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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Radar Observations of Asteroid 1620 Geographos

Goldstone radar observations of Geographos from August 28 through September 2, 1994 yield over 400 delay-Doppler images whose linear spatial resolutions range from approx. 75 to approx. 151 in, and 138 pairs of dual-polarization (OC, SC) spectra with one-dimensional resolution of 103 m. Each data type provides thorough rotational coverage. The images contain an intrinsic north/south ambiguity, but the equatorial view allows accurate determination of the shape of the radar-facing part of the asteroid's pole-on silhouette at any rotation phase. Sums of co-registered images that cover nearly a full rotation have defined the extremely elongated shape of that silhouette. Here we present individual images and co-registered sums over approx. 30 deg of rotation phase that show the silhouette's structural characteristics in finer detail and also reveal numerous contrast features "inside" the silhouette. Those features include several candidate craters as well as indications of other sorts of large-scale topographic relief, including a prominent central indentation. Protuberances at the asteroid's ends may be related to the pattern of ejecta removal and deposition caused by the asteroid's gravity field. The asteroid's surface is homogeneous and displays only modest roughness at centimeter-to-meter scales. Our estimates of radar cross section and the currently available constraints on the asteroid's dimensions are consistent with a near-surface bulk density between 2 and 3 g/cu cm. The delay-Doppler trajectory of Geographos' center of mass has been determined to about 200 m on August 28 and to about 100 m on August 31, an improvement of two orders of magnitude over pre-observation ephemerides.

Ostro, Steven J.↗
NASA NTRS1996

Radar Observations of Asteroid 1620 Geographos

Goldstone radar observations of Geographos from August 28 through September 2, 1994 yield over 400 delay-Doppler images whose linear spatial resolutions range from approximately 75 - 151 m, and 138 pairs of dual-polarization (OC, SC) spectra with one-dimensional resolution of 103 m. Each data type provides thorough rotational coverage. The images contain an intrinsic north/south ambiguity, but the equatorial view allows accurate determination of the shape of the radar-facing part of the asteroid's pole-on silhouette at any rotation phase. Sums of co-registered images that cover nearly a full rotation have defined the extremely elongated shape of that silhouette (S. J. Ostro, K. D. Rosema, R. S. Hudson, R. F. Jurgens, J. D. Giorgini, R. Winkler, D. K. Yeomans, D. Choate, R. Rose, M. A. Slade, S. D. Howard, and D. L. Mitchell 1995, Nature 375, 474-477). Here we present individual images and co-registered sums over approximately 30 deg of rotation phase that show the silhouette's structural characteristics in finer detail and also reveal numerous contrast features "inside" the silhouette. Those features include several candidate craters as well as indications of other sorts of large-scale topographic relief, including a prominent central indentation. Protuberances at the asteroid's ends may be related to the pattern of ejecta removal and deposition caused by the asteroid's gravity field. The asteroid's surface is homogeneous and displays only modest roughness at centimeter-to-meter scales. Our estimates of radar cross section and the currently available constraints on the asteroid's dimensions are consistent with a near-surface bulk density between 2 and 3 g/cc. The delay-Doppler trajectory of Geographos' center of mass has been determined to about 200 m on August 28 and to about 100 m on August 31, an improvement of two orders of magnitude over pre-observation ephemerides.

Ostro, Steven J.↗
NASA NTRS1998

Geologic Landforms and Processes on Icy Satellites

During the first reconaissence of the satellites of the outer solar system conducted by the Voyager missions (1979-1989), a surprising diversity of unusual geologic landforms were observed, in some cases with bewildering complexity (e.g., Triton). Impact features were certainly expected but the variety of volcanic, diapiric, tectonic, impact, and erosional landforms was only remotely suggested by some early theoretical works. These diagnostic features are manifestations of the internal composition, thermal history, and dynamical evolution of these bodies. It is the job of the geologist to interpret the morphology, stratigraphy, and composition of these deposits and structures to ascertain what materials were mobilized in the interior, in what amount, and the mechanism and cause of their mobilization. In this chapter, we review what is know about these features and what constraints can be placed on composition and thermal history. Particular emphasis is placed on volcanic features, as these are most directly related to satellite composition and thermal history. The surface spectra, high albedos, and low bulk densities of the satellites of the outer solar system indicate that water and other ices are abundant on these bodies, particularly on their surfaces. Ices, particularly water ice, are less dense than silicates and will tend to float and form crusts during differentiation or partial melting of the interior. Ices therefore take the place of silicates as 'crust-forming' minerals and dominate geologic processes on icy satellites. Melted ices form magma bodies, and sometimes are extruded as lavas, an unusual but still valid perspective for terrestrial geologists. The unusual properties of some ices, including their low melting temperatures, and low strengths (as well as the decrease in density on the freezing of water ice), will ultimately be very important in interpreting this record.

