Engineering topics

Wiens, R. C.

Publications and source records attributed to Wiens, R. C..

47 records · Page 3

NASA NTRS2003

The Genesis Solar Wind Collection Mission: Current Status

The NASA Genesis spacecraft was launched August 8, 2001 on a mission to collect samples of solar wind for greater than or equal to 2 years and then return them to Earth in 2004. Detailed analyses of the solar wind ions implanted into high-purity collection substrates will subsequently be carried out in earth-based laboratories using various mass spectrometry techniques. These analyses are expected to determine key isotopic ratios and elemental abundances in the solar wind and, by extension, in the solar photosphere. Further, the photospheric composition is thought to be representative of the solar nebula with a few exceptions so that the Genesis mission will provide a baseline for the average solar nebula composition with which to compare present-day compositions of planets, meteorites, and asteroids. The implications of the solar oxygen isotopic composition have been discussed. A list of other isotopic and elemental measurement objectives, and some of the rationale behind them, is given.

Barraclough, B. L.↗

NASA NTRS2003

AGE (Argon Geochronology Experiment): An Instrument for Geochronology on the Surface of Mars

As our knowledge of the planet Mars continues to grow, one parameter that remains elusive is the absolute chronology of the planet s geological history. Although crater counts have provided a robust relative chronology, impactor fluxes are poorly enough known that there are places on Mars where the absolute age is uncertain by a factor of two or more. To resolve these uncertainties, it will be necessary to either analyze well-documented samples returned to the Earth from the Martian surface or to perform in situ measurements with sufficient precision. Sample return is still at least a decade away, and even then it might be from a biologically interesting area that might be geologically complex. Hence an in situ measurement, within an uncertainty of 20% or better, could greatly improve our knowledge of the history of Mars. With funding from the Planetary Instrument Definition and Development Program (PIDDP), we have been working on an instrument to perform potassium-argon (K-Ar) and cosmic-ray exposure (CRE) dating in situ on the surface of Mars. For either of these techniques, it is necessary to measure the abundance of one or more major or minor elements (K in the case of KAr; all majors and minors in the case of CRE) and the abundance and isotopes composition of a noble gas (Ar in the case of K-Ar; He, Ne and Ar for CRE dating). The technology for either of these types of measurements exists, but has never before been integrated for a spacecraft. We refer to the instrument as AGE, the Argon Geochronology Experiment (although we will measure the noble gases He and Ne as well for CRE ages). We report here on the basic components that go into such an instrument, both those that use existing technology and those that had to be developed to create the integrated package.

Swindle, T. D.↗

NASA NTRS2003

Genesis Solar-Wind Sample Return Mission: The Materials

The Genesis spacecraft has two primary instruments which passively collect solar wind. The first is the collector arrays , a set of panels, each of which can deploy separately to sample the different kinds of solar wind (regimes). The second is the concentrator, an electrostatic mirror which will concentrate ions of mass 4 through mass 25 by about a factor of 20 by focusing them onto a 6 cm diameter target. When not deployed, these instruments fit into a compact canister. After a two year exposure time, the deployed instruments can be folded up, sealed into the canister, and returned to earth for laboratory analysis. Both the collector arrays and the concentrator will contain suites of ultra-high purity target materials, each of which is tailored to enable the analysis of a different family of elements. This abstract is meant to give a brief overview of the Genesis mission, insight into what materials were chosen for flight and why, as well as head s up information as to what will be available to planetary scientist for analysis when the solar-wind samples return to Earth in 2003. Earth. The elemental and isotopic abundances of the solar wind will be analyzed in state-of-the-art laboratories, and a portion of the sample will be archived for the use of future generations of planetary scientists. Technical information about the mission can be found at www.gps.caltech.edu/genesis.

Jurewicz, A. J. G.↗

NASA NTRS2002

Solar-Wind Conditions During the Initial Phase of the Genesis Mission

We describe solar-wind conditions, including relative fractions of the solar-wind regimes (interstream, coronal hole, coronal mass ejections), during initial Genesis solar-wind sample collection, and give implications for eventual sample analysis. Additional information is contained in the original extended abstract.

Wiens, R. C.↗

NASA NTRS2002

A Combined Remote LIBS and Raman Spectroscopic Study of Minerals

In this paper, we explore the use of remote LIBS combined with pulsed-laser Raman spectroscopy for mineral analysis at a distance of 10 meters. Samples analyzed include: carbonates (both biogenic and abiogenic), silicates, and sulfates. Additional information is contained in the original extended abstract.

Hubble, H. W.↗

NASA NTRS2000

Genesis Solar-Wind Sample Return Mission: The Materials

This abstract is a brief overview of the Genesis mission. Included is an instrument description, what materials were chosen for capturing solar wind and why, and information as to what will be available for analysis when the samples return to Earth in 2003.

