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NASA NTRS1999

Punctured Parallel and Serial Concatenated Convolutional Codes for BPSK/QPSK Channels

As available bandwidth for communication applications becomes scarce, bandwidth-efficient modulation and coding schemes become ever important. Since their discovery in 1993, turbo codes (parallel concatenated convolutional codes) have been the center of the attention in the coding community because of their bit error rate performance near the Shannon limit. Serial concatenated convolutional codes have also been shown to be as powerful as turbo codes. In this dissertation, we introduce algorithms for designing bandwidth-efficient rate r = k/(k + 1),k = 2, 3,..., 16, parallel and rate 3/4, 7/8, and 15/16 serial concatenated convolutional codes via puncturing for BPSK/QPSK (Binary Phase Shift Keying/Quadrature Phase Shift Keying) channels. Both parallel and serial concatenated convolutional codes have initially, steep bit error rate versus signal-to-noise ratio slope (called the -"cliff region"). However, this steep slope changes to a moderate slope with increasing signal-to-noise ratio, where the slope is characterized by the weight spectrum of the code. The region after the cliff region is called the "error rate floor" which dominates the behavior of these codes in moderate to high signal-to-noise ratios. Our goal is to design high rate parallel and serial concatenated convolutional codes while minimizing the error rate floor effect. The design algorithm includes an interleaver enhancement procedure and finds the polynomial sets (only for parallel concatenated convolutional codes) and the puncturing schemes that achieve the lowest bit error rate performance around the floor for the code rates of interest.

Acikel, Omer Fatih↗
NASA NTRS1998

Proposed Mars Surveyor Landing Sites in Northern Meridiani Sinus, Southern Elysium Planitia, and Argyre Planitia