Schenk, Paul M.↗
NASA NTRS2000

Development and Testing of Cooled CMCs for High Thermal Flux Applications

Ceramic Matrix Composites (CMCS) offer the potential for significant weight savings and improved performance for a range of propulsion components utilizing refractory materials. This paper describes the fabrication and testing of functionally graded CMCs produced via a low cost process that represents an order of magnitude cost savings over conventionally fabricated CMCS. Test cylinders were fabricated, characterized and evaluated during exposure to high thermal fluxes of up to 10MW/meters squared at the Laser Hardened Materials Evaluation Laboratory (LHMEL). The bulk density of the CMC tubes was approximately 2.2 grams per cubic centimeters. The performance of cryogenically cooled CMCs was compared with uncooled CMCs against similar thermal loads, and fundamental property data collected for this relatively new breed of CMC. Finally, test thrust cells were fabricated from the functionally graded composite and tested using liquid H2 and O2 propellants at NASA Glen.

Patterson , Mark↗
NASA NTRS2000

BOREAS TE-1 SSA Soil Lab Data

This data set was collected by TE-1 to provide a set of soil properties for BOREAS investigators in the SSA. The soil samples were collected at sets of soil pits in 1993 and 1994. Each set of soil pits was in the vicinity of one of the five flux towers in the BOREAS SSA. The collected soil samples were sent to a lab, where the major soil properties were determined. These properties include, but are not limited to, soil horizon; dry soil color; pH; bulk density; total, organic, and inorganic carbon; electric conductivity; cation exchange capacity; exchangeable sodium, potassium, calcium, magnesium, and hydrogen; water content at 0.01, 0.033, and 1.5 MPascals; nitrogen; phosphorus; particle size distribution; texture; pH of the mineral soil and of the organic soil; extractable acid; and sulfur. The data are stored in tabular ASCII text files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Hall, Forrest G.↗
NASA NTRS2000

BOREAS TE-2 NSA Soil Lab Data

This data set contains the major soil properties of soil samples collected in 1994 at the tower flux sites in the Northern Study Area (NSA). The soil samples were collected by Hugo Veldhuis and his staff from the University of Manitoba. The mineral soil samples were largely analyzed by Barry Goetz, under the supervision of Dr. Harold Rostad at the University of Saskatchewan. The organic soil samples were largely analyzed by Peter Haluschak, under the supervision of Hugo Veldhuis at the Centre for Land and Biological Resources Research in Winnipeg, Manitoba. During the course of field investigation and mapping, selected surface and subsurface soil samples were collected for laboratory analysis. These samples were used as benchmark references for specific soil attributes in general soil characterization. Detailed soil sampling, description, and laboratory analysis were performed on selected modal soils to provide examples of common soil physical and chemical characteristics in the study area. The soil properties that were determined include soil horizon; dry soil color; pH; bulk density; total, organic, and inorganic carbon; electric conductivity; cation exchange capacity; exchangeable sodium, potassium, calcium, magnesium, and hydrogen; water content at 0.01, 0.033, and 1.5 MPascals; nitrogen; phosphorus: particle size distribution; texture; pH of the mineral soil and of the organic soil; extractable acid; and sulfur. These data are stored in ASCII text files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Veldhuis, Hugo↗
NASA NTRS2001

Odyssey Comet Nucleus Orbiter: The Next Step in Cometary Exploration

Cometary nuclei are the most primitive bodies in the solar system, containing a cosmo-chemical record of the primordial solar nebula. Flyby missions to comets, such as those that encountered Comet Halley in 1986, provide a glimpse at this record. However, to study a cometary nucleus in detail requires a rendezvous mission, i.e., a nucleus orbiter. Only an orbiter provides the ability to map the entire nucleus surface at high resolution, to study the complex chemistry in the cometary coma and its variation with time, and to determine the mass and bulk density of the nucleus, key parameters in understanding how small bodies first formed in the solar nebula. A nucleus orbiter also provides the opportunity to sense the nucleus surface in preparation for more ambitious landing and sample return missions in the future. Additional information is contained in the original extended abstract.

