Two-Way Orbits

This paper introduces a new set of compatible orbits called “Two-Way Orbits,” whose ground track path is a closed-loop trajectory that intersects at certain points with tangent intersections. The spacecraft passes over these tangent intersections once in a prograde mode and once in a retrograde mode. Motivations are found for the need to have simultaneous observations of the same target area in both Earth observation and reconnaissance systems. The general mathematical model to design a Two-Way Orbit is presented for the specific case where the tangent points are experienced at the orbit extremes, perigee and apogee. As for the general case, Two-Way Orbit conditions are formulated and numerically solved. Results show that, in general, Two-Way Orbits could be formed over any point on Earth. Since Two-Way Orbits use compatible orbits, the theory of Flower Constellations can be applied to them. Using these Two-Way Orbits, this paper also introduces the Two-Way Flower Constellations that have one spacecraft prograde and one retrograde passing simultaneously over the tangent intersection.     

6. Environmental Context

On Earth, the Archaean aeon lasted from 4.0 to 2.5 Ga; it corresponds to a relatively stable period. Compared with today, internal Earth heat production was several times greater resulting in high geothermal flux that induced the genesis of rocks such as komatiites and TTG suites, which are no more generated on Earth since 2.5 Ga. Similarly, the details of plate tectonic modalities (plate size, plate motion rate, plate thickness, tectonic style, irregular crustal growth, etc...) were different of modern plate tectonics. Both atmosphere and ocean compositions have been progressively modified and the greater heat production favoured the development of hydrothermalism and therefore created niches potentially favourable for the development of some forms of life. Catastrophic events such as giant meteorite falls or world-sized glaciations drastically and suddenly changed the environment of Earth surface, thus being able to strongly affect development of life. Even if specialists still debate about the age of the oldest indubitable fossil trace of life, Archaean can be considered as having been extremely favourable for life development and diversification.     

Re-testing the JET-X Flight Module No. 2 at the PANTER facility

The Joint European X-ray Telescope (JET-X) was the core instrument of the Russian Spectrum-X- γ space observatory. It consisted of two identical soft X-ray (0.3–10 keV) telescopes with focusing optical modules having a measured angular resolution of nearly 15 arcsec. Soon after the payload completion, the mission was cancelled and the two optical flight modules (FM) were brought to the Brera Astronomical Observatory where they had been manufactured. After 16 years of storage, we have utilized the JET-X FM2 to test at the PANTER X-ray facility a prototype of a novel X-ray polarimetric telescope, using a Gas Pixel Detector (GPD) with polarimetric capabilities in the focal plane of the FM2. The GPD was developed by a collaboration between INFN-Pisa and INAF-IAPS. In the first phase of the test campaign, we have re-tested the FM2 at PANTER to have an up-to-date characterization in terms of angular resolution and effective area, while in the second part of the test the GPD has been placed in the focal plane of the FM2. In this paper we report the results of the tests of the sole FM2, using an unpolarized X-ray source, comparing the results with the calibration done in 1996.     

Initial orbit determination using multiple observations

A novel approach for initial orbit determination based on multiple angles-only observations is presented. The proposed technique is iterative and uses Lagrangian coefficients, f and g. The proposed method does not show singularity for the coplanar cases. In addition, the method is capable of handling multiple observations, providing higher accuracy, whereas the level of the algorithm complexity and processor running time remain almost invariant. The technique presented is compared with the Double r-iteration and Gauss’ methods using data corrupted by noise to simulate true measurements. Results show that the proposed method is a valid alternative to the classical methods of orbit determination.     

Dripping into unsaturated rock underground excavations: model testing at the Yucca Mountain exploratory studies facility

This paper presents a probabilistic formulation of unsaturated flow through rough multi-segmented fractures, with emphasis on Dripping Initiation Time (DIT), and attempts to explain the fast flow paths detected at the Yucca Mountain (YM) Exploratory Studies Facility (ESF). Three scenarios of parameters were used to test the validity of the model with these fast flow paths. The scenarios differed in the DITs and the corresponding parameter configurations were also tested for three different stratigraphic horizon depths. Each depth represented a different location where fast flow has been detected at YM. The first depth corresponds to the Bow Ridge Fault; the second represents a network of steep fractures and cooling joints with large variability in dip; and the third location, probably connected to the Diabolous Ridge Fault, has a flow path that is low dipping. Monte Carlo simulations for each configuration and depth produced probabilistic results from nine scenarios for DITs, which are quite consistent with field observations.     