Our objective is to propose two landing sites that the Mars Surveyor 2001 Lander and Athena Rover could go to on Mars that should meet the safety requirements of the spacecraft landing system and optimize surface operations (chiefly driven by power and communications requirements). An additional site within Argyre Planitia, initially proposed by Parker to the Mars Surveyor Landing Site program, is also proposed for potential consideration for post-2001 missions to Mars, as it is well outside the current latitude limits for the Athena Rover. All three sites are designed to be situated as close to a diversity of geologic units within a few kilometers of the landing site so that diversity can be placed in a geologic context. This objective is very different from the Mars Pathfinder requirement to land at a site with a maximum chance for containing a diversity of rocks within a few tens of meters of the lander. That requirement was driven by the Sojourner mobility limit of a few tens of meters. It can be argued that the Athena project, with its much larger mobility capability, might actually want to avoid such a site, because placing collected samples in geologic context would be difficult. While it has been argued, both before and after the Mars Pathfinder landing, that the provenance for local blocks may be determined by orbiter spectra, primarily from the MGS TES instrument, our ability to do so has yet to be demonstrated. Indeed, several months after conclusion of the Pathfinder mission, we have yet to reach a consensus on the composition of local materials. Our primary data set for selecting a landing site within the latitude and elevation constraints of the 2001 mission is the Viking Orbiter image archive. The site must be selected to place the landing ellipse so as to avoid obvious hazards, such as steep slopes, large or numerous craters, or abundant large knobs. For this purpose, we chose a resolution limit of better than 50 m/pixel. This necessarily excludes from the present study images from current and future orbiter spacecraft, until such data does become readily available. Within each proposed region, it may be possible to identify additional sites once these data become available. Second, the fine-component thermal inertia data, should be greater than about 5 or 6 cgs Units (10(exp -3) cal/sq cm s(exp -0.5)/K). Low thermal inertias imply dusty environments, which could pose a mobility hazard. Similarly, the albedo of the site should not be particularly high, which would also suggest dusty surfaces. Low albedos are preferred, as they often coincide with low Viking red:violet ratios and indicate less dusty surfaces. Next, the Modeled Block Abundance should also not be too high or too low. Based on the Viking Lander and Mars Pathfinder experiences, percentages of blocks should be on the order of 5-25%. Too many blocks could pose a hazard to the landing and mobility. Too few blocks could also indicate a dusty surface. Primary Landing Site: Northern Meridiani Sinus (Proposed by T. J. Parker and K., S. Edgett) Vital Statistics: (1) Latitude, Longitude: 0-3 N, 350-2 W. *Elevation (Viking): about0.5-1.5 Ian. (2) Viking Orbiter Image coverage: Excellent coverage by 15 - 25 m/pixel images (orbits 709A and 410B). Possible stereo coverage in region where two orbits overlap (probably small parallax angle, as these orbits are not listed in NASA Contractor Report 3501) (3) Albedo: about .18 -.26 (4) Block Abundance: 5-26% (5)Fine-Component Thermal Inertia: 5-9 cgs units This region consists of bright deposits similar to those described by Edgett et al, that also lie within a prominent dark albedo region. These deposits are flat-lying, to such a degree that they ramp against topography rather than draping over it. This led Edgett and Parker to suggest that they may be subaqueous sediments, possibly lacustrine or marine evaporites, laid down sometime from the late Noachian to middle Hesperian (age determination pending crater counts). A contact between this material and elevated, dissected highlands to the south was identified , and is described by Edgett et al. Our desire in proposing this landing site is to sample the edge of this deposit where it has been exposed through etching, presumably eolian deflation (the deposit, though in the highlands, is itself only lightly to moderately cratered). This should enable access to in situ stratigraphy. The actual landing site will be selected where slopes are not expected to be steep, such that the rover itself should be able to traverse them and sample layered materials on the way, either up or down the slope. Perhaps due to uncertainties at this time as to the friability or meter-scale roughness of the deposit, it might make sense to place the landing ellipse on the exhumed highland surface adjacent to the deflated margin of the deposit and plan on driving to the deposit rather than landing on it and driving downslope. This should also enable imaging the margin for evidence of layering should it prove too difficult to climb. A target ellipse on the highland surface should also allow Athena access to ancient Noachian highland materials, particularly if placed near crater ejecta or an inlier of knobby material. Secondary Landing Site: Southern Elysium Planitia (Proposed by T. J. Parker) Vital Statistics: (1) Latitude, Longitude: 1.5-3.5 S, 195-198 W. (2) Elevation (Viking): -1.0 km. (3) Viking Orbiter Image coverage: Excellent coverage by 15 - 25 m/pixel images (orbit 725). Possible stereo coverage between images from beginning and end of orbit that overlap (probably small parallax angle) (4) Albedo: about .27-.28 (5) Block Abundance: 4-7% (6) Fine-Component Thermal Inertia: about 3 cgs units This region consists of eroded knobby material, probably of Noachian age, though much of the crater population has been destroyed, that is onlapped at a sharp contact by an extensive plains unit in southern Elysium Planitia that is Amazonian in age. The plains materials have been attributed to unusually low-viscosity flood lavas from fissures south of the Elysium volcanic rise, or to lacustrine materials associated with a large, Amazonian lake at the source of Marte Vallis. Parker and Schenk presented evidence in support of the latter interpretation, though they attributed the putative shore morphology to an embayment of a northern plains ocean into the southern Elysium region. Detailed examination of the margin of the deposit, showing erosion, not simply burial, of small crater rims and fluidized ejecta blankets, also points to lacustrine or marine sedimentation rather than volcanic plains burial. The plains surface exhibits a "crusty" appearance that many researchers have attributed to pressure ridges in lava flows. In a lacustrine context, they also resemble pressure ridges in desiccated evaporite deposits and salt-rimmed pools (now dry) similar in scale and morphology to spectacular, hundred meter-scale pool rims in alkaline Lake Natron, East African Rift. The eroded highland margin surface adjacent to these plains appears to be fairly smooth, even at 15 m/pixel. Isolated knob inliers are scattered from a few kilometers to several tens of "kilometers apart. Heights of the knobs have not been measured yet but, based on experience with similar features in the Pathfinder landing ellipse, are probably typically on the order of several tens of meters high and smaller, though some of the largest knobs in the region are probably up to a few hundred meters high. Two craters larger than a kilometer in diameter, with fluidized deposits, lie nearby the proposed landing site. Very high-resolution images from MOC should help to determine whether a landing site navigable by the Athena rover could be placed in this region. The space between knobs and craters is large enough to enable placement of a target landing ellipse between them but still provide access to one or more of them and to the margin of the Elysium plains material. Post-2001 Mars Surveyor Landing Site: Argyre Planitia (Proposed by T. J. Parker) Vital Statistics: (1) Latitude, Longitude: 55-56 S, 41-43 W. (2) Elevation (Viking): 1.0 km. (3) Viking Orbiter Image coverage: Excellent coverage by 40 m/pixel images (orbits 567B, 568B, and 569B). Excellent stereo coverage with large parallax angles over the entire landing site region, and much of central and southern Argyre. (4) Albedo: about .23-.24 (5) Block Abundance: No data (6) Fine-Component Thermal Inertia: No data The floors of both the Argyre and Hellas basins contain etched layered materials that are probably thick accumulations of channel or lacustrine sediments. The deposits in Hellas are much more eroded than those in Argyre, and Hellas lacks a channel outlet. Argyre is unique in that Uzboi Vallis flowed out of the basin, requiring overflow of a standing body of water within Argyre. This makes it the largest impact basin on Mars with channels both draining into it and flowing out from it. Hellas' channels may be catastrophic flood channels, whereas Argyre was fed by modest-scale valley networks, though the outlet at Uzboi Vallis was a catastrophic flood Highland craters and basins of this kind should be high-priority landing targets for missions intended to focus on the search for either prebiotic organic materials or even simple fossil microorganisms. Basins with internally-draining valley networks should be preferred over flood channels, as they could have provided the long-term influx of water favorable to the origin of life. (Catastrophic floods are not conducive to fossil preservation, due to their very short durations and high transportation energies). They also afford an opportunity to study the evolution of the planet's climate and volatiles during the period of time between the late Noachian and early Hesperian, when a drastic change from a proposed early warm, wet climate to one more closely resembling the modern environment is thought to have occurred. Large basin

