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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
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NASA NTRS2018

Arcjet Ablation of Stony and Iron Meteorites

A test campaign was conducted placing meteorites in the 60 MW plasma Arcjet Interaction Heating Facility at NASA Ames Research Center, with the aim to achieve flight-relevant conditions for asteroid impacts in Earth's atmosphere and to provide insight into how meteoritic materials respond to extreme entry heating environments. The test conditions at heat flux of 4000 W/m2 and 140 kPa stagnation pressure are comparable to those experienced by a 30-meter diameter asteroid moving at 20 km/s velocity at 65 km altitude in the Earth's atmosphere. Test objects were a stony type H5 ordinary chondrite (Tamdakht) and an iron type IAB-MG meteorite (Campo Del Cielo), and included the terrestrial analogs Dense Flood Basalt and Fused Silica. All samples were exposed for only a few seconds in the plasma stream. Significant melt flow and vaporization was observed for both the stony and iron meteorites during exposure. Mass loss from spallation of fragments was also observed. Vapor emitted atomic lines from alkali metals and iron, but did not emit the expected MgO molecular band emissions. The meteoritic melts flowed more rapidly, indicating lower viscosity, than those of Fused Silica. The surface recession was mapped. The effective heat of ablation derived from this showed that ablation under these conditions occurred in the melt-dominated regime. Ablation parameters have an effect on ground damage estimates. A bias in ablation parameters towards the melt-dominated regime would imply that impacting asteroids survive to lower altitude, and therefore could possibly have airbursts with a larger ground damage footprint.

Arcjet↗
NASA NTRS1993

Collision lifetimes and impact statistics of near-Earth asteroids

We have examined the lifetimes of Near-Earth asteroids (NEA's) by directly computing the collision probabilities with other asteroids and with the terrestrial planets. We compare these to the dynamical lifetimes, and to collisional lifetimes assumed by other workers. We discuss the implications of the differences. The lifetimes of NEA's are important because, along with the statistics of craters on the Earth and Moon, they help us to compute the number of NEA's and the rate at which new NEA's are brought to the vicinity of the Earth. Assuming that the NEA population is in steady-state, the lifetimes determine the flux of new bodies needed to replenish the population. Earlier estimates of the lifetimes ignored (or incompletely accounted for) the differences in the velocities of asteroids as they move in their orbits, so our results differ from (for example) Greenberg and Chapman (1983, Icarus 55, 455) and Wetherill (1988, Icarus 76, 1) by factors of 2 to 10. We have computed the collision rates and relative velocities of NEA's with each other, the main-belt asteroids, and the terrestrial planets, using the corrected method described by Bottke et. al. (1992, GRL, in press). We find that NEA's typically have shorter collisional lifetimes than do main-belt asteroids of the same size, due to their high eccentricities, which typically give them aphelia in the main belt. Consequently, they spend a great deal of time in the main belt, and are moving much slower than the bodies around them, making them 'sitting ducks' for impacts with other asteroids. They cross the paths of many objects, and their typical collision velocities are much higher (10-15 km/s) than the collision velocities (5 km/s) among objects within the main belt. These factors combine to give them substantially shorter lifetimes than had been previously estimated.

