Papers by Yukihiro Takahashi
Jupiter Magnetospheric Orbiter and Trojan Asteroid Explorer in EJSM (Europa Jupiter System Mission)
EGUGA, May 1, 2010
Abstract Europa Jupiter System Mission (EJSM) is an international mission to explore and Jupiter,... more Abstract Europa Jupiter System Mission (EJSM) is an international mission to explore and Jupiter, its satellites and magnetospheric environment in 2020s. EJSM consists of (1) The Jupiter Europa Orbiter (JEO) by NASA,(2) the Jupiter Ganymede Orbiter (JGO) by ESA, ...
Relationship between duration of optical emission of sprites and charge moment change of their parent CG

Planetary lightning flash and thundercloud observation with spacecraft and telescope
epsc, Oct 1, 2011
ABSTRACT It has been revealed that lightning is an good proxy of atmospheric circulation in the E... more ABSTRACT It has been revealed that lightning is an good proxy of atmospheric circulation in the Earth. In planetary exploration, such as Venus and Jupiter, where very limited in-situ measurements can be made, the lightning measurement would be a powerful tool. Recently it is reported that the magnetometer on board Venus Express detected whistler mode waves whose source could be lightning discharge occurring well below the spacecraft. In order to identify the discharge phenomena in the atmosphere of Venus without ambiguity, we sent a high-speed optical sensor to Venus, the lightning and airglow camera, LAC onboard Akatsuki. In Jupiter, the latest observational and theoretical studies suggest that strong moist convective clouds, that is thunderclouds, in Jupiter's atmosphere are very important. It is not only because of an essential ingredient of meteorology of Jupiter, which determines the large scale structures such as belt/zone and big ovals, but also as a potentially very useful tool for probing the water abundance of the deep atmosphere, which is crucial to constrain the behavior of volatiles in early solar system. We would suggest a very simple high-speed imaging unit onboard Jovian orbiter, Optical Lightning Detector, OLD, optimized for detecting optical emissions from lightning discharge in Jupiter. OLD consists of radiation-tolerant CMOS sensors and two H Balmer Alpha line (656.3nm) filters. In normal sampling mode the frame intervals is 29ms with a full frame format of 512x512 pixels and in high-speed sampling mode the interval could be reduced down to 0.1ms by concentrating a limited area of 30x30 pixels. Weight, size and power consumption are about 1kg, 16x7x5.5 cm (sensor) and 16x12x4 cm (circuit), and 4W, respectively, though they can be reduced according to the spacecraft resources in EJSM orbiters. Also we plan to investigate the optical flashes using a ground-based middle-sized telescope, which will be built by Hokkaido University, with narrow-band high speed imaging unit. Observational strategy with such optical lightning detectors and spectral imagers, which enable us to estimate the horizontal motion and altitude of clouds, are to be discussed.
Challenge of lightning detection with LAC on board Akatsuki spacecraft
EGUGA, Apr 1, 2016
木星氷衛星探査衛星 JUICE - 日本がリードするサイエンス

Earth, Planets and Space, May 25, 2018
The existence of lightning discharges in the Venus atmosphere has been controversial for more tha... more The existence of lightning discharges in the Venus atmosphere has been controversial for more than 30 years, with many positive and negative reports published. The lightning and airglow camera (LAC) onboard the Venus orbiter, Akatsuki, was designed to observe the light curve of possible flashes at a sufficiently high sampling rate to discriminate lightning from other sources and can thereby perform a more definitive search for optical emissions. Akatsuki arrived at Venus during December 2016, 5 years following its launch. The initial operations of LAC through November 2016 have included a progressive increase in the high voltage applied to the avalanche photodiode detector. LAC began lightning survey observations in December 2016. It was confirmed that the operational high voltage was achieved and that the triggering system functions correctly. LAC lightning search observations are planned to continue for several years.

