Recent refinements and increased capabilities in balloon vertical performance analysis

A balloon vertical performance analysis model named THERMTRAJ (THERMal TRAJectory) was developed in the late '70's. This model combines the vertical equation of motion with heat balance equations to predict the balloon altitude, vertical rate, skin and gas temperatures versus time. THERMTRAJ provided significant improvement in performance analysis capabilities, but suffers from inadequacies, e.g., 1) assumed spherical shape, with maximum volume fixed, and; 2) crude modeling of balloon solar absorptivity. Under the auspices of the National Aeronautics And Space Administration balloon research and development program, several improvements have been incorporated, including; a) redetermination of maximum volume and computation of balloon shape, and; b) continuous computation of gas loss due to small leaks and/or programmed venting. A method of modeling the solar radiation input which accounts for the higher absorptivity of load tapes and the presence of cap layers has also been incorporated. A significant increase in capability was achieved by incorporating generalized autoballast control algorithms. Current simulation/actual performance comparisons are presented for several balloon flights, and additional refinements under investigation are identified.