Hypervelocity impact microfoil perforations in the LEO space environment (LDEF, MAP AO-023 experiment)

The Microabrasion Foil Experiment comprises arrays of frames, each supporting two layers of closely spaced metallic foils and a back-stop plate. The arrays, deploying aluminum and brass foil ranging from 1.5 to some 30 microns were exposed for 5.78 years on NASA's LDEF at a mean altitude of 458 km. They were deployed on the North, South, East, West, and Space pointing faces; results presented comprise the perforation rates for each location as a function of foil thickness. Initial results refer primarily to aluminum of 5 microns thickness or greater. This penetration distribution, comprising 2,342 perforations in total, shows significantly differing characteristics for each detector face. The anisotropy confirms, incorporating the dynamics of particulate orbital mechanics, the dominance of incorporating extraterrestrial particulates penetrating thicknesses greater than 20 microns in Al foil, yielding fluxes compatible with hyperbolic geocentric velocities. For thinner foils, a disproportionate increase in flux of particles on the East, North, and South faces shows the presence of orbital particulates which exceed the extraterrestrial component perforation rate at 5 micron foil thickness by a factor of approx. 4

The in-situ cometary particulate size distribution measured for one comet: P/Halley

The close approach of Giotto to comet Halley during its 1986 apparition offered an opportunity to study the particulate mass distribution to masses of up to one gram. Data acquired by the front end channels of the highly sensitive mass spectrometer PIA and the dust shield detector system, DIDSY, provide definition to the detected distribution as close as 1000 km to the nucleus. Dynamic motion of the particulates after emission leads to a spatial differentiation affecting the size distribution in several forms: (1) ejecta velocity dispersion; (2) radiation pressure; (3) varying heliocentric distance; and (4) anisotropic nucleus emission. Transformation of the in-situ distribution from PIA and DIDSY weighted heavily by the near-nucleus fluxes leads to a presumed nucleus distribution. The data lead to a puzzling distribution at large masses, not readily explained in an otherwise monotonous power law distribution. Although temporal changes in nucleus activity could and do modify the in-situ size distribution, such an explanation is not wholly possible, because the same form is observed at differing locations in the coma where the time of flight from the nucleus greatly varies. Thus neither a general change in comet activity nor spatial variations lead to a satisfactory explanation

Preliminary results from the dust flux monitoring instrument during the encounter of Stardust spacecraft with Wild-2 comet

On January 2, 2004, the Stardust spacecraft successfully encountered the Wild-2 comet. The Dust Flux Monitoring Instrument (DFMI) provided quantitative measurements of dust particle fluxes and particle mass distributions throughout the entire flythrough

Resolving LDEF's flux distribution: Orbital (debris?) and natural meteoroid populations

A consistent methodology for the collation of data from both penetration and perforation experiments and from data in the Meteoroid and Debris Special Investigator Group (M-D SIG) data-base has led to the derivation of the average impact flux over LDEF's exposure history 1984-1990. Data are first presented for LDEF's N,S,E,W and Space faces ('offset' by 8 deg and 'tilted' by 1 deg respectively). A model fit is derived for ballistic limits of penetration from 1 micron to 1mm of aluminium target, corresponding to impactor masses from 10(exp -18) kg (for rho sub p = 2g/cu cm) to 10(exp -10) kg (for rho sub p = 1g/cu cm). A second order harmonic function is fitted to the N,S,E, and W fluxes to establish the angular distribution at regular size intervals; this fit is then used to provide 'corrected' data corresponding to fluxes applicable to true N,S,E,W and Space directions for a LEO 28.5 degree inclination orbit at a mean altitude of 465 km

A possible explanation for the inconsistency between the Giotto grain mass distribution and ground-based observations

Giotto measured the in situ Halley dust grain mass distribution with 2 instruments, Particle Impact Analyzer and Dust Impact Detection System (DIDSY), as well as the total intercepted mass from the deceleration of the spacecraft (Giotto Radio-Science Experiment, GRE). Ground based observations made shortly before encounter have fluxes much higher than would be predicted from Giotto data. It is concluded that Giotto DIDSY and GRE data represent observations of dust originating from a narrow track along the nucleus. They are consistent with ground based data, if assumptions are made about the level of activity along this track. The actual size distribution that should be used for modeling of the whole coma should not include the large mass excess actually observed by Giotto. Extrapolation of the small grain data should be used, since for these grains the velocity dispersion is low and temporal changes at the nucleus would not affect the shape of the mass distribution