Japan Geoscience Union, 2017
Current weather radars used for short-term precipitation forecast mostly detect rain/snow droplet... more Current weather radars used for short-term precipitation forecast mostly detect rain/snow droplets, which prevents from fully observing rapidly growing cumulus clouds that could cause severe weather until rain/snowfall starts. Phased array radars and other new radars have gradually been enabling to detect clouds but building and operating such radars would be expensive. In order to develop inexpensive methods to observe clouds before precipitation starts, images of the clouds captured with visible light cameras could be used to locate and make measurements of clouds. Previous studies have succeeded in locating clouds by calibrating cameras using various objects and landmarks, such as topographic features, locations of an airplane, the sun and stars. However, for the practical monitoring of clouds, it is important to investigate the proper conditions when capturing images to observe the clouds without any external calibration. In order to observe the clouds, 4 images of the same clou...
木星氷衛星探査衛星JUICE - 日本がJUICE で目指すサイエンス

Japan Geoscience Union, 2017
Currently, short-term rain/snow forecast is largely based on weather radars that observe rain/sno... more Currently, short-term rain/snow forecast is largely based on weather radars that observe rain/snow particles in the air and therefore cannot fully cover the clouds which may cause severe weather. New radars have recently been developed to detect clouds but the construction and maintenance of radars would be expensive. In order to develop low-cost methods to observe clouds, images of clouds captured with digital cameras could be used to locate and make measurements of clouds. Previous studies attempted to calibrate cameras using various objects and landmarks, such as topographic features, locations of airplanes and stars. However, for the practical cloud monitoring, it is important to develop methods to observe clouds without any external calibration but the proper photographic conditions for the task are yet to be carefully examined. In order to examine the optimum conditions, images of the cloud-like objects, a lump of cotton and a piece of clay, were taken from different angles wi...

Earth, Planets and Space, 2016
AKATSUKI is the Japanese Venus Climate Orbiter that was designed to investigate the climate syste... more AKATSUKI is the Japanese Venus Climate Orbiter that was designed to investigate the climate system of Venus. The orbiter was launched on May 21, 2010, and it reached Venus on December 7, 2010. Thrust was applied by the orbital maneuver engine in an attempt to put AKATSUKI into a westward equatorial orbit around Venus with a 30-h orbital period. However, this operation failed because of a malfunction in the propulsion system. After this failure, the spacecraft orbited the Sun for 5 years. On December 7, 2015, AKATSUKI once again approached Venus and the Venus orbit insertion was successful, whereby a westward equatorial orbit with apoapsis of ~440,000 km and orbital period of 14 days was initiated. Now that AKATSUKI's long journey to Venus has ended, it will provide scientific data on the Venusian climate system for two or more years. For the purpose of both decreasing the apoapsis altitude and avoiding a long eclipse during the orbit, a trim maneuver was performed at the first periapsis. The apoapsis altitude is now ~360,000 km with a periapsis altitude of 1000-8000 km, and the period is 10 days and 12 h. In this paper, we describe the details of the Venus orbit insertion-revenge 1 (VOI-R1) and the new orbit, the expected scientific information to be obtained at this orbit, and the Venus images captured by the onboard 1-µm infrared camera, ultraviolet imager, and long-wave infrared camera 2 h after the successful initiation of the VOI-R1.

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 2010
EJSM (Europa Jupiter System Mission) is a planned Jovian system mission with three spacecraft aim... more EJSM (Europa Jupiter System Mission) is a planned Jovian system mission with three spacecraft aiming at coordinated observations of the Jovian satellites especially Europa and the magnetosphere, atmosphere and interior of Jupiter. It was formerly called "Laplace" mission. In October 2007, it was selected as one of future ESA scientific missions Cosmic Vision (2015-2025). From the beginning, Japanese group is participating in the discussion process of the mission. JAXA will take a role on the magnetosphere spinner JMO (Jupiter Magnetosphere Orbiter). On the other hand, ESA will take charge of JGO (Jupiter Ganymede Orbiter) and NASA will be responsible for JEO (Jupiter Europa Orbiter). In February 2009, EJSM is prioritized as the first candidate of outer planet flagship mission and mission study continues in the course of Cosmic Vision. The expected launch time of EJSM will be expected in 2020. Currently we are seeking a possibility to combine JMO with a proposed solar sail mission of JAXA for Jupiter and one of Trojan asteroids.