Bottke, W. F., Jr.↗
NASA NTRS1994

Consequences of impacts of small asteroids and comets with Earth

The fragmentation of a small asteroid in the atmosphere greatly increases its cross sections for aerodynamic braking and energy dissipation. At a typical impact velocity of 22 km/s, the atmosphere absorbs more than half the kinetic energy of stony meteoroids with diameters, D(sub m), less than 220 m and iron meteoroids with D(sub m) less than 80 m. The corresponding diameter for comets with impact velocity 50 km/s is D(sub m) less than 1600 m. Most of the atmospheric energy dissipation occurs in a fraction of a scale height, so large meteors appear to 'explode' or 'flare' at the end of their visible paths. This dissipation of energy in the atmosphere protects the earth from direct impact damage (e.g., craters), but it produces a blast wave that can do considerable damage. The area of destruction around the impact point in which the over-pressure in the blast wave exceeds 4 lb/sq in = 2.8 x 10(exp 5) dynes/cu cm, which is enough to knock over trees and destroy buildings, increases rapidly from zero for chondritic meteoroids less than 56 m in diameter (15 megatons) to about 200 sq km for those 80 m in diameter (48 megatons); the probable diameter of the tunguska impactor of 1908 is about 80 m. Crater formation and earthquakes are not significant in land impacts by stony asteroids less than about 200 m in diameter because of the air protection. A tsunami is probably the most devastating type of damage for asteroids 200 m to 1 km in diameter. An impact by an asteroid this size anywhere in the Atlantic would devastate coastal areas on both sides of the ocean. An asteroid a few kilometers across would produce a tsunami that would reach the foothills of the Appalachian Mountains in the upper half of the East Coast of the United States. Most of Florida is protected from a tsunami by the gradual slope of the ocean off its coast, which causes most of the tsunami energy to be reflected back into the Atlantic. The atmosphere plume produced by asteroids with diameters exceeding about 120 m cannot be contained by the atmosphere, so this bubble of high-temperature gas forms a new layer on top of the atmosphere. The dust entrapped in this hot gas is likely to have optical depths exceeding tau = 10 for asteroids with diameters exceeding about 0.5 to 1 km. The optical flux from asteroids 60 m or more in diameter is enough to ignite pine forests. However, the blast wave from an impacting asteroid goes beyond the radius in which the fire starts. The blast wave tends to blow out the fire, so it is likely that the impact will char the forest, as at Tunguska, but the impact will not produce a sustained fire. Because comets dissipate their energy much higher in the atmosphere than asteroids, they illuminate a much larger region and their blast wave is weaker. So they are much more effective in producing large fires. This suggests that the KT impactor was a comet rather than an asteroid.

Hills, J. G.↗
NASA NTRS2015

Asteroid Geophysics and Quantifying the Impact Hazard

Probably the major challenge in understanding, quantifying, and mitigating the effects of an impact on Earth is understanding the nature of the impactor. Of the roughly 25 meteorite craters on the Earth that have associated meteorites, all but one was produced by an iron meteorite and only one was produced by a stony meteorite. Equally important, even meteorites of a given chemical class produce a wide variety of behavior in the atmosphere. This is because they show considerable diversity in their mechanical properties which have a profound influence on the behavior of meteorites during atmospheric passage. Some stony meteorites are weak and do not reach the surface or reach the surface as thousands of relatively harmless pieces. Some stony meteorites roll into a maximum drag configuration and are strong enough to remain intact so a large single object reaches the surface. Others have high concentrations of water that may facilitate disruption. However, while meteorite falls and meteorites provide invaluable information on the physical nature of the objects entering the atmosphere, there are many unknowns concerning size and scale that can only be determined by from the pre-atmospheric properties of the asteroids. Their internal structure, their thermal properties, their internal strength and composition, will all play a role in determining the behavior of the object as it passes through the atmosphere, whether it produces an airblast and at what height, and the nature of the impact and amount and distribution of ejecta.

stony meteorite↗
NASA NTRS1985

Impacts on Explorer 46 from an Earth orbiting population

Explorer 46 was launched into Earth orbit in August 1972 to evaluate the effectiveness of using double-wall structures to protect against meteoroids. The data from the Meteoroid Bumper Experiment on Explorer 46 is reexamined and it is concluded that most of the impacts originated from an Earth orbiting population. The probable source of this orbiting population is solid rocket motors fired in Earth orbit.

Kessler, D. J.↗
NASA NTRS2007

Solar Dynamics Observatory High Gain Antenna Handover Planning

The Solar Dynamics Observatory (SDO) is planned to launch in early 2009 as a mission to study the solar variability and its impact on Earth. To best satisfy its science goal, SDO will fly in a geosynchronous orbit with an inclination of approximately 29 deg. The spacecraft attitude is designed so that the science instruments point directly at the Sun with high accuracy. One of SDO's principal requirements is to obtain long periods of uninterrupted observations. The observations have an extremely high data volume so SDO must be in continuous contact with the ground during the observation periods. To maintain this contact, SDO is equipped with a pair of high gain antennas (HGAs) transmitting to a pair of ground antennas at the SDO ground station (SDOGS) located in White Sands, New Mexico. Either HGA can transmit to either SDOGS antenna. Neither HGA can be powered down. During a portion of each year, each of the HGA beams will intersect with the SDO body for a portion of the orbit. The original SDO antenna contact plan used each HGA for the half of each year during which its beam would not intersect the spacecraft. No data would be lost except, possibly, when switching from one antenna to another. After this plan was adopted, further analysis showed that daily handovers would be necessary for significant periods of the year. This unexpected need for extensive handovers necessitated that a handover design be developed to minimize the impact on the mission. This antenna handover design was developed and successfully tested with simulated data using the slew rate limits from preliminary jitter analysis. Subsequent analysis provided significant revision of allowed rates requiring modification of the handover plans.

