Yoshitaka Saito

We have performed a series of cosmic-ray electron observations using balloon-borne emulsion chambers since 1968. While we previously reported the results from subsets of the exposures, the final results of the total exposures up to 2001 are presented here. Our successive experiments have yielded a total exposure of 8.19 m2 sr day at altitudes of 4.0-9.4 g cm-2. The performance of the emulsion chambers was examined by accelerator beam tests and Monte Carlo simulations, and the on-board calibrations were carried out by using the flight data. In this work, we present the cosmic-ray electron spectrum in the energy range from 30 GeV to 3 TeV at the top of the atmosphere, which is well represented by a power-law function with an index of -3.28 ± 0.10. The observed data can also be interpreted in terms of diffusive propagation models. The evidence of cosmic-ray electrons up to 3 TeV suggests the existence of cosmic-ray electron sources at distances within 1 kpc and times within 1 × 105 yr ago. © 2012. The American Astronomical Society. All rights reserved.

The tandem balloon system with a super-pressure balloon and a zero-pressure balloon is a vehicle which can fly a long duration flight changing the level flight altitudes. This system requires a super-pressure balloon with good capacity to endure high pressure. A pumpkin shaped 3-m balloon with 20 μm polyethylene films covered by a Vectran net with diamond shapes was developed and showed the excellent capacity to endure the pressure of 9,600 Pa on the ground test. A flight test of a tandem balloon system with a super-pressure balloon of the same model and a 2-kg rubber balloon was performed on June 1, 2011, from the Taiki Aerospace Research Field. It was launched in the early morning and the flight lasted crossing the sunrise. It was found that the temperature of the skin of the super-pressure balloon changed by 30 degrees before and after the sunrise and the lift of a rubber balloon at night flight decreased by 5 % after the launch. These parameters are quite useful to evaluate the required capability for the pressure resistance of super-pressure balloons, and to determine the lift of rubber balloons for future tandem systems. Development to enlarge the super-pressure balloon will be continued to provide the system for future scientific experiments.

Development of a balloon to fly at higher altitudes is one of the most attractive challenges for scientific balloon technologies. After reaching the highest balloon altitude of 53.0 km using the 3.4 μm film in 2002, a thinner balloon film with a thickness of 2.8 μm was developed. A 5000 m 3 balloon made with this film was launched successfully in 2004. However, three 60,000 m 3 balloons with the same film launched in 2005, 2006, and 2007, failed during ascent. The mechanical properties of the 2.8 μm film were investigated intensively to look for degradation of the ultimate strength and its elongation as compared to the other thicker balloon films. The requirement of the balloon film was also studied using an empirical and a physical model assuming an axis-symmetrical balloon shape and the static pressure. It was found that the film was strong enough. A stress due to the dynamic pressure by the wind shear is considered as the possible reason for the unsuccessful flights. A 80,000 m 3 balloon with cap films covering 9 m from the balloon top will be launch in 2011 to test the appropriateness of this reinforcement. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.

The super-pressure balloon (SPB) has been expected to be a flight vehicle that can provide a long flight duration to science. Since 1997, we have developed the SPB. Now we are at the phase of developing an SPB of a practical size. In 2009, we carried out a test flight of a pumpkin-shaped SPB with a 60,000 m 3 volume. The undesirable result of this flight aroused us to resolve the deployment instability of the pumpkin-shaped SPB, which has been known as one of the most challenging issues confronting SPB development. To explore this deployment issue, in 2010, we carried out a series of ground tests. From results of these tests, we found that an SPB design modified from pumpkin, named "tawara", can be a good candidate to greatly improve the deployment stability of the lobed SPB. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.