Predicting global thunderstorm activity for sprite observations from the International Space Station
ABSTRACT The global rate of sprites occurring above thunderstorms, estimated from the ISUAL satel... more ABSTRACT The global rate of sprites occurring above thunderstorms, estimated from the ISUAL satellite data, is ~0.5 per minute (Chen et al., 2008). During the summer 2011, in the framework of the "Cosmic Shore" project, we conducted a concentrated attempt to image sprites from the ISS. The methodology for target selection was based on that developed for the space shuttle MEIDEX sprite campaign (Ziv et al., 2004). There are several types of convective systems generating thunderstorms which differ in their effectiveness for sprite production (Lyons et al., 2009), and so we had to evaluate the ability of the predicted storms to produce sprites. We used the Aviation Weather Center (http://aviationweather.gov) daily significant weather forecast maps (SIGWX) to select regions with high probability for convective storms and lightning such that they were within the camera filed-of-view as deduced from the ISS trajectory and distance to the limb. In order to enhance the chance for success, only storms with predicted "Frequent Cb" and cloud tops above 45 Kft (~14 km) were selected. Additionally, we targeted tropical storms and hurricanes over the oceans. The accuracy of the forecast method enabled obtaining the first-ever color images of sprites from space. We will report the observations showing various types of sprites in many different geographical locations, and correlated parent lightning properties derived from ELF and global and local lightning location networks. Chen, A. B., et al. (2008), Global distributions and occurrence rates of transient luminous events, J. Geophys. Res., 113,A08306, doi:10.1029/2008JA013101 Lyons, W. A., et al. (2009), The meteorological and electrical structure of TLE-producing convective storms. In: Betz et al. (eds.): Lighting: principles instruments and applications, Springer-Science + Business Media B.V.. Ziv, B., Y. Yair, K. Pressman and M. Fullekrug, (2004), Verification of the Aviation Center global forecasts of Mesoscale Convective Systems. Jour. App. Meteor., 43, 720-726.
Space Science Reviews, 2008
The propagation of extremely low frequency (ELF, 3 Hz to 3 kHz) radio waves and resonant phenomen... more The propagation of extremely low frequency (ELF, 3 Hz to 3 kHz) radio waves and resonant phenomena in the spherical Earth-ionosphere cavity has been studied for almost fifty years. When such a cavity is excited by naturally occurring broadband electromagnetic radiation, resonances can develop if the equatorial circumference is approximately equal to an integral number of wavelengths of the propagating electromagnetic waves; these are termed Schumann resonances. They provide information not only about thunderstorm and lightning activity on the Earth, and their relation to climate, but also on the properties of the low ionosphere. Similar investigations can be performed for any other planet or satellite, provided that it has an ionosphere. F. Simões ( )

Space Science Reviews, 2008
Lightning activity in Venus has been a mystery for a long period, although many studies based on ... more Lightning activity in Venus has been a mystery for a long period, although many studies based on observations both by spacecraft and by ground-based telescope have been carried out. This situation may be attributed to the ambiguity of these evidential measurements. In order to conclude this controversial subject, we are developing a new type of lightning detector, LAC (Lightning and Airglow Camera), which will be onboard Planet-C (Venus Climate Orbiter: VCO). Planet-C will be launched in 2010 by JAXA. To distinguish an optical lightning flash from other pulsing noises, high-speed sampling at 50 kHz for each pixel, that enables us to investigate the time variation of each lightning flash phenomenon, is adopted. On the other hand, spatial resolution is not the first priority. For this purpose we developed a new type of APD (avalanche photo diode) array with a format of 8 × 8. A narrow band interference filter at wavelength of 777.4 nm (OI), which is the expected lightning color based on laboratory discharge experiment, is chosen for lightning measurement. LAC detects lightning flash with an optical intensity of average of Earth's lightning or less at a distance of 3 Rv. In this paper, firstly we describe the background of the Venus lightning study to locate our spacecraft project, and then introduce the mission details. It is well known to us that lightning on Earth is usually produced by strong convective clouds. According to recent global surveys from ground and spacecraft, the average