Parker, T. J.↗
NASA NTRS1998

Deep Basalt Aquifers in Orcus Patera, Elysium Basin Mars: Perspectives for Exobiology Exploration

Direct indicators of shorelines, spillways, and terraces allowed to determine the extent of the Elysium Paleolake between the contour-lines 1000 and 500 m below the Martian datum. The Elysium Paleolake is bordered north by Orcus Patera (14N/181W), which lies west of the Tartarus Montes and Tartarus Colles. The Orcus Patera displays an ellipse-shaped collapsed caldera of 360-km long and 100-km wide. Viking topographic data show that the bottom of the caldera is located at 2500 below the Martian datum, and surrounded by a steep-walled ram art which crest is located at about 0 m elevation. Considering the localization of Orcus Patera in the Elysium paleolake, its altimetry, and the magmatic origin of this caldera, we propose the existence of a paleolake in Orcus Patera generated (a) by juvenile water from magma during the Noachian period, and (b) by intermittent influx of the Elysium Basin from Hesperian to Amazonian. Results are encouraging to consider this site as a potential high-energy source environment for microbial communities. are circumscribed by a 50-km wide lava field mapped as Noachian material. The structure of Orcus Patera represents the record of material erupted from a magmatic reservoir. The caldera is enclosed by steep inner walls (25% measured from topographic data), values which could be in agreement with the presence of a deep magmatic reservoir, as suggested by the typology of Crumpler et.al. The depth of the caldera might be due to the collapse of the magma reservoir, and the release of gases accompanying the magma thermal evolution. Origins of water for the paleolake(s): The water that generated a paleolake in Orcus Patera may have come from two origins: (1) Juvenile water: Plescia and Crips estimated a magma H20 content by weight between 0.5% and 1.5% using for the first value a comparison with terrestrial basalt, and for the second values from a Martian meteorite. The amount of H20 can be estimated by the volume of erupted lava, and the lava content of the caldera. In this study, we adopt a water content of 1%. The total volume of magma that has been contained in the caldera, and the volume of lava contained in the observed lava field is about 110 x 10(exp 6) cubic km, that gives a total volume of 1.10 x 10(exp 6) cubic km of water. The juvenile water expelled by the overpressure within the magma chamber charged with desolved water-vapor may have moved into the crust. The decrease in overburden pressure led to bubble formation. The ascent of these bubbles generated a pressurization of the magma, which was sufficient to fracture the overlaying magma layer, (2) Water from Elysium paleolake. During the Amazonian, the rise of the Elysium paleolake level generated an overspilling that supplied the caldera with water. The southern portion of the crest shows a deep gap 12-km wide at -1500 m elevation, locating the gap between 500 to 1000 in below the assumed water of Elysium paleolake, thus facilitating the influx of Elysium paleolake water into Orcus Patera. Bathymetric calculations give a floor area of 25,500 sq km at -2000 m elevation, and a water volume of 42,000 cubic km, with a lake-level at -1500 m. A substantial amount of water may have percolated through the fractured lava, and part of the volume may have overspilled the northern crest of Orcus Patera to debouch in the Tartarus Montes region. We envision the formation of a subsurface aqueous environment in basaltic rocks at the contact of the two water-source origins, possibly the percolating surface lake water, and more likely the juvenile water. Similarly to terrestrial calderas, Orcus Patera might be surrounded by ring-fractures caused by the collapse of the magma chamber that followed the release of gases. These ring-fractures may have been covered later by sedimentation in the caldera (lacustrine, aeolian, and volcanic), and by mass wasting. The detumescence of the magma in the caldera, and the vesiculation of the juvenile water may have operated simultaneously. Comparatively to terrestrial melts, Martian iron-rich melts are denser. This greater density implies greater effusion rates (eight-times terrestrial values), and larger fissuration widths (two-times terrestrial ones). With increasing vesiculation of magma, the bubbles interact with one-another because there are of similar pressure. They make a magma froth at the contact with the caldera surface, and on the walls of the fractures. In the saturated magma, froth, where the volume ratio of gases-to-liquid is about 4:1, the bubbles form a huge surface area of interconnected spaces. Bubbles near the caldera surface disrupt the magma, and fragmentation takes place, which moves downward through the magma column. On Earth, the bubbles are likely to grow between 1 and 50 mm in diameter due to the difference between the magma surface tension, and the bubble supersaturation pressure. The Martian low-pressure at surface level is likely to accelerate the expansion of the bubbles, and increase their final diameter and number, creating more voids in the magma. The strong magma froth with enclosed juvenile water bubbles interconnected with exsolved gas bubbles constitute a potential geothermal environment for geochemical energy production from basalt and water that does not require excessive temperatures. This process can start at +20C. Similar types of environments have been shown on Earth as potential energy sources for microbial metabolism, and could have provided deep aqueous basaltic niches for possible Martian microorganisms, even geologically recently. During the Amazonian, combination of volcanism and water activity still existed on Mars. Moreover, this type of potential niches open ways for investigation of possible oases of extinct or extant life, not only on paleolakes, and surface hydrothermalism spring areas, but also all large systems of fossae, which combine hydrologic and volcanic activities, and which provide an energy source, and an underground shelter to prevent surface UV bombardment. Additional information contained in the original.

