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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Bulk Hydrogen Content OF High-Silica Rocks in Gale Crater With the Active Dynamic Albedo of Neutrons Experiment

The Mars Science Laboratory (MSL) Curiosity rover recently traversed over plateaus of mafic aeolian sandstones (the 'Stimson' formation) that overlie mudstones (the 'Murray' formation). Within the Stimson formation we observed many lighter-toned, halo-forming features, that are potentially indicative of fluid alteration (see Fig. 1). These halo features extend for tens of meters laterally and are approx.1 meter wide. The halo features were characterized by Curiosity's geochemical instruments: Alpha Proton X-Ray Spectrometer (APXS), Chemin, Chemcam and Sample Analysis at Mars (SAM). With respect to the host (unaltered) Stimson rocks, fracture halos were significantly enriched in silicon and low in iron [1]. Changes in hydrogen abundance (due to its large neutron scattering cross section) greatly influence the magnitude of the thermal neutron response from the Dynamic Albedo of Neutrons (DAN) instrument [2]. There are also some elemental species, e.g. chlorine, iron, and nickel, that have significant microscopic neutron absorption cross sections. These elements can be abundant and variable results provide a useful estimate of the lower bound for bulk hydrogen content (assuming a homogeneous distribution).

Gabriel, T. S. J.↗
NASA NTRS2016

Evidence for the Kinematic Sunyaev-Zel'dovich Effect with the Atacama Cosmology Telescope and Velocity Reconstruction from the Baryon Oscillation Spectroscopic Survey

We use microwave temperature maps from two seasons of data from the Atacama Cosmology Telescope at 146 GHz, together with the "Constant Mass" CMASS galaxy sample from the Baryon Oscillation Spectroscopic Survey to measure the kinematic Sunyaev-Zel'dovich (kSZ) effect over the redshift range z1/4 0.4-0.7. We use galaxy positions and the continuity equation to obtain a reconstruction of the line-of-sight velocity field. We stack the microwave temperature at the location of each halo, weighted by the corresponding reconstructed velocity. We vary the size of the aperture photometry filter used, thus probing the free electron profile of these halos from within the virial radius out to three virial radii, on the scales relevant for investigating the missing baryons problem. The resulting best fit kSZ model is preferred over the no-kSZ hypothesis at 3.3 and 2.9 sigma for two independent velocity reconstruction methods, using 25,537 galaxies over 660 square degrees. The data suggest that the baryon profile is shallower than the dark matter in the inner regions of the halos probed here, potentially due to energy injection from active galactic nucleus or supernovae. Thus, by constraining the gas profile on a wide range of scales, this technique will be useful for understanding the role of feedback in galaxy groups and clusters. The effect of foregrounds that are uncorrelated with the galaxy velocities is expected to be well below our signal, and residual thermal Sunyaev-Zel'dovich contamination is controlled by masking the most massive clusters. Finally, we discuss the systematics involved in converting our measurement of the kSZ amplitude into the mean free electron fraction of the halos in our sample.

Schaan, Emmanuel S.↗
NASA NTRSDate not supplied

TPSAS-NF1676L-32105-DND

NASA Langley Research Center is developing the High-Altitude Lidar Observatory (HALO) system to address the observational needs of NASA’s weather, climate, carbon cycle, and atmospheric composition focus areas. HALO is a multi-function airborne lidar being developed to measure atmospheric H2O and CH4 mixing ratios and aerosol/cloud/ocean optical properties using the Differential Absorption Lidar (DIAL) and High Spectral Resolution Lidar (HSRL) techniques, respectively. To respond to a wide range of airborne process studies, HALO can be rapidly reconfigured to provide either CH4 DIAL+HSRL, H2O DIAL+HSRL, or CH4 DIAL+H2O DIAL measurements using three different laser transmitters. During spring 2018 NASA Langley demonstrated the world’s first combined airborne CH4 DIAL and HSRL measurements from the Langley King Air aircraft during four test flights. The HALO methane configuration also participated in the Long Island Sound Tropospheric Ozone Study (LISTOS) air quality field campaign on the NASA B200 aircraft. The flown instrument configuration employed the DIAL technique at 1645 nm for column and multi-layer range resolved measurements of CH4 concentrations, and the HSRL technique at 532 nm to make independent, unambiguous retrievals of aerosol extinction and backscatter. It also employed the standard backscatter technique at 1064 nm and is polarization-sensitive at the 1064/532 nm wavelengths. The addition of the HSRL channels provides context to the airborne CH4 DIAL measurements such as source attribution, transport, and vertical mixing through mixed layer height retrievals, as well as providing the critical capability to validate aerosol induced biases from passive space-borne measurements of column CH4. In this presentation we focus on the instrument capabilities, initial CH4 measurements over oil and gas production sites in coordination with the ACT-America campaign, CH4 signatures over the Long Island Sound domain during the LISTOS campaign, and prospects for future airborne campaigns with cohosted payloads consisting of active and passive sensors.

