Browsing by Subject "Mars"
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Item A model for the development of a lobate alpine rock glacier in southwest Colorado, USA: implications for water on Mars(Texas A&M University, 2004-09-30) Degenhardt, John JeromeRock glaciers play a significant role in the alpine debris transport system. For practical and engineering considerations, identifying the internal structure and its relationship to surface characteristics is significant in terms of how a rock glacier settles during periods of melting, and the mode of deformation. A better understanding of these factors is important for engineers, engineering geologists and geomorphologists who must make prudent evaluations of rock glaciers as potential sites for human development and uses. It is equally important for evaluating potential stores for water on other planets such as Mars. Ground penetrating radar (GPR) shows that the internal structure of a lobate rock glacier located in the San Juan Mountains of southwest Colorado consists of continuous to semi-continuous horizontal layers of ice-supersaturated sediments and coarse blocky rockslide debris which likely formed through catastrophic episodes of rockfall from the cirque headwall. Folds in the uppermost layers correspond to the surface expression of ridges and furrows, indicating that compressive stresses originating in the steep accumulation zone are transmitted downslope through the rock glacier. The rock glacier is a composite feature that formed by a process involving the development and overlap of discrete flow lobes that have overridden older glacial moraine and protalus rampart materials. The latter materials have been incorporated into the present flow structure of the rock glacier. The discovery of rock glacier-like features on Mars suggests the presence of flowing, or once-flowing ice-rock mixtures. These landforms, which include lobate debris aprons, concentric crater fill and lineated valley fill, hold significant promise as reservoirs of stored water ice that could be used as fuel sources for human exploration of Mars and provide a frozen record of the climatic history of the planet. To this end, the rock glacier in this study was used as a surrogate for similar Martian landforms. Liquid water, found to be abundant in this rock glacier, occurs within a network of interconnected channels that permeate throughout the landform. In terms of water storage within Martian analogs, consideration must include the possibility that some water ice may be stored in relatively pure form within lenses and vein networks that are supplied by seasonal frost accumulation and/or water influx from below.Item Adaptive control for Mars atmospheric flight(2009-05-15) Restrepo, Carolina IsabelThe new vision for space exploration will focus on sending humans to the moon and eventually to Mars. This endeavor presents new challenges that are critically di?erent from the past experience with robotic missions to Mars. For example, the strict landing accuracy requirements for a manned space vehicle make it necessary to ?y a controlled entry trajectory rather than a more robust ballistic entry trajectory used for some robotic missions. The large variations in Mars atmospheric properties make a controlled entry and a safe precision landing for manned missions a di?cult engineering problem. Model reference adaptive control is a candidate solution for the Mars entry control problem. This type of controller has an adaptation mechanism that reduces tracking errors in the presence of uncertain parameters such as atmospheric density or vehicle properties. This thesis develops two di?erent adaptive control systems for the Mars ellipsled, a vehicle which is much larger than those that carried robotic payloads to Mars in the past. A sample mission will have multiple ellipsleds arriving at Mars carrying an assortment of payloads. It is of critical importance that the vehicles land in close proximity to each other to best assure that the crew has manageable access to their payloads. The scope of this research encompasses the atmospheric ?ight of the ellipsled, starting at the entry interface point through the ?nal parachute deployment. Tracking performance of an adaptive controller for prescribed entry trajectories in the pres?ence of atmospheric and vehicle model uncertainties is shown here. Both adaptive controllers studied in this thesis demonstrate successful adaptation to uncertainties in the Martian atmosphere as well as errors in the vehicle properties. Based on these results, adaptive control is a potential option for controlling Mars entry vehicles.Item Aeolian dune dynamics and the stratigraphic record(2016-12) Brothers, Sarah Christian; Kocurek, Gary; Byrne, Shane; Hern, Caroline; Holt, John; Mohrig, DavidDunes and dune fields are dynamic features that respond to the unique boundary conditions under which they evolve by changing migration habits, types and frequencies of