Propulsion Risk Reduction Activities for Non-Toxic Cryogenic Propulsion

The Propulsion and Cryogenics Advanced Development (PCAD) Project s primary objective is to develop propulsion system technologies for non-toxic or "green" propellants. The PCAD project focuses on the development of non-toxic propulsion technologies needed to provide necessary data and relevant experience to support informed decisions on implementation of non-toxic propellants for space missions. Implementation of non-toxic propellants in high performance propulsion systems offers NASA an opportunity to consider other options than current hypergolic propellants. The PCAD Project is emphasizing technology efforts in reaction control system (RCS) thruster designs, ascent main engines (AME), and descent main engines (DME). PCAD has a series of tasks and contracts to conduct risk reduction and/or retirement activities to demonstrate that non-toxic cryogenic propellants can be a feasible option for space missions. Work has focused on 1) reducing the risk of liquid oxygen/liquid methane ignition, demonstrating the key enabling technologies, and validating performance levels for reaction control engines for use on descent and ascent stages; 2) demonstrating the key enabling technologies and validating performance levels for liquid oxygen/liquid methane ascent engines; and 3) demonstrating the key enabling technologies and validating performance levels for deep throttling liquid oxygen/liquid hydrogen descent engines. The progress of these risk reduction and/or retirement activities will be presented

Quantification of Flow Unit and Bounding Element Properties and Geometries, Ferron Sandstone, Utah: Implications for Heterogeneity in Gulf Coast Tertiary Deltaic Reservoirs

Outcrop mapping, field permeability measurements, petrographic analyses, petrophysical measurements, and pore-level modeling studies are being conducted on exposures of the Ferron Sandstone, east-central Utah, to develop a better understanding of the dimensions and internal arrangement of flow units, baffles, and barriers in sandstone gas reservoirs. The ultimate goals of this work are to establish methods for applying outcrop studies to reservoir characterization and to develop reservoir models that will guide infill drilling to maximize incremental gas reserve growth from fluvial-deltaic sandstone reservoirs. Activities during the second year of this 3-year project focused on data collection and preliminary interpretations. Mapping and field permeability measurements were initiated on the seaward-stepping Ferron unit 2 sandstone. These results will provide a comparison with data collected during the 1990 field season when landward-stepping sandstones of Ferron unit 3 were examined. Framework grain and cement mineralogy and the composition of intergranular material were quantified for selected samples from unit 3. Petrophysical measurements were completed on 24 specimens from units 2, 4, and 3. Sections of the pore-level modeling code were rewritten to improve accuracy and efficiency, and scenarios were developed to model the effects of grain size, cementation, and compaction on porosity, single-phase permeability, and formation factor. Preliminary results indicate that important differences exist in the internal geometry of landward- and seaward-stepping fluvial-deltaic sandstones. It was also found that closer-spaced permeability measurements improved the resolution of permeability structure. Petrographic studies documented differences in composition between fluvial, transgressive, delta-front, and distributary-channel sandstones; these differences in rock composition are reflected by differences in the mean permeability of these facies as measured on outcrop. Initial comparisons of pore-level model results with measured petrophysical properties are encouraging and suggest that refinements based on examination of the analyzed samples will lead to a close match between observed and modeled behavior.Bureau of Economic Geolog

Quantification of Flow Unit and Bounding Element Properties and Geometries, Ferron Sandstone, Utah: Implications for Heterogeneity in Gulf Coast Tertiary Deltaic Reservoirs

Outcrop exposures are being studied to quantify the internal permeability distribution of fluvial-deltaic sandstones, which results in reservoir compartments bounded by baffles or barriers to gas flow. This information will be used to develop reservoir models that can guide infill drilling to optimize incremental gas reserve growth from sandstone reservoirs. The objectives are being accomplished through integration of (1) outcrop characterization, (2) petrophysical measurements, and (3) pore-level modeling. Projected long-term benefits of the study are two-fold. First, increased understanding of internal architecture and improved methods for quantification of heterogeneity will facilitate development of strategies to minimize risk in the extended development of fluvial-dominated deltaic gas reservoirs. Second, targeting of incremental gas resources in mature reservoirs will lead to extended recovery of a low-cost, low-risk resource. Results of the first year of studies show that the architecture, geometry, and internal permeability distribution of fluvial-deltaic sandstones are generally predictable and that a four-order hierarchy of bounding surfaces exists. Initial tests have been completed, and reliable measurements of petrophysical properties of flow units, flow baffles, and flow barriers are being performed on outcrop samples. Development of a pore-level simulator has been essentially completed. Results, in general, indicate that the field approach is sound and that information gained on outcrop can be used to produce realistic reservoir models.Bureau of Economic Geolog

Quantifying Reservoir Heterogeneity Through Outcrop Characterization: 1. Architecture, Lithology, and Permeability Distribution of a Seaward-Stepping Fluvial-Deltaic Sequence, Ferron Sandstone (Cretaceous), Central Utah