Weissman, P. R.↗
NASA NTRS2002

Intercontinental Bistatic Radar Test Observation of Asteroid 1998 WT24

We describe the first intercontinental planetary radar test performed in Italy observing the near Earth asteroid (NEA) 33342 (1998 WT24) in December 2001 by means of the bistatic configurations Goldstone (California, USA)-Medicina (Italy) and Evpatoria (Ukraine)-Medicina. The experiment goal was to characterize the system for realtime radar follow-up observations of NEAs and artificial orbiting debris, in the framework of a feasibility study which aims at using the Sardinia Radio Telescope, at present under construction, also as a planetary radar facility. We report the preliminary results of the radar observations carried out by the IRA-CNR (Instituto di Radioastronomia - Consiglio Nazionale delle Ricerche) and the OATo (Osservatorio Astronomico di Torino) groups, aimed at exploring the scientific potentials of a new space radar program, using the existing facilities in Italy. The planetary radar technique is uniquely capable of investigating geometry and surface properties of various solar system objects, demonstrating advantages over the optical methods in its high spatial resolution and ability to obtain three-dimensional images. A single radar detection allows to obtain extremely accurate orbital elements, improving the instantaneous positional uncertainties by orders of magnitude with respect to an optically determined orbit. Radar is a powerful means to spatially resolve NEAs by measuring the distribution of the echo power in time delay (range) and Doppler frequency (line-of-sight velocity) with extreme precision in each coordinate, as it provides detailed information about the target physical properties like size, shape, rotation, near-surface bulk density and roughness and internal density distribution. The Medicina 32m antenna had been successfully used for the first time as the receiving part of a bistatic configuration during a test experiment (September 2001) held to check the capabilities of the entire data acquisition system. This test was possible thanks to the collaboration undertaken with the Evpatoria radar station, and consisted in the observation of the ETALON-1 low orbit satellite

Righini, S.↗
NASA NTRS2002

Morphologies, Processing and Properties of Ceramic Foams from Pre-Ceramic Foams from Pre-Ceramic Polymer Routes

The current research is focused on processing ceramic foams that have potential as a thermal protection material. Ceramic foams with different architectures were formed from the pyrolysis of pre-ceramic polymers at 1200 C in different atmospheres. In some systems a sacrificial polyurethane was used as the blowing agent. We have also processed foams using sacrificial fillers to introduce controlled cell sizes. Each sacrificial filler or blowing agent leads to a unique morphology. The effect of different fillers on foam morphologies will be presented. The presentation will also focus on characterization of these foams in terms of mechanical and thermal properties. Foams processed using these approaches having bulk densities ranging from 0.15 to 0.9 g per cubic centimeter and a cell sizes from 5 to 500 micrometers. Compression strengths ranged from 2 to 7 MPa for these materials.

Stackpoole, Mairead↗
NASA NTRS2002

Morphologies, Processing and Properties of Ceramic Foams and Their Potential as TPS Materials

The current research is focused on processing ceramic foams with compositions that have potential as a thermal protection material. The use of pre-ceramic polymers with the addition of sacrificial blowing agents or sacrificial fillers offers a viable approach to form either open or closed cell insulation. Our work demonstrates that this is a feasible method to form refractory ceramic foams at relatively low processing temperatures. It is possible to foam complex shapes then pyrolize the system to form a ceramic while retaining the shape of the unfired foam. Initial work focused on identifying suitable pre-ceramic polymers with desired properties such as ceramic yield and chemical make up of the pyrolysis product after firing. We focused on making foams in the Si system (Sic, Si02, Si-0-C), which is in use in current acreage TPS systems. Ceramic foams with different architectures were formed from the pyrolysis of pre-ceramic polymers at 1200 C in different atmospheres. In some systems a sacrificial polyurethane was used as the blowing agent. We have also processed foams using sacrificial fillers to introduce controlled cell sizes. Each sacrificial filler or blowing agent leads to a unique morphology. The effect of different fillers on foam morphologies and the characterization of these foams in terms of mechanical and thermal properties are presented. We have conducted preliminary arc jet testing on selected foams with the materials being exposed to typical re-entry conditions for acreage TPS and these results will be discussed. Foams processed using these approaches have bulk densities ranging from 0.15 to 0.9 g/cm3 and cell sizes ranging from 5 to 500 pm. Compression strengths ranged from 2 to 7 MPa for these systems. Finally, preliminary oxidation studies have been conducted on selected systems and will be discussed.

