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At least 1,063 records · Page 59

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NASA NTRS2005

BIOGEOCHEMICAL STUDIES OF PHOTOSYNTHETIC MICROBIAL MATS AND THEIR BIOTA

Photosynthetic microbial mats offer an opportunity to define holistic functionality at the millimeter scale. At the same time. their biogeochemistry contributes to environmental processes on a planetary scale. These mats are possibly direct descendents of the most ancient biological communities; communities in which oxygenic photosynthesis might have been invented. Mats provide one of the best natural systems to study how microbial populations associate to control dynamic biogeochemical gradients. These are self- sustaining, complete ecosystems in which light energy absorbed over a dial (24 hour) cycle drives the synthesis of spatially-organized, diverse biomass. Tightly-coupled microorganisms in the mat have specialized metabolisms that catalyze transformations of carbon, nitrogen, sulfur, and a host of other elements.

DesMarais, David↗

NASA NTRS2018

NASA Low Power Stirling Convertor for Small Landers, Probes, and Rovers Operating in Darkness

A variety of mission concepts have been studied by NASA and the U. S. Department of Energy that would utilize low power Radioisotope Power Systems (RPS) for probes, landers rovers, and repeaters. These missions would contain science instruments distributed across planetary surfaces or near objects of interest where solar flux is insufficient for using solar cells. Landers could be used to provide data like radiation, temperature, pressure, seismic activity, and other surface measurements for planetary science and to inform future mission planners. The studies proposed using fractional versions of the General Purpose Heat Source (GPHS) or multiple Light Weight Radioisotope Heater Units (LWRHU) to heat power conversion technologies for science instruments and communication. Dynamic power systems are capable of higher conversion efficiencies, which could enable equal power using less fuel or more power using equal fuel, when compared to less efficient static power conversion technologies. Providing spacecraft with more power would decrease duty cycling of basic functions and, therefore, increase the quality and abundance of science data. Low power Stirling convertors are being developed at NASA Glenn Research Center (GRC) to provide future micro spacecraft with electrical power by converting heat from one or more LWRHUs. An initial design converts multiple watts of heat to one watt of electrical power output using a Stirling convertor. Development of the concept includes maturation of convertor and controller designs, performance evaluation of an evacuated metal foil insulation, and development of system interfaces. Demonstration of the convertor is planned and represents a new class of RPS with power levels an order of magnitude lower than previous practical designs.

Wilson, Scott D.↗

NASA NTRS2018

NASA Low-Power Stirling Convertor for Small Landers, Probes, and Rovers Operating in Darkness

A variety of mission concepts have been studied by NASA and the U. S. Department of Energy that would utilize low power Radioisotope Power Systems (RPS) for landers, probes, and rovers. These missions would contain science measuring instruments distributed across planetary surfaces or near objects of interest where solar flux is insufficient for using solar cells. Landers could be used to provide data like wind, temperature, pressure, seismic activity, and other planetary measurements to mission planners or future explorers. The studies proposed using fractional versions of the General Purpose Heat Source (GPHS) or multiple Light Weight Radioisotope Heater Units (LWRHU) to heat power conversion technologies for science instruments and communication. Dynamic power systems are capable of higher conversion efficiencies, which could enable equal power using less fuel or more power using equal fuel, when compared to less efficient static power conversion technologies. Providing spacecraft with more power would decrease duty cycling of basic functions and, therefore, increase the quality and abundance of science data. Low power Stirling convertors are being developed at NASA Glenn Research Center (GRC) to provide future micro spacecraft with electrical power by converting heat from one or more LWRHUs. An initial design converts multiple Watts of heat to one Watt of electrical power output using a Stirling convertor. Development of the concept includes maturation of convertor and controller designs, performance evaluation of an evacuated metal foil insulation, and development of system interfaces.

