Takumi ABE

Copyright © 2016 by the International Astronautical Federation (IAF). All rights reserved. Japan's Venus Climate Orbiter Akatsuki was proposed to ISAS (Institute of Space and Astronautical Science) in 2001 as an interplanetary mission. We made 5 cameras with narrow-band filters to image Venus at different wavelengths to track the cloud and minor components distribution at different heights to study the Venusian atmospheric dynamics in 3 dimension. It was launched on May 21st, 2010 and reached Venus on December 7th, 2010. With the thrust by the orbital maneuver engine, Akatsuki tried to go into the westward equatorial orbit around Venus with the 30 hours' orbital period, however it failed by the malfunction of the propulsion system. Later the spacecraft has been orbiting the sun for 5 years. On December 7th, 2015 Akatsuki met Venus again after the orbit control and Akatsuki was put into the westward equatorial orbit whose apoapsis is about 0.44 million km and orbital period of 14 days. Its main target is to shed light on the mechanism of the fast atmospheric circulation of Venus. The systematic imaging sequence by Akatsuki is advantageous for detecting meteorological phenomena with various temporal and spatial scales. We have five photometric sensors as mission instruments for imaging, which are 1 m-infrared camera (IR1), 2 m-infrared camera (IR2), ultra-violet imager (UVI), long-wave infrared camera (LIR), and lightning and airglow camera (LAC). These photometers except LIR have changeable filters in the optics to image in certain wavelengths. Akatsuki's long elliptical orbit around Venus is suitable for obtaining cloud-tracked wind vectors over a wide area continuously from high altitudes. With the observation, the characterizations of the meridional circulation, mid-latitude jets, and various wave activities are anticipated. The technical issues of Venus orbit insertion in 2015 and the scientific new results will be given in this paper.

Lithium ejection system (LES) is one of the chemical payloads for the ionosphere observation. Lithium is selected as the chemical tracer to detect optically the neutral winds, and the thermite loaded in LES played a role of the heat sauce to vaporize the solid phase lithium. This device has been launched by the Japanese sounding rocket, S-520, from Uchinoura space center in 2007. Gaseous lithium was successfully injected into the space, and the red colored cloud was able to be observed from the ground. The concept was explained in early papers, and their design was shown that the thermite including lithium or sodium pellets was directly charged in the canister. Thermite is ignited by the pyrotechnics and generates the high temperature chemical products which give the vaporization energy of the released materials. The payload design was considered that the instruments on board which acts by the pyrotechnics need to be equipped with the safe and arm device (SAD) from the safety standard. The final design obtained the safety and the reliability of this device for storing and handling. Lithium in the canister is able to be removed with ease, and the tracer materials will be able to replace lithium to other one if necessary. 13 LES canisters were fabricated for ISAS-NASA international collaborative space science mission. This paper reports the results of the design study and the specification of LES.

The primary objectives of the sounding rocket experiment, S-520-25, are to deploy an electro-conductive bare tape tether in space and to study the electron current-collection by the tape tether when biased positively. Before the space experiment, we have carried out laboratory experiments on the plasma collection by the tape tether in a large space science chamber at ISAS/JAXA. This paper presents the major results on the currentvoltage characteristics of the tape tether in the plasma environment which simulates the ionospheric plasma It was found that the tether current approached to the prediction by the Orbit Motion Limit (OML) theory as the tether voltage was increased up to 500 V. In the high voltage region more than 200 V, we often observed the discharge at the surface of the tether that damaged the tether material.

Pressure measurements in scientifi c balloon and sounding rocket experiments in the upper atmosphere are technologically and scientifi cally important. An onboard small pressure gauge developed in this study is the quartz friction gauge, which is based on the principle that the resonance impedance of a quartz oscillator varies with the pressure of ambient gas. The gauge has a wide measuring range (10^5 - 10^<-2> Pa), which corresponds to the atmospheric pressure from the ground to an altitude of about 100 km. The sensor part and data processing part weigh 100 g and 200 g, respectively. In addition, power consumption of less than 1 W is achieved with this gauge. The gauge is suited for high altitude balloon experiments because the weight of their instruments is severely limited. A tuningfork-shaped quartz oscillator in the gauge is widely used for wrist watches and the structure has a high resistance to vibration and shock, and thus the gauge is applicable to sounding rocket experiments that require onboard instruments to have high environment resistance. In this paper, we report on a performance demonstration test of the newly developed quartz friction gauge using the BU30-5 balloon experiment.