interactions, and morphologies. As such, dunes convey information about changing atmospheric and surface conditions on planetary bodies including Earth, Mars, Venus, and Titan, and the stratigraphic record left by these bedforms is used to interpret the evolution of paleoclimate and surface environments. In four parts this work examines how the dynamics of individual dunes, dune fields, and aeolian systems influence stratigraphic architectures across multiple spatial scales. At White Sands Dune Field, New Mexico, the decadal histories of defect and bedform repulsion-type interactions are traced through a time-series of images. The resultant stratigraphic architectures are derived from plan-view exposures and ground penetrating radar sensing of dune interiors. This is the first documentation of the unique stratigraphic architectures that result from interactions between dunes. Within Chasma Boreale, Planum Boreum, Mars, boundary conditions controlling the discrete geomorphic expressions of the Hyperboreae Undae dune fields are evaluated using morphologic distributions. The distributions reveal that dune field expressions change over short horizontal scales and are dependent upon wind regime and sediment state, which operate under the background condition of dune induration by ice. Hyperboreae Undae form only part of the Chasma Boreale sediment system, however. Perennial layered ice deposits also are present on the floor of the reentrant. The changing balance of ice- and sand-dominated processes in space and time have resulted in an accumulation that transitions between ancient aeolian cavi unit-style accumulation and modern layered ice deposit-style accumulation. These accumulations can be interpreted through aeolian sequence stratigraphy. Findings from the Chasma Boreale transitional sediment system are applied to nearby outcrops of a transitional section of ancient cavi unit, which formed in an environment analogous to the modern Chasma Boreale sediment system. A sequence interpretation of the transitional cavi unit stratigraphic succession demonstrates how the aeolian system transitioned into overlying water ice deposits without a gap in the geologic record, verifying that the cavi unit and NPLD should be unified under a sequence stratigraphic framework.Item Aeolian dune-field boundary conditions and dune interactions related to dune-field pattern formation on Earth and Mars(2009-12) Ewing, Ryan Cotter; Kocurek, GaryAeolian dune fields form some of the most striking patterns on Earth and Mars. These patterns reflect the internal dune dynamics of self-organization within boundary conditions, which are the unique set of environmental variables within which each dune field evolves. Dune-field pattern self-organization occurs because of interactions between the dunes themselves and the rich diversity of dune-field patterns arises because boundary conditions alter the type and frequency of dune interactions. These hypotheses are explored in three parts. First, source-area geometry and areal limits are two newly recognized boundary conditions. Measurements of crest length and spacing from satellite images of dune patterns with point and line source-area geometries show an increase in crest length and spacing over distance, whereas crest length and spacing in plane-sourced patterns emerge equally across the dune field. The areal limit boundary condition is the size and shape of the dune field itself. Empirical measurements from ten dune fields ranging over four orders of magnitude in area show that spacing increases and defect density decreases as the area of the dune field increases. A simple analytical model indicates that dune fields that are five times longer in the dune migration direction can achieve the greatest spacing for a given area. Second, time-series aerial photographs and airborne LiDAR show that fully developed, crescentic aeolian dunes at White Sands, New Mexico, interact and the dune pattern organizes in systematically similar ways as wind ripples and subaqueous dunes and ripples. Interaction type, classified as constructive, regenerative or neutral in terms of pattern development, changes spatially with the pattern because of the imposition of the line-source area and sediment availability boundary conditions. Upwind dominance by constructive interactions at the field line-source yields to neutral and regenerative interactions in the sediment availability-limited field center. Third, the dune-field pattern in the Olympia Undae Dune Field on Mars is comprised of two generations of dunes. This scenario of pattern reformation with a new wind regime shows that the emergence of the younger pattern is controlled by the boundary condition of the antecedent dune topography imposed upon the interaction between the younger and older patterns.Item Determining Nighttime Atmospheric Optical Depth Using Mars Exploration Rover Images(2013-07-22) Bean, Keri MarieMartian clouds and dust play an important part