Development of future concepts and plans for the ULDB program

Abstract

A long duration, heavy load stratospheric balloon system has long been a “Holy Grail” of the ballooning community. Recent advances in material technology and manufacturing techniqties have combined with the well known elastica or “pumpkin” shape design to bring an Ultra Long Duration Balloon (ULDB) to near reality. The ULDB concept was originally centered on a series of mate&l and seaming teclm.ology studies sponsored by NASA/WFF in the mid 1990’s. The material work was based on reinforcing layers of film with fiber scrim and laminating thin layers of film to light weight fabric. The latter of the t\\s material concepts proved to be the most compatible with available seaming technologies. -in 1996, protot)pe sphere tests took place that suggested that the sphere shape was not the optimum shape for the ULDB from a stress standpoint. Just prior to the award of the ULDB development contract to Raven Ifidustries. it was decided that the shape for the ULDB would be an ablate spheroid known as Euler’s Elastica. Thisshape transfers almost all pressure loads to longitudinal tendons that run down each seam. A great deal of research and development work has been undertaken to optimize the strength and weight of these tendons. The design of the tendons as well as the design of the ULDB subsystems are described in this paper. The results of the two most recent burst tests of pumpkin shaped balloons are presented with plans for the flight test balloons.