The Venus Climate Orbiter mission (PLANET-C), one of the future planetary missions of Japan, aims at understanding the atmospheric circulation of Venus. Meteorological information will be obtained by globally mapping clouds and minor constituents successively with 4 cameras at ultraviolet and infrared wavelengths, detecting lightning with a high-speed imager, and observing the vertical structure of the atmosphere with radio science technique. The equatorial elongated orbit with westward revolution fits the observation of the movement and temporal variation of the atmosphere which rotates westward. The systematic, continuous imaging observations will provide us with an unprecedented large dataset of the Venusian atmospheric dynamics. Planet-C will be launched in 2010 and will reach Venus in 5 months. Nominal operation period is 2 earth years.

A fully reusable rocket vehicle is proposed as a sounding rocket for observations of atmospheric phenomena, micro-gravity experiments and so on. Vehicle systems and ground / flight operations are designed for such science observations. For the development of the reusable rocket, a small test vehicle was built and flight-tested. This Reusable Vehicle Testing (RVT) lessons campaign provide repeated experiences of turnaround operations and vertical take-off and landing flights. In the present design of the reusable sounding rocket, the total length and maximum diameter of the vehicle is about 10m and 3m, respectively. The vehicle is propelled by the propulsion system composed of four liquid hydrogen / liquid oxygen engines. The weight of a payload carried to 120 km altitude is 100kg in the nose-fairing. The instrument for observations can be reused because of the repeated flight. The turnaround time for one flight is less than 24 hours (1 day). In the typical ballistic flight up to 120 km, the flight environments under 10(-5)G acceleration is able to be made for about 120 sec. The flight Mach number can be subsonic around the summit in the trajectory. These properties of reusable sounding rocket are expected to be useful and effective for many science missions.

The coordinated sounding rocket and ground-based observations were conducted in Norway on 13 December 2004. The main objective of this campaign is to elucidate the dynamics and energetics in the lower thermosphere associated with the auroral energy input. The instruments on board the rocket successfully performed their measurements, and provided the temperature and density of molecular nitrogen, auroral emission rate, and the ambient plasma parameters, while neutral wind, neutral temperature, the auroral images and the ionospheric parameters were observed by ground-based measurements. In this paper, we present a summary of this campaign and preliminary results.

The dynamics of neutral atmosphere is closely coupled with the behavior of ionized gas and chemical process in the lower thermosphere-mesosphere region. The measurement of the neutral wind at the height region is important to study those processes. So far the neutral wind has been independently measured by a radar-tracking of foil chaffs: a micro rocket is needed for the wind measurement in addition to a main, big rocket which carries other scientific instruments. In order to conduct simultaneous wind and other measurements onboard a single rocket, we have developed two types of foil chaff ejection systems to be installed in a sounding rocket. We have tested two foil chaff ejection systems: 1) foil chaffs are accommodated in an airtight cylinder case whose sealing cap is removed with one atmospheric pressure, 2) foil chaffs are accommodated in the splitted cylinder, which is ejected by a spring. These two ejection systems were loaded on a sounding rocket S-310-29, which was launched on the 10th, January, 2000. About 20,000 pieces of foil chaff in total were successfully ejected during the downleg of the rocket, around the height of 100km, 341sec after the launch. The foil chaff were tracked in the height range of 95.0-88.5km by the primary radar and the velocity and direction of the neutral wind were obtained.

Mid-lattitude sporadic E (Es) layers have been observed for a long time and the formation mechanism based on the wind shear theory is currently acceptd among the science community. However, no satisfactory theory which discusses the energetics of the Es layer exists because of the lack of the accurate electron temperature measurement. v-i characteristic curves were obtained by means of a glass-sealed Langmuir probe onboard the rocket S-310-27 which was launched on the 25th, January, 1998. Detail study of the v-i characteristic curves clearly shows the effect of the secondary electrons from the electrode surface, which should be taken into account to derive the accurate daytime electron density from the ion-current region of the v-i characteristic curve. The careful analysis of the ion current shows the wavy structure in the height profile, which is concluded to be produced by the internal gravity wave. The electron temperature in the Es peak which appeared at the height of 92-93km was about 500K higher than of the possible netral temperature (about 200K). In this report, we will discuss the reliability of these results and provide the basic informations to study the energetics of the Es in the future studies.

