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NASA NTRSDate not supplied

Effects of Basalt Composition on a Martian Analogue Magma-Sediment Hydrothermal System Studied Through Thermochemical Modeling

High-temperature hydrothermal systems have been identified on Mars associated with both hypervelocity impacts and magmatic activity on Mars’s early history [1, 2]. These processes may have produced habitable environments by providing heat, energy, and volatile species necessary to support microbial life [3, 4]. Hydrothermal systems formed after the intrusion of mafic magmas in sedimentary rocks are of particular interest when investigating the habitability of high-temperature aqueous environments on Mars [5, 6],because during magma-sediment contact metamorphism bond fluids (e.g. in ice, pore spaces, minerals) are mobilized favoring the alteration of the country rocks and the release of bio-essential elements [7, 8]. The chemistry and mineralogy of these systems on Mars are not well constrained and, for this reason, terrestrial analogues need to be investigated. Costello et al. [5] and Crandall et al. [6] have studied a mafic dike intruding the Jurassic Entrada sandstone (Colorado Plateau, UT). The intrusion has produced a hydrothermal system with Cl-CO2 rich fluids and near-neutral pH, which induced chemical and mineralogical changes in the dike and in the sediments [5, 6]. The system reached temperatures higher than 700 °C around the contact zone [6], but lower temperatures (< 200 °C) were reached as the system cooled down [5] making the environment potentially habitable [6]. However, previous studies do not consider compositional differences between the terrestrial dike and basaltic rocks on Mars [9, 10] making difficult a direct comparison between alteration mineralogy and brine chemistry of terrestrial and martian systems. Here, we use thermochemical modelling to investigate how differences in bulk dike composition will affect secondary mineral assemblages and fluid chemistry.

S Cogliati↗

NASA NTRS1980

EVA manipulation and assembly of space structure columns

Assembly techniques and hardware configurations used in assembly of the basic tetrahedral cell by A7LB pressure-suited subjects in a neutral bouyancy simulator were studied. Eleven subjects participated in assembly procedures which investigated two types of structural members and two configurations of attachment hardware. The assembly was accomplished through extra-vehicular activity (EVA) only, EVA with simulated manned maneuvering unit (MMU), and EVA with simulated MMU and simulated remote manipulator system (RMS). Assembly times as low as 10.20 minutes per tetrahedron were achieved. Task element data, as well as assembly procedures, are included.

Loughead, T. E.↗

NASA NTRS2002

Media Calibration in the Deep Space Network: A Status Report

A new media calibration system (MCS) has been implemented at the Goldstone complex of the DSN (Deep Space Network). It is intended to calibrate the delay of radio signals imposed by the neutral atmosphere. The system provides periodic measurements of both the static dry and fluctuating wet components of this delay. In particular, the system will calibrate the fluctuations in line of sight path delay due to atmospheric water vapor that we believe will dominate the error budget for several radio science and radio astronomy experiments. We have compared two of these media calibration systems with a connected element interferometer on a 21 km baseline. In this report we describe a total of 30 observations in which a radio source was tracked for an hour or more and the delay residuals then calibrated using the MCS. The accuracy of the comparison appears to be limited by systematic errors in the interferometer, which are under investigation. However, our results do indicate that the MCS can meet or exceed the two-way Allan standard deviation specification of 1.5 x 10( exp -15) on time scales of 2,000 - 10,000 sec, as required by the Cassini GWE (Gravitational Wave Experiment) for two way Doppler tracking.

Naudet, Charles J.↗

NASA NTRS1986

A new instrument to measure charged and neutral cometary dust particles at low and high impact velocities

A new class of dust particle detector, the PVDF dust detector, was designed for space missions such as the Halley Comet missions where the particle impact velocity is very high. It is demonstrated that this same PVDF detector (operating in a different mode) also has the capability of detecting dust particles having low velocity (approx. 100 m/s). This low velocity detection capability is extremely important in terms of planned missions requiring measurement of low velocity dust particles such as comet rendezvous missions. An additional detecting element (charge induction cylinder) was also developed which, when combined with a PVDF detector, yields a system which will measure the charge (magnitude and sign) carried by a cometary particle as well as the particle velocity and mass for impact velocities in the range 100 to 500 m/s. Since the cylinder-PVDF detector system has a relatively small geometry factors, an array of PVDF detectors was included having a total sensing area of 0.1 sq m for measurements in regions of space where the dust flux is expected to be low. The characteristics of the detectors in this array have been chosen to provide optimum mass sensitivity for both low-velocity cometary dust as well as high-velocity asteroid associated and interplanetary dust.

