, Charles D.↗

NASA NTRS1989

Droplet model for autocorrelation functions in an Ising ferromagnet

The autocorrelation function of Ising spins in an ordered phase is studied via a droplet model. Only noninteracting spherical droplets are considered. The Langevin equation which describes fluctuations in the radius of a single droplet is studied in detail. A general description of the transformation to a Fokker-Planck equations and the ways in which a spectral analysis of that equation can be used to compute the autocorrelation function is given. It is shown that the eigenvalues of the Fokker-Planck operator form (1) a continuous spectrum of relaxation rates starting from zero for d = 2, (2) a continuous spectrum with a finite gap for d = 3, and (3) a discrete spectrum for d greater than 4, where d is the spatial dimensionality. Detailed solutions for various cases are presented.

Tang, Chao↗

NASA NTRS1982

Propagation of spinning acoustic modes in partially choked converging ducts

A computer model based on the wave-envelope technique is used to study the propagation of spinning acoustic modes in converging hard-walled and lined circular ducts carrying near sonic mean flows. The results show that with increasing spinning mode number the intensification of the acoustic signal at the throat decreases for upstream propagation. The influence of the throat Mach number, frequency, boundary-layer thickness, and liner admittance on the propagation of spinning modes is considered.

Nayfeh, A. H.↗

NASA NTRS1940

The aileron as an aid to recovery from the spin

As part of a general investigation by the NACA of factors that affect the spin, the use of the aileron as an aid to recovery from the spin was studied. Tests of 10 different models, covering a wide range of mass distribution, were made in the NACA free-spinning tunnel to determine the effects of a large downward deflection of the outboard aileron and of normal angular deflections of the ailerons upon recovery characteristics. The results indicate that the direction of aileron setting, with or against the spin, which will aid recovery from the spin depends upon the airplane weight distribution. For monoplanes and for biplanes with lower-wing ailerons, ailerons with the spin will be favorable when the weight is distributed chiefly along the fuselage (single-engine airplanes) and ailerons against the spin will be favorable when the weight is distributed chiefly along the wings (multi engine airplanes). Downward movement of the outboard aileron through a large angle will not always be effective in aiding recovery, the effectiveness of such a movement also being dependent upon the weight distribution of the airplane.

Neihouse, A I↗

NASA NTRS2009

Measuring Massive Black Hole Binaries with LISA

The coalescence of two massive black holes produces gravitational waves (GWs) which can be detected by the space-based detector LISA. By measuring these waves, LISA can determine the various parameters which characterize the source. Measurements of the black hole masses and spins will provide information about the growth of black holes and their host galaxies over time. Measurements of a source's sky position and distance may help astronomers identify an electromagnetic counterpart to the GW event. The counterpart's redshift, combined with the GW-measured luminosity distance, can then be used to measure the Hubble constant and the dark energy parameter $w$. Because the potential science output is so high, it is useful to know in advance how well LISA can measure source parameters for a wide range of binaries. We calculate expected parameter estimation errors using the well-known Fisher matrix method. Our waveform model includes the physics of spin precession, as well as subleading harmonics. When these higher-order effects are not included, strong degeneracies between some parameters cause them to be poorly determined by a GW measurement. When precession and subleading harmonics are properly included, the degeneracies are broken, reducing parameter errors by one to several orders of magnitude.

Lang, Ryan N.↗