We already realized the transparent wave absorver using resistive-film at 60 GHz. The necessity of transparent wave absorber at X band for radars is increasing. In this paper, we try to realize the two-layered transparent wave absorber using resistive-film at X band. As a result, we can show the design charts as the function of dielectric constant and thickness of glass, and can confirm that the transparent wave absorber has the reflection loss of more than 17dB at 8.5〜11.5 [GHz].

We present a possible suggestion method to measure a permittivity of material without cutting a sample by means of the rectangular cavity resonator. A theoretical discussion on the possibility is given in this paper by studying the relationship between the material permittivity and a resonance frequency of the electromagnetic field inside cavity which is calculated by the FDTD method. We show the permittivity measurement chart by which the permittivity can be estimated from the measured resonant frequency. The permittivity estimated has a reasonable agreement with an empirical value within an error of several percents. The present result supports the validity of the present method.

In this paper, the author discusses the error due to deformation of sample on permittivity measurement by standing-wave method on rectangular waveguide using Finite Difference Time Domain. The analytical model is considered the samples of four different deformed cases; (1) undeformed and no-loss sample, (2) undeformed and lossy sample, (3) deformed and no-loss sample, and (4) deformed and lossy sample. <br>As a result, it is confirmed that a deformation of the sample has strong influence on an accuracy of complex permittivity measurement. Specifically, the auther presents an interesting relation between the measurement error and the degree of sample deformation, including quantitative value of the error as a function of geometrical relation of the sample deformation with respect to the electric field distribution.

We discuss a new method to measure a permittivity of sample material with the rectangular cavity resonator. A merit of this method is that it is unnesessary to cut the material so as to be inserted fit for the cavity size, and therfore experimental error related to the material dimension is avoidable. Theoretical calculation of the cavity resonant frequency, obtained by the FDTD method, is compared to measured one, for several cases of material width and the permittivity. Both freqiencies are in a reasonable agreement each other within an error of a few percents. The present result suggests that this method is very convetional and effective for the permittivity measurement and it also has a possibility for further application of the permittivity estimation which does not require any processing of the material.

We present a possible suggestion of a way to measure a permittivity without cutting a sample material by means of the rectangular cavity resonator. The theoretical discussion on the possibility is made in this paper, based on the time variation and the resonance frequency of electromagnetic field inside cavity which is calculated by the FDTD method. The material permittivity estimated from the resonance frequency has a reasonable agreement with theoretical one within an error of a few percents. The present result suggests a possibility for further application of the permittivity estimation which does not require any processing of the material.

Standing-wave method in a rectangular waveguide is a convenient method for measuring the permittivity of the materials. But it is found the error due to the deformation became large when the test sample is deformated. In this paper, we applied FDTD which is powerful tool for solving waveguide problem to evaluate the error due to the deformation. As the results, we can estimate the error as a function of the deformation of sample.

In this paper,we discuss on an aplication of the range doppler imaging to measurement of a wave absorbing characteristices without using a wave darkroom.For the 300x3OOmm metal plate,the measureable range of higher than 4O〜5OdB has been obtained.The nor mal incident characteristices of both vertical and porizontal polarization are in close agreement with the theoretial values. These results show that this metod can be applicable to the measurement method of absorbing not in the wave darkroom,but in an usual room.

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Thermal electrons in the upper ionosphere are being studied by means of the scientific satellite "AKEBONO". The measurements are electron temperature, electron density and the distribution of electrons in the energy range of 0&acd;5eV. An overview of the experiment is given and preliminary results on the protonosphere and field aligned current region are presented.

Low energy component of protons in the solar wind was found by means of an observation with the spacecraft "SAKIGAKE". This component is always accompanied by a sudden change in the solar wind parameters such as interplanetary shocks. The difference of bulk speed between the low energy component and normal one amounts to about 60-140km/s, and is strongly affected by the configuration of the interplanetary magnetic field. It is shown that this low energy component was produced by the gyromotion of protons, through an acceleration mechanism, e. g., Fermi process. Furthermore, it seems that there are two types of accelerative process, though these mechanisms are unknown.

Numerical simulations of Boltzmann's equation have been carried out in order to investigate the anisotropy of the electron energy distribution in the topside F region ionosphere. The equation contains both electron-electron collisions and electron-ion collisions. The simulations were compared with the observational data obtained with the electron temperature probe on board the Ohzora satellite. The results show that the anisotropy of the electron energy distribution can be generated in the topside F region ionosphere and that the electron energy distribution can differ from the Maxwell distribution, when an electric field or temperature gradient (heat flux) exists in the plasma. The simulations also indicate the dependence of electron density on the anisotropy of the ionospheric electron energy distribution.