Shigeo Ohta

Thin-film balloon for high altitude observation

Abstract 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.

Balloon-borne electron telescope with scintillating fibers

We describe a new balloon-borne cosmic-electron telescope that incorporates a trigger system and an imaging calorimeter. It is designed to observe high-energy electrons with an energy greater than 10 GeV. The rejection of the background protons is performed by using the trigger system in real time and the off-line analysis of three-dimensional shower profiles observed in the imaging calorimeter. The calorimeter consists of scintillating-fiber belts, emulsion plates and lead plates (approximately 8r.1.thick in total). In order to observe the direction of showers, two belts in each depth are set at right angles with each other. Image intensifier is used to amplify the number of photons from scintillating fibers, and CCD camera is attached at the output window of the image intensifier. The telescope was launched at Sanriku Balloon Center, and it was flown for 12 hours at the level altitude. By preliminary analysis, we observed about 700 electrons over 10 GeV under 4g cm-2 of average residual atmosphere. The flux of electrons is consistent with previous observations.

Feasibility study of EVAL balloons

Abstract 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.

Guidance experiment of gliding parachute dropped from balloon

The recovery operation of sounding rocket of ISAS takes much time and cost due to its long down range, amounted to approximately 300km off shore. The recovery system using gliding parachute is expected to be a hopeful candidate because of its maneuverability and high-glide performance. ISAS has been so far developing it through wind tunnel tests with sub-scaled model and drop test from helicopter at low altitude with full-scaled model. In June 1994, the opportunity was took for the autonomous flight test of recovery system with gliding parachute, released from balloon at altitude of about 8km. The autonomous flight control was carried out during descent by the on-boarded computer with GPS data and geomagnetic attitude data. The control was proportional to the directional deviation between the present attitude and the target. It was satisfactory below the altitude of 2km. In this paper the experiment using balloon was described in detail and the results obtained were also reported.