Military applications include self-sealing fuel tanks on vehicles or aircraft. Commercial applications include leak protection systems for railroad tank cars or tanker trucks carrying hazardous materials.
Any manned missions to extraterrestrial locations will require shelter structures for a variety of purposes ranging from habitat to biomass production. Such shelters need to be constructed in such a way as to minimize stowed volume and payload weight. The structures must also be very durable and have the ability to survive punctures without collapsing. Ways of increasing available crew-load volume without greatly increasing launch weight or volume are also sought.
Inflatable structures are ideal candidates for habitat structures for several reasons: (1) they feature the low stowage volume and payload weight; (2) deployed volume can be easily increased without large increases in launch weight or volume; and (3) they offer unique opportunities for incorporating intelligent and/or multifunctional systems such as self-healing capability, power generation and storage, sensor systems, and radiation protection.
An inflatable, rigidizable shelter system was developed based on Rigidization on Command (ROC) technology incorporating not only the required low-stowage volume and lightweight character achieved from an inflatable/rigidizable system, but also a self-healing foam system incorporated between the rigidizable layers of the final structure to minimize the damage caused by any punctures to the structure.
The technology builds functionality into a conventional inflatable habitat structure by incorporating a light, rigidizable composite material that can be used to make up the outer shell of the habitat structure. This composite material is used to form the two outer layers of a “sandwich” structure in which the inner layer is comprised of a foam-generating system with two components designed and placed such that they will mix upon impact and quickly seal any breaches to the habitat structure, thereby preserving the internal atmosphere of the habitat. The light, rigidizable composite is comprised of a woven glass fabric impregnated with a resin specially formulated to cure upon exposure to ultraviolet (UV) light. These composites cure extremely quickly upon exposure to UV light, either from sunlight or from other UV sources including lamps and LEDs (light emitting diodes). These composites can be extremely strong and tough, depending upon which components are employed in the resin formulation.
The inner foam self-healing system is comprised of separately encapsulated layers of the two major components of urethane foams — polyol and isocyanate — containing all the necessary catalysts, surfactants, and blowing agents required for function. The two layers are assembled next to each other and, in the event of a puncture, both layers rupture, initiating contact of the two components. The subsequent foaming is rapid and serves to rapidly seal the system. A subscale prototype demonstrator has been designed that will allow for demonstration of all aspects of this technology including deployment, UV rigidization of composite structures using LED illumination, and scaling of punctures using an encapsulated polyurethane foam system.
The encapsulated polyurethane foam system forms the functional heart of this innovation and will greatly enhance the lifetime of inflatable habitat structures on the lunar surface or elsewhere in the solar system. Encapsulating the components ensures a proper ratio of materials to achieve the foam reaction needed for sealing, and the components are chosen such that they will react quickly and with the generation of a large volume of foam in order to seal a puncture.