Grin, E. A.↗
NASA NTRS2000

The Dynamics of Miscible Interfaces: A Space Flight Experiment

Experiments as well as accompanying simulations are described that serve in preparation of a space flight experiment to study the dynamics of miscible interfaces. The investigation specifically addresses the importance of both nonsolenoidal effects as well as nonconventional Korteweg stresses in flows that give rise to steep but finite concentration gradients. The investigation focuses on the flow in which a less viscous fluid displaces one of higher viscosity and different density within a narrow capillary tube. The fluids are miscible in all proportions. An intruding finger forms that occupies a fraction of the total tube diameter. Depending on the flow conditions, as expressed by the Peclet number, a dimensionless viscosity ratio, and a gravity parameter, this fraction can vary between approximately 0.9 and 0.2. For large Pe values, a quasi-steady finger forms, which persists for a time of O(Pe) before it starts to decay, and Poiseuille flow and Taylor dispersion are approached asymptotically. Depending on the specific flow conditions, we observe a variety of topologically different streamline patterns, among them some that leak fluid from the finger tip. For small Pe values, the flow decays from the start and asymptotically reaches Taylor dispersion after a time of O(Pe). Comparisons between experiments and numerical simulations based on the 'conventional' assumption of solenoidal velocity fields and without Korteweg stresses yield poor agreement as far as the Pe value is concerned that distinguishes these two regimes. As one possibility, we attribute this lack of agreement to the disregard of these terms. An attempt is made to use scaling arguments in order to evaluate the importance of the Korteweg stresses and of the assumption of solenoidality. While these effects should be strongest in absolute terms when steep concentration fronts exist, i.e., at large Pe, they may be relatively most important at lower values of Pe. We subsequently compare these conventional simulations to more complete simulations that account for nonvanishing divergence as well as Korteweg stresses. While the exact value of the relevant stress coefficients are not known, ballpark numbers do exist, and their use in the simulations indicates that these stresses may indeed be important. We plan to evaluate these issues in detail by means of comparing a space experiment with corresponding simulations, in order to extract more accurate Korteweg stress coefficients, and to confirm or deny the importance of such stresses.