Wilson, Scott D.↗

NASA NTRS2018

NASA Low Power Stirling Convertor for Small Landers, Probes, and Rovers Operating in Darkness

Wilson, Scott↗

NASA NTRS2021

SERENA: Particle Instrument Suite for Determining the Sun-Mercury Interaction from BepiColombo

The ESA-JAXA BepiColombo mission to Mercury will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric particle dynamics at Mercury as well as their interactions with solar wind, solar radiation, and interplanetary dust. The particle instrument suite SERENA (Search for Exospheric Refilling and Emitted Natural Abundances) is flying in space on-board the BepiColombo Mercury Planetary Orbiter (MPO) and is the only instrument for ion and neutral particle detection aboard the MPO. It comprises four independent sensors: ELENA for neutral particle flow detection, Strofio for neutral gas detection, PICAM for planetary ions observations, and MIPA, mostly for solar wind ion measurements. SERENA is managed by a System Control Unit located inside the ELENA box. In the present paper the scientific goals of this suite are described, and then the four units are detailed, as well as their major features and calibration results. Finally, the SERENA operational activities are shown during the orbital path around Mercury, with also some reference to the activities planned during the long cruise phase.

S. Orsini↗

NASA NTRS1987

Collisional and dynamical processes in moon and planet formation

Research on a variety of dynamical processes relevant to the formation of planets, satellites and ring systems is discussed. The main focus is on studies of accretionary formation of early protoplanets using a numerical model, structures and evolution of ring systems and individual bodies within planetary rings, and theories of lunar origin.

Chapman, C. R.↗

NASA NTRS1988

Lunar and planetary studies

This grant supports the core program in planetary astronomy at Caltech. The research includes observations in the IR, sub-mm, mm and cm wavelengths at national and Caltech observatories with a strong emphasis on integrating the observations with spacecraft data and with models of atmospheric structure, dynamics and chemistry. Muhleman's group made extensive observations of Saturn, Uranus and Neptune which are being interpreted in terms of deep atmospheric structures which are obvious in the 2 and 6 cm maps of Saturn and Uranus. The microwave measurements are one of the few sources of information below the 2 bar level. Goldreich is investigating the dynamics of narrow rings with postdoctoral fellow, Pierre-Yves Longaretti. Their work has focused on the role of collisional stresses on the precession of the rings, since the Voyager radio science results imply that the previous model based on the ring's self-gravity is not the entire story. In addition Borderies, Goldreich and Tremaine have completed an investigation of the dynamics of the Encke division in Saturn's A ring.

Muhleman, Duane O.↗

NASA NTRS1988

Mercury

Papers are presented on future observations of and missions to Mercury, the photometry and polarimetry of Mercury, the surface composition of Mercury from reflectance spectrophotometry, the Goldstone radar observations of Mercury, the radar observations of Mercury, the stratigraphy and geologic history of Mercury, the geomorphology of impact craters on Mercury, and the cratering record on Mercury and the origin of impacting objects. Consideration is also given to the tectonics of Mercury, the tectonic history of Mercury, Mercury's thermal history and the generation of its magnetic field, the rotational dynamics of Mercury and the state of its core, Mercury's magnetic field and interior, the magnetosphere of Mercury, and the Mercury atmosphere. Other papers are on the present bounds on the bulk composition of Mercury and the implications for planetary formation processes, the building stones of the planets, the origin and composition of Mercury, the formation of Mercury from planetesimals, and theoretical considerations on the strange density of Mercury.

Vilas, Faith↗

NASA NTRS2000

Measurement Requirements for Improved Modeling of Arcjet Facility Flows

Current efforts to develop new reusable launch vehicles and to pursue low-cost robotic planetary missions have led to a renewed interest in understanding arc-jet flows. Part of this renewed interest is concerned with improving the understanding of arc-jet test results and the potential use of available computational-fluid- dynamic (CFD) codes to aid in this effort. These CFD codes have been extensively developed and tested for application to nonequilibrium, hypersonic flow modeling. It is envisioned, perhaps naively, that the application of these CFD codes to the simulation of arc-jet flows would serve two purposes: first. the codes would help to characterize the nonequilibrium nature of the arc-jet flows; and second. arc-jet experiments could potentially be used to validate the flow models. These two objectives are, to some extent, mutually exclusive. However, the purpose of the present discussion is to address what role CFD codes can play in the current arc-jet flow characterization effort, and whether or not the simulation of arc-jet facility tests can be used to eva1uate some of the modeling that is used to formu1ate these codes. This presentation is organized into several sections. In the introductory section, the development of large-scale, constricted-arc test facilities within NASA is reviewed, and the current state of flow diagnostics using conventional instrumentation is summarized. The motivation for using CFD to simulate arc-jet flows is addressed in the next section, and the basic requirements for CFD models that would be used for these simulations are briefly discussed. This section is followed by a more detailed description of experimental measurements that are needed to initiate credible simulations and to evaluate their fidelity in the different flow regions of an arc-jet facility. Observations from a recent combined computational and experiment.al investigation of shock-layer flows in a large-scale arc-jet facility are then used to illustrate the current state of development of diagnostic instrumentation, CFD simulations, and general knowledge in the field of arc-jet characterization. Finally, the main points are summarized and recommendations for future efforts are given.

