矢野 創

In order to analyse the elements of dust particles in space, we have been developing a reflectron-type dust TOF-MS (Time-Of-Flight Mass Spectrometer) with a curved electric field. Now we have done performance experiments of our device by impacting hypervelocity microparticles with a Van de Graaff accelerator at HIT (High Fluence Irradiation Facility, University of Tokyo), where carbon particles of 0.3-2.0 mum in diameter are accelerated up to 5-20 km/s which are comparable with the velocity of dust particles in space. The results showed the device has higher mass resolution than the system with a parallel reflecting region under the same experiment situation by factor 2 or 3. Moreover the TOF spectra showed the higher detection efficiency, and the value was 10 times higher compared to the parallel reflectron TOF-MS. These effective results are considered to be caused by a curved electric field in a reflecting region.

170 hypervelocity impact signatures on the MLI and SSM surfaces of the SFU spacecraft were studied their three dimensional morphology and elemental analysis to discriminate them by natural origin from those by artificial debris. Ratio of meteoroids against debris, with some "unknown" and "undetermined" origins, is compared to results from previously retrieved spacecraft. those of LDEF, EuReCa and HST. The impact flux on the Sun pointing face is also compared with (C) 1999 COSPAR. Published by Elsevier Science Ltd.

The capabilities of combining Aerogel (A) as a passive target and position-sensitive impact sensing (PSIS) are examined; experimental performance factors are established from tests on Hypervelocity Impact Facilities at the University of Kent and previous space deployment. Results of system requirements analysis favour the deployment of large area detectors. Analysis of the in-flight impact sensor signals yields the position, time and exposure pointing direction of the tracks containing the impactor residues, which are analysed after retrieval. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

For the purpose of simulating the surface alteration process called "space weathering", experiments of pulse laser irradiation, proton implantation, and laser irradiation to proton implanted samples were performed and reflectance spectra of altered materials were measured. To simulate the impact heating by micrometeorite bombardments, we made a new apparatus using a pulse laser whose pulse duration is 6-8 nanoseconds, comparable with a timescale of micrometeorite impacts. We find that the degree of space weathering, i.e., change of reflectance spectrum should depend on mineral composition. Laser irradiation onto olivine produces the largest reduction of albedo and the highest reddening of reflectance spectrum. In general, variation of olivine spectra is much larger than that of pyroxenes, Depths of absorption bands do not change in the scaled spectra, The olivine spectrum after the laser irradiation can match spectra of some olivine asteroids within a subtype of S-type asteroids. Comparison of Vesta spectrum with altered pyroxene spectra suggests that Vesta surface would be relatively older than olivine asteroids. We also investigate the influence of solar wind proton and pyroxene FeO content. The proton implantation causes small changes in olivine and enstatite spectra. Implanted protons do not influence spectral change by the laser irradiation: the laser irradiation and the proton implantation do not produce multiplicative but additive changes on the reflectance spectra, FeO content of pyroxenes does not relate to the degree of reflectance change.

Recent close encounters to Europa, a giant Jovian satellite, by the Galileo spacecraft reenforced the hypothesis that there might exist a liquid ocean of H2O in Europa. It can be assumed that Europa, like the Earth, has biological systems under its sub surface ocean, and that marine organisms consume chemical nutrients released by geological activities even though there is no sunlight. The purpose of this paper is to introduce conceptual and feasibility studies of a spacecraft mission to explore Europa's hypothetical sub-surface ocean. In this paper, we present possible searches for the possible biological evidence through the observation of traces. We analyze the scientific rationale, the methodology and the instrumentation of our investigation held in this mission. The designs of spacecraft and mission profile is' also reviewed. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

The Space Flyer Unit (SFU) has provided investigators in Japan with our first opportunity to conduct an extensive post-flight analysis (PFA) of particulate impacts on a retrieved satellite, and thereby further our goals in space debris research (Kibe et al., 1997). The PFA has now been in progress for some time, and in this paper the present status of our investigations is reported, our findings to date are briefly summarised, and finally a plan for the immediate future is outlined. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

We report on three dimensional morphology of about 100 hypervelocity impact craters on the Teflon radiators of the SFU spacecraft measured by scanning laser microscope and X-ray CT technique. We also performed impact calibration experiments using a two-stage light-gas gun at ISAS with alumina, glass and copper bead projectiles of diameters 50 to 80 mu m at velocities from 3.5 to 4.5 km/s, in order to reproduce impact crater profiles formed in space. As a result, the depth to diameter ratio of these impact craters constrains bulk density, velocity and size of impactors, which are complementary information to elemental analysis regarding the origin of the impactors, namely meteoroids or space debris. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

