Thermal Modeling of NASA's Super Pressure Pumpkin Balloon

Abstract

This paper presents a thermal study of the thin-film super pressure pumpkin balloon under development by the National Aeronautics and Space Administration (NASA). The pumpkin balloon is a high-altitude pressurized vessel. It is designed for long duration flights upwards of 100 days over any type of environment at a near constant altitude within the stratosphere. A balloon’s flight performance is particularly susceptible to atmospheric effects. The mid-latitude day-night cycle affects the internal pressure significantly and to maintain altitude, a positive internal pressure must exist. The thermal characterization, therefore, is an important element in its development. Thermal modeling is an ongoing project within NASA’s Balloon Program and is a necessary aspect in pressurized balloon development. Updated radiative film properties experimentally tested by a third party are compared to previously measured radiative properties. Thermal Desktop, an add-on package of AutoCAD was used to perform all thermal analyses; a representation of the pumpkin balloon structure was completed in AutoCAD. The following analysis is a continuation of the previous thermal analyses of spherical thin-film balloons. Previous spherical models were characterized well; however, it is more realistic to model the pumpkin balloon shape which has a greater surface area compared to the spherical balloon. The shape of the structure is an important facet in the overall thermal study. This effort has focused on analyzing the true geometry, shape, and materials of an actual balloon. Lobing of individual gores, a unique characteristic of the pumpkin balloon, is modeled in this study. The addition of load bearing tendons, which have different radiative properties, completes the representation of the structure. Solar and Thermal Radiation are the primary drivers in balloon performance. Convection of helium, the pressurized gas, and outside air influence the structure as well. The super pressure balloon was modeled in different working environments for both hot and cold cases. The cases relating to Australia over-flight are also near-extreme environments and provide a basic boundary of thermal effects. The results of this study will aid in the super pressure balloon development and may be applied to other facets of balloon analysis including balloon flight performance and balloon design. I. Introduction HERMAL analysis of scientific balloons and their components is an ongoing area of study within the National Aeronautic and Space Administration’s (NASA) Balloon Program Office. NASA’s scientific balloons provide the scientific community a low cost sub-orbital carrier of scientific instruments; over the years these balloons have offered an effective and efficient platform for science. This work is an attempt to expound on previous thermal analyses performed by both Tracy Bohaboj 1 and Henry M. Cathey, Jr. 2 Previous work has involved both spherical and natural shape balloons through various analytical mediums. However, an appropriate thermal analysis of NASA’s Ultra Long Duration Balloon (ULDB), a pressurized pumpkin balloon whose geometry and components are dissimilar to previous models, has yet to be performed. The analyses contained herein specifically continue Bohaboj’s work with representative spherical models through the use of the software package, Thermal Desktop®; a C&R Technologies software package that is integrated into AutoCAD has been shown to provide realistic studies of thin-film materials in both steady state and transient conditions. Furthermore, this work is part of the continuum of accurate thermal analyses of scientific balloons. Thus, the objective herein is to incorporate the geometry of the pumpkin shape balloon and its components and their properties in new thermal analyses. The results of the pumpkin shape balloon analysis will be compared to the zero pressure and spherical shaped balloons.