矢野 創

After global observations of asteroid 25143 Itokawa by the Hayabusa spacecraft, we selected the smooth terrain of the Muses Sea for two touchdowns carried out on 19 and 25 November 2005 UTC for the first asteroid sample collection with an impact sampling mechanism. Here, we report initial findings about geological features, surface condition, regolith grain size, compositional variation, and constraints on the physical properties of this site by using both scientific and housekeeping data during the descent sequence of the first touchdown. Close-up images revealed the first touchdown site as a regolith field densely filled with size-sorted, millimeter- to centimeter-sized grains.

During the interval from September through early December 2005, the Hayabusa spacecraft was in close proximity to near-Earth asteroid 25143 Itokawa, and a variety of data were taken on its shape, mass, and surface topography as well as its mineralogic and elemental abundances. The asteroid's orthogonal axes are 535, 294, and 209 meters, the mass is 3.51 x 10(10) kilograms, and the estimated bulk density is 1.9 +/- 0.13 grams per cubic centimeter. The correspondence between the smooth areas on the surface ( Muses Sea and Sagamihara) and the gravitationally low regions suggests mass movement and an effective resurfacing process by impact jolting. Itokawa is considered to be a rubble-pile body because of its low bulk density, high porosity, boulder-rich appearance, and shape. The existence of very large boulders and pillars suggests an early collisional breakup of a preexisting parent asteroid followed by a re-agglomeration into a rubble-pile object.

Spectra of persistent meteor trains were observed at wavelength between 300 and 930 nm. Two obtained train spectra during the 1998 and 2001 Leonid meteor showers are reported here. During the 1998 Leonids, one train was detected by a photographic camera with a spectrograph covering 370 - 640 nm region. On the other hand, during the 2001 Leonids, video observations were carried out using image intensified cameras in ultraviolet (UV), visible and near infrared (near-IR) wavelengths. Temperatures in persistent trains have been measured by atmospheric O-2 A( 0,1) band at the wavelength near 864.5 nm. From a video spectrum obtained just 7 s after parent. reball's. are, a rotational temperature of 250 K at altitude of 88.0 +/- 0.5 km was estimated. We can say that the cooling time scale of train strongly depends on the initial mass of its. reball at least for Leonids. Based on cooling constant calculated from our results, we estimated a temperature of similar to 130 K as a final exothermic temperature at early stage of persistent trains.

Ferroelectric lead zirconate titanate (PZT) elements were studied by directly bombarding them with hypervelocity silver particles. The mass and velocity of these hypervelocity silver particles ranged from 1 to 80 pg and 2 to 6 km/s, respectively. This report examines the pulsed signals observed immediately after collision. The first cycle of the pulse is discussed because the information on impact is presumably recorded on the wave form. The experimental data were analyzed using the wave form that was generated immediately after collision. Consequently, the following conclusions were made: (1) the sensitivity of the element is independent of the thickness of element, (2) the pulse height is proportional to the particle momentum over the measured range, and (3) the wave form is not explicitly related to the velocity of the particles at the time of collision. The potential of a single PZT element acts as a real-time detector for hypervelocity microparticles is discussed. (c) 2005 American Institute of Physics.

A response from piezoelectric lead-zirconate-titanate elements was investigated by bombarding them with hypervelocity iron particles. The observed signal form was clearly dependent on the particle velocity during collisions. The signal form exhibited oscillations for particle velocities less than 6 km/s, whereas it changed drastically into a solitary pulse above 20 km/s. This behavior was exclusively classified based on the velocity. The rise time of the solitary pulse in the output form had a good correlation with the velocity at impact. The change in the form was discussed in terms of elastic and plastic states by regarding Young's modulus as a criterion between both states. It is proposed that a single piezoelectric element has the potential to detect the velocity of particles in space. (c) 2005 American Institute of Physics.

High-definition TV spectra in the ultraviolet - visible region were obtained during the 2002 Leonid aircraft campaign. We analyze the spectra of the brightest fireball that appeared at 03(h)47(m)54(s) UT on Nov. 19, 2002 and identify the neutral atoms, mainly MgI, FeI, CaI, and NaI in the observed wavelengths between 300 - 650 nm. The singly ionized atomic emissions, CaII and MgII lines, also appeared in the spectrum in several epochs during the series of video frames. From analysis of the spectra, time variation in the abundances of metallic atoms, along with their electronic excitation and blackbody temperatures, were obtained assuming the Local Thermal Equilibrium (LTE) condition. Both Fe and Ca abundances relative to Mg are lower than the solar abundance, while Na is slightly higher. We found correlation between the excitation temperature and the abundance of Ca, which suggests incomplete evaporation of the Ca due to intrinsic refractoriness. A search for bands of CHON-related molecules, such as OH and CN, is not successful in the brightest fireball in this study.

