Experimental investigation on silica dust lofting due to charging within micro-cavities and surface electric field in the vacuum chamber

The charged dust particles can be mobilized electrostatically by the repulsion between the adjacent grains and the surface electric field due to the incoming electron current and the charge accumulation within the micro-cavities. In this study, the experimental results of the initial vertical launching velocities and the maximum dust heights are compared with the estimated values for the lofted spherical dust grains by the patch surface charging equations. Silica particles with the sizes between <6 and 45?µm in radius are loaded on a graphite plate, and they are exposed to the electron beam with 450?eV energy under 4?×?10^?3?Pa vacuum chamber pressure. During the first set of the experiments, the dust samples are tested without an initial compression process and an additional horizontal electric field. Second, the dust samples are compressed by two different weights in order to increase the packing density under approximately 780.7?Pa and 3780?Pa. Finally, the dust grains are placed between the two parallel aluminum plates to apply approximately 2000?V/m and 4800?V/m horizontal electric field. A high-speed camera is used to record the transportation of the dust grains together with a microscopic telescope, and the results point out that the patch surface dust-charging model estimations are in agreement with the first experiments. On the other hand, the dust particles from the compressed samples are lofted with higher velocities than the estimations, and the number of the dust lofting observations decreases significantly, which demonstrates the importance of the micro-cavities and the increased charging requirement to overcome the contact forces. When the horizontal electric field is present, the initial vertical launching velocities are measured to be lower than the other experiments, which can be attributed to the decreased charging requirement for the dust lofting as a result of inter-particle collisions and rolling motion. According to the experimental results, the electrostatic dust transportation can be controlled not only by the ambient plasma and the solar irradiation on the airless planetary bodies, but also by the surface properties such as the contact surfaces between the dust grains, the number of the micro-cavities related to the packing density, and the presence of the horizontal electric field contributing to the external forces by other particle motions.     

Physiologic and metabolic responses of wheat seedlings to elevated and super-elevated carbon dioxide

The metabolic consequence of suboptimal (400 μmol mol⁻¹ or ppm), near-optimal (1500 ppm) and supra-optimal (10,000 ppm) atmospheric carbon dioxide concentrations [CO₂] was investigated in an attempt to reveal plausible underlying mechanisms for the differential physiological and developmental responses to increasing [CO₂]. Both non-targeted and targeted metabolite profiling by GC–MS and LC–MS were employed to examine primary and secondary metabolites in wheat (Triticum aestivum, cv Yocoro rojo) continuously exposed to these [CO₂] levels for 14, 21 and 28 days. Metabolite profile was altered by both [CO₂] and physiological age. In general, plants grown under high [CO₂] exhibited a metabolite profile characteristic of older plants under ambient CO₂. Elevated [CO₂] resulted in higher levels of phosphorylated sugar intermediates, though no clear trend in the content of reducing sugars was observed. Transient starch content was enhanced by increasing [CO₂] to a much greater extent at 10,000 ppm CO₂ than at 1500 ppm CO₂. The percentage increase of starch content resulting from CO₂ enrichment declined as plants develope. In contrast, elevated [CO₂] promoted the accumulation of secondary metabolites (flavonoids) progressively to a greater extent as plants became mature. Elevated [CO₂] to 1500 ppm induced a higher initial growth rate, while super-elevated [CO₂] appeared to negate such initial growth promotion. However, after 4 weeks, there was no difference in vegetative growth between 1500 and 10,000 ppm CO₂-grown plants, both elevated CO₂ levels resulted in an overall 25% increase in biomass over the control plants. More interestingly, elevated atmospheric [CO₂] reduced evapotranspiration rate (ET), but further increase to the supra-optimal level resulted in increased ET (a reversed trend), i.e. ET at 1500 ppm < ET at 10,000 ppm < ET at 400 ppm. The differential effect of elevated and super-elevated CO₂ on plants was further reflected in the nitrogen dynamics. These results provide the potential metabolic basis for the differential productivity and stomatal function of plants grown under elevated and super-elevated CO₂ levels.     

