S. Ohta

Plastic balloons with thin polyethylene films for high altitude observations

Abstract 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.

High altitude balloons with ultra thin polyethylene films

Abstract 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.

Polar patrol balloon project in Japan

Abstract Since 1984, the National Institute of Polar Research and the Institute of Space and Astronautical Science have studied the feasibility of a long-term circumpolar balloon experiment, called Polar Patrol Balloon (PPB) project. This project aims at establishing a PPB system to bring scientific payloads in the stratosphere over the Antarctic region. Three test flights in 1987 and 1990 at Syowa Station convinced us that the PPB would have a good chance of coming back to the launching area, provided that we utilize the advantage of no sunset during the summer season in Antarctica. The PPB experiments were consequently made in 1990 to 1991. PPB #1 which was launched on 25 Dec 1990 reached a height of 30 km and drifted westwards. At 22:30 (UT) on 8 Jan 1991, the PPB passed 400 km north of Syowa Station; this means that the PPB accomplished a complete circumpolar flight over Antarctica. Second flight (#2) was successively launched on 5 Jan 1991. A further 3rd flight (#3) was carried out for 23–28 Sept 1991 when an Antarctic ozone hole was well developed.

A balloon-borne electron telescope with scintillating fibers

Abstract A new balloon-borne cosmic-electron telescope incorporating a trigger system and an imaging calorimeter is described. The trigger system is adopted to select electrons with energies above 10 GeV, and to reduce the background protons to about 1%. The imaging calorimeter consists of scintillating-fiber belts, emulsion plates and lead plates (∼8 radiation length thick in total). Two-dimensional profiles of shower development are observed with the scintillating fibers. An analysis of the profiles might reject 95 % of the miss-triggered protons at 85 % electron efficiency. The telescope was launched at Sanriku in September 1995, and flown for twelve hours at the average altitude of 38 km. We observed about 700 electrons over 10 GeV under 4 g cm −2 of average residual atmosphere.

Semi-dynamic launching method for scientific balloons

Abstract 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.

Flight demonstration of a superpressure balloon by three-dimensional gore design

Abstract On May 15, 1999, a balloon with a volume of 3,100 cubic meters was successfully launched from Sanriku Balloon Center of Japan. It became a superpressure balloon at 19.2km in altitude with 20% pressure difference to the ambient atmosphere. This is the first superpressure balloon capable of suspending a heavy payload. It was designed by the new ‘three-dimensional gore design’ method and was based on a pumpkin shape balloon with bulges of small radii between adjacent load tapes without the help of film extensibility. The balloon climbed up to 21.6km in altitude by dropping the ballast and held out against a 64% pressure difference over the ambient atmosphere. This flight test proved the capability of large stratospheric superpressure balloons by this new design method.

The improvement of the static launch method in Japan

Abstract 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.

First results obtained by RUNJOB campaign

Abstract 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.

Microgravity experiment system utilizing a balloon

Abstract 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.

Automatic control of balloon altitude

Abstract An ascentmeter with a sensitivity of 1 cm/s was applied to the automatic control of balloon altitudes. In the flight tests made in 1980 and 1981, the automatic control system was successfully operated to keep a balloon altitude constant during sunset or to descend a balloon with a constant speed.