The X-15/HL-20 operations support comparison

During the 1960's, the United States X-15 rocket-plane research program successfully demonstrated the ability to support a reusable vehicle operating in a near-space environment. The similarity of the proposed HL-20 lifting body concept in general size, weight, and subsystem composition to that of the X-15 provided an opportunity for a comparison of the predicted support manpower and turnaround times with those experienced in the X-15 program. Information was drawn from both reports and discussions with X-15 program personnel to develop comparative operations and support data. Based on the assumption of comparability between the two systems, the predicted staffing levels, skill mix, and refurbishment times of an operational HL-20 appear to be similar to those experienced by the X-15 for ground support. However, safety, environmental, and support requirements have changed such that the HL-20 will face a different operating environment than existed at Edwards during the 1950's and 1960's. Today's operational standards may impose additional requirements on the HL-20 that will add to the maintenance and support burden estimate based on the X-15 analogy

A space transportation system operations model

Presented is a description of a computer program which permits assessment of the operational support requirements of space transportation systems functioning in both a ground- and space-based environment. The scenario depicted provides for the delivery of payloads from Earth to a space station and beyond using upper stages based at the station. Model results are scenario dependent and rely on the input definitions of delivery requirements, task times, and available resources. Output is in terms of flight rate capabilities, resource requirements, and facility utilization. A general program description, program listing, input requirements, and sample output are included

Field-calibrated model of melt, refreezing, and runoff for polar ice caps : Application to Devon Ice Cap

Acknowledgments R.M.M. was supported by the Scottish Alliance for Geoscience, Environment and Society (SAGES). The field data collection contributed to the validation of the European Space Agency Cryosat mission and was supported by the Natural Sciences and Engineering Research Council, Canada, the Meteorological Service of Canada (CRYSYS program), the Polar Continental Shelf Project (an agency of Natural Resources Canada), and by UK Natural Environment Research Council consortium grant NER/O/S/2003/00620. Support for D.O.B. was provided by the Canadian Circumpolar Institute and the Climate Change Geoscience Program, Earth Sciences Sector, Natural Resources Canada (ESS contribution 20130371). Thanks are also due to the Nunavut Research Institute and the communities of Resolute Bay and Grise Fjord for permission to conduct fieldwork on Devon Ice Cap. M.J. Sharp, A. Gardner, F. Cawkwell, R. Bingham, S. Williamson, L. Colgan, J. Davis, B. Danielson, J. Sekerka, L. Gray, and J. Zheng are thanked for logistical support and field assistance during the data collection. We thank Ruzica Dadic, two other anonymous reviewers, and the Editor, Bryn Hubbard, for their helpful comments on an earlier version of this paper and which resulted in significant improvements.Peer reviewedPublisher PD

Acid Sulfate Weathering on Mars: Results from the Mars Exploration Rover Mission

Sulfur has played a major role in the formation and alteration of outcrops, rocks, and soils at the Mars Exploration Rover landing sites on Meridiani Planum and in Gusev crater. Jarosite, hematite, and evaporite sulfates (e.g., Mg and Ca sulfates) occur along with siliciclastic sediments in outcrops at Meridiani Planum. The occurrence of jarosite is a strong indicator for an acid sulfate weathering environment at Meridiani Planum. Some outcrops and rocks in the Columbia Hills in Gusev crater appear to be extensively altered as suggested by their relative softness as compared to crater floor basalts, high Fe(3+)/FeT, iron mineralogy dominated by nanophase Fe(3+) oxides, hematite and/or goethite, corundum-normative mineralogies, and the presence of Mg- and Casulfates. One scenario for aqueous alteration of these rocks and outcrops is that vapors and/or fluids rich in SO2 (volcanic source) and water interacted with rocks that were basaltic in bulk composition. Ferric-, Mg-, and Ca-sulfates, phosphates, and amorphous Si occur in several high albedo soils disturbed by the rover's wheels in the Columbia Hills. The mineralogy of these materials suggests the movement of liquid water within the host material and the subsequent evaporation of solutions rich in Fe, Mg, Ca, S, P, and Si. The presence of ferric sulfates suggests that these phases precipitated from highly oxidized, low-pH solutions. Several hypotheses that invoke acid sulfate weathering environments have been suggested for the aqueous formation of sulfate-bearing phases on the surface of Mars including (1) the oxidative weathering of ultramafic igneous rocks containing sulfides; (2) sulfuric acid weathering of basaltic materials by solutions enriched by volcanic gases (e.g., SO2); and (3) acid fog (i.e., vapors rich in H2SO4) weathering of basaltic or basaltic-derived materials

Spherulitic Growth of Hematite Under Hydrothermal Conditions: Insights into the Growth Mechanism of Hematite Spherules at Meridiani Planum Mars.

