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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 1,171 records · Page 65
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NASA NTRS1988

EUVE/XTE orbit decay study

The Explorer Platform (EP) program currently comprises two missions, the Extreme Ultraviolet Explorer (EUVE) and the X-ray Timing Explorer (XTE), each of which consists of a scientific payload mounted to the EP. The EP has no orbit maintenance capability. The EP with the EUVE payload will be launched first. At the end of the EUVE mission, the spacecraft will be serviced by the Space Transportation System (STS), and the EUVE instrument will be exchanged for the XTE. The XTE mission will continue until reentry or reservicing by the STS. Because the missions will be using the EP sequentially, the orbit requirements are unusually constrained by orbit decay rates. The initial altitude must be selected so that, by the end of the EUVE mission (2.5 years), the spacecraft will have decayed to an altitude within the STS capabilities. In addition, the payload exchange must occur at an altitude that ensures meeting the minimum XTE mission lifetime (3 years) because no STS reboost will be available. Studies were performed using the Goddard Mission Analysis System to estimate the effects of mass, cross-sectional area, and solar flux on the fulfillment of mission requirements. In addition to results from these studies, conclusions are presented as to the accuracy of the Marshall Space Flight Center solar flux predictions.

Richon, K.↗
NASA NTRS1988

Lower bound on e+e- decay of massive neutrinos

Astronomical observations of SN1987A, such as the light curve, spectral intensities of lines, the X-ray emissions, etc., constrain the lifetime for the decay of a heavy neutrino 1 MeV less than or equivalent to m sub nu H less than or equal to 50 MeV through nu sub H yields nu sub 1+e(+)+e(-) exceeds 4 x 10 to the 15th exp(-m sub nuH/5MeV) seconds. Otherwise. resulting ionization energy deposits and stronger X-ray emission would have been observed. This coupled with traditional cosmological considerations argues that the lifetime of tau-neutrinos probably exceeds the age of the universe. This in turn would imply the standard cosmological mass bound does apply to nu sub tau, namely m sub nu sub tau less than or equivalent to 100 h squared eV (where h is the Hubble constant in units of 100 km/sec/mpc). The only significant loophole for these latter arguments would be if nu sub tau primarily decays rapidly into particles having very weak interactions.

Cowsik, R.↗
NASA NTRS1988

Cosmic string catalysis of skyrmion decay

The Callan-Witten picture is developed for monopole catalyzed skyrmion decay in order to analyze the corresponding cosmic string scenario. It is discovered that cosmic strings (both ordinary and superconducting) can catalyze proton decay, but that this catalysis only occurs on the scale of the core of the string. In order to do this we have to develop a vortex model for the superconducting string. An argument is also given for the difference in the enhancement factors for monopoles and strings.

Gregory, Ruth↗
NASA NTRS1988

Trajectory analysis for low thrust maneuvers and drag decay in low earth orbit operations

In the 1990s low earth orbit operations are anticipated which will include the Space Station and orbital maneuver vehicle (OMV) serviceable satellites requiring reboost and coordination despite drag decay and oblateness effects. A low thrust targeting algorithm is described applicable to Space Station and the OMV. Tests were made with Space Station reboost requirements and an oblate gravity model. The reboost requirements were determined based on projected station growth, atmospheric models and anticipated flight profiles. The targeting algorithm as well as the algorithm for predicting orbital decay are perturbation formulations of more 'transcendental' systems and are used in interactive personal computer simulations. Performance results and a discussion for the Space Station problems are provided.

Kelly, W. D.↗
NASA NTRS1989

Cosmic strings and baryon decay catalysis

Cosmic strings, like monopoles, can catalyze proton decay. For integer charged fermions, the cross section for catalysis is not amplified, unlike in the case of monopoles. The catalysis processes are reviewed both in the free quark and skyrmion pictures and the implications for baryogenesis are discussed. A computation of the cross section for monopole catalyzed skyrmion decay is presented using classical physics. Also discussed are some effects which can screen catalysis processes.