Normally, reentry bodies, even if they are to be recovered, are not equipped with onboard instruments such as transponders, which are useful for real-time position monitoring of the reentry bodies during the flight. This is because the surrounding plasma generated by the aerodynamic heating makes the transponder positioning nonsense as the blackout phenomena. If we could know the trajectory during the reentry phase, even if it's not monitored in real-time, the information will be a great help for the rapid recovery. The radiation from the highly-heated reentry body during the aerodynamic heating has enough intense radiation in visible region for the detection on the ground. This paper investigates a method of optical capturing of the reentry bodies by means of the visible radiation from the bodies during the aerodynamic heating. And a result of the optical tracking actually carried out on the occasion of the reentry of the REV capsule is also presented.

An ultraviolet-visible spectrum between 300 and 450 nm of a cometary meteoroid that originated from 55P/Tempel-Tuttle was investigated, and its new molecules, induced by atmospheric interaction, were discovered. The spectroscopy was carried out using an intensified high-definition TV camera with a slitless reflection grating during the 2001 Leonid meteor shower over Japan. A best-fit calculation mixed with atoms and molecules confirmed the first discovery of N-2(+) B (2) Sigma(u)(+) --> X (2) Sigma(g)(+) bands in the UV meteor spectrum. The N-2(+) temperature was estimated to be 10,000 K with a low number density of 1.55 x 10(5) cm(-3). Such unexpectedly strong ultraviolet emission, in particular for N-2(+) (1, 0) at 353.4 nm, is supposed to be formed through the wide dimensions of high-temperature regions caused by a large meteoroid. Spectroscopic observations of reentry capsules will provide us with good opportunities for confirming the discovered N-2(+).

New production methods of silica aerogel with high and low refractive indices have been developed. A very slow shrinkage of alcogel at room temperature has made possible producing aerogel with high refractive indices of up to 1.265 without cracks. Even higher refractive indices than 1.08, the transmission length of the aerogel obtained from this technique has been measured to be about 10 to 20 mm at 400 nm wave length. A mold made of alcogel which endures shrinkage in the supercritical drying process has provided aerogel with the extremely low density of 0.009g/cm(3), which corresponds to the refractive index of 1.002. We have succeeded producing aerogel with a wide range of densities.

Hypervelocity collisions of microparticles with a lead-zirconate-titanate piezoelectric element are examined. The waveforms thus obtained depend on the velocities during collision, and are classified into three categories. In particular, the first cycle of the signal observed immediately after collision is essential to obtain information on the impact. In each category, experimental formulas that are functions of the impact velocity are established based on experimental data. It is concluded that a single piezoelectric element can potentially measure the velocity and/or momentum of hypervelocity microparticles in real time. In the abovementioned context, the new dust detectors are described.

Piezoelectric lead-zirconate-titanate (PZT) elements were Studied by directly bombarding hypervelocity silver and iron particles in the velocity range of 2-63 km/s. This report focuses on the concept of "immediately after collision". This concept was realized in the leading part of a pulsed signal that exhibited no effects due to reflection. The signal form was discussed from the viewpoint that information on impact was recorded by the waveform. The results indicated that the output amplitude was independent of the thickness of a PZT element, and that the waveform was explicitly related to the velocity at collision. Further, it appeared as an oscillating form at velocities less than 6 km/s. As the velocity increased, it gradually changed to a solitary pulse. The rise time of the single solitary waveform was linearly related to velocities above 6 km/s. The potential of a single PZT element is discussed as a real-time detector for hypervelocity microparticles. (c) 2005 Published by Elsevier Ltd on behalf of COSPAR.

An ultraviolet-visible spectrum between 300 and 450 nm of a cometary meteoroid that originated from 55P/Tempel-Tuttle was investigated, and its new molecules, induced by atmospheric interaction, were discovered. The spectroscopy was carried out using an intensified high-definition TV camera with a slitless reflection grating during the 2001 Leonid meteor shower over Japan. A best-fit calculation mixed with atoms and molecules confirmed the first discovery of N2+ (B-X) bands in the UV meteor spectrum. The N2+ temperature was estimated to be 10,000 K with a low number density of 1.55 x 10^5 cm-3. Such unexpectedly strong ultraviolet emission, in particular for N2+(1,0) at 353.4 nm, is supposed to be formed through the wide dimensions of high-temperature regions caused by a large meteoroid. Spectroscopic observations of reentry capsules will provide us with good opportunities for confirming the discovered N2+.