Maxworthy, Tony↗
NASA NTRS2002

Surprises from a Deep ASCA Spectrum of the Broad Absorption Line Quasar PHL 5200

We present a deep (approx. 85 ks) ASCA observation of the prototype broad absorption line quasar (BALQSO) PHL 5200. This is the best X-ray spectrum of a BALQSO yet. We find the following: (1) The source is not intrinsically X-ray weak. (2) The line-of-sight absorption is very strong, with N(sub H) = 5 x 10(exp 23)/sq cm. (3) The absorber does not cover the source completely; the covering fraction is approx. 90%. This is consistent with the large optical polarization observed in this source, implying multiple lines of sight. The most surprising result of this observation is that (4) the spectrum of this BALQSO is not exactly similar to other radio-quiet quasars. The hard X-ray spectrum of PHL 5200 is steep, with the power-law spectral index alpha approx. 1.5. This is similar to the steepest hard X-ray slopes observed so far. At low redshifts, such steep slopes are observed in narrow-line Seyfert 1 (NLS1) galaxies, believed to be accreting at a high Eddington rate. This observation strengthens the analogy between BALQSOs and NLS1 galaxies and supports the hypothesis that BALQSOs represent an early evolutionary state of quasars. It is well accepted that the orientation to the line of sight determines the appearance of a quasar: age seems to play a significant role as well.

Mathur, Smita↗
NASA NTRS2002

Evidence of Spin and Energy Extraction in a Galactic Black Hole Candidate: The XMM-NEWTON/EPIC SPECTRUM of XTE 11650-500

We observed the Galactic black hole candidate XTE J1650-500 early in its fall of 2001 outburst with the XMM-Newton European Photon Imaging pn Camera (EPIC-pn). The observed spectrum is consistent with the source having been in the very high state. We h d a broad, skewed Fe Kar emission line that suggests the primary in this system may be a Kerr black hole and that indicates a steep disk emissivity profile that is hard to explain in terms of a standard accretion disk model. These results are quantitatively and qualitatively similar to those from an XMM-Newton observation of the Seyfert galaxy MCG -6-30-15. The steep emissivity in MCG -6-30-15 may be explained by the extraction and dissipation of rotational energy from a black hole with nearly maximal angular momentum or from material in the plunging region via magnetic connections to the inner accretion disk. If this process is at work in both sources, an exotic but fundamental general relativistic prediction may be confirmed across a factor of l0(exp 6) in black hole mass. We discuss these results in terms of the accretion flow geometry in stellar-mass black holes and the variety of enigmatic phenomena often observed in the very high state.

Miller, J. M.↗
NASA NTRS2004

Nonlinear Longitudinal Mode Instability in Liquid Propellant Rocket Engine Preburners

Nonlinear pressure oscillations have been observed in liquid propellant rocket instability preburner devices. Unlike the familiar transverse mode instabilities that characterize primary combustion chambers, these oscillations appear as longitudinal gas motions with frequencies that are typical of the chamber axial acoustic modes. In several respects, the phenomenon is similar to longitudinal mode combustion instability appearing in low-smoke solid propellant motors. An important feature is evidence of steep-fronted wave motions with very high amplitude. Clearly, gas motions of this type threaten the mechanical integrity of associated engine components and create unacceptably high vibration levels. This paper focuses on development of the analytical tools needed to predict, diagnose, and correct instabilities of this type. For this purpose, mechanisms that lead to steep-fronted, high-amplitude pressure waves are described in detail. It is shown that such gas motions are the outcome of the natural steepening process in which initially low amplitude standing acoustic waves grow into shock-like disturbances. The energy source that promotes this behavior is a combination of unsteady combustion energy release and interactions with the quasi-steady mean chamber flow. Since shock waves characterize the gas motions, detonation-like mechanisms may well control the unsteady combustion processes. When the energy gains exceed the losses (represented mainly by nozzle and viscous damping), the waves can rapidly grow to a finite amplitude limit cycle. Analytical tools are described that allow the prediction of the limit cycle amplitude and show the dependence of this wave amplitude on the system geometry and other design parameters. This information can be used to guide corrective procedures that mitigate or eliminate the oscillations.

Sims, J. D.↗
NASA NTRS2002

Stereo transparency and the disparity gradient limit

Several studies (Vision Research 15 (1975) 583; Perception 9 (1980) 671) have shown that binocular fusion is limited by the disparity gradient (disparity/distance) separating image points, rather than by their absolute disparity values. Points separated by a gradient >1 appear diplopic. These results are sometimes interpreted as a constraint on human stereo matching, rather than a constraint on fusion. Here we have used psychophysical measurements on stereo transparency to show that human stereo matching is not constrained by a gradient of 1. We created transparent surfaces composed of many pairs of dots, in which each member of a pair was assigned a disparity equal and opposite to the disparity of the other member. For example, each pair could be composed of one dot with a crossed disparity of 6' and the other with uncrossed disparity of 6', vertically separated by a parametrically varied distance. When the vertical separation between the paired dots was small, the disparity gradient for each pair was very steep. Nevertheless, these opponent-disparity dot pairs produced a striking appearance of two transparent surfaces for disparity gradients ranging between 0.5 and 3. The apparent depth separating the two transparent planes was correctly matched to an equivalent disparity defined by two opaque surfaces. A test target presented between the two transparent planes was easily detected, indicating robust segregation of the disparities associated with the paired dots into two transparent surfaces with few mismatches in the target plane. Our simulations using the Tsai-Victor model show that the response profiles produced by scaled disparity-energy mechanisms can account for many of our results on the transparency generated by steep gradients.