We have been developing a Compton-scattering-type hard-X-ray polarimeter sensitive over the energy range from ∼60 keV to ∼300 keV for Gamma-Ray Burst (GRB) studies. The polarimeter consists of four identical modules each with a field of view of ±45°. To estimate the instrument performance accurately, we have investigated the instrument's response for gamma rays incident off-axis. We report here results of computer simulations coupled with basic experiments using polarized X-ray beams. As a result of this work we estimate that our polarimeter can detect the polarization for ∼100 GRBs in 5 years at 99% confidence level if the degree of polarization is higher than 40%. © 2011 IEEE.

The lobed-pumpkin shaped super-pressure balloon is able to withstand high pressure due to its small local curvature of the film being independent of the balloon size. It yields the small local curvature as a bulge among adjacent load ropes connected between the top and the bottom fittings. The small curvature is also expected if the balloon is covered by a diamond-shaped net with vertically elongated shape. In addition to the merit of the small curvature, the method using the daimond-shaped net has following merits; 1. the weight of the film is reduced since a weak but light film is able to be used by covering the balloon with a fine mesh net which mesh size is determined without depending on the gore width, 2. the deployment problem known for the lobed-pumpkin balloon can be solved due to its lack of additional films, 3. the capacity of resist pressure is not reduced due to the manufacturing error, since the local distortion of the mesh size does not affect the global balloon shape. We made a small balloon with a 3 m diameter using a 20 μm polyethylene film and a Kevlar net, and performed an inflation test which showed an expected burst pressure. We are going to make larger balloons for the ground inflation tests and launch a larger super-pressure balloon as a part of a tandem balloon system in 2011.

A zero-pressure balloon used for scientific observation in the stratosphere has an unmanageable limitation that its floating altitude decreases during a nighttime because of temperature drop of the lifting gas after a sunset. Once a practical size of super-pressure balloon without venting ducts was developed, its lifetime can extend very long because the volume may not change. We proposed a new super-pressure balloon design, which is constructed by a concept of `lobed-pumpkin with lobed-cylinder' and can adapt a single design for balloons of a wide range of volumes. The advantage and formulation of this new design are presented in this paper. The results of a flight test as well as indoor inflation experiments are also considered to study the validity of the design and fabrication method. This new shape could realize a powered balloon system in the future because of its reduced drag shape.

The CALET payload will be installed in the Japanese Experiment Module Exposed Facility (JEM-EF) of the International Space Station (ISS). We developed a balloon-borne payload to evaluate the performance of CALET by carrying out precursor flights for the electron and gamma-ray observations. The first flight of bCALET-1 (balloon-borne CALET prototype) was carried out in 2006, and the enhanced version, bCALET-2, was successfully flown in August 2009. The bCALET-2 is composed of IMaging Calorimeter (IMC) and Total AbSorption Calorimeter (TASC). The IMC has an area of 256 mm × 256 mm, and is consisted of 8 layers of scintillating fiber belts with a total 3.6 radiation lengths of tungsten plates interleaved within the fiber planes for imaging the pre-shower development. TASC is consisted of crossed BGO logs (25 mm × 25 mm × 300 mm in each) with a total of 13.4 radiation lengths depth, for measuring the total energy deposit of incoming shower particles. The geometry factor is nearly 320 cm2sr over 10 GeV. We succeeded the observation of the electron energy spectrum in 1 GeV ∼ several 10 GeV electron and the atmospheric gamma-rays in 1 GeV ∼ a few 10 GeV, which are consistent with previous observations by BETS. The results are compared with simulations for confirming the detector performance.

We have been developing a new telemetry tracking and command (TT&C) system for the balloon experiment,and aiming to utilize the new TT&C system from 2012. As the first step to shift to this new system, we have developed a simplified new TT&C system which is mounted at the bottom of the balloon, executes the termination command and used for the balloon tracking after the termination. We call this system backup system, relative to main system mounted in the main gondola, and we will start its practical use from 2010. In this paper, we report the outline of the new TT&C and backup systems, and the brief summary of R&D which has been done.