Modeling and parameter uncertainties for aircraft flight control system design

Values of plant dynamic uncertainties for some recent aircraft design and development programs are given. Histories of pertinent aerodynamic, inertial, and structural parameter variations are given for a period of time from program initiation to aircraft certification. These data can be used as typical of future vehicles so that control system design concepts are evaluated with due consideration to their sensitivity to uncertainties in plant dynamics

Computing Heavy Elements

Reliable calculations of the structure of heavy elements are crucial to address fundamental science questions such as the origin of the elements in the universe. Applications relevant for energy production, medicine, or national security also rely on theoretical predictions of basic properties of atomic nuclei. Heavy elements are best described within the nuclear density functional theory (DFT) and its various extensions. While relatively mature, DFT has never been implemented in its full power, as it relies on a very large number (~ 10^9-10^12) of expensive calculations (~ day). The advent of leadership-class computers, as well as dedicated large-scale collaborative efforts such as the SciDAC 2 UNEDF project, have dramatically changed the field. This article gives an overview of the various computational challenges related to the nuclear DFT, as well as some of the recent achievements.Comment: Proceeding of the Invited Talk given at the SciDAC 2011 conference, Jul. 10-15, 2011, Denver, C

Penetration rates over 30 years in the space age

Experimental data from spacecraft providing impact penetration rates and cratering for metallic targets is reviewed. Data includes NASA Explorers 16 and 23 and the Pegasus series, the second US-UK satellite Ariel 2, Space Shuttle STS-3 (MFE), recovered surfaces on Solar Max Satellite, The Long Duration Exposure Facility (LDEF) and EuReCa TiCCE. Factors concerning exposure to the environment are considered and, especially, material properties which affect the penetration resistance. Reference to a common material, Aluminum alloy 2024-T3, is effected and the data then compared to define firstly an average impact flux over the period. The data is examined, in the context of possible satellite and space debris growth rates, to determine the constancy of the flux. This also provides strong constraints on the current space debris component. It is found that the impact data are consistent with domination by natural meteoroid sources. Growth rates are not evident within the period 1980-1990 and Eureca TiCCE fluxes in 1993, for particles penetrating foils of around 10 microns thickness, supports the constancy of the flux. At larger dimensions the 1993 Eureca TiCCE fluxes show an 8-fold increase but this is considered not inconsistent with the selective exposure to meteoroid streams of a satellite stabilized in heliocentric co-ordinates for an 11 month period

GEO debris and interplanetary dust: fluxes and charging behavior

In September 1996, a dust/debris detector: GORID was launched into the geostationary (GEO) region as a piggyback instrument on the Russian Express-2 telecommunications spacecraft. The instrument began its normal operation in April 1997 and ended its mission in July 2002. The goal of this work was to use GORID's particle data to identify and separate the space debris to interplanetary dust particles (IDPs) in GEO, to more finely determine the instrument's measurement characteristics and to derive impact fluxes. While the physical characteristics of the GORID impacts alone are insufficient for a reliable distinction between debris and interplanetary dust, the temporal behavior of the impacts are strong enough indicators to separate the populations based on clustering. Non-cluster events are predominantly interplanetary, while cluster events are debris. The GORID mean flux distributions (at mass thresholds which are impact speed dependent) for IDPs, corrected for dead time, are 1.35x10^{-4} m^{-2} s^{-1} using a mean detection rate: 0.54 d^{-1}, and for space debris are 6.1x10^{-4} m^{-2} s^{-1} using a mean detection rate: 2.5 d^{-1}. Beta-meteoroids were not detected. Clusters could be a closely-packed debris cloud or a particle breaking up due to electrostatic fragmentation after high charging.Comment: * Comments: 6 pages, 4 postscript figures, in Dust in Planetary Systems 2005, Krueger, H. and Graps, A. eds., ESA Publications, SP in press (2006). For high resolution version, see: http://www.mpi-hd.mpg.de/dustgroup/~graps/dips2005/GrapsetalDIPS2005.pd