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著者人数: 22名, Accepted: 2011-11-09, 資料番号: SA1003234000

著者人数: 20名, Accepted: 2011-05-04, 資料番号: SA1003239000

著者人数：19名, Accepted: 2009-10-07, 資料番号: SA1000727000

著者人数: 23名, 資料番号: SA1000072000

著者人数: 18名, 資料番号: SA1000073000

We have observed cosmic-ray electrons from 10 to 1000 GeV by a long duration balloon flight using Polar Patrol Balloon (PPB) in Antarctica. The observation was carried out for 13 days at an altitude of 35 km in January 2004. The detector is an imaging calorimeter composed of scintillating-fiber belts and plastic scintillators inserted between lead plates. The geometrical factor of detector is about 600 cm 2 sr and the total thickness of lead absorber is 9 radiation lengths. The performance of the detector has been confirmed by the CERN-SPS beam test and also investigated by Monte-Carlo simulations. New telemetry system using a commercial satellite of iridium, power supply by solar batteries, and automatic level control using CPU have successfully been developed and operated during the flight. We have collected 5.7 × 10 3 events over 100 GeV including nearly 100 candidates of primary electrons.

Polar patrol balloon experiments were carried out at Syowa Station in Antarctica from 2002 to 2004. Two balloons were launched for the purpose of observing phenomena in the polar atmosphere and one was done for the observation of high energy cosmic electrons. We developed a new housekeeping system including communication device using the Iridium satellite network, an auto-level controller driven by a new program for keeping the flight altitude, and a power management system for solar cells combined with secondary batteries. Two balloons for studying phenomena in the Antarctic atmosphere launched on January 13, 2003 made flights for 18 days and 25 days, respectively. All the housekeeping system worked well during the flights as we expected. Based on these experiments, we adjusted parameters for the altitude control system and the power management system. We launched a balloon for the cosmic electron observation on January 4, 2004. It flew 13 days around the Antarctica with the perfect operation of the onboard housekeeping system. We hope that fruitful scientific results will be obtained from these long-duration flights.

Development of a balloon to fly at higher altitudes is one of the most attractive challenges in scientific balloon technologies. After reaching the highest record setting balloon altitude of 53.0 km using the 3.4 μm film in 2002, we tried to make a thinner balloon film. In 2003, we developed a forming die and an air-ring and succeeded in forming a film with a thickness of 3.0 μm and a width of 220 cm. Using this film, we manufactured a balloon with a volume of 5000 m3 and succeeded in flying the balloon up to an altitude of 46.0 km. We then searched for a good combination of resins to make a thinner and wider film and obtained films with widths of 280 cm, and a thickness of 3.0 μm at first, and then 2.8 μm. In 2004, we performed balloon experiments making a 30,000 m3 balloon with the 3.0 μm film and a 5000 m3 balloon with the 2.8 μm film. Both balloons were well manufactured and reached the highest altitudes of 50.7 and 42.6 km, respectively.

Launching a large balloon in a limited launching field is a long standing problem in Japan. The largest balloon ever launched successfully was 200,000 m3 in volume. It was launched in 1973. A larger balloon with a volume of 500,000 m3 was tried later, but it burst during the ascending phase. For launching balloons with a large lift exceeding 500 kg, the conventional static launching method had the most serious problem with possible damage to the polyethylene film of the balloon caused by the holding mechanism. After that, we had developed a new static launching method to launch balloons with a total lift of 1.0 ton. For launching a large balloon with a total lift above 1.5 ton, the new static launching method had a weak point in that if there was an air bubble in the folded part of the balloon, it may puncture the balloon as it is pushed by a spool. To avoid this problem, we developed a semi-dynamic launching method in 1999 using a launcher fixed to the ground leaving a freedom of rotation around the vertical axis. We have launched some balloons using the method and have gradually enriched our experience in using this system. In 2003, we successfully launched a balloon with a volume of 500,000 m3 by using the method. This balloon was made of polyethylene films with a thickness of 20 μm and it is the largest balloon ever launched in Japan.