The 3rd Suzaku international Conference "Energetic Cosmos : from Suzaku to ASTRO-H" (June 29-July 2, 2009. Grand Park Otaru Hotel), Otaru, Hokkaido JapanWe have been developing a hard X-ray polarimeter with high sensitivity, called as a PHENEX (Polarimetry for High ENErgy X-rays) polarimeter. We constructed prototype PHENEX polarimeter and carried out a preliminary observation of the Crab Nebula on June 13th, 2006 as a balloon-borne experiment. Though we confirmed from the data that PHENEX polarimeter detected hard X rays from the Crab Nebula with a significance of 8 sigma, the degree and the direction of polarization with high accuracy could not be determined because of the trouble for attitude control system (ACS) and the small detection area of the prototype polarimeter. We improved the PHENEX polarimeter and carried out a balloon-borne experiment in June 2009 launching from Taiki Aerospace Research Field to observe the polarization of the Crab Nebula with higher accuracy. In this paper, we will report the summary of this experiment.Meeting sponsors: The University of Tokyo, The Institute of Physical and Chemical Research, The Japan Society for the Promotion of Science

The tandem balloon system has been known as a candidate system for long duration flight balloons. In this paper, the properties of the system are analytically studied in a new way by introducing an extendable suspension wire in the Sky Anchor configuration, which consists of a zero-pressure main balloon suspending a payload and a super-pressure balloon suspended below the payload. It was found that extension of the suspension wire between the payload and the super-pressure balloon can extend the capability of the tandem system; the altitude of the zero-pressure balloon can be changed without any consumables except some energy, and the day-night oscillation of the balloon altitude can be suppressed. This property is useful as the vehicle for long duration flights. It is also pointed out that the method to control the altitude of a balloon using an additional suspended super-pressure balloon can also be applied for super-pressure balloons. © 2009 COSPAR.

Since 1971, numerous balloons have been launched from the Japanese balloon base, the Sanriku Balloon Center (SBC). Through these years, balloon technologies have been developed continuously and many scientific achievements have resulted. Recently, however, because of the limited area of the launching pad of the SBC, we have been faced with the difficulty of safely launching large balloons. To solve this issue, we decided to move the balloon base from the SBC to the Taiki Aerospace Research Field (TARF) in northern Japan. The TARF had an existing huge hanger and a paved launch pad capable of being utilised for balloon operations. To evolve the TARF into a new balloon base, new balloon facilities have been constructed at the TARF and equipment was transferred from the SBC to the TARF during July 2007 and March 2008. The SBC was closed in September 2007, and the new base became operational in May 2008. The new base at the TARF is designed to launch larger balloons with greater safety and to perform balloon operations more effectively than ever before. In the summer of 2008, we carried out the first series of the balloon campaign at the TARF, and succeeded in two engineering flights of stratospheric balloons. By the success of these flights, we have verified that the whole system of the new balloon base is well established. © 2009 COSPAR.

We have been developing a hard X-ray polarimeter with high sensitivity, called as a PHENEX (Polarimetry for High ENErgy X rays) polarimeter. We constructed prototype PHENEX polarimeter and carried out a preliminary observation of the Crab Nebula on Jun. 13th 2006 as a balloon-borne experiment. Though we confirmed from the data that PHENEX polarimeter detected hard X rays from the Crab Nebula with a significance of 8σ, the degree and the direction of polarization with high accuracy could not be determined because of the trouble for attitude control system (ACS) and the small detection area of the prototype polarimeter. We already have fixed the ACS trouble and improved the detector to realize the observation of the Crab Nebula with higher accuracy. In this paper, we will report the improvement of PHENEX polarimeter and present the expected performance of the improved PHENEX polarimeter.

The Japanese balloon base was moved from the Sanriku Balloon Center (SBC) to the Taiki Aerospace Research Field (TARF). The SBC was closed in September 2007, and the new base at the TARF became operational in May 2008. In 2008, the first series of balloon flights at the TARF was carried out. By the success of these flights, we verified that the whole system of the new balloon base is well established. From FY 2009, regular balloon operations with science payloads started at the TARF. In May/June 2009, flight operations of three science experiments were carried out successfully. Five more science flights are planned at the TARF in August/September 2009.