of the radiative transfer and energy balance budget. To assist in fully understanding the impact of clouds and dust, the complete diurnal cycle needs to be characterized. One of the best methods to track diurnal variations on Mars is by measuring optical depth. The spatial and temporal trends of optical depth give insight into the dust and water cycles of the Martian atmosphere. Until now, spacecraft could only obtain optical depth during the day. In this thesis, nighttime images from the Mars Exploration Rover Spirit are used to calculate nighttime optical depth using photometric methods to capture star flux. Bright stars in well-known constellations are used in this analysis. The observed flux was compared to the expected flux to give nighttime optical depth values. The observed nighttime optical depth was consistently similar to the daytime optical depth values on both an individual image and sol-averaged basis. Recommendations are made going forward to use the Mars Science Laboratory Curiosity for conducting an optimal nighttime optical depth campaign to fully characterize the diurnal dust and water cycles of Mars. The Curiosity rover is well suited for nighttime imaging and can potentially provide valuable insight into the nighttime dust and cloud trends.Item Evidence for changes in coastline-controlled base level from fluvial stratigraphy at Aeolis Dorsa, Mars(2014-12) Cardenas, Benjamin Thomas; Mohrig, David; Kocurek, GaryThere is evidence that a subset of fluvial deposits at Aeolis Dorsa, a basin on Mars, preserve incised valleys carved and filled during changes in base level, which was likely controlled by water surface elevation of a large lake or sea. Three low-albedo, channelized corridors, each several tens of kilometers long, contain relict point bars and scooped boundaries at their bases, indicating that the base and lateral extent of each corridor was defined by a migrating, net-erosional river. Above the basal deposits are stacks several tens of meters thick of “inverted sinuous ridges”, which are channel-filling deposits that have been exhumed and topographically inverted. Indicators of avulsions, channel re-occupations, an overall flattening of basal topography, and confinement of inverted sinuous ridges to the dark corridors are evidence of the gradual filling of a valley cut by the basal migrating river. Valley incision and fill are common responses to sea level change on Earth. Aeolis Dorsa is currently open to the northern lowlands of Mars, where an ocean has been hypothesized to have once existed, although a large lake could have also controlled base level. Cross-cutting valleys require at least two episodes of base level fall and rise. The magnitudes of the base level changes are estimated at about 80 meters, based on the thickness of the valley-filling stratigraphy. Meander asymmetry is consistent with a southeastern flow direction, and is supported by a set of branching fluvial deposits 40 km to the southeast which, qualitatively, appear to be deltaic in origin.Item FLUKA Simulation of the Radiation Environment on the Surface of Mars(2013-07-10) Northum, JeremyUncertainties persist regarding the assessment of the carcinogenic risk associated with galactic cosmic ray (GCR) exposure. The GCR spectrum peaks in the range of 300 MeV/n to 700 MeV/n and is comprised of elemental ions from H to Ni. While Fe ions represent only 0.03% of the GCR spectrum in terms of particle abundance, they are responsible for nearly 30% of the dose equivalent in free space. Because of this, radiation biology studies focusing on understanding the biological effects of GCR exposure generally use Fe ions. Acting as a thin shield, the Martian atmosphere alters the GCR spectrum in a manner that significantly reduces the importance of Fe ions. Additionally, albedo particles emanating from the regolith complicate the radiation environment. The present study uses the Monte Carlo code FLUKA to simulate the response of a tissue-equivalent proportional counter on the surface of Mars to produce dosimetry quantities and microdosimetry distributions. The dose equivalent rate on the surface of Mars was found to be 0.18 Sv/y with an average quality factor of 2.9 and a dose mean lineal energy of 18.4 keV/?m. Albedo neutrons accounted for 25% of the dose equivalent. Additionally, differential energy spectra were generated in order to determine the fractional contribution to frequency, dose, and dose equivalent for each elemental ion from H to Ni on the surface of Mars. Fe ions were found to account for just 1.3% of the dose equivalent while H and He ions were found to account for 32% and 17%, respectively. It is anticipated that these data will provide relevant benchmarks for use in future risk assessment and mission planning studies.Item Local Dynamics of Synoptic Waves in the Martian Atmosphere(2011-10-21) Kavulich, Michael J., Jr.The sources and sinks of energy for transient waves in the Martian atmosphere are