We present the first ground-based observational evidence of the zodiacal dust bands originally discovered by the Infrared Astronomical Satellite (IRAS) and confirmed by the Cosmic Background Explorer (COBE). Our photometric observations have been performed on Mauna Kea, Hawaii, between 1997 October 29 and November 2, using a 24 mm wide-angle lens attached to a cooled CCD camera, and a blue filter centered at 440 nm. Photometric data of the morning zodiacal light have revealed the presence of zodiacal dust bands at ecliptic latitudes beta = 0 degrees, 3 degrees, and +/- 10 degrees, as well as additional faint structures at approximately beta = +/- 5 degrees, between solar elongations epsilon = 75 degrees and 90 degrees. The brightness of dust bands is approximately 2%-3% of the background zodiacal light. Moreover, our observation of the Gegenschein has discovered dust bands at beta = +2 degrees, -4 degrees, and -9 degrees at 165 degrees less than or equal to epsilon less than or equal to 185 degrees. Using the separation of the inner dust band pair observed in two different regions of epsilon, we estimate the parallactic distance of this band pair to be about 1.6 AU from the Sun.

We have investigated in the laboratory the capture in aerogel (density 92.5±0.5 kg m-3) of small particles travelling at (5.1±0.2) km s-1. The particles used were soda glass spheres and irregularly shaped olivine and iron particles, with mean diameters in the range 75-355 microns. We have measured the impact site for each particle, characterised by the mean diameter of the entrance hole in the aerogel, the minimum and maximum radii of the damaged region in the surface of the aerogel around the entrance hole, the length of the track in the aerogel caused by passage of the particle into the aerogel's interior, and the diameter of the captured particle (if seen) found near the end of the track. For each type of particle we establish relationships between the observed parameters and the pre-impact particle size. We find that the processes resulting in the observed surface features and the capture of the particles in the interior of the aerogel are different. We also find that the particle shape (spherical/irregular) does not unduly influence penetration depths in the aerogel. We have studied the effects of non-normal incidence on the observed impact features and find that the angle of incidence can be reconstructed to within ±2°. We compare the laboratory obtained data with that measured for four particles captured in a sample of aerogel flown in a Low Earth Orbit on board the EuReCa spacecraft. The density of one of the particles is predicted to be (1776±346) km m-3. Using the ability to reconstruct impact direction the probable nature of the particles is shown to be micrometeoroids with retrograde trajectory. © 1999 Elsevier Science Ltd. All rights reserved.

Based on our initial visual selection (IVS) criteria and low vacuum (LV)-SEM/EDS data, we successfully selected candidates of unmelted chondritic Antarctic micrometeorites (AMMs) from the unsorted sample set collected by Maurette's group in 1991. AEM data of some of the selected microparticles show that they are unmelted but probably dehydrated AMMs. An AMM candidate, 91-1-C4,contains ferroan (around Fo30) olivine grains which have planar channels parallel to (001). Their textures quite resemble those shown in the initial stage of iddingsite formation of olivine phenocrysts in terrestrial b...

Since the early development of the cosmic dust research that started almost a century ago, a wide variety of the sample collection techniques has been developed. Such direct sampling of cosmic dust (or micrometeoroids, micrometeorites, interplanetary dust particles (IDP)) has enabled subsequent analyses of these extra-terrestrial micro particles at ground laboratories in great detail. In coming years, Japan will have an array of new opportunities of cosmic dust collection from space, stratosphere and Antarctica. However each collection site causes certain biases of samples in terms of physical and chemical alterations, selection effects and contamination. Here we review the cosmic dust collection from deep sea sediments, Greenland blue lakes, Antarctic ice cores, stratosphere and both near-Earth and interplanetary space, together with a brief description of the curation system of the samples being operated by NASA/JSC.