Piezoelectric lead-zirconate-titanate was studied by bombarding with silver particles in the mass range from 2 to 100 pg, and the velocity range from 2 to 8 km/s. Output signals were uniquely identified on impact. It was found that incident energies above 100 nJ were measured unambiguously by a single lead-zirconate-titanate element. The detector characteristics were studied with respect to incident particle energy, angular dependence and size effects. Even though we have still unknown processes inherent in this detection method, the piezoelectric element has a potential as a real-time detector, if it is well calibrated. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

Silica aerogel has been used as a capturing medium for micrometeoroids and space debris. Several previous investigations suggest that aerogel could capture hypervelocity particles macroscopically intact. However, it has not been fully evaluated whether retrieved grains retain their pristine mineralogy. This study attempts to evaluate the intact survivability of high-speed projectiles in aerogel using impact experiments. Such experiments are essential for rigorous examination or further scientific discussion on the samples of on-going and future sample return missions in which aerogels are/will be used as capturing media. We fired two kinds of micrometeoroid analog materials into aerogel with a two-stage light gas gun (2-4 km/s), serpentine and cronstedtite, which are commonly found in CM/CI, and CM chondrites, respectively. As these hydrated minerals are broken down into anhydrous ones at relatively low temperatures it is suitable for the evaluation of thermal alteration during the capturing process. The retrieved residues were examined with SEM/EDS, Synchrotron Radiation-XRD, and TEM/EDS. The SR-XRD analysis revealed that most of the volumes of residues are mineralogically unaltered. TEM observations show that one serpentine grain shot at 4 km/s has an unaltered crystalline part inside, an amorphous layer, and the outermost molten aerogel layer. One cronstedtite grain shot at 3 km/s, also examined by TEM, was found to have an unaltered interior as well as a vesiculated silicate melt layer. Image analysis revealed both mineral grains reduced their volume down to 10% of the original on average. These results suggest that it is possible to capture serpentine and cronstedtite particles; mineralogically intact with lid the aerogel. at least in the interior of each particle, below 4 km/s, in spite of their large volume loss. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

As one of the potential candidates of the "post-MUSES-C" minor body exploration to be launched around 2010, we have investigated scientific justifications and feasible mission scenarios. Two mission types are focused on among many other proposed mission concepts. One is the multiple rendezvous and sample return mission to asteroids whose spectral type is already known. The other is the multiple fly-bys and sample return mission to an asteroid family. This paper reports the preliminary design results of these two proposed missions. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

During the Leonid MAC 2002 airborne mission, we carried out a wide-field TV observation of the strong activity of the Leonid meteor shower from 03h30m UT through 11h50m UT on 2002 November 19. Two narrow peaks of the storm activities were observed at around 04h03m UT and 10h49m UT, with peak influx rates (mag less than or equal to + 6.5) of 1.63 x 10(-5) km(-2) s(-1) and 1.95 x 10(-5) km(-2) s(-1), respectively. Even in the full-Moon condition, the activity level of these twin peaks were comparable to that of the storm observed in 2001 over Japan. The first peak activity generated by the 7-revolution-old dust trail (ejection in 1767) was rich in bright meteors, including the fireball-class, compared to the second peak corresponding to the 4-revolution-old dust trail (ejection in 1866). The magnitude distribution indices (-2.5 less than or equal to mag less than or equal to + 3.5) were 1.70 +/- 0.10 in the first peak (7-rev) and 2.03 +/- 0.05 in the second peak (4-rev). The correlation between the observed peaks and several theoretical predictions is discussed.

We have succeeded in detecting a dust trail along the orbit of the short-period comet 81P/Wild 2, the target of the Stardust mission, which will fly by 81P/Wild 2 in 2004 January. This is the first discovery in optical wavelengths for which an IR counterpart ( such as from IRAS) has not been reported. The detected trail extends from the nucleus to a point 2.degrees3 (0.14 AU) back along the orbit. Its width is 9" (1.4 x 10(4) km) near the nucleus. Based on a comparison between models and the observed properties of the dust trail, it is likely that the trail is composed of dust particles with a diameter of similar to1 mm (corresponding to 0.5 mg in mass). During the flyby phase of the Stardust spacecraft, it is likely that the spacecraft will experience impacts of such large dust particles along the comet's orbit as well as from smaller grains in the cometary coma. With an impact velocity of trail particles of 6.1 km s(-1), the impact fluence of 0.5 mg trail particles onto the Stardust spacecraft will be similar to0.80 day(-1) inside the dust trail. However, the Whipple bumper shields should prevent physical disruption of the spacecraft by impacting particles of up to 1 cm in size. Thus, unless the 1 mm trail dust impacts cause severe attitude control problems for the spacecraft, they may not be critically hazardous to the mission but instead may provide a unique opportunity for the first in situ flux measurement of a comet dust trail, using the Whipple bumper shield dust flux monitors.

