Investigation of Martian H2O and CO2 via gamma-ray spectroscopy

The evolution and present state of water and carbon dioxide on Mars are discussed. Researchers wished to determine how effectively questions regarding the distribution of water and carbon dioxide on Mars may be addressed with orbital gamma ray spectrometer data. Several simple, multi-layer models of the Martian surface were formulated to address problems such as the ice/dust ratio of layered deposits; the distribution, depth and concentration of ground ice; the thickness of north polar perennial ice; the thickness of the carbon dioxide layer over the south polar cap; the thickness of the seasonal carbon dioxide frost cap; and the water content of the seasonal frost cap. The results indicate that the Mars Observer gamma ray spectrometer will be a powerful tool for investigating the distribution and stratigraphy of volatiles on Mars

In situ XRF and gamma ray spectrometer for Mars sample return mission

A combined in situ X-ray fluorescence (XRF) and passive gamma ray spectrometer instrument is proposed for the chemical elemental analysis of various Martian surfaces and samples. The combined instrument can be carried on board a rover. The passive gamma ray or the neutron excited gamma ray system would be used to determine the elemental composition of the Martian surface while the rover is in motion. The XRF system would be used to perform analysis either on the Martian surface or on collected samples when the rover is stationary. The latter function is important both in cataloging the collected samples and in the selection of samples to be returned to earth. For both systems, data accumulation time would be on the order of 30 minutes. No sample preparation would be necessary

Remote geochemical experiment package for Discovery class missions

Remote sensing x-ray and gamma-ray spectrometers can be used to infer elemental composition on atmosphereless bodies, such as asteroids, the moon, and Mercury. The composition of the planetary body and variations in its surface chemistry are of fundamental importance in understanding the formation and dynamics of that body. Thus, for Discovery class missions, x-ray fluorescence (XRF), gamma-ray spectrometer (GRS), or a combined Geochemical Experiment Package (GEP) have been proposed. These instruments can meet the mission science objectives, while still meeting the weight, power, and cost constraints. These missions include the Near Earth Asteroid Rendezvous, the Main-belt Asteroid Rendezvous, and others such as HERMES (Mercury Orbiter). This paper presents the results of calculations done to assess the sensitivity of a combined instrument to obtain elemental compositions of planetary bodies with an uncertainty small enough to be scientifically useful

Synchronous Motor Lateral Vibration Dynamics - Diagnosis, Resolution, And Field Implementation.

LecturePg. 27-38A large, double ended drive synchronous motor experienced severe, limiting lateral vibration during commissioning of a major plant expansion. The motor driving a centrifugal compressor providing process air is decoupled during startup from a gearbox and steam turbine by a clutch. Steam generated by waste heat from the process drives the turbine under normal operation and the synchronizing clutch is engaged, reducing the motor load requirements. Excessive running speed ( 1 x) lateral vibrations came to light when the motor was run solo during field commissioning. Extreme sensitivity to small trim balance weight changes on the exciter end led to extensive field tests to identify the source of the problem. Rotordynarnic analyses and coupled running tests confirmed an overhang resonance, and revealed the only possible short term solution to be the addition of a third bearing on the motor shaft to control the overhang mode. Field installation of a 14 inch diameter tilting pad bearing, located on the clutch hub at the motor shaft end, was completed quickly to allow plant startup to proceed. In situ machining of the hub on the shaft, while the motor remained installed in the field, was required to assure proper journal shape and rapid project completion. This paper describes the process of problem identification, measurement/verification, rotordynarnic analyses, resolution, and field implementation. Before and after field vibration measurements are presented to illustrate the success of the solution and demonstrate the additional instrumentation required

Aluminum Abundance on the Surface of Mercury: Application of a New Background-Reduction Technique for the Analysis of Gamma-Ray Spectroscopy Data

A new technique has been developed for characterizing gamma-ray emission from a planetary surface in the presence of large background signals generated in a spacecraft. This technique is applied to the analysis of Al gamma rays measured by the MESSENGER Gamma-Ray Spectrometer to determine the abundance of Al on the surface of Mercury. The result (Al/Si = 0.29-0.13+0.05) is consistent with Al/Si ratios derived from the MESSENGER X-Ray Spectrometer and confirms the finding of low Al abundances. The measured abundance rules out a global, lunar-like feldspar-rich crust and is consistent with previously suggested analogs for surface material on Mercury, including terrestrial komatiites, low-iron basalts, partial melts of CB chondrites, and partial melts of enstatite chondrites. Additional applications of this technique include the measurement of other elements on Mercury's surface as well as the analysis of data from other planetary gamma-ray spectrometer experiments