In January 1996, STS-72 (OV-105) successfully retrieved the Space Flyer Unit (SFU). Japan's first retrievable spacecraft had successfully completed it's 10 month mission in LEO at an orbital altitude of some 480km and inclination of 28.5̊. Once returned to Kennedy Space Centre and removed from the pay load bay a post flight investigation of SFU commenced. This investigation continued whilst SFU underwent safing procedures in the Astrotech Facility (ASO), Florida, and on it's return to Japan. Since de-integration of the payloads, from SFU, all exposed surfaces have been designated for detailed scanning and configuration control to determine the impact damage received from micrometeoroid and space debris particulates. In accordance with IADC and in light of the advent of the International Space Station all the data collected from this investigation shall be made available to the public and archived. To this end the SFU archive is being created as part of NAL's World Wide Web site (WWW). The WWW pages hold all images related to impact sites located on the SFU surfaces including multi-layer insulation MLI (aluminised Kapton™ top surface) second surface mirrors SSM (silvered Teflon™ top surface), scuff plates (painted aluminium). These images were taken at various magnifications (100-800x) and focal depths to determine and measure features seen. The results of the primary analysis (measured hole diameters etc.) are also available on the WWW site. This paper describes the current contents of the WWW site, showing examples of the pages and images available, plans for further development and updating and access information.

The Space Flyer Unit (SFU) was retrieved by the space shuttle in January 1995, and is presently being subjected to a post-flight analysis with emphasis on the detection and documentation of hypervelocity impact features from space debris and micrometeoroids. A summary of the analysis procedure is presented here. Some results from preliminary eye surveys are also provided. In addition, more detailed results from high-resolution imaging of craters on two peripheral second-surface mirrors (SSMs) are given, and the morphology of the craters detected in these surfaces is discussed. First results of hypervelocity impact calibration tests are also included.

In January 1996, STS-72 successfully retrieved Japan's Space Flyer Unit after a 10-month excursion in low Earth orbit. It was apparent from observations of the spacecraft that many surfaces had undergone changes from pre-flight condition. Not unlike other retrieved spacecraft (EuReCa, LDEF), SFU exhibited signs of impact damage, atomic oxygen erosion effects and general "wear and tear". During ground operations at Astrotech, Florida, the opportunity was afforded to inspect SFU for the effects of contamination and document impact sites and other interesting features. In total 16 wipes were taken from around the periphery of the spacecraft, along MLI interfaces and special areas of interest. All faces were wiped to determine any directionality dependence with regard to material deposition. Alongside the wiping of the spacecraft a set contamination monitors and witness plates were installed around the SFU and MGSE to observe the molecular deposition/non-volatile residue (NVR) and particle fallout that occurred during the de-servicing period in the ASO HPF (post hydrazine de-servicing) and a second set deployed to monitor fallout during the shipment back to Japan. The results of the contamination wipes and monitors are presented here. © 1998 Elsevier Science Ltd.

The Space Flyer Unit (SFU) was retrieved from space after its 10-month mission in January 1996. Here we report the first findings from the post flight analysis of its Kapton MLI and Teflon radiators in terms of impact flux, crater morphology and implications of impactors' origins. The impact flux on the Sun face is also compared with the LDEF, EuReCa and HST data. On the Kapton MLI, some directional information can be deduced and its capture cell Structure promises a high survivability of, residues for chemical analysis. The peripheral flux variation is not inconsistent with the EuReCa data favouring for the Earth's apex. The anti-sun face flux exceeded the Sun face by a factor of 1.7. The size distribution index of the impact features on the Sun face Teflon agreed with the certain size ranges of the previous spacecraft. Plans of forthcoming studies such as detailed CCD/laser scanning, calibration impact experiments and chemical analysis are also addressed. (C) 1997 COSPAR. Published by Elsevier Science Ltd.

In January 1996, STS-72 (OV-105) successfully retrieved the Space Flyer Unit (SFU). Japan's first retrievable spacecraft had successfully completed it's 10 month mission in LEO at an orbital altitude of some 480km and inclination of 28.5 degrees. Once returned to Kennedy Space Centre and removed from the payload bay a post flight investigation of SFU commenced This investigation continued whilst SFU underwent safing procedures in the Astrotech Facility (ASO), Florida, and on it's return to Japan. Since de-integration of the payloads, from SFU, all exposed surfaces have been designated for detailed scanning and configuration control to determine the impact damage received from micrometeoroid and space debris particulates. In accordance with IADC and in light of the advent of the International Space Station all the data collected from this investigation shall be made available to the public and archived. To this end the SFU archive is being created as part of NAL's World Wide Web site (WWW). The WWW pages hold all images related to impact sites located on the SFU surfaces including multi-layer insulation MLI (aluminised Kapton(TM) top surface) second surface mirrors SSM (silvered Teflon(TM) top surface), scuff plates (painted aluminium). These images were taken at various magnifications (100-800x) and focal depths to determine and measure features seen. The results of the primary analysis (measured hole diameters etc.) are also available on the WWW site, This paper describes the current contents of the WWW site, showing examples of the pages and images available, plans for further development and updating and access information.