資料番号: SA4636313000

資料番号: SA4653354000

資料番号: SA4647206000

資料番号: SA0200001000

A lead-zirconate-titanate (PZT) element was studied by bombarding silver particles in the mass range from I to 100 pg, and the velocity from 2 to 6 km/s. Output signals were uniquely identified on impact and characterized by Fourier analysis. It was found that incident energies above 100 nJ were uniquely determined by a single PZT element. We discussed its potential as a real-time detector for space dust and debris.

Microwave emission due to hypervelocity impacts on metallic plates has been found. The targets used in the experiment are aluminum plates with various thicknesses. The projectile, a nylon cylinder with metal screw of 0.21 gm, was accelerated up to the velocity of 4 km/s; a heterodyne receiver detected the microwave at 22 GHz. The emission is a random sequence of pulses with several nanosecond width, which lasts more than 10 mus. The phenomenon seems to be dependent on the extent of target destruction through the formation of impact craters or penetration. If so, we could use the characteristics of the phenomena to better understand the mechanical destruction process. We propose several models for the cause of this microwave generation and study them on the basis of timing relation of observed events. (C) 2002 American Institute of Physics.

A PZT element was studied by bombarding silver particles in the mass range from 1 to 100 pg, and the velocity from 2 to 6 km/s. Output signals were uniquely identified on impact. They were processed on Fourier analysis. We found a simple selection rule using a relationship between Fourier components to discriminate junk events. By using the selection rule, we picked up events, by which a linear relationship between impact energy and output amplitude of the element was established It was found that incident energies above 100 nJ were determined uniquely by a single PZT element.

Recent studies suggested that even relatively small asteroids preserve considerable amount of regolith. Yet it is still not possible to fully understand their surface conditions only from ground observation. Thus we have developed a single sampling device that suits from metal-silicate hard surfaces to regolith layers for MUSES-C, the world's first sample return mission to a near Earth object. We report its mechanism and sampling sequence, together with results of sampling efficiency tests for 1G and micro-G gravity levels. In the vacuum micro-G environment, each sampling with this device promises several hundred mg to several g of target material fragments collected.

Spectroscopic observations of 2001 Leonid meteor storm were carried out using a intensified HDTV camera equipped with a reflective grating covering 300 - 850 nm wavelength range. Hydroxyl radical in the cometary meteoroids was observed in fireballs and persistent trains. A good knowledge of the relationship between meteor and comet or meteorite is needed for understanding of the cometary volatiles. In this paper, we show the first detection of OH A-X (0-0) emission from the ground-based meteor observation and discuss about the origin of the discovered OH.

The Japanese Antarctic Research Expedition (JARS) teams have started collection of unmelted and melted micrometeorites (MMs) in Antarctica since 1996. Some results of the consortium studies are: (1) relatively common occurrence of magnesiowustite (MW) in unmelted MMs, (2) coexistence of MW with low-Ca pyroxene in moderately heated MMs, and (3) evidence that MMs were formed as small particles, rather than fragments of larger bodies, within < a few Ma.

This paper reports the impact craters formed by Ag microparticles impacts, comparing with the TOF-MS (Time-Of-Flight Mass Spectrometer) spectra obtained simultaneously. The TOF spectra suggested that ions were hardly produced on AI target compared to Mo and Au targets. To determine the reason for this and to select the best material that ionizes the impacting dust particles, we observed impact craters on these targets with SEM and STM. Our results suggest that the ionization depends on the materials and that the combination of target and projectile materials causes the differences of crater shape and the Ag residue distribution.

Laboratory investigations of impact residues captured on the solar cells from the Hubble Space Telescope and on insulation foils from the Space Flyer Unit demonstrate preservation of abundant and diverse micrometeoroid and space debris remnants. Micrometeoroid residues often appear as complex melts of poly-mineralic origin derived from silicates, carbonates, metals and metal sulfides. The space debris includes paint-flakes, metal alloys and possible reactor coolant, but the most abundant components are aluminium and aluminium oxide remnants from solid rocket motor operation. The impactor origins have now been compared with the theoretical flux models for Low Earth Orbit.