Stackpoole, Mairead↗
NASA NTRS2003

Soil Moisture Retrieval Through Changing Corn Using Active/Passive Microwave Remote Sensing

An extensive field experiment was conducted from May-early October, 2002 at the heavily instrumented USDA-ARS (U.S. Dept. of Agriculture-Agricultural Research Service) OPE3 (Optimizing Production Inputs for Economic and Environmental Enhancement) test site in Beltsville, MD to acquire data needed to address active/passive microwave algorithm, modeling, and ground validation issues for accurate soil moisture retrieval. During the experiment, a tower-mounted 1.4 GHz radiometer (Lrad) and a truck-mounted dual-frequency (1.6 and 4.75 GHz) radar system were deployed on the northern edge of the site. The soil in this portion of the field is a sandy loam (silt 23.5%, sand 60.3%, clay 16.1%) with a measured bulk density of 1.253 g/cu cm. Vegetation cover in the experiment consisted of a corn crop which was measured from just after planting on April 17, 2002 through senescence and harvesting on October 2. Although drought conditions prevailed during the summer, the corn yield was near average, with peak biomass reached in late July.

ONeill, P. E.↗
NASA NTRS2004

Sampling Strategy and Curation Plan of "Hayabusa" Asteroid Sample Return Mission

On the 9th May 2003 JST, Japanese spacecraft MUSES-C was successfully launched from Uchinoura. The spacecraft was directly inserted to interplanetary trajectory and renamed as Hayabusa , or "Falcon" to be the world s first sample return spacecraft to a near Earth asteroid (NEA). The NEA (25143)Itokawa (formerly known as "1998SF36") is its mission target. Its orbital and physical characteristics were well observed; the size is (490 +/- 100)x (250 +/- 55)x(180 +/- 50) m with about 12-hour rotation period. It has a red-sloped S(IV)-type spectrum with strong 1- and 2-micron absorption bands, analogous to ordinary LL chondrites with space weathering effect. Assuming its bulk density, the surface gravity level of Itokawa is in the order of 10 micro-G with its escape velocity = approx. 20 cm/s.

Yano, H.↗
NASA NTRS2004

On the Dielectric Properties of the Martian-like Surface Sediments

We have undertaken laboratory electromagnetic characterization of the total set of minerals identified by TES on the Martian surface in order to investigate experimentally the dielectric properties of the sediments covering it in the frequency range from 1 to 30 MHz. Volcanic Rocks with a well defined mineralogy and petrology from potential terrestrial analogues sites have also been included in the study. Our primary objective is to evaluate the range of electrical and magnetic losses that may be encountered by the various Radar sounding and imaging experiments dedicated to map the Martian subsurface searching for underground water. The electromagnetic properties of these Mars-like materials will be presented as a function of various geophysical parameters, such as porosity, bulk density and temperature. The secondary objective, is to locate regions were surface dielectric conditions are suitable for subsurface sounding.

Heggy, E.↗
NASA NTRS2002

Near-term lander experiments for growing plants on Mars: requirements for information on chemical and physical properties of Mars regolith

In order to support humans for long-duration missions to Mars, bioregenerative Advanced Life Support (ALS) systems have been proposed that would use higher plants as the primary candidates for photosynthesis. Hydroponic technologies have been suggested as the primary method of plant production in ALS systems, but the use of Mars regolith as a plant growth medium may have several advantages over hydroponic systems. The advantages for using Mars regolith include the likely bioavailability of plant-essential ions, mechanical support for plants, and easy access of the material once on the surface. We propose that plant biology experiments must be included in near-term Mars lander missions in order to begin defining the optimum approach for growing plants on Mars. Second, we discuss a range of soil chemistry and soil physics tests that must be conducted prior to, or in concert with, a plant biology experiment in order to properly interpret the results of plant growth studies in Mars regolith. The recommended chemical tests include measurements on soil pH, electrical conductivity and soluble salts, redox potential, bioavailability of essential plant nutrients, and bioavailability of phytotoxic elements. In addition, a future plant growth experiment should include procedures for determining the buffering and leaching requirements of Mars regolith prior to planting. Soil physical tests useful for plant biology studies in Mars regolith include bulk density, particle size distribution, porosity, water retention, and hydraulic conductivity.