Gregory, Ruth↗
NASA NTRS1990

Cosmic strings and baryon decay

The current literature is reviewed on baryon decay catalysis by cosmic string. A summary is presented of the main arguments for decay catalysis.

Gregory, Ruth↗
NASA NTRS1989

Does mass accretion lead to field decay in neutron stars?

Adopting the hypothesis of accretion-induced magnetic field decay in neutron stars, the consequent evolution of a neutron star's spin and magnetic field are calculated. The results are consistent with observations of binary and millisecond radio pulsars. Thermomagnetic effects could provide a possible physical mechanism for such accretion-induced field decay.

Shibazaki, N.↗
NASA NTRS1990

Solar neutron decay proton observations in cycle 21

Measurement of the flux and energy spectrum of the protons resulting from the decay of solar flare neutrons gives unique information on the spectrum of neutrons from 5 to 200 MeV. Neutrons from three flares have been observed in this manner during solar cycle 21. The use of the decay protons to determine neutron energy spectra is reviewed, and new and definitive energy spectra are presented for the two large flares on June 3, 1982 and April 25, 1984.

Evenson, Paul↗
NASA NTRS1991

Magnetic flux transport of decaying active regions and enhanced magnetic network

Several series of coordinated observations on decaying active regions and enhanced magnetic network regions on the sun were carried out jointly at Big Bear Solar Observatory and at the Huairou Solar Observing Station of the Bejing Astronomical Observatory in China. The magnetic field evolution in several regions was followed closely for three to seven days. The magnetic flux transport from the remnants of decayed active regions was studied, along with the evolution and lifetime of the magnetic network which defines the boundaries of supergranules. The magnetic flux transport in an enhanced network region was studied in detail and found to be negative. Also briefly described are some properties of moving magnetic features around a sunspot. Results of all of the above studies are presented.

Wang, Haimin↗
NASA NTRS1991

Bragg scattering measurement of atmospheric plasma decay

The decay processes of the plasma layers generated by two intersecting microwave pulses in 1 torr dry air are investigated by Bragg scattering method. The results of measurement show that the electrons decay initially at the three-body attachment rate. However, when enough negative molecule ions are produced through the electron attachment process, the regeneration of electrons via detachment process is increased and eventually balances out the electron attachment loss. The net electron loss is then dominated by the recombination process. The temporal evolution of electron density has also been reproduced by the numerical result of a system of three modal equations for a best fit detachment rate.

Zhang, Y. S.↗
NASA NTRS1991

Test of the decaying dark matter hypothesis using the Hopkins Ultraviolet Telescope

Sciama's hypothesis that the dark matter associated with galaxies, galaxy clusters, and the intergalactic medium consists of tau neutrinos of rest mass 28-30 eV whose decay generates ultraviolet photons of energy roughly 14-15 eV, has been tested using the Hopkins Ultraviolet Telescope flows aboard the Space Shuttle Columbia. A straightforward application of Sciama's model predicts that a spectral line from neutrino decay photons should be observed from the rich galaxy cluster Abell 665 with an SNR of about 30. No such emission was detected. For neutrinos in the mass range 27.2-32.1 eV, the observations set a lower lifetime limit significantly greater than Sciama's model requires.

Davidsen, A. F.↗
NASA NTRS1991

Selective decay and coherent vortices in two-dimensional incompressible turbulence

Numerical solution of two-dimensional incompressible hydrodynamics shows that states of near minimal ratio of enstrophy to energy can be attained in times short compared with the flow decay time, confirming the simplest turbulent selective decay conjecture, and suggesting that coherent vortex structures do not terminate nonlinear processes. After all possible vortex mergers occur, the vorticity attains a particlelike character, suggested by the late-time similarity of the streamlines to Ewald potential contours.

