In flight tests performed in Hitachi City, Ibaraki Prefecture in the early hours of August 4, a dirigible with a hull made from Kuraray's VECTRAN climbed, for the first time, to the stratosphere. Kuraray's VECTRAN polyarylate fiber, one of the superfibers, is a synthetic fiber that offers the same strength as steel at one-fifth to one-sixth the weight. It also has superior low-temperature performance characteristics.
These tests were undertaken in connection with the Stratospheric Platform concept promoted by the Ministry of Education, Culture, Sports, Science and Technology and the Ministry of Public Management, Home Affairs, Posts and Telecommunications. The 47-meter long dirigible climbed to an altitude of 16,400m. In the future, it is planned to send a dirigible 250 meters in length to 20,000 meters, and this flight test was a significant step toward that goal.
In 1990, Kuraray became the first firm in the world to bring a polyarylate superfiber to market when it introduced VECTRAN. It has approximately six times the strength of ordinary textile-use polyester, and the same strength as steel fibers. Because it is a type of synthetic polyester fiber, it does not absorb water, and water has virtually no effect on it. For these reasons, it is well suited for the extremely frigid atmospheric conditions of the stratosphere. These properties resulted in its selection for use in the air bags used to cushion precision instruments on their ballistic descent to the surface of Mars on NASA's 1997 Mars mission.
Kuraray's EVAL film was selected for use on the exterior of the dirigible's hull for its superior gas-barrier properties. EVAL is a resin with 10,000 times the gas-barrier efficiency of polyethylene, making it one of the best gas barriers of all the plastics. It is used worldwide as a food packaging material, and has recently been adopted for plastic automobile gas tanks. EVAL was chosen in the test flight as the gas barrier to prevent the escape of the helium gas with which the dirigible was filled. This is more challenging in the stratosphere, where atmospheric density is one-fifteenth to one-twentieth what it is at sea level.
The dirigible to be used in the next flight test will be larger (60 meters in length, with propellers and communications equipment installed). Kuraray intends to remain actively involved in the Stratospheric Platform concept.