Fletcher, Douglas G.↗

NASA NTRS2013

A Resolved Debris Disk Around the Candidate Planet-hosting Star HD 95086

Recently, a new planet candidate was discovered on direct images around the young (10-17 Myr) A-type star HD 95086. The strong infrared excess of the system indicates that, similar to HR8799, Beta Pic, and Fomalhaut, the star harbors a circumstellar disk. Aiming to study the structure and gas content of the HD 95086 disk, and to investigate its possible interaction with the newly discovered planet, here we present new optical, infrared, and millimeter observations. We detected no CO emission, excluding the possibility of an evolved gaseous primordial disk. Simple blackbody modeling of the spectral energy distribution suggests the presence of two spatially separate dust belts at radial distances of 6 and 64 AU. Our resolved images obtained with the Herschel Space Observatory reveal a characteristic disk size of approx. 6.0 × 5.4 (540 × 490 AU) and disk inclination of approx 25 deg. Assuming the same inclination for the planet candidate's orbit, its reprojected radial distance from the star is 62 AU, very close to the blackbody radius of the outer cold dust ring. The structure of the planetary system at HD 95086 resembles the one around HR8799. Both systems harbor a warm inner dust belt and a broad colder outer disk and giant planet(s) between the two dusty regions. Modeling implies that the candidate planet can dynamically excite the motion of planetesimals even out to 270 AU via their secular perturbation if its orbital eccentricity is larger than about 0.4. Our analysis adds a new example to the three known systems where directly imaged planet(s) and debris disks coexist.

gas content↗

NASA NTRS2014

Modeling Materials: Design for Planetary Entry, Electric Aircraft, and Beyond

NASA missions push the limits of what is possible. The development of high-performance materials must keep pace with the agency's demanding, cutting-edge applications. Researchers at NASA's Ames Research Center are performing multiscale computational modeling to accelerate development times and further the design of next-generation aerospace materials. Multiscale modeling combines several computationally intensive techniques ranging from the atomic level to the macroscale, passing output from one level as input to the next level. These methods are applicable to a wide variety of materials systems. For example: (a) Ultra-high-temperature ceramics for hypersonic aircraft-we utilized the full range of multiscale modeling to characterize thermal protection materials for faster, safer air- and spacecraft, (b) Planetary entry heat shields for space vehicles-we computed thermal and mechanical properties of ablative composites by combining several methods, from atomistic simulations to macroscale computations, (c) Advanced batteries for electric aircraft-we performed large-scale molecular dynamics simulations of advanced electrolytes for ultra-high-energy capacity batteries to enable long-distance electric aircraft service; and (d) Shape-memory alloys for high-efficiency aircraft-we used high-fidelity electronic structure calculations to determine phase diagrams in shape-memory transformations. Advances in high-performance computing have been critical to the development of multiscale materials modeling. We used nearly one million processor hours on NASA's Pleiades supercomputer to characterize electrolytes with a fidelity that would be otherwise impossible. For this and other projects, Pleiades enables us to push the physics and accuracy of our calculations to new levels.

Supercomputing↗

NASA NTRS2015

Parallel Study of HEND, RAD, and DAN Instrument Response to Martian Radiation and Surface Conditions

Nuclear detection methods are being used to understand the radiation environment at Mars. JPL (Jet Propulsion Laboratory) assets on Mars include: Orbiter -2001 Mars Odyssey [High Energy Neutron Detector (HEND)]; Mars Science Laboratory Rover -Curiosity [(Radiation Assessment Detector (RAD); Dynamic Albedo Neutron (DAN))]. Spacecraft have instruments able to detect ionizing and non-ionizing radiation. Instrument response on orbit and on the surface of Mars to space weather and local conditions [is discussed] - Data available at NASA-PDS (Planetary Data System).