Presented here are the latest results of the post-flight analysis of the Space Flyer Unit, Japan's first retrievable spacecraft. The morphology of impact features in silverised Teflon second-surface mirrors (SSMs) and Kapton multi-layer insulation (MLI) is Morphological comparisons are made between laboratory and space impacts into MLI material. Flux figures are shown for various SFU surfaces and compared with fluxes from earlier spacecraft, such as the Long Duration Exposure Facility and EuReCa. A summary of the hypervelocity impact calibration programme is given, including laboratory tests carried out at 5 km s(-1) and around 3.5 km s(-1) into Kapton film of various thicknesses. The results of these tests are shown.

記事種別: 会議・学会報告・シンポジウム

On retrieval from Low Earth Orbit (LEG), the solar arrays from the European Retrievable Carrier(EuReCa) and one solar array wing of the Hubble Space Telescope (HST) were inspected for micrometeoroid and space debris impact damage. 703 and 814 impact sites respectively were analysed in detail. Interpretation of particle parameters from this large data set can yield a useful measurement of the micrometeoroid and debris flux in LEG. Due to similar orbital parameters, this then provides a flux measurement complimentary to those measured by the Timeband Capture Cell Experiment (TiCCE) of the EuReCa spacecraft and detectors and exposed surfaces on the Long Duration Exposure Facility (LDEF). To allow comparison of data from the space retrieved solar cells to previous data, solar cell material, glass and aluminium targets were impacted for inter-calibration using the University of Kent's Light Gas Gun (LGG). An average of 20 impact sites on each target material per shot were measured. It was decided to consider only non-perforations of the 150 micron thick CMX cover glass, common to both EuReCa and HST solar cells. Trends in crater morphology of the laboratory impacts are discussed and compared to those from space impacts. The effects of impact angle and crater scaling with particle size are investigated and a conversion from appropriate solar cell crater parameters to the ballistic limit in aluminium is presented.

The continued analyses of penetrating impacts on MAP foils of Aluminium and Brass have produced data for several LDEF faces, i.e., Space, West, and East. These data have immediate bearing on the interpretation and design of devices to detect the penetration of a thin metallic firm by a dust grain which have been tested both in the laboratory and in space. A crucial component of the analysis has been the theoretical calculation utilizing CTH, a Sandia National Laboratory Hydrodynamic computer code/1/ to assess the parameters of the hypervelocity penetration event. In particular theoretical hydrodynamic calculations have been conducted to simulate the hypervelocity impact event where various cosmic dust grain candidates, e.g., density = 0.998, 2.700, 7.870 (gm/cm(3)), and velocities, i.e., 7 - 16 km/s, have been utilized to reproduce the events. Theoretical analyses of hypervelocity impact events will be reported which span an extensive matrix of values for velocity, density and size. Through a comparison between LDEF MAP foil measurements and CTH hydrocode calculations these analyses will provide an interpretation of the most critical parameters measured for space returned materials, i.e., for thin films, the diameter of the penetration hole, D-h, and for semi-infinite targets, the depth-to-diameter ratio of craters, D-c/T-c. An immediate consequence of a comparison, of CTH calculations with space exposed materials will be an enhancement of the coherent model developed by UKC-USS researchers to describe penetration dynamics associated with LDEF MAP foils.

In situ collection of cosmic dust and space debris on the Low Earth Orbit has yielded a new perspective of the near Earth dust environment. The hypervelocity impact craters on the trailing side of the Long Duration Exposure Facility were converted into the projectile sizes and the physical and elemental comparison with interplanetary dust particles captured in the stratosphere was carried out. The size distribution agreed well while some chemical elements of LDEF samples suggested a fluctuation due to massive energy transfer during the hypervelocity impact in space. A possible selection process is discussed. Also, future opportunity of in situ detection of meteor showers is foreseen as long as new intact-capture materials are properly developed. © 1994.

SEM observations have been carried out since 1987 with microparticales contained in medium and shallow depth ice cores retrieved at Mizuho Station (1984 : 70°42'S, 44°20'E, 2230m) and at the Advance Camp (1985,74°12'S, 34°59'E, 3200m) in East Queen Maud Land, Antarctica. Results of observations including morphological classification of particles have been published (HIGASHI et al. : Bull. Galcier Res., 8,31,1990). Addition of observational data from cores of shallow depth at Mizuho, and Asuka Stations (1989 : 71°34'S, 24°08'E, 930m) in Antarctica, and also at Site J in Greenland (1989 : 66°...