NASA Discipline Space Human Factors↗
NASA NTRS1998

Flight-Simulated Launch-Pad-Abort-to-Landing Maneuvers for a Lifting Body

The results of an in-flight investigation of the feasibility of conducting a successful landing following a launch-pad abort of a vertically-launched lifting body are presented. The study attempted to duplicate the abort-to-land-ing trajectory from the point of apogee through final flare and included the steep glide and a required high-speed, low-altitude turn to the runway heading. The steep glide was flown by reference to ground-provided guidance. The low-altitude turn was flown visually with a reduced field- of-view duplicating that of the simulated lifting body. Results from the in-flight experiment are shown to agree with ground-based simulation results; however, these tests should not be regarded as a definitive due to performance and control law dissimilarities between the two vehicles.

Jackson, E. Bruce↗
NASA NTRS2004

Constraints on Early Mars Evolution and Dichotomy Origin from Relaxation Modeling of Dichotomy Boundary in the Ismenius Region

The Martian dichotomy is a global feature separating the northern and southern hemispheres. The 3.5 - 4 Gyr old feature is manifested by a topographic difference of 2-6 km and crustal thickness difference of approx. 15 - 30 km between the two hemispheres. In the Ismenius region, sections of the boundary are characterized by a single scarp with a slope of approx. 20 deg. - 23 deg. and are believed to be among the most well preserved parts of the dichotomy boundary. The origin of the dichotomy is unknown. Endogenic hypotheses do not predict the steep slopes (scarps) of the dichotomy boundary. Exogenic models for forming the northern lowlands by impact cratering, associate the scarps along the dichotomy boundary with craters' rims, but are not globally consistent with the topography and gravity. In order to better understand the origin of the Martian dichotomy, it is necessary to know if the steep scarps along the boundary represent the original shape of the dichotomy. Smrekar et al. presented evidence showing that the boundary scarp in Ismenius is a fault along which the highland crust was down faulted. We test whether the relaxation process could produce faulting along the dichotomy boundary and examine the crustal and mantle conditions that would allow for faulting to occur within 1 Gyr and preserve the long wavelength topography over another 3 Gyr. We approach the problem by a combination of numerical and semi-analytical modeling. We test different viscosity profiles and crustal thicknesses by comparing our modeled magnitude, location and timing of plastic strain and displacements to detailed geologic observations in the Ismenius region.

Guest, A.↗
NASA NTRS2005

Volcanism and Volatile Recycling on Venus from Lithospheric Delamination

Venus has an unmoving lithosphere, a young surface indicative of volcanic resurfacing, and a wide variety of volcanic and tectonic features. The planet s ubiquitous magmatic features include 100,000 small shield volcanoes as well as the descriptively named pancakes, ticks, and arachnoids [1]. Coronae, volcanic and tectonic features up to 2,600 km in diameter, have been attributed to lithospheric interactions with upwelling plumes [e.g., 2], but more recently to delamination of the lower lithosphere with [3] or without [4] a central upwelling. Lavas issuing from different volcanic features appear to have a range of compositions, as evidenced by their apparent viscosities and by data from Soviet landers. Steep-sided or "pancake" domes [e.g., 5] appear to consist of more viscous magma [6], perhaps silicic compositions created by remelting basaltic crust [7]. These steep-sided domes are associated with coronae and with shield volcanoes effusing basaltic magmas [7,8] with apparently low viscosities (low enough to allow fluid flow for hundreds of km, creating channels reminiscent of water rivers on Earth). Pancake domes, in contrast, can be up to 3 km in height and have volumes from 30 to approx.3,000 km3 [calculated from data in 8], and hundreds dot the planet [6-8].