The Sanriku Balloon Center (SBC), which belongs to the Institute of Space and Astronautical Science, was built in 1971. The launching field of SBC was 140 m in length and 20 m in width. In Japan, the balloon launching method that we have been using since 1971 is a kind of static launching method. In 1998, we extended the launching field 20 m in length and created a new launcher at this point. We have recently developed a “semi-dynamic” launching method. This newly developed launcher is different from the launcher used in the dynamic launching method, it is fixed to the ground creating freedom of rotation around the vertical axis. It is also possible for the launcher to lift up a payload to a height of 5 m from the ground. We succeeded in launching the first test balloon by using this new launching method on September 6, 1999. Utilizing the new launching machine, it became possible to launch a balloon with a volume of 1,000,000 m 3 and a total lift of 2 tons, even in Japan.

The balloon group at the Institute of Space and Astronautical Science (ISAS) has studied to develop high altitude balloons that could reach an altitude of more than 40 km with a light payload in order to meet the requirements of observations at extremely high altitudes. In 1999, we developed a ultra thin balloon film with a thickness of 3.4 μm. It is synthesized with a new catalyst, metallocene, and has a ultimate strength of ∼650 kg/cm 2 at −80°C. Using the film, we made the first balloon with 1,000 m 3 in volume and 2.6 kg in weight. We launched the balloon from Sanriku Balloon Center on September 1, 1999 and it successfully reached an altitude of 37.1 km. In 2000, we prepared the second balloon with 5,000 m 3 in volume with 6.8 kg in weight. It was launched on June 7, 2000 and it successfully reached an altitude of 43.0 km. Such light weight balloons are planned to be used for scientific studies in near future.

The development of high altitude balloons will enrich many areas of scientific observation. A high altitude balloon fabricated using improved technology with thin Winzen polyethylene films has been flown in the upper atmosphere. A light weight balloon carrying small instruments can reach an altitude higher than 40 km. In contrast to sounding rockets, the balloon-borne experiment provides a unique opportunity to stay at a high altitude for more than a few hours at low cost. We have developed methods for fabricating large balloons for scientific observation and have also established a new belt sealer and successful launching system. In January 27, 1997, a thin-film balloon with a volume of 120,000 m 3 , carrying a payload of 11.8 kg, reached an altitude of 50.2 km which is the highest balloon altitude ever in Japan. This shows that a thin-film balloon is suitable for high altitude observations and can fill the gap between satellite and conventional balloon altitudes.

We report experimental results obtained by using a wide-gap type emulsion chamber flown in the first Japanese-Russo joint balloon project, called RUNJOB ( RU ssia- N ippon JO int B alloon-program). Two balloons were launched from Kamchatka in July 1995, and both were recovered successfully near the Volga River. The exposure time was 130 hours for the first flight and 168 hours for the second. The mean ceiling altitude, in both flights, was 32 km corresponding to 10 g/cm 2 . Total area of the emulsion chamber was 0.8 m 2 , and the thickness 0.385 and 2.28 collision m.f.p.'s for vertically incident proton- and iron-primaries, respectively. We detected 381 showers using Fuji-#200-type X-ray film; of these 174 showers were due to atmospheric secondary γ-rays, and the rest 207 came from nuclear components. The energy range covers 20∼200 TeV for proton-primary, 3∼30 TeV/nucleon for helium-primary, and 0.7∼5 TeV/nucleon for iron-primary. We give the energy spectra for various elements (proton, helium, …, iron) as well as the all-particle spectrum and the average mass of the cosmic-ray primaries.

We describe a new Low Altitude Space Communication System (LASCOS), which was completed in 1996 by the Institute of Space and Astronautical Science in Japan. This system consists of a mobile balloon tracking and receiving station and networks which connect them to the Sanriku Balloon Center in Iwate Municipality and the Institute of Space and Astronautical Science (ISAS) in Kanagawa Municipality. This station and the SBC receiving station are connected via telephone lines, i. e. an Integrated Services Digital Network (ISDN) or an analog communication network. Balloon trajectory monitoring, telecommand transmission operation and telemetry data acquisition can be done from any computer terminal through the LASCOS. LASCOS has built-in flexibility to adapt to a foreign balloon station. The number of individuals necessary to operate it minimum. LASCOS will be used for long range tracking and balloon expedition. We present the results of its first test with an actual balloon flight.