Detection of lightning discharges on Venus has been attempted using both radio waves and optical ... more Detection of lightning discharges on Venus has been attempted using both radio waves and optical methods for over 40 years. For optical observations, claims of lightning detection were controversial due to the lack of time resolution of optical emissions that is needed to separate lightning from artificial or natural noise. Here we show the first high-time-resolution light curve of a transient optical phenomenon observed by the Lightning and Airglow Camera (LAC), a dedicated instrument on the Venus orbiter Akatsuki. The observed transient was 10 times brighter than a typical terrestrial lightning flash and had a duration of a few hundred milliseconds, whereas that of typical Earth lightning is only a millisecond. These characteristics are not typical, but are well within the variability of Earth lightning. An origin as a bolide flare cannot be excluded, but considering the expected occurrence frequency of meteoroids at Venus, is improbable. The low flash rate and long duration deter...
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 2010
The microsatellite SPRITE-SAT developed by Tohoku University was launched in January 2009. Regard... more The microsatellite SPRITE-SAT developed by Tohoku University was launched in January 2009. Regarding the thermal system of SPRITE-SAT, the mathematical model, the parameter determination for the heat transfer coefficients, and the comparison between the estimate and real temperature in flight mode are shown in this paper. The precision of thermal analysis using the simple 7-node model was solved. The estimate error of temperature in orbit is less than 5 degrees Celsius in panels with most of instruments.
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN, 2012
The 50-kg class micro satellite RISING-2 is now under development by Tohoku University and Hokkai... more The 50-kg class micro satellite RISING-2 is now under development by Tohoku University and Hokkaido University. The development is at Flight Model phase and some components are tested to evaluate its specifications. In this paper, the endurance tests using vacuum chamber and thermal test chamber in Tohoku University are described. There was no problem in those tests. In addition, the attitude control accuracy of the RISING-2 was analyzed in the simulation. This simulation based on component specifications and also included noise data. The results show the pointing error angle was less than required error angle.
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, SPACE TECHNOLOGY JAPAN, 2009
An S-520 sounding rocket was launched in the summer of 2007 in order to observe magneto electric ... more An S-520 sounding rocket was launched in the summer of 2007 in order to observe magneto electric phenomena in high sky and to verify a new spectroscopic observation method. A Multi-Spectrum Imager (MSI) was developed for the latter aim. The observation device is equipped a spectroscopic camera with a liquid crystal tunable filter and a pointing system to control the pointing direction to take spectroscopic images of a target against the spin of the rocket body. With the successful flight of the sounding rocket, the MSI succeeded in taking and sending approximately 30 pictures and the house keeping data.

Tohoku University and Hokkaido University have been developing a series of 50kg-class scientific ... more Tohoku University and Hokkaido University have been developing a series of 50kg-class scientific microsatellites for years. The first micro-satellite was the SPRITE-SAT successfully launched in January 2009 by Japanese H-IIA launcher, which had a mass of about 44 kg and was designed to observe Transient Luminous Events (TLE) in Earth upper atmosphere. SPRITE-SAT was given an operational name of RISING-1 after the launch. Following this satellite, two successor 50kg-class micro-satellites for constellational Earth observation with different types of observation instruments including 5m GSD multi-spectral High-Precision Telescopes (HPT) were initiated. These micro-satellites are namely RISING-2 and RISESAT. The flight model of the RISING-2 is ready for the launch planned in late 2013, and the development of RISESAT will be completed for the launch by the end of Japanese fiscal year of 2013. Both orbits are planned to be sun-synchronous Low Earth Orbit. These micro-satellites will be utilized for constellational Earth observation for planned mission life time of more than two years.
ISUAL multi-band observations of elves
2011 XXXth URSI General Assembly and Scientific Symposium, 2011
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Papers by Yukihiro Takahashi