Hashmall, Joseph A.↗
NASA NTRS2007

Solar Dynamics Observatory High Gain Antenna Handover Planning

The Solar Dynamics Observatory (SDO) is planned to launch in early 2009 as a mission to study the solar variability and its impact on Earth. To best satisfy its science goal, SDO will fly in a geosynchronous orbit with an inclination of approximately 29 deg. The spacecraft attitude is designed so that the science instruments point directly at the Sun with high accuracy. One of SDO s principal requirements is to obtain long periods of uninterrupted observations. The observations have an extremely high data volume so SDO must be in continuous contact with the ground during the observation periods. To maintain this contact, SDO is equipped with a pair of high gain antennas (HGAs) transmitting to a pair of ground antennas at the SDO ground station (SDOGS) located in White Sands, New Mexico. Either HGA can transmit to either SDOGS antenna. Neither HGA can be powered down. During a portion of each year, each of the HGA beams will intersect with the SDO body for a portion of the orbit. The original SDO antenna contact plan used each HGA for the half of each year during which its beam would not intersect the spacecraft. No data would be lost except, possibly, when switching from one antenna to another. After this plan was adopted, further analysis showed that daily handovers would be necessary for significant periods of the year. This unexpected need for extensive handovers necessitated that a handover design be developed to minimize the impact on the mission. This antenna handover design was developed and successfully tested with simulated data using the slew rate limits from preliminary jitter analysis. Subsequent analysis provided significant revision of allowed rates requiring modification of the handover plans.

Hashmall, Joseph A.↗
NASA NTRSDate not supplied

Simultaneous lidar profiling of water vapor, aerosol, and wind over the eastern Pacific and implications for observational challenges on clouds, circulation, and climate sensitivity

Moist convective processes and related circulations are key components of the Earth’s climate system. Improving our understanding of moisture and cloud processes over oceans is especially challenging due to observational limitations, but also important due to the large radiative effects of cloud over ocean as well as the ties to local and global-scale circulations. A unique dataset for addressing these topics was collected over 5 flights with the NASA HALO (water vapor DIAL and aerosol HSRL) and DAWN (Doppler wind) lidar systems onboard the NASA DC-8 aircraft during the spring 2019 ADM-Aeolus Cal/Val test flight campaign. High-resolution water vapor, aerosol/cloud, and wind profiles were simultaneously collected and complimented with in situ high-resolution dropsonde measurements of temperature, relative humidity, and wind profiles. Airborne lidar measurements of these key variables captured both large-scale spatial variability across different cloud and atmospheric conditions as well as finer features, providing insight into processes from large-scale circulations down to aerosol/cloud interactions. The 5 flights spanned the northeast Pacific and southwest U.S. from 6 N to 52 N and 112 W to 157 W and captured several features of interest including moist layers from the ascending region of the Hadley circulation, very dry layers above midlatitude marine stratocumulus and cloud-free planetary boundary layers, and cloud top height and spatial variability. High covariance of aerosol and water vapor in the free troposphere was also observed for the first time. Preliminary analysis of these data sets will be presented as they apply to clouds and circulations, supplemented by model reanalysis to inform how regional water vapor structure and large-scale motion may contribute to observed shallow cloud formations and other meteorological processes that underpin our current understanding of how these state variables couple to impact the Earth’s weather and climate systems. The potential of complementary measurements in future field campaigns will also be mentioned.

Brian James Carroll↗
NASA NTRS1978

Interplanetary dust - Possible implications for comets and presolar interstellar grains

Interplanetary dust is important to studies of the origin of the solar system because it is material from comets and asteroids, the smallest surviving bodies from the early solar system. The fact that comets are the major suppliers of the millimeter meteoroids which produce optical meteors suggests that a significant fraction of the submillimeter portion of the meteoroid complex is also cometary material. While comets are probably the major source, it is important to remember that the dust presently impacting the earth was probably generated by a number of different parent bodies. The collection of interplanetary dust is considered and a description is presented of the physical properties of interplanetary dust, taking into account the structure, elemental composition, and mineralogy.