Hematite-rich spherules were discovered embedded in sulfate-rich outcrop rock and as lag deposits of whole and broken spherules by the Opportunity rover at Meridiani Planem [1-6]. The Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES), which has a wider spectral range compared to the Mars Exploration Rover Mini-TES, provided an important constraint that hematite-rich spherules are dominated by emission along the crystallographic c-axis [7-10]. We have previously synthesized hematite spherules whose mineralogic, chemical, and crystallographic properties are strikingly similar to those for the hematite-rich spherules at Meridiani Planum [11]. The spherules were synthesized in the laboratory along with hydronium jarosite and minor hydronium alunite from Fe-Al-Mg-S-Cl acid sulfate solutions under hydrothermal conditions. The reaction sequence was (1) precipitation of hydronium jarosite, (2) jarosite dissolution and precipitation of hematite spherules, and (3) precipitation of hydronium alunite upon depletion of hydronium jarosite. The spherules exhibit a radial growth texture with the crystallographic c-axis aligned along the radial direction, so that thermal emission spectra have no hematite emissivity minimum at approx.390/cm similar to the emission spectra returned by MGS TES. The objective of this paper is to expand on our initial studies [11] to examine the morphological evolution during growth of spherules starting from sub-micrometer crystals to spherules many orders of magnitude in size

Short Range-Ordered Minerals: Insight into Aqueous Alteration Processes on Mars

Short range-ordered (SRO) aluminosilicates (e.g., allophane) and nanophase ferric oxides (npOx) are common SRO minerals derived during aqueous alteration of basaltic materials. NpOx refers to poorly crystalline or amorphous alteration products that can be any combination of superparamagnetic hematite and/or goethite, akaganeite, schwertmannite, ferrihydrite, iddingsite, and nanometer-sized ferric oxide particles that pigment palagonitic tephra. Nearly 30 years ago, SRO phases were suggested as alteration phases on Mars based on similar spectral properties for altered basaltic tephra on the slopes of Mauna Kea in Hawaii and Martian bright regions measured by Earth-based telescopes. Detailed characterization of altered basaltic tephra on Mauna Kea have identified a variety of alteration phases including allophane, npOx, hisingerite, jarosite, alunite, hematite, goethite, ferrihydrite, halloysite, kaolinite, smectite, and zeolites. The presence of npOx and other Fe-bearing minerals (jarosite, hematite, goethite) was confirmed by the M ssbauer Spectrometer onboard the Mars Exploration Rovers. Although the presence of allophane has not been definitely identified on Mars robotic missions, chemical analysis by the Spirit and Opportunity rovers and thermal infrared spectral orbital measurements suggest the presence of allophane or allophane-like phases on Mars. SRO phases form under a variety of environmental conditions on Earth ranging from cold and arid to warm and humid, including hydrothermal conditions. The formation of SRO aluminosilicates such as allophane (and crystalline halloysite) from basaltic material is controlled by several key factors including activity of water, extent of leaching, Si activity in solution, and available Al. Generally, a low leaching index (e.g., wet-dry cycles) and slightly acidic to alkaline conditions are necessary. NpOx generally form under aqueous oxidative weathering conditions, although thermal oxidative alteration may occasional be involved. The style of aqueous alteration (hydrolytic vs. acid sulfate) impacts which phases will form (e.g., oxides, oxysulfates, and oxyhydroxides). Knowledge on the formation processes of SRO phases in basaltic materials on Earth has allowed significant enhancement in our understanding of the aqueous processes at work on Mars. The 2011 Mars Science Laboratory (MSL) will provide an instrument suite that should improve our understanding of the mineralogical and chemical compositions of SRO phases. CheMin is an X-ray diffraction instrument that may provide broad X-ray diffraction peaks for SRO phases; e.g., broad peaks around 0.33 and 0.23 nm for allophane. Sample Analysis at Mars (SAM) heats samples and detects evolved gases of volatile-bearing phases including SRO phases (i.e., carbonates, sulfates, hydrated minerals). The Alpha Particle X-ray Spectrometer (APXS) and ChemCam element analyzers will provide chemical characterization of samples. The identification of SRO phases in surface materials on MSL will be challenging due to their nanocrystalline properties; their detection and identification will require utilizing the MSL instrument suite in concert. Ultimately, sample return missions will be required to definitively identify and fully characterize SRO minerals with state-of-the-art laboratory instrumentation back on Earth

Aqueous Alteration on Mars

Aqueous alteration is the change in composition of a rock, produced in response to interactions with H2O-bearing ices, liquids, and vapors by chemical weathering. A variety of mineralogical and geochemical indicators for aqueous alteration on Mars have been identified by a combination of surface and orbital robotic missions, telescopic observations, characterization of Martian meteorites, and laboratory and terrestrial analog studies. Mineralogical indicators for aqueous alteration include goethite (lander), jarosite (lander), kieserite (orbiter), gypsum (orbiter) and other Fe-, Mg-, and Ca-sulfates (landers), halides (meteorites, lander), phyllosilicates (orbiter, meteorites), hematite and nanophase iron oxides (telescopic, orbiter, lander), and Fe-, Mg-, and Ca-carbonates (meteorites). Geochemical indicators (landers only) for aqueous alteration include Mg-, Ca-, and Fe-sulfates, halides, and secondary aluminosilicates such as smectite. Based upon these indicators, several styles of aqueous alteration have been suggested on Mars. Acid-sulfate weathering (e.g., formation of jarosite, gypsum, hematite, and goethite), may occur during (1) the oxidative weathering of ultramafic igneous rocks containing sulfides, (2) sulfuric acid weathering of basaltic materials, and (3) acid fog (i.e., vapors rich in H2SO4) weathering of basaltic or basaltic-derived materials. Near-neutral or alkaline alteration occurs when solutions with pH near or above 7 move through basaltic materials and form phases such as phyllosilicates and carbonates. Very low water:rock ratios appear to have been prominent at most of the sites visited by landed missions because there is very little alteration (leaching) of the original basaltic composition (i.e., the alteration is isochemical or in a closed hydrologic system). Most of the aqueous alteration appears to have occurred early in the history of the planet (3 to 4.5 billion years ago); however, minor aqueous alteration may be occurring at the surface even today (e.g., in thin films of water or by acid fog)