Elkins-Tanton, L. T.↗
NASA NTRS2005

Experimental Study of Large-Amplitude Faraday Waves in Rectangular Cylinders

Experiment on single-mode Faraday waves having two, thee, and four wavelengths across a rectangular cylinder of high aspect ratio is the subject of discussion. Previous experiments recently done by Henderson & Miles (1989) and by Lei Jiang et. a1 (1996) focused on Faraday waves with one and two wavelengths across rectangular cylinders. In this experimental study the waves steepness ranges from small at threshold levels to a large amplitude which according to Penny & Price theory (1952) approaches the maximum sustainable amplitude for a standing wave. The waves characteristics for small amplitudes are evaluated against an existing well known linear theory by Benjamin & Ursell (l954) and against a weakly nonlinear theory by J. Miles (1984) which includes the effect of viscous damping. The evaluation includes the wave neutral stability and damping rate. In addition, a wave amplitude differential equation of a linear theory including viscous effect by Cerda & Tirapegui (1998) is solved numerically to yield prediction of temporal profiles of both wave damping and wave formation at the threshold. An interesting finding from this exercise is that the fluid kinematic viscosity needs to increase ten times in order to obtain good agreement between the theoretical prediction and the experimental data for both wave damping and wave starting. For large amplitude waves, the experimental data are evaluated against the theory of Penny & Price which predicts wave characteristics of any amplitude up to the point at which the wave reaches its maximum amplitude attainable for a standing wave. The theory yields two criteria to show the maximum wave steepness, the vertical acceleration at the wave crest of half the earth gravity field acceleration and the including angle at the crest of 90 degrees. Comparison with experimental data shows close agreement for the wave crest acceleration but a large discrepancy for the including angle. Additional information is included in the original extended abstract.

Iek, Chanthy↗
NASA NTRS2006

Passive imaging based multi-cue hazard detection spacecraft safe landing

Accurate assessment of potentially damaging ground hazards during the spacecraft EDL (Entry, Descent and Landing) phase is crucial to insure a high probability of safe landing. A lander that encounters a large rock, falls off a cliff, or tips over on a steep slope can sustain mission ending damage. Guided entry is expected to shrink landing ellipses from 100-300 km to -10 km radius for the second generation landers as early as 2009. Regardless of size and location, however, landing ellipses will almost always contain hazards such as craters, discontinuities, steep slopes, and large rocks. It is estimated that an MSL (Mars Science Laboratory)-sized lander should detect and avoid 16- 150m diameter craters, vertical drops similar to the edges of 16m or 3.75m diameter crater, for high and low altitude HAD (Hazard Detection and Avoidance) respectively. It should also be able to detect slopes 20' or steeper, and rocks 0.75m or taller. In this paper we will present a passive imaging based, multi-cue hazard detection and avoidance (HDA) system suitable for Martian and other lander missions. This is the first passively imaged HDA system that seamlessly integrates multiple algorithm-crater detection, slope estimation, rock detection and texture analysis, and multicues- crater morphology, rock distribution, to detect these hazards in real time.

hazard detection↗
NASA NTRS2007

Global Properties of X-Ray Flashes and X-Ray-Rich GRBs Observed by Swift

We describe and discuss the spectral and temporal characteristics of the prompt emission and X-ray afterglow emission of X-ray flashes (XRFs) detected and observed by Swift between December 2005 and September 2006. We compare these characteristics to a sample of X-ray rich gamma-ray bursts (XRRs) and conventional classical gamma-ray bursts (C-GRBs)observed during the same period. We confirm the correlation between Epeak and fluence noted by others and find further evidence that XRFs and C-GRBs form a continuum. We also confirmed that our known redshift samples are consistent with the correlation between the peak energy (Epeak) and the isotropic radiated energy (Eiso), so called the Epeak-Eiso relation. The spectral properties of X-ray afterglows are similar to those of gamma-ray burst afterglows, but the temporal properties of the two classes are quite different. We found that the light curves of C-GRBs afterglow show a break to steeper indices (shallow-to-steep break) at much earlier times than do XRF afterglows. Moreover, the overall luminosity of X-ray afterglows of XRFs are systematically smaller by a factor of two or more compared with that of C-GRBs. These distinct differences in the X-ray afterglow between XRFs and C-GRBs are key to understanding not only a mysterious shallow-to-steep phase in the X-ray afterglow but also the unique nature of XRFs.