Time-Resolved Data Acquisition for In Situ Subsurface Planetary Geochemistry

The current gamma-ray/neutron instrumentation development effort at NASA Goddard Space Flight Center aims to extend the use of active pulsed neutron interrogation techniques to probe the subsurface geochemistry of planetary bodies in situ. All previous NASA planetary science missions, that used neutron and/or gamma-ray spectroscopy instruments, have relied on a constant neutron source produced from galactic cosmic rays. One of the distinguishing features of this effort is the inclusion of a high intensity 14.1 MeV pulsed neutron generator synchronized with a custom data acquisition system to time each event relative to the pulse. With usually only one opportunity to collect data, it is difficult to set a priori time-gating windows to obtain the best possible results. Acquiring time-tagged, event-by-event data from nuclear induced reactions provides raw data sets containing channel/energy, and event time for each gamma ray or neutron detected. The resulting data set can be plotted as a function of time or energy using optimized analysis windows after the data are acquired. Time windows can now be chosen to produce energy spectra that yield the most statistically significant and accurate elemental composition results that can be derived from the complete data set. The advantages of post-processing gamma-ray time-tagged event-by-event data in experimental tests using our prototype instrument will be demonstrated

Variations in the Abundances of Potassium and Thorium on the Surface of Mercury: Results from the MESSENGER Gamma-Ray Spectrometer

A technique for converting gamma-ray count rates measured by the Gamma-Ray Spectrometer on the MESSENGER spacecraft to spatially resolved maps of the gamma-ray emission from the surface of Mercury is utilized to map the surface distributions of the elements Si, O, and K over the planet's northern hemisphere. Conversion of the K gamma-ray count rates to elemental abundances on the surface reveals variations from 300 to 2400 ppm. A comparison of these abundances with models for the maximum surface temperature suggests the possibility that a temperature-related process is controlling the K abundances on the surface as well as providing K to the exosphere. The abundances of K and Th have been determined for several geologically distinct regions, including Mercury's northern smooth plains and the plains interior to the Caloris basin. The lack of a significant variation in the measured Th abundances suggests that there may be considerable variability in the K/Th abundance ratio over the mapped regions

Major-Element Abundances on the Surface of Mercury: Results from the MESSENGER Gamma-Ray Spectrometer

Orbital gamma-ray measurements obtained by the MESSENGER spacecraft have been analyzed to determine the abundances of the major elements Al, Ca, S, Fe, and Na on the surface of Mercury. The Si abundance was determined and used to normalize those of the other reported elements. The Na analysis provides the first abundance estimate of 2.9 plus or minus 0.1 wt% for this element on Mercury's surface. The other elemental results (S/Si = 0.092 plus or minus 0.015, Ca/Si = 0.24 plus or minus 0.05, and Fe/Si = 0.077 plus or minus 0.013) are consistent with those previously obtained by the MESSENGER X-Ray Spectrometer, including the high sulfur and low iron abundances. Because of different sampling depths for the two techniques, this agreement indicates that Mercury's regolith is, on average, homogenous to a depth of tens of centimeters. The elemental results from gamma-ray and X-ray spectrometry are most consistent with petrologic models suggesting that Mercury's surface is dominated by Mg-rich silicates. We also compare the results with those obtained during the MESSENGER flybys and with ground-based observations of Mercury's surface and exosphere

Sacred turf: the Wimbledon tennis championships and the changing politics of Englishness

© 2015 Taylor & Francis. This article is about ‘Wimbledon’, widely celebrated – not least in its own publicity material – as the world’s premier tennis tournament. It examines ‘Wimbledon’ essentially as a text (hence the inverted commas), viewed politically and historically. In this context, ‘Wimbledon’ is seen as a signifier of a certain kind of Englishness, carefully adapted to meet changing social and economic circumstance. Loose parallels are drawn between the cultural trajectory of ‘Wimbledon’ and that of the British royal family. The transmutations of ‘Wimbledon’ as a tennis championship are also seen as reflecting Britain’s decline as a world power during the twentieth century