investigated, applying diagnostic techniques developed for the analysis of terrestrial baroclinic waves to output from a Mars General Circulation Model. These diagnostic techniques include the vertically averaged eddy kinetic energy and regression analysis. The results suggest that the primary source of the kinetic energy of the waves is baroclinic energy conversion in localized regions. It is also shown that there exist preferred regions of baroclinic energy conversion. In addition, it is shown that downstream baroclinic development plays an important role in the evolution of the waves and in the baroclinic energy conversion process. This is the first time that evidence for downstream baroclinic development has been found for an atmosphere other than the terrestrial one.Item Mars Exploration Rover (MER) Panoramic Camera (Pancam) Twilight Image Analysis for Determination of Planetary Boundary Layer and Dust Particle Size Parameters(2012-02-14) Grounds, Stephanie BethHow the dust cycle works on Mars is a key atmospheric issue, as the dust cycle is arguably the dominant cycle in the current Martian climate. In addition, how much is known about the Martian planetary boundary layer is mostly determined from models with very little in-situ data from contemporaneous studies to validate such boundary layer characteristic assumptions, and the model studies have not been able to define a known height for a possible boundary layer on Mars using ground-based investigations prior to this research. The Mars Exploration Rovers (MERs), however, show promise in offering a unique chance to take surface-based measurements to offer support for dust and boundary layer measurements made from remote sensors. There are three main objectives of this study: to constrain the late-afternoon maximum height of the boundary layer for both MER sites, to constrain the mean particle size and variance of the size distribution in the atmosphere, and to use these results to demonstrate that sunset and twilight imaging is a useful survey of otherwise difficult-to-determine parameters that are needed in several tools for studying Mars? atmosphere. A modeling approach using twilight-based Sun imaging by the MERs (Sol 1959 for Spirit and Sol 695 for Opportunity) is used to constrain boundary layer and dust particle size parameters. After determining which parameters control which observables, resulting elevations and azimuths are matched up to specific observations from the available MER datasets. A Monte Carlo code produces the model that is then compared to Sol data with plotting of resulting error. Results include PBL height and structure estimations and plots along with generalized particle size information for each MER site on the given Sol. Figures show comparisons of this study?s particle size results with that of previous studies as well as maps of fit qualities for boundary layer parameters compared to a contemporaneous modeled scale height estimation. Results show promise for planning future MER-based campaigns and models.Item Mars north polar ice stratigraphy project : a curriculum module for 5th grade(2011-08) Chavez, Augustine Faustino; Holt, John W., Ph.D.; Wilson, Clark R.This report is explores the need for a curriculum module for late elementary school students by looking at what drives student interests and motivations in pursuing careers in the sciences. The curriculum module created is composed of visual aids, including video animations, a 3-D scale model, and a hands-on, guided classroom activity. Exploring the stratigraphy on Mars Planum Boreum northern polar ice cap using radargrams from the Mars Reconnaissance Orbiter and modeling sublimation of Carbon Dioxide with a dry ice experiment, the curriculum module will be tested and improved upon over the next academic year in a 5th grade classroom with intent for submission to NASA for funding and eventual dissemination to the general public. The goal of the project is to add new, engaging dimensions to space science activities and to understanding of fundamental geologic principles, using real-time applications to foster interest and motivate students to enter the fields of the geosciences in the future.Item Morphology of the Planum Boreum basal unit, Mars, and constraints on the origin and timing of icy circumpolar deposits(2015-05) Brothers, Thomas Charles; Holt, John W., Ph. D.; Wood, Lesli J; Tanaka, Kenneth; Kocurek, Gary A; Mohrig, DavidData from the Shallow Radar instrument on Mars Reconnaissance Orbiter have enabled detailed scientific exploration of martian ice. Orbital ground penetrating radar enabled scientists to study subsurface ice stratigraphy, to uncover the geologic structure of ice on Mars with remarkable results for the north pole. On the north pole of Mars sits a massive, approximately two kilometer thick, deposit of pure water ice. This deposit is underlain with a sand and ice mixture that reaches 1.5 km maximum thickness. This dissertation examines the