Jurewicz, A. J. G.↗

NASA NTRS1996

Three-color resonance ionization spectroscopy of Zr in Si

As our society becomes technologically more complex, computers are being used in greater and greater numbers of high consequence systems. Giving a machine control over the lives of humans can be disturbing, especially if the software that is run on such a machine has bugs. Formal reasoning is one of the most powerful techniques available to demonstrate the correctness of a piece of software. When reasoning about software and its development, one frequently encounters expressions that contain partial functions. As might be expected, the presence of partial functions introduces an additional dimension of difficulty to the reasoning framework. This difficulty produces an especially strong impact in the case of high consequence systems. An ability to use formal methods for constructing software is essential if we want to obtain greater confidence in such systems through formal reasoning. This is only reasonable under automation of software development and verification. However, the ubiquitous presence of partial functions prevents a uniform application to software of any tools not specifically accounting for partial functions. In this paper we will describe a framework for reasoning about software, based on the nonstrict explicit domain approach, that is applicable to a large class of software/hardware systems. In this framework the Hoare triples containing partial functions can be reasoned about automatically in a well-defined and uniform manner.

Hansen, C. S.↗

NASA NTRS1988

Noble gases released by vacuum crushing of EETA 79001 glass

An EETA 79001 glass sample was crushed in a vacuum to observe the gases released. About 15 pct of the total gas concentrations were a mixture of a small amount of SPB-type gas with larger proportions of another air-like component. Less than 5 pct of the SPB gas was released by crushing, while 36-40 pct of the EETV (indigenous) gas was crush-released. The results are consistent with a siting of the EETV component in 10-100 micron vesicles seen in the glass. It is suggested that the SPB component is either in vesicles less than 6 microns in diameter or is primarily sited elsewhere.

Wiens, R. C.↗

NASA NTRS1988

On the siting of gases shock-emplaced from internal cavities in basalt

Laboratory experiments were carried out on shock-emplaced gases from Servilleta basalt samples that contained gas-filled cavities to answer the following questions: (1) what is the role of shock melting in trapping gases; (2) how are the glassy pockets that contain trapped gases formed; and (3) are the gases trapped in laboratory shocked basalts sited similarly to, and emplaced with the same efficiency as, the gases in the EETA 79001 shergottite? Noble gases were extracted by stepped combustion and crushing followed by shock at 40 GPa, and were analyzed for abundances. Results obtained indicate that noble gases trapped from internal cavities of shock-exposed basalt are associated with glass and are sited predominantly in microvesicles, with a significant fraction of the gases released by crushing. The presence of gas-filled cavities prior to shock results in substantially greater shock effects locally. Thus, glassy pockets similar to those seen in EETA 79001 can be produced in situ within a matrix shocked to only moderate pressures. However, the siting of the gases points to a more complex scenario.

Wiens, R. C.↗

NASA NTRS1988

Laboratory shock emplacement of noble gases, nitrogen, and carbon dioxide into basalt, and implications for trapped gases in shergottite EETA 79001

Basalts from the Servilleta flows, Taos, NM, described by Lofgren (1983) were analyzed by mass spectrometry for shock-implanted noble gases, N2, and CO2 (which were isotopically labeled) after an exposure to 20-60 GPa shock in the presence of 0.0045-3.0 atm of ambient gas. The results were compared with data available on the constituents of the EETA 79001 meteorite. As expected, the samples shocked in this study attained emplacement efficiencies significantly lower than those apparent for lithology C of EETA 79001. Possible explanations for this difference include atmospheric overpressure at the time of EETA 79001 exposure to shock, the trapping of gas already in vugs by the intruding melt material, or the collapse of gas-filled vugs to form gas-laden glass inclusions.

Wiens, R. C.↗

NASA NTRS1986

The case for a Martian origin of the shergottites. II - Trapped and indigenous gas components in EETA 79001 glass

The isotopic composition of N, Ar, Ne, and He, trapped in an uncrushed sample of the antarctic shergottite EETA 79001, was analyzed by subjecting the evacuated sample to stepped heating in the presence of 100 mtorr of oxygen. The isotopic composition of nitrogen (with the delta-N-15 value of greater than 300 percent) and the elemental ratios Ar-36/N-14 and Ar-40/N-14 were covariant along mixing lines passing through the Martian atmospheric composition. The results of this and previous analyses are consistent with a two-component nitrogen system in which about 84 ppb of trapped Martian atmospheric N is mixed in variable proportions with another, more thermally labile N component during stepped heating. The isotopic Ar-36/Ar-38 ratio of the EETA 79001 is different from that of the earth atmosphere by about 25 percent.

Wiens, R. C.↗