A zero-pressure balloon used for scientific observation in the stratosphere has an unmanageable limitation that its floating altitude decreases during a nighttime because of temperature drop of the lifting gas. Since a super-pressure balloon may not change its volume, the lifetime can extend very long. We had introduced so called the 'lobed-pumpkin' type of super-pressure balloon that can realize a full-scale long-duration balloon and it will be in practical use in the very near future. As for larger super-pressure balloons, however, we still have some potential difficulties to be resolved. We here propose a new design suitable for a larger super-pressure balloon, which is roughly 'lobed pumpkin with lobed cylinder' and can adapt a single design for balloons of a wide range of volumes. Indoor inflation tests were successfully carried out with balloons designed and made by the method. It has been shown that the limit of the resisting pressure differential for a new designed balloon is same as that of a normal lobed-pumpkin balloon.

A simple attitude control system for a balloon experiment has been developed. This system aims to achieve an accuracy of 0.1 deg in azimuth for a small payload with a diameter of 1.5 m and a moment of inertia of 100 kg·m². It will be first flown with the Polarimetry for High ENErgy X-rays (PHENEX) experiment, which is to observe the polarization of astronomical objects in the hard X-ray energy region. The system is composed of the attitude sensors (sun sensors, geomagnetic aspect sensors, and an optical fiber gyro), read-out modules, CPU, output modules (PC104 based boards), and actuators (a torsion relief motor and a reaction wheel motor with their drivers). In this paper, after introducing these modules, the properties of the sensors and the control system based on the ground will be reviewed.

Proton exchange membrane fuel cell offers higher energy density than the existing battery technologies for high-energy applications, and it is a promising power source for various industries including aerospace vehicles. We have been developing and testing a non-external humidified fuel cell system for high-altitude balloons, which require simple, light, and easy-to-operate power systems. This system consists of three major subsystems-a fuel cell stack, a reactant supply subsystem, and an electrical control subsystem. Ground performance testing in a vacuum chamber simulating the high-altitude vacuum condition was performed before the flight. Then, a demonstration flight of the fuel cell system was launched using a large balloon for verifying its performance under practical high-altitude conditions. Cell voltage variations synchronized with oxygen pressure spikes were observed that were probably caused by condensed product water plugging the flow passages of the back pressure regulator. Flight results indicated that the fuel cell system operated better when water was expelled as vapor, rather than in the liquid form. In addition, a back pressure regulator should be installed to avoid the accumulation of water droplets for realizing a stable performance. © 2009 Elsevier B.V. All rights reserved.

Astrophysics with All-Sky X-Ray observations: 3rd International MAXI Workshop (RIKEN, 10-12 June 2008)On X-ray and hard X-ray astronomy, the polarization is the last key. It is very useful to understand the radiation mechanism of gamma-ray bursts and pulsars, magnetic structure of supernova remnants, space-time curvature near black hole, and so on. However, the observation for the polarization has been rarely carried out for about 30 years since the observation of the Crab Nebula in X-ray region. It is because of the difficulty for development of the polarimeter with high sensitivity. We have been developing a hard X-ray polarimeter with high sensitivity, called as a PHENEX (Polarimetry for High ENErgy X rays) polarimeter. The PHENEX polarimeter is Compton scattering type polarimeter sensitive to the energy range from 40 keV to 200 keV and is constructed assembling several detectors called as "unit counter". The unit counter is a detector utilizing Compton scattering and it has a modulation factor of 53 % and a detection efficiency of 20 % at 80 keV. We constructed prototype PHENEX polarimeter with four unit counters and carried out a preliminary observation of the Crab Nebula on Jun. 13th 2006 as a balloon-borne experiment. Though we confirmed that the PHENEX detected hard X rays from the Crab Nebula with significance of 8 sigma, the degree and the direction of the polarization could not be determined with high accuracy because the attitude control system does not function correctly. Now we are improving the performance of the ACS and the polarimeter to realize the observation of the Crab Nebula with higher accuracy in the next balloon-borne experiment. In this paper, we will present the follows: (1) summary of the PHENEX polarimeter and preliminary observation of Crab Nebula; (2) fix of the ACS trouble; (3) improvement of the PHENEX polarimeter; (4) expected performance for the next observation.Physical characteristics: Original contains color illustrations