The internal architecture of natural gas reservoirs fundamentally controls production efficiency and the volume of gas unrecovered at abandonment. To better understand reservoir complexity, we investigated relations between sandstone architecture and permeability structure of landward-stepping (wave-modified) Ferron deltaic sandstones exposed in central Utah. Deltaic sandstones extend 4 mi along sediment-transport direction in the landward-stepping Ferron genetic sequence GS 5. Most sand was deposited in transgressive, delta-front, and distributary-channel facies. Distributary channels constitute the principal reservoir facies because mean permeability in distributary-channel sandstones is approximately twice that of delta-front and transgressive sandstones, and because distributary-channel sandstones are well developed. Channel architecture, bounding-surface character, and permeability distribution change systematically from landward to seaward position in the system. Near the landward limit, mean permeability is 300 md, mud occurs as clasts along channel-flank bounding surfaces, and permeability systematically decreases upward. Near the seaward extent of the system, mean permeability is 750 md, mud is segregated into discrete strata-bounding sand bodies, and vertical permeability trends are uniformly high. Statistical analysis shows that lithofacies are the fundamental sandstone architectural units. Similar lithofacies have similar permeability character, regardless of position in the facies tract. Variable preservation of lithofacies controls permeability distribution throughout the channel system. Semivariogram analysis shows that vertical and horizontal permeability correlation distances correspond to distances between bounding surfaces and to sand-body dimensions. Diagenetic overprint is minor, owing to low burial temperatures.Bureau of Economic Geolog

Quantifying Reservoir Heterogeneity Through Outcrop Characterization: 2. Architecture, Lithology, and Permeability Distribution of a Seaward-Stepping Fluvial-Deltaic Sequence, Ferron Sandstone (Cretaceous), Central Utah

The internal architecture of natural gas reservoirs fundamentally determines gas migration, production efficiency, and the volume of gas unrecovered at abandonment. To determine the style and scale of reservoir complexity in fluvially dominated (seaward-stepping) deltaic reservoirs, we investigated relations between sandstone architecture and permeability distribution in seaward-stepping deltaic Ferron genetic sequence (GS) 2 sandstone outcrops in central Utah. Distributary-channel, mouth-bar, and delta-front deposits are the volumetrically important sand repositories in the Ferron GS 2. Mouth-bar facies are laterally extensive and relatively simple sand bodies with moderate mean permeabilities. Distributary channels also have good permeability but are narrow, sinuous, and separated from mouth-bar sandstones by low-permeability bounding surfaces, making them difficult targets for development. Statistical analyses of permeability data show that lithofacies are the fundamental sandstone architectural elements. Therefore, lithofacies are the basic units that should be used to construct reservoir models. The variable preservation of lithofacies controls permeability throughout the system. Vertical and horizontal permeability correlation distances correspond to distances between bounding surfaces and to macroform dimensions. Estimates based on field-scale mapping show that 91 percent of the reservoir area could be contacted at 320-acre well spacing. Sandstone architecture and permeability relations of the Ferron GS 2 are similar to those in Lake Creek (Wilcox Group, Texas Gulf Coast) reservoirs. This outcrop-reservoir comparison confirms that outcrop data are transferable to reservoirs.Bureau of Economic Geolog

The connection between polymer collapse and the onset of jamming

Previous studies have shown that the interiors of proteins are densely packed, reaching packing fractions that are as large as those found for static packings of individual amino-acid-shaped particles. How can the interiors of proteins take on such high packing fractions given that amino acids are connected by peptide bonds and many amino acids are hydrophobic with attractive interactions? We investigate this question by comparing the structural and mechanical properties of collapsed attractive disk-shaped bead-spring polymers to those of three reference systems: static packings of repulsive disks, of attractive disks, and of repulsive disk-shaped bead-spring polymers. We show that attractive systems quenched to temperatures below the glass transition $T \ll T_g$ and static packings of both repulsive disks and bead-spring polymers possess similar interior packing fractions. Previous studies have shown that static packings of repulsive disks are isostatic at jamming onset, i.e. the number of contacts $N_c$ matches the number of degrees of freedom, which strongly influences their mechanical properties. We find that repulsive polymers are hypostatic at jamming onset, but effectively isostatic when including quartic modes. While attractive disk and polymer packings are hyperstatic, we identify a definition for interparticle contacts for which they can also be considered as effectively isostatic. As a result, we show that the mechanical properties (e.g. scaling of the potential energy with excess contact number and low-frequency contribution to the density of vibrational modes) of weakly attractive disk and polymer packings are similar to those of ${\it isostatic}$ repulsive disk and polymer packings. Our results demonstrate that static packings generated via attractive collapse or compression of repulsive particles possess similar structural and mechanical properties.Comment: 17 pages, 16 figures, 2 appendice

Proterozoic crustal evolution of central East Antarctica: Age and isotopic evidence from glacial igneous clasts, and links with Australia and Laurentia