Matthaeus, William H.↗
NASA NTRS1990

Enstrophy budget in decaying compressible turbulence

The interaction of vorticity and shock waves in decaying compressible turbulence is investigated by direct numerical simulation of the Navier-Stokes equation using a spectral method with 64-cubed collocation points. The Taylor microscale Reynolds number decreases from 36 to 17 and the rms Mach number from 0.8 to 0.4 during the decay. It is observed that vorticity is created inside curved shocks through baroclinic interaction and intensified by the compression of fluid elements. Vortex stretching is, on the other hand, dominant outside shocks and is responsible for enhancing the strength of vorticity. A dipole of vorticity is typically created at the vertex of curved shocks, the structure of which is explained in terms of jump relations of velocity derivatives across a curved shock.

Kida, Shigeo↗
NASA NTRS1991

Re-ionization and decaying dark matter

Gunn-Peterson tests suggest that the Universe was reionized after the standard recombination epoch. A systematic treatment is presented of the ionization process by deriving the Boltzmann equations appropriate to this regime. A compact solution for the photon spectrum is found in terms of the ionization ratio. These equations are then solved numerically for the Decaying Dark Matter scenario, wherein neutrinos with mass of order 30 eV radiatively decay producing photons which ionize the intergalactic medium. It was found that the neutrino mass and lifetime are severely constrained by Gunn-Peterson tests, observations of the diffuse photon spectrum in the ultraviolet regime, and the Hubble parameter.

Dodelson, Scott↗
NASA NTRS1992

Discovery of orbital decay in SMC X-1

The results are reported of three observations of the binary X ray pulsar SMC X-1 with the Ginga satellite. Timing analyses of the 0.71 s X ray pulsations yield Doppler delay curves which, in turn, provide the most accurate determination of the SMC X-1 orbital parameters available to date. The orbital phase of the 3.9 day orbit is determined in May 1987, Aug. 1988, and Aug. 1988 with accuracies of 11, 1, and 3.5 s, respectively. These phases are combined with two previous determinations of the orbital phase to yield the rate of change in the orbital period: P sub orb/P sub orb = (-3.34 + or - 0.023) x 10(exp -6)/yr. An interpretation of this measurement and the known decay rate for the orbit of Cen X-3 is made in the context of tidal evolution. Finally, a discussion is presented of the relation among the stellar evolution, orbital decay, and neutron star spinup time scales for the SMC X-1 system.

Levine, A.↗
NASA NTRS1992

High-energy gamma-ray emission from pion decay in a solar flare magnetic loop

The production of high-energy gamma rays resulting from pion decay in a solar flare magnetic loop is investigated. Magnetic mirroring, MHD pitch-angle scattering, and all of the relevant loss processes and photon production mechanisms are taken into account. The transport of both the primary ions and the secondary positrons resulting from the decay of the positive pions, as well as the transport of the produced gamma-ray emission are considered. The distributions of the gamma rays as a function of atmospheric depth, time, emission angle, and photon energy are calculated and the dependence of these distributions on the model parameters are studied. The obtained angular distributions are not sufficiently anisotropic to account for the observed limb brightening of the greater than 10 MeV flare emission, indicating that the bulk of this emission is bremsstrahlung from primary electrons.

Mandzhavidze, Natalie↗
NASA NTRS1992

Can neutrino decay-driven mock gravity save hot dark matter?

The radiative decay of a 30 eV neutrino with a lifetime of order 10 exp 23-24 s has recently been shown to yield a satisfactory explanation of a wide range of problems in astrophysics. In this paper, it is investigated whether the photon flux generated by the radiative decay of a massive neutrino is capable of generating sufficient radiation pressure to cause a 'mock gravitational' collapse of primordial hydrogen clouds. It is shown that when using neutral hydrogen as a source of opacity for mock gravity the time scale for mock gravitational collapse is significantly larger than the expansion time scale. Thus, the model fails as a source of galactic seed perturbations. Furthermore, it is argued that nonlinear feedback mechanisms will be unable to increase the collapse rate of the cloud under mock gravity.

Splinter, Randall J.↗