For a new balloon material, we have been studying the properties of an EVAL (Ethylene-Vinyl-ALcohol) film during a part of few years. The EVAL film is a product of Kurare Plastic Company, and has mechanical properties similar to that of a Mylar film. Besides this strong mechanical strength, we found that the EVAL film has several characteristics which seems to be suitable for the balloon material. Those are: 1. 1. Sandwiched EVAL films laminated by polyethylene films can be heat-sealed, 2. 2. Gas leakage through the EVAL film is extremely low, and for Helium gas, it is almost 100 times less than that of a Mylar film, 3. 3. The EVAL film is transparent in the optical band, while it efficiently absorbs the infrared radiation from the earth. In 1997, we have carried out a test flight from the Sanriku Balloon Center using a small balloon with a volume of 1000 m 3 . The balloon reached an altitude of 22 km successfully and showed a maximum burst pressure of 2.1 g/cm 2 . In this paper, basic properties of the EVAL film and performance of the test balloon are described.

Balloons made of thin films have been frequently used to observe high altitude winds. Such a balloon is also useful to perform some scientific observations now performed by sounding rockets. Since this balloon is lighter than a normal balloon, it can easily reach an altitude more than 40km with a payload less than 10 kg. A ceiling altitude of 48.7 km was achieved by the new balloon with a volume of 30,000m 3 in a test flight in 1995. We need to reduce mechanical stress by attaching an exhaust duct especially for a thin polyethylene balloon. Three types of exhaust ducts were tested in flights in 1995. We have confirmed good performance of the thin polyethylene balloon. The launching device for the high altitude balloon is also described.

The Polar Patrol Balloon (PPB#6) aimed at studying the elemental and isotopic composition of galactic cosmic rays, solar energetic particles cosmic gamma ray bursts and auroral X-rays, and was launched from Syowa Station Antarctica, by the 34th Japanese Antarctic Research Expedition on 5 Jan 1993. The balloon moved westward by 1.5 circumpolar rounds over Antarctica covering 6–13g/cm 2 atmospheric depth and 63°S–70°S geographic latitude. A total of 584 hours of observations was obtained. The balloon trajectory, the observing system and preliminary results of spectra and global distribution of cosmic radiation and auroral X-rays were described.

Trans-oceanic flights between Japan and China have been successfully carried out for three years (from 1986 to 1988), and nine balloons were launched from Kyusyu Island toward China. Although two flights were terminated due to balloon problems during ascending phase, seven balloons reached China successfully and those payload were recovered in the inland of China. During the long duration flights lasting for more than ten hours, the scientific objectives were accomplished by the scientists of both countries in collaboration and many useful data could be obtained.

We have improved the static launch method in the Sanriku Balloon Center (SBC). The motivation of the improvement is to reduce the shock for the scientific instruments during launching and to increase the ability of launching heavier payloads. In the new launch method, the entire balloon train is extended vertically before launch. We have found that the launch condition in the new system is satisfactory, for both lowering shock while launching and maintaining stability of the payload, when the balloon lift is equally divided to the launch rope and the payload suspension rope. Under the new launch method, a payload of more than 1000 kgs has been successfully launched with the launching shock of about 0.3G.

A new static-launch method that we have developed as an improvement of our former method is described. The key procedure is to extend a whole balloon vertically upon the launcher before release, with squeezing the top bubble of the balloon by a soft collar. The new method improved the capability for heavier payload significantly. In 1981, 15 balloons, ranging from 5,000 m 3 to 50,000 m 3 in volume with a total lift from 150 kg to 650 kg, were launched by this new method successfully.

A system for microgravity experiments by using a stratospheric balloon has been planned and developed in ISAS since 1978. A rocket-shaped chamber mounting the experiment apparatus is released from the balloon around 30 km altitude. The microgravity duration is from the release to opening of parachute, controlled by an on-board sequential timer. Test flights were performed in 1980 and in 1981. In September 1983 the first scientific experiment, observing behaviors and brain activities of fishes in the microgravity circumstance, have been successfully carried out. The chamber is specially equipped with movie cameras and subtransmitters, and its release altitude is about 32 km. The microgravity observed inside the chamber is less than 2.9 × 10 −3 G during 10 sec. Engineering aspects of the system used in the 1983 experiment are presented.