Feasibility study of EVAL balloons Original Research Article

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 m3. The balloon reached an altitude of 22 km successfully and showed a maximum burst pressure of 2.1 g/cm2. In this paper, basic properties of the EVAL film and performance of the test balloon a