Design of the Pressurization System for a Novel Inflatable HAPS Vehicle: Development and Simulation

The colonization of the stratosphere thanks to new aircraft configurations has become possible as a result of recent technological development. Inflatable aero-structures represents one of the most promising solution for medium and high weight payload. Blimps and aero static balloons are the most common inflatable aero-structures. They present several limits on movements., speed and controllability. The work presented describes a hybrid inflatable Heavier-Than-Air (HTA) design that permits to go beyond the limits of previous Lighter- Than-Air (L TA) and HTA vehicles, opening new possibilities for their fields of employment. This new design is based on the joint use of aero static and aerodynamic lift, allowing an overall weight and size reduction. This is obtained also thanks to a shape variation during the flight envelope. In particular, this article will primarily focus on describing the modeling of one fundamental characteristic of this new design: the pressure system. It is designed to ensure that the desired shape is achieved when required while maintaining the structural integrity of the envelope. These demands required to develop a numerical model to predict the behavior of the gas inside the envelope at each phase of the preplanned mission profile. The specific characteristics of the vehicle required to develop more than a simple modeling of the gas expansion, due to the need to simulate also the effect of the valve required to eject the gas to not exceed the nominal overpressure. The first phase of the lift-off is designed to be purely aero static, relying on the lift generated by the LTA gas. The close interaction between the gas behavior and the lift force required to devise a model of the vertical motion, too. Moreover, this novel vehicle was designed to continuously cruise in the stratosphere during several days, being thus subjected to extreme variations of outside temperature and pressure. These aspects, coupled with the solar radiation affecting the extensive surface of the envelope, required an accurate modeling of the atmospheric characteristics and of the solar radiation at various quote. Finally, the structural integrity of the vehicle during the descending phase was design to be carried on by supplying compressed air produced by compressors to the envelope. The modeling of the required compressed air's mass flow and compression ratio was also implemented for every instant of the descending phase. The energy required by the compressors will be supplied by photovoltaic cells installed on top of the envelop. Electrical and thermal models of photovoltaic cells were also developed and implemented to accurate estimate values of the available energy. After a general description of the key features of the total design of the new hybrid inflatable HTA vehicle proposed in this work, a deeply description of all the mentioned developed models will be given, detailing all the assumptions, the equations and the limits that define the developed model. In the last section, the results for a simulated mission profile will be shown and discussed in depth. Finally, a summary of the future works to validate the developed model will be described.