Mars↗

NASA NTRS2021

SERENA: Particle Instrument Suite for Determining the Sun-Mercury Interaction from BepiColombo

Mercury’s environment↗

NASA NTRSDate not supplied

Advances in Design Capabilities for Planetary Missions from the NASA Entry Systems Modeling and Instrumentation Portfolio

The Entry Systems Modeling project (ESM) is supported by both the NASA Space Technology and the Science Mission Directorates and focuses on developing simulation tools and validated models for characterizing the performance of entry systems tailored to planetary destinations across the Solar System. ESM is organized into six technical capability areas that together address all relevant factors related to spacecraft entry, as well as some aspects of descent: Thermal Protection System (TPS) Materials; Aerothermodynamics; Entry & Descent Vehicle Dynamics; Guidance, Navigation, and Control; Vehicle Systems Analysis; and Advanced Tools and Numerical Methods. Development within the capability areas is undertaken explicitly with a focus on transition and infusion to science missions, human exploration missions, and commercial space activities. The present talk details developments that specifically impact science missions, including simulation tool capabilities that aid in mission design and model development to understand entry system performance at a given destination. Examples of the successful infusion and transition of such project outcomes to science missions also are provided. Several simulation tool development efforts within ESM have resulted in new design capabilities for missions. One such outcome is improved toolsets for mission trajectory and concept of operations design. Specifically, an initiative to couple a leading tool for entry, ascent/descent, and orbital trajectory optimization (Program to Optimize Simulated Trajectories II or POST2) to those used within the Agency for interplanetary trajectory optimization (Copernicus and Monte) has made substantial progress, with the outcomes to date promising to allow efficient trajectory optimization across mission phases. Additionally, toolchains for the evaluation of vehicle performance during entry and descent have been developed that allow assessment of multi-dimensional aeroheating on detailed vehicle geometries, characterization of deployment and inflation of parachutes, and assessment of vehicle dynamic stability during descent. These capabilities are achieved by coupling diverse sets of physics together – material response, computational fluid dynamics, radiation, and vehicle dynamics – to suitably describe complex entry and descent phenomena. Several model development and validation efforts for specific destinations and entry regimes also are underway within the ESM project. For instance, new experimental capabilities to validate radiation models at low densities/high altitudes recently have been established with project support, specifically the Low-Density Shock Tube (LDST) at the NASA Ames Research Center Electric Arc Shock Tube (EAST) facility. The LDST is being leveraged to develop improved models of shock layer kinetics and radiation in Titan atmospheres, while future studies will be conducted in the LDST and the existing high velocity shock tube to provide validation data for radiation models of Venus, Ice Giants, and Mars atmospheres. Models describing the aerothermal and thermo-structural performance of Thermal Protection System (TPS) materials has been another focus, with multiscale modeling activities on-going for the two leading TPS materials applicable to a range of entry conditions and science missions: the Phenolic-Impregnated Carbon Ablator (PICA) and woven materials like 3D Mid-Density Carbon Phenolic (3MDCP). A continual effort is made to infuse and transition outcomes from ESM simulation tool and model development activities into relevant science missions. Significant progress has been made on this front, with missions such as Dragonfly, DAVINCI, and Mars Missions benefitting from project outcomes. The groundwork also is being laid to provide insights into forward looking missions to Gas/Ice Giants as well as for potential sample returns.

Justin Haskins↗

NASA NTRS1999

The Role of Gravity Waves in Generating Equatorial Oscillations in Modulating Atmospheric Tides

We discuss a Numerical Spectral Mode (NSM) that extends from the ground up into the thermosphere and incorporates Hines' Doppler spread parameterization (DSP) for small scale gravity waves (GW). This model is applied to describe the seasonal variations in the mean zonal circulation, the semi-annual and quasi-biennial oscillations (SAO and QBO), as well as the tides and planetary waves in the middle atmosphere. Initial results showed that this model can reproduce the salient features observed, including the QBO extending into the upper mesosphere inferred from UARS measurements. The model has now been extended to simulate also: (a) the zonal circulation of the lower stratosphere and upper troposphere, and (b) the upwelling at equatorial latitudes associated with the Brewer Dobsen circulation that affects the dynamics significantly as pointed out by Dunkerton. Upward vertical winds increase the period of the QBO observed from the ground. To compensate for that, one needs to increase in the model the eddy diffusivity and the GW momentum flux, bringing the latter closer to values recommended in the DSP. This development is conducive to extending the QBO and SAO to higher latitudes through global scale momentum redistribution. Multi-year interannual oscillations are generated through wave filtering by the solar driven annual oscillation in the zonal circulation. In a 3D version of the model, wave momentum is absorbed and dissipated by tides and planetary waves. A somewhat larger GW source (well within the DSP range) is then required to generate realistic QBO and SAO amplitudes. Since GW momentum is deposited in the altitude regime of increasing winds, the amplitude of the diurnal tide is amplified and its vertical wavelength is reduced at altitudes between 70 and 120 km. Wave filtering by the mean zonal circulation causes the GW flux to peak during equinox, and this produces a large semi-annual variation in the tide that has been observed on UARS. Without the diurnal tide, the semidiurnal tide would also be modulated in this way. But the diurnal tide filters out the GW preferentially during equinox, so that the semidiurnal tide tends to peak during solstice. Under the influence of GW, the tides are modulated significantly by planetary waves that are generated preferentially during solstice in part due to baroclinic instability.