Rory Barton-Grimley↗
NASA NTRSDate not supplied

Overview of the Lunar Transit Trajectory Performed by the Power and Propulsion Element of NASA’s Gateway

NASA has committed to returning to the moon, landing the first woman and the next man on its surface. To support a sustained lunar presence, NASA is designing an orbital platform to be assembled in an orbit near the moon called the Near Rectilinear Halo Orbit (NRHO). This platform is known as the Gateway and its purpose it to support missions primarily to the lunar south pole. As NASA continues to study ways to reduce the cost of lunar exploration, a simplification implemented in 2020combinedthe first two elements of the Gateway, the Power and Propulsion Element (PPE) and NASA’s Habitation and Logistics Outpost (HALO), onto a single commercial launch vehicle (CLV). When launched together, the PPE and HALO make up the first two elements of NASA’s Gateway and exceed the performance capacity of commercially available launch vehicles to deliver directly to the moon. The delivery of the Gateway is enabled by and takes advantage of the high efficiency of the PPEs high-power Solar Electric Propulsion (SEP) system to transfer a significant starting mass from an initial Earth orbit to final insertion into the NRHO. The PPE is a 50-kW class high power solar electric propulsion stage comprised of two different types of electric thruster strings. The SEP system is operated in two different modes, a high thrust and high Isp (specific impulse), to both maximize the final delivered mass and attempt to minimize the time spent in the Van Allen Belts early in the transit trajectory. Additionally, this SEP system brings the capability to the assembled Gateway for transfer between orbits in cislunar space. This paper captures the preliminary low thrust lunar transfer reference trajectory to be flown by the PPE it delivers itself and HALO via a spiral trajectory from launch vehicle insertion to insertion into the NRHO as well as a preliminary reference round trip transfer of the Gateway from the NRHO to a Distant Retrograde Orbit (DRO) using the PPE. Once in its final NRHO, the Gateway is being designed to enable long duration human and robotic exploration of the lunar south pole as a precursor to Mars. The Gateway’s low thrust lunar transit trajectory is envisioned to prove out the application of and flight of a high-power SEP system as a demonstration of technologies applicable to the enabling of future human space exploration.

human exploration↗
NASA NTRSDate not supplied

Mission Design Strategies for Rendezvous and Servicing of Sun-Earth Libration Point Missions