Since 1971, numerous balloons have been launched from the Japanese balloon base, the Sanriku Balloon Center (SBC). In these 37 years, balloon technologies have been developed continuously and plenty of scientific achievements have been derived. Recently, however, we have been faced difficulties to further develop Japanese balloon activities. To solve this issue, we moved the Japanese balloon base from the SBC to the Taiki Aerospace Research Field (TARF). In FY 2007, new balloon facilities were constructed and the equipments were transferred. In 2008 summer, we carried out the fi rst series of the balloon campaign at the TARF, and succeeded in the fi rst launch of the stratospheric balloon from the TARF.

In order to make the two-dimensional image for auroral X-rays and to obtain the energy spectrum of aurora with energy range from 30keV to 778keV , the Polar Patrol Balloons No8 and No10 ( PPB#8 and PPB#10) were launched in rapid succession to form a cluster of balloons during their flight on Jan. 13, 2003 from Syowa Station. They drifted westward 0.5 circumpolar rounds over Antarctica, covering 9-12 g / cm^2 atmospheric depth and 55°.5-66°.4 geomagnetic latitude. From Jan. 22 to 25, 2003, several auroral events were detected by PPB#8 and PPB#10 at the same time. On Jan.23, 2003, PPB#10 and PPB#8 observed auroral X-ray events in succession. PPB#8 which was locate about 650km west from PPB#10 observed auroral X-ray event after PPB#10 with delay time 218sec. It is suggested that the auroral X-ray source region moved from east to west with speed of about 3.0km/s. In this paper, we present the feature of these concurrently observed auroral X-ray events.

Proton exchange membrane fuel cells (PEMFCs), which generate electrical energy as long as they are supplied with fuels and oxidants, have been receiving signifi cant attentions so that they offer higher specifi c energy densities than existing battery technologies in high-energy applications. We had been developing a 100 W-class fuel cell system that keeps electrolyte membrane well-hydrated without external humidification and can operates stably even under low pressure condition. The system aiming for super-pressure balloons had been tested emulating stratospheric conditions. Based on the previous works, the demonstration fl ight using the large balloon equipping the fuel cell system was launched to verify its performance in a practical high-altitude environment.

We have been developing a hard X-ray polarimeter with high sensitivity, called as a PHENEX (Polarimetry for High ENErgy X rays) polarimeter. We constructed prototype PHENEX polarimeter and carried out a preliminary observation of the Crab Nebula on Jun. 13th 2006 as a balloon-borne experiment Though we confirmed from the data that PHENEX polarimeter detected hard X rays from the Crab Nebula with a significance of 8 sigma, the degree and the direction of polarization with high accuracy could not be determined because of the trouble for attitude control system (ACS) and the small detection area of the prototype polarimeter. Now we are fixing the ACS trouble and improving the detector to realize the observation of the Crab Nebula with higher accuracy in the next balloon-borne experiment. In this paper, we will mainly explain about the improvement of the PRENEX polarimeter and present the expected performance for the next observation.

We have been designing a polarimeter for Gamma-Ray Bursts (GRBs) sensitive to the energy range from 60 keV to 300 keV. It is a Compton-scattering-type polarimeter and it consists of four modules. The field of view for one module is +/- 45 degrees. To estimate the performance, it is important to investigate the response for the irradiation from off-axis. So we had basic experiments with polarized beam and computer simulation. As the results, we recognized that it can measure the polarization for 19 GRBs per year at 99% confidence level if the degree of polarization is higher than 40 %.