Rock clasts entrained in glacial deposits sourced from the continental interior of Antarctica provide an innovative means to determine the age and composition of ice-covered crust. Zircon U-Pb ages from a suite of granitoid clasts collected in glacial catchments draining central East Antarctica through the Transantarctic Mountains show that crust in this region was formed by a series of magmatic events at ∼2.01, 1.88–1.85, ∼1.79, ∼1.57, 1.50–1.41, and 1.20–1.06 Ga. The dominant granitoid populations are ca. 1.85, 1.45 and 1.20–1.06 Ga. None of these igneous ages are known from limited outcrop in the region. In addition to defining a previously unrecognized geologic history, zircon O and Hf isotopic compositions from this suite have: (1) mantle-like δ18O signatures (4.0–4.5‰) and near-chondritic Hf-isotope compositions (εHf ∼ +1.5) for granitoids of ∼2.0 Ga age; (2) mostly crustal δ18O (6.0–8.5‰) and variable Hf-isotope compositions (εHf = −6 to +5) in rocks with ages of ∼1.88–1.85, ∼1.79 and ∼1.57 Ga, in which the ∼1.88–1.79 Ga granitoids require involvement of older crust; (3) mostly juvenile isotopic signatures with low, mantle-like δ18O (∼4–5‰) and radiogenic Hf-isotope signatures (εHf = +6 to +10) in rocks of 1.50–1.41 Ga age, with some showing crustal sources or evidence of alteration; and (4) mixed crustal and mantle δ18O signatures (6.0–7.5‰) and radiogenic Hf isotopes (εHf = +3 to +4) in rocks of ∼1.2 Ga age. Together, these age and isotopic data indicate the presence in cratonic East Antarctica of a large, composite igneous province that formed through a punctuated sequence of relatively juvenile Proterozoic magmatic events. Further, they provide direct support for geological correlation of crust in East Antarctica with both the Gawler Craton of present-day Australia and Proterozoic provinces in western Laurentia. Prominent clast ages of ∼2.0, 1.85, 1.57 and 1.45 Ga, together with sediment source linkages, provide evidence for the temporal and spatial association of these cratonic elements in the Columbia supercontinent. Abundant ∼1.2–1.1 Ga igneous and metamorphic clasts may sample crust underlying the Gamburtsev Subglacial Mountains, indicating the presence of a Mesoproterozoic orogenic belt in the interior of East Antarctica that formed during final assembly of Rodinia.Field and analytical portions of this project were supported by the National Science Foundation (award 0944645)

Femtosecond Thermionic Emission in the Space-Charge Limited Regime

We study femtosecond-laser-pulse-induced electron emission from W(100), Al(110), and Ag(lll) in the sub-damage regime (1–44 mJ/cm2 fluence) by simultaneously measuring the incident-light reflectivity, total electron yield, and electron-energy distribution curves of the emitted electrons. The total-yield results are compared with a space-charge-limited extension of the Richardson-Dushman equation for short-time-scale thermionic emission and with particle-in-a-cell computer simulations of femtosecond-pulsed-induced thermionic emission. Quantitative agreement between the experimental results and two calculated temperature-dependent yields is obtained and shows that the yield varies linearly with temperature beginning at a threshold electron temperature of ~0.25 eV The particle-in-a-cell simulations also reproduce the experimental electron-energy distribution curves. Taken together, the experimental results, the theoretical calculations, and the results of the simulations indicate that thermionic emission from nonequilibrium electron heating provides the dominant source of the emitted electrons. Furthermore, the results demonstrate that a quantitative theory of space-charge-limited femtosecond-pulse-induced electron emission is possible

Establishment of a positive-readout reporter system for siRNAs

The use of small interfering RNA molecules for therapeutic applications requires development of improved delivery systems, a process that would be facilitated by a non-invasive positive-readout mouse model for studying siRNA pharmacodynamics. Positive readout would yield better signal/noise ratios than existing negative-readout systems. We have engineered a positive-readout luciferase reporter system, activated by successful delivery of siRNA targeting the lac repressor. Co-transfection of a plasmid expressing lac repressor and a plasmid expressing firefly luciferase under the control of an RSV promoter, containing two lac operator sites, resulted in 5.7-fold lower luciferase activity than luciferase-encoding plasmid alone. Inhibition was reversed following addition of synthetic inducer, IPTG, which elevated luciferase expression to normal levels and confirmed functionality of the lac operon. Delivery of 1nM siRNA targeting lac repressor to repressor/reporter co-transfected cells was sufficient to fully restore luciferase expression to levels observed in the absence of repressor. Maximum expression was observed after 48hr, with a rapid decrease thereafter due to the short half life of luciferase. The luciferase positive-readout reporter system is therefore a dynamic indicator of successful RNAi delivery in vitro and could be adapted to generate a transgenic mouse capable of reporting RNAi activity non-invasively in vivo