With the launch of the James Webb Space Telescope (JWST) and future launches of the Roman Space Telescope (RST) and larger telescopes such as the proposed Habitable Worlds Observatory (HWO), the questions of where and how to rendezvous to enable servicing of these telescope missions arise. To aid in determining the allowable locations to rendezvous for servicing from a trajectory design approach, our previous research and analysis has shown feasible transfer trajectories between the Sun-Earth Libration L2 region (Quasi-Halo orbit) and the Earth Moon vicinity (Distant Retrograde Orbit (DRO), Quasi-Halo Orbit, Halo Orbit, and Near Rectilinear Halo Orbit (NRHO)), along with the related transfer constraints and the corresponding total fuel mass costs. We now focus on operational-like optimal scenarios for these transfers to complete a rendezvous to permit servicing at various Libration orbit locations. In this paper, we address how operational navigation and maneuver execution uncertainties impact the rendezvous timing and fuel mass (via ΔV). While optimization techniques are applied to ensure minimal ΔVs, we also analyze various transfer trajectory durations and rendezvous arrival geometries. The analysis presented includes dynamical system approaches and applies optimization through several tools including the Adaptive Trajectory Design (ATD) module as an initial guess, numerical computation using the General Mission Analysis Tool (GMAT) and Systems Tool Kit (STK) with higher fidelity perturbation modeling, and recently developed optimization tools that incorporate dynamical systems directly into the optimization process. Transfer trajectory options examined include a direct transfer from Earth versus departures from the previously examined Earth-Moon regime orbits, e.g. NRHOs and DROs. A return from Sun-Earth to lunar vicinity for a complete servicing after a rendezvous in Sun-Earth orbit is also considered. The resultant ΔV’s for each scenario is provided with discussions on various transfer trades, rendezvous considerations, and orbital limitations from the dynamical systems. A Poincare-like mapping of trajectory and rendezvous conditions categorize feasible and optimum transfer approaches, dependent on Sun-Earth orbit mission parameters. The focus of this research addresses questions for upcoming trades regarding servicing options for current and future Sun-Earth L1 and L2 missions. By doing a comprehensive analysis approach (dynamical systems + high fidelity optimization with true operational constraints), this paper will serve as a guide for mission architecture and operational trade considerations.

Maneuver Design↗
NASA NTRS1976

Encounters of spherical galaxies. I - Galaxy models with one stellar population. II - Galaxy models with two stellar populations

Close encounters between two spherical galaxies of equal size and consisting of only one stellar population are calculated using models of elliptical galaxies constructed according to King's (1966) method. The mass loss and the change in internal energy are computed under the assumption that the stars do not change their velocity or density distributions during the encounters. The results for a specific case are compared with the calculations of Gallagher and Ostriker (1972), who employed the observed brightness distribution and the derived density distribution of the E1 galaxy NGC 3379. For models with one stellar population, the results suggest that the radius of a galactic halo would have to be at least 200 kpc for appreciable mass loss to occur over the history of a galaxy in a rich cluster. The calculations are then extended to include a halo population characterized by a high central velocity dispersion. In this case, it is found that the halo population of sufficiently large galaxies can be dispersed without appreciably affecting the main population. It is suggested that the missing mass of many clusters of galaxies may be located in an intergalactic sea of faint stars making up an envelope for the centrally located gE galaxies.

Biermann, P.↗
NASA NTRS1976

Consequences of a lifetime greater than 10 to the 7th power years for galactic cosmic rays

The implications of recent determinations of the cosmic-ray lifetime are discussed. It is concluded that the observations are consistent with a 'dynamical halo' model in which cosmic rays are confined in an outward-moving galactic halo by self-generated hydromagnetic waves. Alternative models which do not incorporate a halo, but which have the cosmic rays propagate in regions of reduced density in the galactic disk, are also briefly discussed.

Jokipii, J. R.↗
NASA NTRS1979

Contingency study for the third international Sun-Earth Explorer (ISEE-3) satellite

The third satellite of the international Sun-Earth Explorer program was inserted into a periodic halo orbit about L sub 1, the collinear libration point between the Sun and the Earth-Moon barycenter. A plan is presented that was developed to enable insertion into the halo orbit in case there was a large underperformance of the Delta second or third stage during the maneuver to insert the spacecraft into the transfer trajectory. After one orbit of the Earth, a maneuver would be performed near perigee to increase the energy of the orbit. A relatively small second maneuver would put the spacecraft in a transfer trajectory to the halo orbit, into which it could be inserted for a total cost within the fuel budget. Overburns (hot transfer trajectory insertions) were also studied.

Dunham, D. W.↗
NASA NTRS1979

Primordial inhomogeneities in the expanding universe. II - General features of spherical models at late times

This paper studies the density profile that forms around a spherically symmetric bound central core immersed in a homogeneous-background k = 0 or k = -1 Friedmann-Robertson-Walker cosmological model, with zero pressure. Although the density profile in the linearized regime is almost arbitrary, in the nonlinear regime certain universal features of the density profile are obtained that are independent of the details of the initial conditions. The formation of 'halos' ('holes') with densities greater than (less than) the average cosmological density is discussed. It is shown that in most regions 'halos' form, and universal values are obtained for the slope of the ln (density)-ln (radius) profile in those 'halos' at late times, independently of the shape of the initial density profile. Restrictions are derived on where it is possible for 'holes' to exist at late times and on how such 'holes' must have evolved.