Mars Dust Counter (MDC) is a light-weight (730g) impact-ionization dust detector on board NOZOMI, a Japanese Mars mission, which was launched on July 4th 1998. The main aim of MDC is to detect the predicted Martian dust rings / tori. It can also cover velocity-mass ranges of interplanetary and interstellar dust particles. By August 2000, MDC had detected more than 60 dust particles. In 1999, it detected five fast particles probably of interstellar origin. For five years from 1999 to 2003, NOZOMI will orbit the sun and MDC can measure interplanetary and interstellar dust between the Earth's and Mars' orbits.

In-situ dust detectors have been calibrated by dust electrostatic accelerators that can accelerate projectiles to expected mass and velocity ranges of space debris and micrometeoroids. Unfortunately, In Japan, there was no such a facility dedicated to space science research until our research group was established a few years ago. Therefore, we have developed two high voltage accelerators. One is a modified 3.75MV Van do Graaff accelerator operated by High Fluence Irradiation Facility, Research Center for Nuclear Science and Technology, the University of Tokyo (HIT), and the other is a 100kV accelerator dedicated to dust experiment at the Institute of Space and Astronautical Science (ISAS). The particle velocity using the HIT Van do Graaff accelerator is higher than those reported in other accelerator facilities under the same particle mass conditions and encompasses the desired velocity range of micro-metooroid. Time-Of-Flight dust mass spectrometer and Hybrid dust detector which are under development in Japan have been investigated using HIT dust accelerators. We have also constructed a 100kV electrostatic accelerator designed for easier handling and lower cost operation which is dedicated to dust acceleration, because the HIT Van do Graaff accelerator is being used for ion beam experiments mainly. (C) 2001 Elsevier Science Ltd. All rights reserved.

A microparticle (dust) ion source has been installed in the 3.75 MV Van de Graaff electrostatic accelerator and a new beam line for microparticle experiments has been built at the HIT facility of Research Center for Nuclear Science and Technology, the University of Tokyo. Microparticle acceleration has been successful in obtaining expected velocities of 1-20 km/s or more for micron- or submicron-sized particles. Development of in situ dust detectors on board satellites and spacecraft in the expected mass and velocity range of micrometeoroids and investigation of hypervelocity impact phenomena by using time-of-flight mass spectrometry, impact Rash measurement and scanning electron microscope observation for metals, polymers and semiconductors bombarded by micron-sized particles have been started. (C) 2001 Elsevier Science Ltd. All rights reserved.

From November 1998 to January 1999,the 39th Japanese Antarctic Research Expedition (JARE-39) undertook Japanese first large-scale collection of Antarctic micrometeorites (AMMs), with sizes larger than 10μm, at the Meteorite Ice Field around the Yamato Mountains in Antarctica (at three different locations, for a total of 24 collection sites). The number of collected AMMs larger than 40μm is estimated to be about 5000. Here we present the general characterization (i.e., micro-morphology and surface chemical composition using SEM/EDS) of ∿810 AMMs chosen from 5 of the 24 sites. Additionall...

Determination of the frequency and importance of impacts by space debris and micrometeoroids of below 1mm in size is best achieved by examining spacecraft surfaces that have been exposed in the near-Earth orbital environment. Post-flight investigation of the returned surface not only allows the measurement of particle flux and the dimensions of individual impact features, but also the composition and origin of the impacting bodies. Impact residue analysis is inherently a difficult task, as a particle traveling at speeds of between 5 and 70 km s(-1) leaves little chemical evidence following a hypervelocity collision. Notwithstanding this difficulty, returned surfaces from a range of spacecraft, including the Long Duration Exposure Facility (LDEF), the Space Flyer Unit (SFU), the Hubble Space Telescope (HST) and Salyut 7-Kosmos 1686 station, have enabled detailed studies on the chemistry of both micrometeoroids and space debris. The development of new dedicated capture cells, e.g. aerogel, should enable even more detailed studies of the micro-particle populations in Earth orbits, and beyond.

Microwave emission due to a hypervelocity impact has been detected using direct detection and heterodyne detection schemes. This phenomena could be used as tools to study hypervelocity impacts or to sense space debris collisions to spacecraft. The projectile is a cylinder of 1 cm diameter and 1 cm length of the polycarbonate material, and is accelerated by a rail-gun which utilizes the electromagnetic force due to the current in plasma. Obtained velocity was 6.9 km/sec.