Mayr, H. G.↗

NASA NTRS2017

Effects of Variable Eccentricity on the Climate of an Earth-Like World

The Kepler era of exoplanetary discovery has presented the Astronomical community with a cornucopia of planetary systems very different from the one which we inhabit. It has long been known that Jupiter plays a major role in the orbital parameters of Mars and its climate, but there is also a long-standing belief that Jupiter would play a similar role for Earth if not for its large moon. Using a three dimensional general circulation model (3-D GCM) with a fully-coupled ocean we simulate what would happen to the climate of an Earth-like world if Mars did not exist, but a Jupiter-like planet was much closer to Earths orbit. We investigate two scenarios that involve evolution of the Earth-like planets orbital eccentricity from 0 to 0.066 on a time scale of 4500 years, and from 0 to 0.283 over 6500 years. We discover that during most of the 6500 year scenario the planet would experience a moist greenhouse effect when near periastron. This could have implications for the ability of such a world to retain an ocean on time scales of 109 years. More Earth-like planets in multi-planet systems will be discovered as we continue to survey the skies and the results herein show that the proximity of large gas giant planets may play an important role in the habitabilty of these worlds. These are the first such 3-D GCM simulations using a fully-coupled ocean with a planetary orbit that evolves over time due to the presence of a giant planet.

Stability↗

NASA NTRS1987

Planetary radar astronomy

The scientific aims, theoretical principles, techniques and instrumentation, and future potential of radar observations of solar-system objects are discussed in a general overview. Topics examined include the history of radar technology, echo detectability, the Arecibo and Goldstone radar observatories, echo time delay and Doppler shift, radar waveforms, albedo and polarization ratio, measurement of dynamical properties, and the dispersion of echo power. Consideration is given to angular scattering laws; the radar signatures of the moon and inner planets, Mars, and asteroids; topographic relief; delay-Doppler radar maps and their physical interpretation; and radar observations of the icy Galilean satellites of Jupiter, comets, and the rings of Saturn. Diagrams, drawings, photographs, and sample maps and images are provided.

Ostro, Steven J.↗

NASA NTRS2015

Mercury-T: A New Code to Study Tidally Evolving Multi-Planet Systems. Applications to Kepler-62

A large proportion of observed planetary systems contain several planets in a compact orbital configuration, and often harbor at least one close-in object. These systems are then most likely tidally evolving. We investigate how the effects of planet-planet interactions influence the tidal evolution of planets. We introduce for that purpose a new open-source addition to the Mercury N-body code, Mercury-T, which takes into account tides, general relativity and the effect of rotation-induced flattening in order to simulate the dynamical and tidal evolution of multi-planet systems. It uses a standard equilibrium tidal model, the constant time lag model. Besides, the evolution of the radius of several host bodies has been implemented (brown dwarfs, M-dwarfs of mass 0:1 M(sub ⨀), Sun-like stars, Jupiter). We validate the new code by comparing its output for one-planet systems to the secular equations results. We find that this code does respect the conservation of total angular momentum. We applied this new tool to the planetary system Kepler-62. We find that tides influence the stability of the system in some cases. We also show that while the four inner planets of the systems are likely to have slow rotation rates and small obliquities, the fifth planet could have a fast rotation rate and a high obliquity. This means that the two habitable zone planets of this system, Kepler-62e ad f are likely to have very different climate features, and this of course would influence their potential at hosting surface liquid water..

Dynamical evolution and stability↗