Olson, D. W.↗
NASA NTRS1982

Analysis of the ultraviolet spectrum of RWT 152 - A subluminous O star with a main-sequence visual spectrum

Observations of luminous early-type stars provide one of the most sensitive ways to detect the low density gas of the interstellar medium. As part of an ongoing program studying the gas in the galactic halo, stars believed to be outside the plane of the Milky Way have been observed. In the interest of studying the halo gas in additional directions, a search has been conducted for candidate stars which are bright enough to be observable with the International Ultraviolet Explorer Satellite (IUE) high dispersion mode and far enough from the galactic plane to provide a long line of sight through the halo gas. One such star is star 152 in the catalog of Rubin, Westpfahl, and Tuve (1974), which is called RWT 152 in the investigation. The IUE spectra of RWT 152 were obtained and analyzed. It appears that RWT 152 is not a young massive star, but rather a low mass object in an advanced stage of evolution.

Ebbets, D. C.↗
NASA NTRS1983

Analysis of optical imagery for Seyfert's Sextet and VV 172

Seyfert's Sextet and VV 172, 5-m photographs have been subjected to image processing to yield field-galaxy density analysis, redshift-scaled imagery, interaction morphology display and enhancement, color difference imagery,modeling of the VV 172 halo, and image texture analysis of the spiral galaxy components of Seyfert's Sextet. An effort is made to evaluate the evidence for physical association of the discordant redshift components of these groups. An especially noteworthy characteristic of the groups is their extended luminous halos. The halo of VV 172 cannot be explained by the overlapping envelopes of galaxies with normal luminosity profiles, and the high redshift spiral galaxy in the Sextet is found to have an asymmetric internal structure and associated filament which suggest gravitational perturbation by the other members of the group.

Sulentic, J. W.↗
NASA NTRS1983

Interstellar absorption lines in the spectrum of 3C 273

Absorption lines near the rest wavelengths of the Si IV doublet (wavelengths 1393.76, 1402.77) with equivalent widths 533 and 235 mA are reported in the spectrum of QSO 3C 273. The profiles show the nature of hot gas along a high-latitude (b = 64 deg) line of sight through our entire halo. The lines have full width at half-maxima of 100 km/s, compared to an instrumental resolution of 35 km/s, are centered at zero velocity, and show no evidence for components with equivalent widths greater than 50 mA at an absolute value of v greater than 75 km/s. The absence of high peculiar velocities is consistent with published spectra of halo gas over shorter pathlengths. The implications of this result are discussed, with particular reference to the possible connection between galactic halos and QSO absorption lines, for which C IV and Si IV usually have a broader velocity range.

York, D. G.↗
NASA NTRS1983

Evidence for X-ray scattering by interstellar dust

X ray images of distant point sources obtained with the Einstein Observatory have been examined for the presence of halos produced by X-ray scattering from interstellar dust. Evidence for detection of dust halos has been obtained by comparing the apparent surface brightness in images of four low-latitude galactic center sources with the surface brightness predicted from the telescope point response function and the simultaneously measured source spectra. This evidence is considerably strengthened by the same comparison using images of two sources at higher galactic latitude, where the column density of dust is expected to be far lower. Simple assumptions indicate the observed scattering halos are consistent with production by the population of dust grains inferred from optical extinction measurements.

Catura, R. C.↗
NASA NTRS1984

Interstellar absorption lines in the spectrum of supernova Evans in M83 (NGC 5236)

It is pointed out that supernovae in other galaxies create spontaneous opportunities to probe spectroscopically the gaseous material in galactic halos. Because of their brightness, supernovae offer an unparalleled chance to obtain spectra with high wavelength resolution and/or signal-to-noise ratio. The present investigation is concerned with observations of visual interstellar lines in the spectrum of a supernova discovered on July 3, 1983, and identified as Type I. The supernova was located 124 arc sec south and 122 arc sec west of the nucleus of M83. Evidence is obtained that for velocities near that of M83, the line of sight toward the supernova contains a complex array of absorption features of Ca II. In both Ca II and Na I, the absorptions associated with M83 are far more prominent than those halfway through the disk (and halo) of the Milky Way Galaxy. It is felt that many of the displaced velocity components in the M83 system arise from a gaseous halo.