The Scientific Balloon Center of ISAS/JAXA has managed balloon-borne experiments in Japan. Since 1971 domestic balloon campaigns have been carried out at Sanriku Balloon Center. In 2007 ten scientific experiments were conducted by seven balloon flights at Sanriku. We have also developed next generation super-pressure balloons and ultra-thin balloons. In order to meet recent user requirements, i.e., stable flights of heavier payloads at the highest possible altitude, Japanese scientific balloons will be operated at Taiki, Hokkaido from 2008. This new balloon facility was constructed to launch the first balloon in May 2008. Standardization of balloons and the balloon system is also in progress, in order to maximize the reliability for our operation of larger balloons with heavier payloads. In this paper, we introduce the new balloon facility in Taiki and discuss the strategy of the Japanese scientific balloon activities. The status of the development of new balloon technologies and international collaborations will also be discussed. © 2009 The Physical Society of Japan.

We carried out electron observations with balloons to investigate acceleration and propagation of electrons in the universe. We developed BETS (Balloon-borne Electron Telescope with Scintillation fibers) for electron observations in Sanriku. We obtained electron energy spectrum from 10 GeV to 100 GeV with it. At higher energies, the energy spectrum of electron might show some structure caused by nearby sources like the Vela supernova remnant. In order to observe the energy spectrum above 100 GeV, we needed a thicker calorimeter and a longer observation time. We developed PPB-BETS (Polar Patrol Balloon-BETS) by improving BETS to carry out a long duration ballooning in Antarctica. Energy spectrum of electrons from 100 GeV to 1000 GeV was obtained by a successful fight for 13 days. The arrival direction of electrons seems to be consistent with isotropic distribution for the data taken with PPB-BETS, although we need better statistics to make it clear. We have a future plan to make an observation of electrons and gamma-rays with a scale model of CALET (CALorimetric Electron Telescope) by long duration ballooning in the southern hemisphere for 2 weeks. We proposed CALET for the cosmic-ray observations on the International Space Station (ISS), and it has been selected as one of mission candidates for the second utilization plan on the Exposure Facility of the Japanese Experiment Module (JEM-EF). We are developing a scale model of 1/16 of CALET. © 2009 The Physical Society of Japan.

We have been designing a polarimeter for Gamma-Ray Bursts (GRBs) sensitive to the energy range from 60 keV to 300 keV. It is a Compton-scattering-type polarimeter and it consists of four modules. The field of view for one module is ±45°. To estimate the performance, it is important to investigate the response for the irradiation from off-axis. So we had basic experiments with polarized beam and computer simulation. As the results, we recognized that it can measure the polarization for 19 GRBs per year at 99% confidence level if the degree of polarization is higher than 40 %. ©2009 IEEE.

To provide long duration and good quality of micro-gravity environment with moderate cost, we proposed and have been developed an experiment system that is released from a high altitude balloon. The experiment system has a double-shell drag-free structure and it is controlled not to collide with the inner shell to realize good quality of micro-gravity environment. This paper shows the configuration of the experiment system and summarizes its five-year development including three flight test results. The fist stage of the development was successfully completed this year. The next step is micro-gravity fall with engine for longer duration of experiment. Another direction of the development is real operation of the system for micro-gravity scientists. Those future plans are also described.

The second flight of microgravity experiment system using a free fall capsule from a high altitude balloon was conducted in May 2007. Using a drag free control, around 10^-4G gravity conditions were obtained for 30 seconds. Results of a combustion experiment with Japanese sparker conducted inside the microgravity experimental unit were also reported.