Economon, T.↗

NASA NTRS1993

Detection of boron, cobalt, and other weak interstellar lines toward Zeta Ophiuchi

Numerous weak lines from interstellar atomic species toward Zeta Ophiuchi were observed with the Goddard High-Resolution Spectrograph. Of particular note are the first interstellar detection of cobalt and the detection of boron in this sight line. These measurements provide estimates for the amount of depletion for the two elements. Boron, a volatile, and cobalt, a refractory element, display the depletion pattern found by Savage et al. (1992). The abundance of phosphorus in the H II region associated with the star was obtained from a detection of P III. Additional weak lines from S I, C I, Ni II, and Cu II were detected for the first time; these lines provide the basis for refinements in oscillator strength and column density. Analysis of the neutral sulfur data indicates that the atomic gas is more widely distributed than the molecular material in the main component.

Federman, S. R.↗

NASA NTRS1996

Optical detector calibrator system

An optical detector calibrator system simulates a source of optical radiation to which a detector to be calibrated is responsive. A light source selected to emit radiation in a range of wavelengths corresponding to the spectral signature of the source is disposed within a housing containing a microprocessor for controlling the light source and other system elements. An adjustable iris and a multiple aperture filter wheel are provided for controlling the intensity of radiation emitted from the housing by the light source to adjust the simulated distance between the light source and the detector to be calibrated. The geared iris has an aperture whose size is adjustable by means of a first stepper motor controlled by the microprocessor. The multiple aperture filter wheel contains neutral density filters of different attenuation levels which are selectively positioned in the path of the emitted radiation by a second stepper motor that is also controlled by the microprocessor. An operator can select a number of detector tests including range, maximum and minimum sensitivity, and basic functionality. During the range test, the geared iris and filter wheel are repeatedly adjusted by the microprocessor as necessary to simulate an incrementally increasing simulated source distance. A light source calibration subsystem is incorporated in the system which insures that the intensity of the light source is maintained at a constant level over time.

Strobel, James P.↗

NASA NTRS1990

Interstellar absorption along the line of sight to Sigma Scorpii using Copernicus observations

From Copernicus observations of Sigma Sco, 57 individual lines of 11 elements plus the molecular species H2 and CO were identified. By using a profile-fitting technique, rather than curves of growth, it was possible to obtain column densities and Doppler b values for up to four separate components along this line of sight. Electron density in the major H I component was derived from the photoionization equilibrium of sulfur, obtaining, n(e) of about 0.3/cu cm. The neutral hydrogen density in the same component was also derived using fine-structure excitation of O I. An H II component is also present in which the electron density was n(e) about 20/cu cm. As a by-product of this analysis, previously undetermined oscillator strengths for two Mn II lines were obtained: for 1162.-017 A, f about 0.023 and for 1164.211 A, f about 0.0086.

Allen, M. M.↗

NASA NTRS1971

Interaction of cosmic rays with interstellar matter and possible excitation of X-ray lines

It is proposed that the excess diffuse cosmic X-rays in the fractional keV energy band are produced as a result of excitation of neutral carbon, sulphur, and argon atoms by cosmic rays, with subsequent emission of the K X-rays of carbon and the L X-rays of sulphur and argon. It is suggested that if the intensities of low energy cosmic rays, and the cross sections for the production of X-ray lines were known, the observations of X-ray lines could provide k direct information concerning abundances of elements in the interstellar regions.

Verma, S. D.↗

NASA NTRS1992

Techniques for the remote sensing of space plasma in the heliosphere via energetic neutral atoms - A review

A survey is conducted for state-of-the-art techniques for detecting energetic neutral atoms (ENAs) in the 100-300 keV range, in regions from the heliospheric boundary to the auroral zones where the solar wind plays a crucial role. While ENA spectrometry allows sampling of the mass and energy distributions of a distant plasma, ENA imaging gives a global view of the structures and dynamics of an extended plasma. The ENA instrument designs discussed share many components which exhibit excellent flight performance as elements in charged-particle analyzers for space missions.

