Stability of Lobed Superpressure Balloons During Ascent

Abstract

It is known from large-scale experiments that the successful deployment of lobed superpressure balloons can depend on the used gas. Some balloons deployed properly during an inflation with air but failed to reach the desired equilibrium configuration for helium. Furthermore, depending on the desired flight altitude, a helium-filled balloon might or might not deploy properly. This paper investigates this phenomenon by studying the stability of lobed superpressure balloons during ascent. It is shown that wrinkles increasingly reduce the stiffness of balloons for a decreasing gas density and an increasing flight altitude such that clefts can develop at very low differential pressures in nearly fully inflated balloons. Nomenclature C nv = symmetry group without horizontal symmetry plane (balloons during ascent) D nh = symmetry group with horizontal symmetry plane (balloons at flight altitude) F = lifting force of balloon at flight altitude f = frequency of buckling mode g = standard gravity h = altitude above sea level h b;t = altitude of bottom, top of balloon above sea level h fli = flight altitude above sea level M hel = molar mass of helium divided by the ideal gas constant m hel = helium mass n = number of lobes of balloon p 0 = air pressure at sea level p air;hel = air, helium pressure p fli air;hel = air, helium pressure at flight altitude r = equatorial radius of fully inflated balloon T 0 = air temperature at sea level T air;hel = air, helium temperature T fli air;hel = air, helium temperature at flight altitude V = volume of balloon V fli = volume of fully inflated balloon at flight altitude p b;t = differential pressure at bottom, top of balloon p fli = differential pressure of balloon at flight altitude during maximum solar exposure = eigenvalue 0 = air density at sea level air = air density fli air;hel = air, helium density at flight altitude 1;2 = first, second principal stress vm = von Mises stress

Pressure-actuated cellular structures

“…The development of this technology started in the 1990s and was severely hindered for more than a decade by stability problems. My main contribution to this project was a redesigned cutting pattern that increased stability by up to 300 % without increasing the overall weight and membrane, tendon stresses [211,212,217,223,224]. A NASA balloon with a diameter of 80 m that is based on this design made a record flight above Antarctica in 2009.…”