nature of the old sand/ice mixture on Mars' north pole. We use this ice to identify early trends in deposition and erosion on Mars' north pole and ultimately to link ice rich deposits that are not part of the polar cap. This multi-part study endeavors to understand and constrain the drivers of Mars' polar ice deposition. With careful stratigraphic analysis we hypothesize that depositional regime has not changed drastically since the upper part of the sand and ice mixture was emplaced in Middle Amazonian time. Sediment supply became limited and ice more plentiful with respect to sand; however, deposition remained aeolian in nature. Additionally, our work finds evidence that circumpolar landforms are related to the central mass of ice on Planum Boreum. We present evidence supporting a coeval evolution of the circumpolar deposits and central Planum Boreum. We also present evidence that refutes these features being part of a more extensive ancient ice cap. This indicates that the processes occurring at Planum Boreum are likely mirrored in nearby landforms such as small craters and isolated ice wedges. This is fundamental to polar science, the processes occurring on Planum Boreum and the processes responsible for deposition of the north polar layered deposits can be analyzed at additional locations. Furthermore, we find that if a climate signal exists in the ice deposits, as has been postulated, these circumpolar features are likely to contain the same climate signal as the central ice cap. Thus, this work unifies the complexity of martian polar processes and suggests future avenues of research.Item On the spiral troughs of Mars(2013-08) Smith, Isaac Blaine; Holt, John W., Ph. D.The north and south polar layered deposits (NPLD and SPLD respectively) of Mars are 2 – 3 km thick and mostly ice, comprising nearly all of the known water reserves on Mars. They are commonly believed to hold a detailed record of recent (~10 – 100 Myr) climate within their layers. Dominating the surface of the NPLD, intriguing spiral depressions called troughs, exhibit a pinwheel appearance. In late 2006, the Shallow Radar (SHARAD) instrument began making observations. SHARAD can detect internal structure within the PLD, making observations that are impossible with instruments that only inspect the surface. SHARAD data reveals a unique stratigraphic record associated with trough formation and migration. The troughs did not exist during deposition of the first half of NPLD accumulation but initiated some 1000 m below the current surface and have migrated as much as 100 km northward. Three processes are responsible for this migration: wind transport, insolation induced sublimation, and atmospheric deposition. I synthesize work from ground penetrating radar, optical imagery, established analogs, and atmospheric modeling in order to derive a process model that describes trough formation and evolution, including migration. The NPLD spiral troughs belong to a larger classification of features called cyclic steps, which can exist in either erosional or depositional environments. On the SPLD, troughs and a variety of other features exist. While SPLD features are more complex than NPLD troughs, they exist due to the same three processes.Item Use of raw Martian and Lunar soils for surface-based reactor shielding(2010-12) Christian, Jose L. 1963-; Landsberger, SheldonFor several decades, the idea of flying and landing a less-than-man-rated nuclear reactor for planetary surface applications has been considered. This approach promises significant mass savings and therefore reduction in launch cost. To compensate for the lack of shielding, it has been suggested the use of in-situ materials for providing radiation protection. This would take the form of either raw dirt walls or processed soil materials into blocks or tile elements. As a first step in determining the suitability of this approach, it is necessary to understand the neutron activation characteristics of these soils. A simple assessment of these activation characteristics was conducted for both Martian and Lunar soils using ORIGEN2.2. An average composition for these soils was assumed. As a baseline material, commonly used NBS-03 concrete was compared against the soils. Preliminary results indicate that over 2.5 times more gamma-radiation production of these soils vs. concrete took place during the irradiation phase (a baseline of 2.4 x 1011 neutrons/sec-cm2 was assumed). This was due primarily to radiative capture on Na23 and Mn55 and subsequent decay of their activation products. This is does not necessarily disqualify these materials as potential shielding material since the -radiation output was only in the order of 4.2 x 108 photons/cm3-sec. Furthermore, these soils did not show any significant activity after shutdown of the neutron source (the reactor), since all activation products had very short half lives. Their performance in this area was comparable to that of NBS-03 concrete.