Hsieh, K. C.↗

NASA NTRS1976

Identification of satellites possibly active during the IMS and their orbital configurations

A survey has been made to identify presently operating as well as planned spacecraft which may contribute measurements of the magnetosphere or interplanetary medium during the IMS. The total set consists of 25 scientific earth-orbiting, 9 heliocentric, and 17 communication, navigation or meteorological spacecraft, which carry environmental monitoring experiments. The orbital elements of each are displayed. In addition, techniques for the display of positions in various orbits are presented to illustrate how interesting configurations can be determined during the IMS. The positions of presently orbiting heliocentric spacecraft are shown at various intervals with respect to the nominal interplanetary magnetic field spiral and the earth. Plots of the latest ISEE-A orbit in solar magnetospheric co-ordinates are presented to determine neutral-sheet crossing.

Vette, J. I.↗

NASA NTRS1990

Physics and astrophysics from a lunar base; Proceedings of the 1st NASA Workshop, Stanford, CA, May 19, 20, 1989

The present conference on physics and astrophysics from a lunar base encompasses space physics, cosmic ray physics, neutrino physics, experiments in gravitation and general relativity, gravitational radiation physics, cosmic background radiation, particle astrophysics, surface physics, and the physics of gamma rays and X-rays. Specific issues addressed include space-plasma physics research at a lunar base, prospects for neutral particle imaging, the atmosphere as particle detector, medium- and high-energy neutrino physics from a lunar base, muons on the moon, a search for relic supernovae antineutrinos, and the use of clocks in satellites orbiting the moon to test general relativity. Also addressed are large X-ray-detector arrays for physics experiments on the moon, and the measurement of proton decay, arcsec-source locations, halo dark matter and elemental abundances above 10 exp 15 eV at a lunar base.

Potter, A. E.↗

NASA NTRS1975

Large Space Telescope - Orbital crew EV maintenance operations

The paper shows that orbital EV maintenance by the crew has a tremendous impact on several areas of the program, including operations, Shuttle interfaces, support equipment rendezvous and berthing, checkout and verification, levels of servicing achievable, logistics and spares and scientific instruments in order to permit changeout and possible future refurbishment. To achieve on-orbit EV maintenance, such challenges as designing for suited-astronaut access to all subsystem equipment elements, minimization for contamination, handling of extremely sensitive instruments, development of translation techniques, and use of existing GFE and hardware must be faced early in the preliminary design and operations analysis phases. All studies to date indicate that on-orbit EV manned maintenance of the LST (Large Space Telescope) is not only feasible but can be designed to be readily within the capability of the EV functioning astronaut. Both 1-g and neutral buoyancy man-in-the-loop simulations further support this point.

Fisher, H. T.↗

NASA NTRS1982

The anomalous X-ray absorption spectrum of Vela X-1

The HEAO 2 satellite's Solid State Spectrometer and Monitor Proportional Counter was used to observe one orbit of the massive X-ray binary Vela X-1. Using spectral fits to the data as a function of orbital phase, the column density and state of the material along the line of sight to the X-ray source has been inferred. The spectrum near orbital phase 0.2 compares favorably with absorption by neutral material with a column density corresponding to plausible values of stellar wind velocity law and total primary mass loss rate. Spectra at later orbital phases, which show unexpected strong absorption features near 2.0 and 2.5 keV, are interpreted as due to absorption by material with suppressed opacity below 2.0 keV. The opacity required to produce the observed features implies either the presence of an intense soft X-ray flux, or altered elemental abundances in the gas near Vela X-1.

Kallman, T. R.↗

NASA NTRS1996

The stability of compressible mixing layers in binary gases

We present the results of a study of the inviscid two-dimensional spatial stability of a parallel compressible mixing layer in a binary gas. The parameters of this study are the Mach number of the fast stream, the ratio of the velocity of the slow stream to that of the fast stream, the ratio of the temperatures, the composition of the gas in the slow stream and in the fast stream, and the frequency of the disturbance wave. The ratio of the molecular weight of the slow stream to that of the fast stream is found to be an important quantity and is used as an independent variable in presenting the stability characteristics of the flow. It is shown that differing molecular weights have a significant effect on the neutral-mode phase speeds, the phase speeds of the unstable modes, the maximum growth rates and the unstable frequency range of the disturbances. The molecular weight ratio is a reasonable predictor of the stability trends. We have further demonstrated that the normalized growth rate as a function of the convective Mach number is relatively insensitive (Approx. 25%) to changes in the composition of the mixing layer. Thus, the normalized growth rate is a key element when considering the stability of compressible mixing layers, since once the basic stability characteristics for a particular combination of gases is known at zero Mach number, the decrease in growth rates due to compressibility effects at the larger convective Mach numbers is somewhat predictable.