Brownlee, D. E.↗
NASA NTRS1980

In Situ Propellant Production for improved sample return mission performance

In Situ Propellant Production (ISPP) on the surface of a target body is evaluated as a potential way to relax sample return mass constraints and to improve mission performance. Utilization of an oxygen/methane bipropellant combination for primary outbound and return propulsion has a significant favorable impact upon Earth escape requirements. A small sample can be returned from Mars using a single Shuttle/IUS(Twin) launch. Performance and design data are presented for the Mars mission. For sample returns from selected Galilean satellites, launch requirements are reduced by fifteen to forty percent. An assessment is made of overall utility of ISPP to planetary missions.

Stancati, M. L.↗
NASA NTRS1985

Occurrence of giant impacts during the growth of the terrestrial planets

Three dimensional Monte Carlo simulations of the accumulation of the terrestrial planets in the absence of gas drag produced results that are in general agreement with the number and distribution of the present planets. The accumulation process appears to be characterized by impact of bodies as large as three times the mass of Mars at velocities of about 9 kilometers per second. These giant impacts on earth may have supplied the material and angular momentum that formed the moon, should have heated earth to the melting point, and may have been responsible for the differences in the content of inert gases of the atmospheres of earth and Venus.

Wetherill, G. W.↗
NASA NTRS1986

Impact experimentation and the microgravity environment: An overview

Impact is an ubiquitous physical process in the solar system. It occurs on all solid bodies and operates over a spectrum of scales, influencing geologic processes ranging from accretion, the early evolution of planetary bodies, the petrogenetic and spatial relations of lunar samples, the surface characteristics and interpretation of spectral data of asteroidal bodies, to the nature of some meteorites. Understanding impact phenomena is therefore paramount in constraining and underpinning a large number of research efforts into fundamental planetary geology. Gravity is an important parameter in impact processes. The physical environment offered by the Space Station represents an unique opportunity to extend the experimental aspect of impact studies into the microgravity (less than 1 g) regime. Through the use of free floating targets, it may be possible to explore in detail phenomena associated with the collision of bodies. Such experiments can address questions regarding early and late accretional processes, catastrophic disruption and asteroidal evolution, as well as the effects of large impacts on the momentum and spin of the target bodies. The last question is of considerable topical interest with respect to the hypothesized origin of the moon by a Mars-sized impact on Earth.

Grieve, R. A. F.↗
NASA NTRS1986

Structural deformation of the Leoville chondrite

A petrofabric study of the Leoville chondrite was performed in order to gain an understanding of its deformation process. Strain values were determined from the chondrules' axial ratios or by the all-object-separation method, and the compaction required to deform Leoville chondrules was calculated from the decrease of radius in the circle-to-ellipse transformation. Structural and strain studies indicate the following order of events experienced by Leoville: (1) formation as an accretionary breccia, (2) compaction and development of foliation, (3) fracturing, possibly due to impact on earth, and (4) terrestrial weathering. Similarities between the axial ratios of chondrules (1.9-2.0) and of the whole meteorite (2.0) indicate either that Leoville deformed homogeneously or that it deformed as a framework of touching chondrules. This amount of strain corresponds to approximately 33 percent uniaxial shortening, assuming constant volume, and is likely to have been caused by compaction due to overburden from progressive accretion on the chondrite body. Diffusional flow is believed to be the mechanism by which olivines in these chondrules deformed.

Cain, P. M.↗
NASA NTRS1986

Comment

Frank et al.'s (1986) suggestion that the earth is impacted by small (100-Mg) comets at the rate of 20/min is reconsidered in the light of recent comet models. The possibility of such a swarm of comets is found to be problematical because of the large number of comets required and because thermal stability arguments, while not excluding such a possibility, imply that it is implausible. In a reply, Frank et al. reaffirm their findings that such small comets, following direct elliptical orbits about the sun, are distributed in a disk centered on the sun and lying near the ecliptic plane at heliocentric radial distances 1-10,000 AU. The presence of these comets in the inner solar system is attributed to the gravitational action of the outer planets, passing stars, or interstellar clouds on comets is more distant orbits.

Mckay, C. P.↗
NASA NTRS1986

Communication satellite technology trends

A chronology of space-Earth interconnectivity is presented. The Advanced Communications Technology Satellite (ACTS) system, Land Mobile Satellite, space-Earth antennas, impact of antenna size on coverage, intersatellite links are outlined. This presentation is represented by graphs and charts only.

Cuccia, Louis↗