Cosmic-ray electrons have been observed in the energy region from 10 GeV to 1 TeV with the PPB-BETS by a long duration balloon flight using a Polar Patrol Balloon (PPB) in Antarctica. The observation was carried out for 13 days at an average altitude of 35 km in January 2004. The PPB-BETS detector is an imaging calorimeter composed of scintillating-fiber belts and plastic scintillators inserted between lead plates. In the study of cosmic-ray electrons, there have been some suggestions that high-energy electrons above 100 GeV are a powerful probe to identify nearby cosmic-ray sources and search for particle dark matter. In this paper, we present the energy spectrum of cosmic-ray electrons in the energy range from 100 GeV to 1 TeV at the top of atmosphere, and compare our spectrum with the results from other experiments. © 2007 COSPAR.

The Scientific Balloon Center of ISAS/JAXA has carried out two balloon campaigns at Sanriku, Iwate, Japan every year. Ten to twelve balloon vehicles are launched annually for scientific and engineering experiments. Since 2005, a Brazilian balloon campaign has also been conducted in cooperation with INPE. In the 2006 Brazilian campaign, large and heavy payloads up to 1500 kg for astronomy will be launched. New generation balloons, such as super-pressure balloons and high-altitude balloons with ultra-thin films, are being developed. The current status and prospect of the Japanese scientific ballooning are discussed. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

Spectroscopic observation of solar flares in the hard X-ray energy range, particularly the 20∼100 keV region, is an invaluable tool for investigating the flare mechanism. This paper describes the design and performance of a balloon-borne hard X-ray spectrometer using CdTe detectors developed for solar flare observation. The instrument is a small balloon payload (gondola weight 70 kg) with sixteen 10x10x0.5 mm CdTe detectors, designed for a 1-day flight at 41 km altitude. It observes in an energy range of 20-120 keV and has an energy resolution of 3 keV at 60 keV. The second flight on 24 May 2002 succeeded in observing a class M1.1 flare. © 2008 Springer Science+Business Media B.V.

Gamma-Ray Burst (GRB) is one of the main topics in the field of astrophysics. Though many types of observation have been carried out since the discovery, the radiation mechanism is still unknown. So we propose the gamma-ray burst detector capable of detecting the polarization. It is POTENTIS (POlarimeter for TransiENT and Intensive Sources). It is a scattering type polarimeter and consists of scintillators and multianode photomultipliers. We are investigating the basic performance through experiments at accelerator facility and balloon-borne experiments. We will report the design and the basic performance.

The microorganism sampling experiment of the stratosphere and the troposphere was conducted by using the airplane by Tokyo University of Pharmacy and Life Science. The bacteria with high ultraviolet resistance have been isolated from stratosphere and the troposphere. However, the highest altitude of the sampling was limited to about 12 km. In this work, collaborative sampling experiment of ISAS and Tokyo University of Pharmacy and Life Science was conducted to collect microbes at the atmosphere in a higher stratosphere. The microbes were filtrated with ultra-membrane filter at high altitude using balloon and the filters were placed on the medium. Several strains of microbes were isolated.

A balloon-borne superconducting submillimeter-wave limb-emission sounder (BSMILES) is powerful tool for observations of stratospheric minor constituents. The third flight experiment of BSMILES was conducted on September 4, 2006 to observe diurnal variation of HO_2. BSMILES carries an offset parabolic maim reflector with a diameter of 300mm, a 630 GHz-band SIS mixer cooled by liquid helium, an acousto-optical spectrometer,and 3-axes fiber-optic gyroscope. The gondola was lifted to an altitude of about 37.9km by a balloon of 200,000m3 in volume. The system operated properly and emission line spectra of O3 and minor constituents were measured.The system was retrieved from the sea after the observation.

The first microgravity experiment using a new free-fall capsule released from 40km altitude was performed on May, 2006 based on a drag-free technique. The fundamental data for analyzing the drag-free control,the flight sequence, and the wireless communication between the capsule and a control room were successfully obtained in the first test flight.