Kozusko, F.↗

NASA NTRSDate not supplied

Simulation of Vacuum Chamber Pressure Distribution with Surrogate Modeling and Uncertainty Quantification

A major challenge in understanding differences in electric propulsion performance in ground tests and in space operations concerns the pressure distribution within the test vacuum chamber. The chamber backpressure is much higher than experienced in space, modifying thruster performance and plume dynamics. Numerical simulation is a key element to determining the background conditions in non-ideal vacuum chamber environments. An important parameter for the accurate simulation of chamber backpressure is the probability that an atom will stick to a cryogenic panel used to pump away the plume gases. This quantity can be used to model vacuum pumps in particle-based kinetic numerical methods. In this work, a three-dimensional direct simulation Monte Carlo code is used to model neutral xenon atoms flowing from the anode of the H9 Hall Effect Thruster within the University of Michigan’s Large Vacuum Test Facility. Simulated pressures are compared with ion gauge pressure measurements to infer the effective sticking coefficient of the chamber’s vacuum pumps. A pressure predicting surrogate model is developed for inference of pump sticking coefficients and for uncertainty quantification. This information enables accurate and useful kinetic simulations of electric propulsion thruster plasma plumes in vacuum chambers.

DSMC↗

NASA NTRS1989

Report from magnetospheric science

By the early 1990s, magnetospheric physics will have progressed primarily through observations made from Explorer-class spacecraft, sounding rockets, ground based facilities, and shuttle based experiments. The global geospace science (GGS) element of the International Solar Terrestrial Physics program, when combined with contributions to the ESA Cluster mission and ground based and computer modeling programs, will form the basis for a major U.S. initiative in magnetospheric physics. The scientific objectives of the GGS program involve the study of energy transport throughout geospace. The Cluster mission will investigate turbulence and boundary phenomena in geospace, particularly at high latitudes on the dayside and in the region of the neutral sheet at geocentric distances of about 20 earth radii on the night side of the earth. The current state of knowledge is reviewed and the goals of these missions are briefly discussed.

Burch, J. L.↗

NASA NTRS1990

Photodissociation regions

Photodissociation regions are interstellar regions of predominantly neutral gas where the FUV radiation field plays a significant role in the chemistry and/or the heating. Photodissociation, grain attenuation of the FUV flux and grain photoelectric heating lead to copious emission of C II (158 microns), O I (63 microns), Si II (35 microns), C I (370,609 microns), H2 vibrotational and CO rotational transitions, and IR continuum. Theoretical models compared with observations diagnose such physical parameters as the density and temperature structure, the elemental abundances, and the FUV radiation field. Applications are made to Orion, M17 and galactic nuclei. Theoretical photodissociation models can explain the correlation in the C II (158 microns) and CO J = 1-0 emission and the correlation of the CO J = 1-0 luminosity with the molecular mass. Theoretical models also point to feedback mechanisms which may control the rate of star formation in galaxies and which may regulate the column density through giant molecular clouds.

Hollenbach, David J.↗

NASA NTRS1980

Solar wind sputtering effects in the atmospheres of Mars and Venus

It is found through an investigation, combining Monte Carlo simulations and analytical techniques, of the direct collisional interaction of an energetic particle flux with the neutral components of a planetary atmosphere, that solar wind sputtering could provide an important exospheric mass sink on both Mars and Venus under appropriate conditions. The computed rates of helium loss in the Venusian atmosphere and of carbon, nitrogen and oxygen in the Martian atmosphere imply that sputtering would have a significant effect on the noble gas budget of Venus and dominate the chemical and photochemical loss processes of Mars. Because of diffusive separation of lighter elements and isotopes, and because the gravitational binding energy is proportional to the mass, the erosion process preferentially removes the lighter components of the atmosphere. Solar wind sputtering could therefore compete with other erosion mechanisms in generating substantial fractionation effects.

Watson, C. C.↗