Rodgers, A. W.↗
NASA NTRS1986

Halogen occultation experiment intergrated test plan

The test program plan is presented for the Halogen Occultation Experiment (HALOE) instrument, which is being developed in-house at the Langley Research Center for the Upper Atmosphere Research Satellite (UARS). This comprehensive test program was developed to demonstrate that the HALOE instrument meets its performance requirements and maintains integrity through UARS flight environments. Each component, subsystem, and system level test is described in sufficient detail to allow development of the necessary test setups and test procedures. Additionally, the management system for implementing this test program is given. The HALOE instrument is a gas correlation radiometer that measures vertical distribution of eight upper atmospheric constituents: O3, HC1, HF, NO, CH4, H2O, NO2, and CO2.

Mauldin, L. E., III↗
NASA NTRS1985

Application of a silicon photodiode array for solar edge tracking in the Halogen Occultation Experiment

The optical and electronic design of the Halogen Occultation Experiment (HALOE) elevation sunsensor is described. This system uses a Galilean telescope to form a solar image on a linear silicon photodiode array. The array is a self-scanned, monolithic charge coupled device. The addresses of both solar edges imaged on the array are used by the control/pointing system to scan the HALOE science instantaneous-field-of-view (IFOV) across the vertical solar diameter during instrument calibration, and then maintain the science IFOV four arcmin below the top edge during the science data occultation event. Vertical resolution of 16 arcsec and a radiometric dynamic range of 100 are achieved at the 0.7 micrometer operating wavelength. The design provides for loss of individual photodiode elements without loss of angular tracking capability. The HALOE instrument is a gas correlation radiometer that is now being developed by NASA Langley Research Center for the Upper Atmospheric Research Satellite.

Mauldin, L. E., III↗
NASA NTRS1986

The galactic corona

The IUE observations and theories involving the gaseous galactic corona of the Milky Way are reviewed. Observational topics emphasized include results relevant to the z distribution, kinematics, and ionic and elemental abundances of the gas. The theories for the support, ionization, and kinematics of the galactic halo appear to require a merging of the ideas associated with the galactic fountain models and the photoionized halo models. The Si IV found in the galactic halo is likely mostly produced by photoionization while the N V is probably mostly produced by collisional ionization in cooling fountain gas; C IV may represent an intermediate case with important contributions from photoionization and from collisional ionization.

Savage, Blair D.↗
NASA NTRS1987

Preliminary results of spectral reflectance studies of tycho crater

The preliminary analysis and interpretation of near infrared spectra obtained for both the interior and exterior deposits associated with the Tycho crater is presented. Specific objectives were: (1) to determine the composition and stratigraphy of the highland crust in the Tycho target site; (2) to determine the likely composition of the primary ejecta which may be present in ray deposits; (3) to investigate the nature of spectral units defined in previous studies; (4) to further investigate the nature and origin of both the bright and dark haloes around the rim crest; and (5) to compare the compositions determined for the Tycho units with those of the Aristarchus crater as well as typical highland deposits. The spectra obtained for the interior areas exhibit similar spectral features. These include relatively strong 1 micron absorption bands whose minima are centered between 0.97 and 0.99 microns and shallow to intermediate continuum slopes. The spectra generally exhibit indications of a 1.3 micron feature consistent with the presence of Fe(2+) bearing plagioclase feldspar. The strong 1 micron absorption features indicate a dominant high Ca clinopyroxene component. Results obtained from the ejecta deposits show that the spectrum of the inner, bright halo is almost identical with those obtained for interior units. The spectrum of the dark halo exhibits a wide, relatively shallow absorption feature centered at 1.01 microns, a 1.3 micron absorption, and a steep continuum slope. This spectrum is interpreted as indicating the presence of pyroxene, Fe-bearing feldspar, and a significant component of Fe-bearing impact melt glass. Finally, the spectra of spots inside Tycho show similarity with certain spectra for Aristarchus. However, the suite of spectra obtained for Tycho exhibits a different trend in terms of band center versus width.

Hawke, B. R.↗