A zero-pressure balloon used for scientific observation has an important limitation that its floating altitude decreases during a nighttime because of the temperature change of the lifting gas between day and night times. Since a superpressure balloon may not change its volume, the lifetime can extend very long. However, only small superpressure balloons could be come to realization, since an impractically large tensile strength had been requested for the balloon envelope owing to the design of sphere type balloon. We proposed so called a `lobed-pumpkin' type superpressure balloon that has a capability to solve this essential problem. Many scaled models were manufactured to be tested indoors to study the validity of the design and fabrication method. Some of them were devoted for flight tests to get an actual environmental condition. A series of experiments detected many issues around the design method and the manufacturing process. Conclusively, we cleared up almost all of them and believe that a superpressure balloon can be realized with a practicable large size near future.

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. To open a new window for hard X-ray astronomy, we have developed a hard X-ray polarimeter called as PHENEX (Polarimetry for High ENErgy X rays). The PHENEX polarimeter is constructed by assembling Compton scattering type polarimeters called as a unit counter, which can achieve the modulation factor and the detection efficiency of 53% and 20% at 80 keV, respectively. Installing four unit counters, we have carried out balloon-borne experiment in Jun.13 2006 to preliminarily observe the polarization of the Crab Nebula in hard X-ray band. It successfully operated on the level flight and observed the Crab Nebula for about one hour. From the analysis of the data, the following three results have been obtained. 1) The ratio of the signal from the Crab Nebula to the background from the blank sky was estimated to be about 1:2.2. 2) The PHENEX polarimeter did not make spurious modulation more than 1.8% on the observation of blank sky. 3) The degree and the direction of the polarization for the Crab Nebula were determined to be 33±26% and 154o?=43 deg, respectively. This result for the polarization is not inconsistent with the previous result by OSO 8 in X-ray band nor the recent one by INTEGRAL in gamma-ray region. Since more precise measurements in hard X-ray band are necessary for the study of the Crab Nebula, we will carry out balloon-borne experiment again in 2009 by the improved PHENEX polarimeter.

The CALorimetric Electron Telescope, CALET, mission is proposed for the Japanese Experiment Module Exposed Facility, JEM-EF, of the International Space Station. The scientific objective is to investigate the origin of the cosmic electrons and gamma-rays in very high energy region. The detector is composed of an imaging calorimeter of scintillating fibers and a total absorption calorimeter. The thickness of all absorber is 36 r.1 for electro-magnetic particles and 1.7m.f.p for protons. Total mass of the payload is nearly 2.500kg, and the effective geometrical factor is 0.5-1.0m2sr. The detector is capable of measuring the electrons from a few GeV to 10 TeV and the gamma-rays from 20MeV to several TeV, keeping the energy resolution within a few % over 10 GeV. The hadron rejection power should be nearly 106 in order to observe the electrons up to 10TeV and it is achieved by measuring the fine structure of shower development. Much higher hadron-rejection power in the gamma-ray observation could be easily attained by the anti-conincidence counter covering the detector. Observation of protons and heavy nulei from 1 to 1000 TeV is also consedered to investigate the acceleartion limit in supernova shocks. We are expecting to launch the CALET around 2010 by the Japanese H-II Transfer Vehicle, HTV. © 2008 The Physical Society of Japan.

We are developing the CALorimetric Electron Telescope, CALET, mission for the Japanese Experiment Module Exposed Facility, JEM-EF, of the International Space Station. Major scientific objectives are to search for the nearby cosmic ray sources and dark matter by carrying out a precise measurement of the electrons in 1 GeV - 20 TeV and gamma rays in 20 MeV - several 10 TeV. CALET has a unique capability to observe electrons and gamma rays over 1 TeV since the hadron rejection power can be larger than 105 and the energy resolution better than a few % over 100 GeV. The detector consists of an imaging calorimeter with scintillating fibers and tungsten plates and a total absorption calorimeter with BGO scintillators. CALET has also a capability to measure cosmic ray H, He and heavy ions up to 1000 TeV. It also will have a function to monitor solar activity and gamma ray transients. The phase A study has started on a schedule of launch in 2013 by H-II Transfer Vehicle (HTV) for 5 year observation.