NASA Center JSC↗
NASA NTRS2003

Physical properties and sixth graders' acceptance of an extruded ready-to-eat sweetpotato breakfast cereal

Extruded ready-to-eat breakfast cereals (RTEBCs) were made from varying levels of sweetpotato flour (SPF), whole-wheat bran (WWB), and extrusion cooking. Moisture, protein, and ash contents were lower in the 100% SPF than the 100% WWB. Carbohydrate, beta-carotene, and ascorbic acid contents were higher in the 100% SPF. Fat, thiamin, riboflavin contents, bulk densities, and the water absorption index were similar for the cereals. However, the expansion ratio was highest in the 100% SPF cereal. The 100% WWB had the lightest color and most fibrous morphology. Extruded RTEBC containing 100% SPF and 75%/25% SPF/WWB were well-liked and acceptable to sixth graders attending an elementary school in Auburn, Alabama, but the 100% WWB was unacceptable.

NASA Program Advanced Human Support Technology↗
NASA NTRS2005

Physical and hydraulic properties of baked ceramic aggregates used for plant growth medium

Baked ceramic aggregates (fritted clay, arcillite) have been used for plant research both on the ground and in microgravity. Optimal control of water and air within the root zone in any gravity environment depends on physical and hydraulic properties of the aggregate, which were evaluated for 0.25-1-mm and 1-2-mm particle size distributions. The maximum bulk densities obtained by any packing technique were 0.68 and 0.64 g cm-3 for 0.25-1-mm and 1-2-mm particles, respectively. Wettable porosity obtained by infiltration with water was approximately 65%, substantially lower than total porosity of approximately 74%. Aggregate of both particle sizes exhibited a bimodal pore size distribution consisting of inter-aggregate macropores and intra-aggregate micropores, with the transition from macro- to microporosity beginning at volumetric water content of approximately 36% to 39%. For inter-aggregate water contents that support optimal plant growth there is 45% change in water content that occurs over a relatively small matric suction range of 0-20 cm H2O for 0.25-1-mm and 0 to -10 cm H2O for 1-2-mm aggregate. Hysteresis is substantial between draining and wetting aggregate, which results in as much as a approximately 10% to 20% difference in volumetric water content for a given matric potential. Hydraulic conductivity was approximately an order of magnitude higher for 1-2-mm than for 0.25-1-mm aggregate until significant drainage of the inter-aggregate pore space occurred. The large change in water content for a relatively small change in matric potential suggests that significant differences in water retention may be observed in microgravity as compared to earth.

NASA Center JSC↗
NASA NTRS2005

Surface Soil Changes Following Selective Logging in an Eastern Amazon Forest

In the Brazilian Amazon, selective logging is second only to forest conversion in its extent. Conversion to pasture or agriculture tends to reduce soil nutrients and site productivity over time unless fertilizers are added. Logging removes nutrients in bole wood, enough that repeated logging could deplete essential nutrients over time. After a single logging event, nutrient losses are likely to be too small to observe in the large soil nutrient pools, but disturbances associated with logging also alter soil properties. Selective logging, particularly reduced-impact logging, results in consistent patterns of disturbance that may be associated with particular changes in soil properties. Soil bulk density, pH, carbon (C), nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg), potassium (K), iron (Fe), aluminum (Al), delta(sup 3)C, delta(sup 15)N, and P fractionations were measured on the soils of four different types of loggingrelated disturbances: roads, decks, skids, and treefall gaps. Litter biomass and percent bare ground were also determined in these areas. To evaluate the importance of fresh foliage inputs from downed tree crowns in treefall gaps, foliar nutrients for mature forest trees were also determined and compared to that of fresh litterfall. The immediate impacts of logging on soil properties and how these might link to the longer-term estimated nutrient losses and the observed changes in soils were studied.

Olander, Lydia P.↗
NASA NTRS1996

Rosetta Radio Science Investigations

The Rosetta Radio Science Investigations (RSI) experiment was selected by the European Space Agency to be included in the International Rosetta Mission to comet P/Wirtanen (launch in 2003, arrival and operational phase at the comet 2011-2013). The RSI science objectives address fundamental aspects of cometary physics such as the mass and bulk density of the nucleus, the gravity field, non-gravitational forces, the size and shape, the internal structure, the composition and roughness of the nucleus surface, the abundance of large dust grains and the plasma content in the coma and the combined dust and gas mass flux on the orbiter. RSI will make use of the radio system of the Rosetta spacecraft.

P/Wirtanen radio science cometary physics cometary↗