Sakamoto, T.↗
NASA NTRS2006

The Phase Curve Survey of the Irregular Saturnian Satellites: A Possible Method of Physical Classification

During its 2005 January opposition, the saturnian system could be viewed at an unusually low phase angle. We surveyed a subset of Saturn's irregular satellites to obtain their true opposition magnitudes, or nearly so, down to phase angle values of 0.01 deg. Combining our data taken at the Palomar 200-inch and Cerro Tololo Inter-American Observatory's 4-m Blanco telescope with those in the literature, we present the first phase curves for nearly half the irregular satellites originally reported by Gladman et al. [2001. Nature 412, 163-166], including Paaliaq (SXX), Siarnaq (SXXIX), Tarvos (SXXI), Ijiraq (SXXII), Albiorix (SXVI), and additionally Phoebe's narrowest angle brightness measured to date. We find centaur-like steepness in the phase curves or opposition surges in most cases with the notable exception of three, Albiorix and Tarvos, which are suspected to be of similar origin based on dynamical arguments, and Siarnaq.During its 2005 January opposition, the saturnian system could be viewed at an unusually low phase angle. We surveyed a subset of Saturn's irregular satellites to obtain their true opposition magnitudes, or nearly so, down to phase angle values of 0.01 deg. Combining our data taken at the Palomar 200-inch and Cerro Tololo Inter-American Observatory's 4-m Blanco telescope with those in the literature, we present the first phase curves for nearly half the irregular satellites originally reported by Gladman et al. [2001. Nature 412, 163-166], including Paaliaq (SXX), Siarnaq (SXXIX), Tarvos (SXXI), Ijiraq (SXXII), Albiorix (SXVI), and additionally Phoebe's narrowest angle brightness measured to date. We find centaur-like steepness in the phase curves or opposition surges in most cases with the notable exception of three, Albiorix and Tarvos, which are suspected to be of similar origin based on dynamical arguments, and Siarnaq.

satellites↗
NASA NTRS2008

A New Approach to Inferences for Pancake Domes on Venus

Figure 1 shows a radar image and topography for flat-topped, steep-sided "pancake" domes on Venus. At least 145 such domes have been identified on Venus [I] and are thought to be volcanic in origin [2]. Based on analysis of the dome surfaces, [3] suggested that only the late stage surface fractures are preserved, indicating entrainment and annealing of fractures during emplacement, consistent with a basaltic composition. Figure 1 shows a radar image and topography for flat-topped, steep-sided "pancake" domes on Venus. At least 145 such domes have been identified on Venus [I] and are thought to be volcanic in origin [2]. Based on analysis of the dome surfaces, [3] suggested that only the late stage surface fractures are preserved, indicating entrainment and annealing of fractures during emplacement, consistent with a basaltic composition.

Glaze, Lori S.↗
NASA NTRS2007

SPOT-VEG Based Analysis of Siberian Silkmoth Outbreak

The spatial and temporal dynamics of an outbreak of the Siberian silkmoth were correlated with topographic features of the affected area using SPOT-VEG data and a high resolution digital elevation model (DEM). In 2002-2003 an outbreak affected approximately 20,000 ha in the South Siberian mountains of Russia. The outbreak began between the elevations of approximately 430- 480 m and on southwest slopes with steepness < 5 degrees. As the pest searched for food it moved up and down slope, resulting in an elevation distribution split within a range of approximately 390-540 m and slope steepness up to 15 degrees. In the final phase the azimuth distribution of damaged stands became even. The correlation between the initial phase and topographic features can be used to prioritize monitoring forest areas most vulnerable to destruction by pests.

Kharuk, Viatcheslav I.↗
NASA NTRS2007

The Trails of Superluminal Jet Components in 3C 111

The parsec-scale radio jet of the broad-line radio galaxy 3C 111 has been monitored since 1995 as part of the 2cm Survey and MOJAVE monitoring observations conducted with the VLBA. Here, we present results from 18 epochs of VLBA observations of 3C 111 and from 18 years of radio flux density monitoring observations conducted at the University of Michigan. A major radio flux-density outburst of 3C 111 occurred in 1996 and was followed by a particularly bright plasma ejection associated with a superluminal jet component. This major event allows us to study a variety of processes associated with outbursts of radio-loud AGN in much greater detail than possible in other cases: the primary perturbation gives rise to the formation of a forward and a backward-shock, which both evolve in characteristically different ways and allow us to draw conclusions about the workflow of jet-production events; the expansion, acceleration and recollimation of the ejected jet plasma in an environment with steep pressure and density gradients are revealed; trailing components are formed in the wake of the primary perturbation as a result of Kelvin- Helmholtz instabilities from the interaction of the jet with the external medium. The jet-medium interaction is further scrutinized by the linear-polarization signature of jet components traveling along the jet and passing a region of steep pressure/density gradients.

Kadler, M.↗