Silica in a Mars analog environment: Ka'u Desert, Kilauea Volcano, Hawaii

Airborne Visible/Near-Infrared Imaging Spectrometer (AVIRIS) data acquired over the Ka'u Desert are atmospherically corrected to ground reflectance and used to identify the mineralogic components of relatively young basaltic materials, including 250–700 and 200–400 year old lava flows, 1971 and 1974 flows, ash deposits, and solfatara incrustations. To provide context, a geologic surface units map is constructed, verified with field observations, and supported by laboratory analyses. AVIRIS spectral end-members are identified in the visible (0.4 to 1.2 μm) and short wave infrared (2.0 to 2.5 μm) wavelength ranges. Nearly all the spectral variability is controlled by the presence of ferrous and ferric iron in such minerals as pyroxene, olivine, hematite, goethite, and poorly crystalline iron oxides or glass. A broad, nearly ubiquitous absorption feature centered at 2.25 μm is attributed to opaline (amorphous, hydrated) silica and is found to correlate spatially with mapped geologic surface units. Laboratory analyses show the silica to be consistently present as a deposited phase, including incrustations downwind from solfatara vents, cementing agent for ash duricrusts, and thin coatings on the youngest lava flow surfaces. A second, Ti-rich upper coating on young flows also influences spectral behavior. This study demonstrates that secondary silica is mobile in the Ka'u Desert on a variety of time scales and spatial domains. The investigation from remote, field, and laboratory perspectives also mimics exploration of Mars using orbital and landed missions, with important implications for spectral characterization of coated basalts and formation of opaline silica in arid, acidic alteration environments

Cosmology and Astrophysics from Relaxed Galaxy Clusters II: Cosmological Constraints

We present cosmological constraints from measurements of the gas mass fraction, $f_{gas}$, for massive, dynamically relaxed galaxy clusters. Our data set consists of Chandra observations of 40 such clusters, identified in a comprehensive search of the Chandra archive, as well as high-quality weak gravitational lensing data for a subset of these clusters. Incorporating a robust gravitational lensing calibration of the X-ray mass estimates, and restricting our measurements to the most self-similar and accurately measured regions of clusters, significantly reduces systematic uncertainties compared to previous work. Our data for the first time constrain the intrinsic scatter in $f_{gas}$, $(7.4\pm2.3)$% in a spherical shell at radii 0.8-1.2 $r_{2500}$, consistent with the expected variation in gas depletion and non-thermal pressure for relaxed clusters. From the lowest-redshift data in our sample we obtain a constraint on a combination of the Hubble parameter and cosmic baryon fraction, $h^{3/2}\Omega_b/\Omega_m=0.089\pm0.012$, that is insensitive to the nature of dark energy. Combined with standard priors on $h$ and $\Omega_b h^2$, this provides a tight constraint on the cosmic matter density, $\Omega_m=0.27\pm0.04$, which is similarly insensitive to dark energy. Using the entire cluster sample, extending to $z>1$, we obtain consistent results for $\Omega_m$ and interesting constraints on dark energy: $\Omega_\Lambda=0.65^{+0.17}_{-0.22}$ for non-flat $\Lambda$CDM models, and $w=-0.98\pm0.26$ for flat constant-$w$ models. Our results are both competitive and consistent with those from recent CMB, SNIa and BAO data. We present constraints on models of evolving dark energy from the combination of $f_{gas}$ data with these external data sets, and comment on the possibilities for improved $f_{gas}$ constraints using current and next-generation X-ray observatories and lensing data. (Abridged)Comment: 25 pages, 14 figures, 8 tables. Accepted by MNRAS. Code and data can be downloaded from http://www.slac.stanford.edu/~amantz/work/fgas14/ . v2: minor fix to table 1, updated bibliograph

Wave Climate Model of the Mid-Atlantic Shelf and Shoreline (Virginia Sea): Model Development, Shelf Geomorphology, and Preliminary Results

A computerized wave climate model is developed that applies linear wave theory and shelf depth information to predict wave behavior as they pass over the continental shelf as well as the resulting wave energy distributions along the coastline. Reviewed are also the geomorphology of the Mid-Atlantic Continental Shelf, wave computations resulting from 122 wave input conditions, and a preliminary analysis of these data