Stability of Al- and F-rich titanite in metacarbonate: petrologic and isotopic constraints from a polymetamorphic eclogitic marble of the internal Sesia Zone (Western Alps)

Al- and F-rich titanite (3.862O₃ <9.33 wt%, 0.931(F, OH)₁Ti_-1O_-1 substitution within single crystals, particularly at grain boundaries with omphacite and/or phengite. In-situ ion microprobe U-Pb analysis of titanite domains that have various Al and F contents yielded apparent ²⁰⁶Pb/²³⁸U ages scattering between 283 and 153 Ma. Chemical and petrological data are indispensable to interpret this complex age distribution, and the good correlation between ²⁰⁶Pb/²³⁸U ratios and Al content indicates that the Al- and F-rich titanite was formed during pre-Alpine metamorphism (𔕑ᆟ Ma). Progressively younger ages are obtained in domains with decreasing Al and F content, suggesting that partial chemical re-equilibration was responsible for the incomplete isotopic resetting during Alpine metamorphism. Petrological and U-Pb data show that Al- and F-rich titanite should be used with caution to infer high-pressure conditions in polymetamorphic carbonate systems.     

A review of the geodynamic constraints on the development and evolution of geothermal systems in the Central Andean Volcanic Zone (18–28°Lat.S)

ABSTRACT

Geothermal exploration in the Central Andean Volcanic Zone (CAVZ) focuses on heat capacities of known geothermal systems, yet the role of faults, veins, fractures and folds on the evolution and migration of fluids is far from complete. Here, we present a compilation of He and Sr isotope data and newly generated structural maps to examine if particular tectonic configurations are associated with fluids migrating from different crustal levels. Accordingly, we defined three tectono-geothermal environments (T1–T3) depicting specific structural arrangements and spatial relation with geothermal and volcanic manifestations. T1 is dominated by left-lateral strike-slip NW-striking faults, and geothermal and volcanic manifestations occur along the traces of these structures. T2 is dominated by N-striking thrust faults and parallel fault-propagated folds, cut and displaced by NW-striking faults. Here, geothermal manifestations occur at fault intersections and at fold hinges. T3 is defined by left-lateral/normal NW-striking faults, with geothermal and volcanic manifestations lying along fault traces. Each tectono-geothermal environment yields distinctive isotope ratios and geothermal reservoir temperatures. T1 shows high helium and low strontium ratios, and temperatures between 220° and 310°C. T3 shows low helium and high strontium ratios and temperatures between 260° and 320°C. T2 isotope ratios fall between T1 and T3, with lowest (130°-250°C) reservoir temperatures. We argue that these particular isotope signatures are due to a structural control on reservoir location and orientation. The orientation of the fracture mesh genetically associated with each tectono-geothermal environment is a first-order control on the migration pathway of fluids. Our model shows that T1 allows fluxing of deeper fluids, T2 promotes storage and favors longer residence times and T3 enhances subvertical fluid migration. Results here help to explain the evolution of geothermal systems in a wider context, including fault systems and Sr and He isotope variations, thus providing a framework for geothermal exploration in the CAVZ.     

Chemical speciation of arsenic in different marine organisms: Importance in monitoring studies

Arsenic is a widely distributed element in the marine environment. Inorganic and organic compounds have extremely different toxicological effects, and their characterization is thus of great utility when monitoring and assessing the impact of arsenic pollution. In this study both the levels of total arsenic and its chemical speciation were analyzed in several marine organisms collected from Cienfuegos Bay (Cuba) following an episode of acute As-contamination. Fish from the more impacted site were characterized by elevated concentrations of arsenic (up to 500 microg/g d.w.) and inorganic species represented the predominant forms in muscle tissues of these organisms.     

Hydrogeological and multi-isotopic approach to define nitrate pollution and denitrification processes in a coastal aquifer (Sardinia,Italy)

Agricultural coastal areas are frequently affected by the superimposition of various processes, with a combination of anthropogenic and natural sources, which degrade groundwater quality. In the coastal multi-aquifer system of Arborea (Italy)—a reclaimed morass area identified as a nitrate vulnerable zone, according to Nitrate Directive 91/676/EEC—intensive agricultural and livestock activities contribute to substantial nitrate contamination. For this reason, the area can be considered a bench test for tuning an appropriate methodology aiming to trace the nitrate contamination in different conditions. An approach combining environmental isotopes, water quality and hydrogeological indicators was therefore used to understand the origins and attenuation mechanisms of nitrate pollution and to define the relationship between contaminant and groundwater flow dynamics through the multi-aquifer characterized by sandy (SHU), alluvial (AHU), and volcanic hydrogeological (VHU) units. Various groundwater chemical pathways were consistent with both different nitrogen sources and groundwater dynamics. Isotope composition suggests a mixed source for nitrate (organic and synthetic fertilizer), especially for the AHU and SHU groundwater. Moreover, marked heterotrophic denitrification and sulfate reduction processes were detected; although, for the contamination related to synthetic fertilizer, the attenuation was inefficient at removing NO₃^? to less than the human consumption threshold of 50 mg/L. Various factors contributed to control the distribution of the redox processes, such as the availability of carbon sources (organic fertilizer and the presence of lagoon-deposited aquitards), well depth, and groundwater flow paths. The characterization of these processes supports water-resource management plans, future actions, and regulations, particularly in nitrate vulnerable zones.