Tolerance of anhydrobiotic eggs of the Tardigrade Ramazzottius varieornatus to extreme environments

Tardigrades are tiny (less than 1?mm in length) invertebrate animals that have the potential to survive travel to other planets because of their tolerance to extreme environmental conditions by means of a dry ametabolic state called anhydrobiosis. While the tolerance of adult tardigrades to extreme environments has been reported, there are few reports on the tolerance of their eggs. We examined the ability of hydrated and anhydrobiotic eggs of the tardigrade Ramazzottius varieornatus to hatch after exposure to ionizing irradiation (helium ions), extremely low and high temperatures, and high vacuum. We previously reported that there was a similar pattern of tolerance against ionizing radiation between hydrated and anhydrobiotic adults. In contrast, anhydrobiotic eggs (50% lethal dose; 1690 Gy) were substantially more radioresistant than hydrated ones (50% lethal dose; 509 Gy). Anhydrobiotic eggs also have a broader temperature resistance compared with hydrated ones. Over 70% of the anhydrobiotic eggs treated at either -196°C or +50°C hatched successfully, but all the hydrated eggs failed to hatch. After exposure to high-vacuum conditions (5.3×10(-4) Pa to 6.2×10(-5) Pa), the hatchability of the anhydrobiotic eggs was comparable to that of untreated control eggs.     

Development status of the high-speed reentry system-DASH

Despite huge amount of data collected by the previous interplanetary spacecraft and probes, the origin and evolution of the solar system still remains unveiled due to limited information they brought back. Thus, the Institute of Space and Astronautical Science (ISAS) of Japan has been given a commitment to pave the way to an asteroid sample return mission: the MUSES-C project. A key to success is considered the reentry with hyperbolic velocity, which has not ever been demonstrated as yet. With this as background, a demonstrator of atmospheric reentry system, DASH, has been designed to demonstrate the high-speed reentry technology as a GTO piggyback mission. The capsule, identical to that of the sample return mission, can experience the targeted level of thermal environment even from the GTO by tracing a specially designed reentry trajectory. After the purpose of the mission was outlined at the last IAF symposium, the final fitting tests have been conducted in the ISAS Sagamihara Campus involving the flight model hardware. Furthermore, a series of rehearsals for recovery have been already executed. The paper describes the current mission status of the project.     

Overview of Differential VLBI Observations of Lunar Orbiters in SELENE (Kaguya) for Precise Orbit Determination and Lunar Gravity Field Study

The Japanese lunar explorer SELENE (Kaguya), which was launched on September 14th, 2007, was the target of VLBI observations over the period November 2007 to June 2009. These observations were made in order to improve the lunar gravity field model, in particular the lower degree coefficients and the model near the limb. Differential VLBI Radio sources, called VRAD instruments, were on-board the subsatellites, Rstar (Okina) and Vstar (Ouna), and the radio signals were observed by the Japanese VERA (VLBI Exploration of Radio Astrometry) network, and an international VLBI network. Multi-frequency and same-beam VLBI techniques were utilized and were essential aspects of the successful observing program. Multi-frequency VLBI was employed in order to improve the accuracy of the orbit determination obtained from the phase delay from the narrow-band satellite signals, while the same-beam VLBI method was used to resolve the cycle ambiguity which is inherent in the multi-frequency VLBI method. The observations were made at three S-band frequencies (2212, 2218 and 2287 MHz), and one X-band frequency (8456 MHz). We have succeeded in correlating the recorded signals from Okina/Ouna, and we obtained phase delays with an accuracy of several pico-seconds at S-band.     

Data Processing at KAGUYA Operation and Analysis Center

The functions of KAGUYA(SELENE) Operation and Analysis Center (SOAC) are to operate three satellites: the main orbiter KAGUYA and two small satellites, Relay satellite OKINA and VRAD (VLBI (Very Long Baseline Interferometry) RADio source) satellite OUNA; and to process, archive and provide mission data. SOAC has two main functional areas, “Tracking and Control system” and “Mission Operation and Data Analysis system.” The former is for operational planning of bus and mission instruments including satellite navigation, and for the implementation of those plans and for the evaluation of satellite conditions. The latter is the system that processes, archives and provides mission data, and which principal investigators use to generate higher-level data products. Data up to the end of the operation in June 2009 have been processed and the total amount of Level-2 data products reaches about 50 TB. The data products have been released to the public since November 2009.