Development and testing of an inflatable capsule for the YES2 project

The YES2 project features a lightweight (about 10 kg), single-stage, inflatable reentry capsule. This paper describes the development, the manufacturing and the testing of the first capsule prototype. The prototype capsule is a 1.5 m diameter sphere-cone. Rigidity is provided by 5 stacked inflatable tori, connected together for single-stage inflation. A laminated solution is used for each torus, comprising two layers of surface-treated Kapton® film for air tightness, and a single layer of Zylon® fabric for structural strength. Design trade-offs involving the location of the valves and the connections to the thermal protection system are addressed and future steps for optimization and testing are discussed. The flight design contains an ablative foam nose and an Alumina-Nextel flexible insulating cover. The design of the capsule is driven by the following aims: a) high stability during reentry, both in the hypersonic and in the subsonic phase; b) low stresses in the inflatable structure; c) high ratio of drag area to total weight; d) affordable thermal loads; e) simple manufacturability, foldability and deployment; f) single-stage inflation already in space for inherent safety, allowing the capsule to land in mainland Europe for the first time in history. Samples of the materials employed have been prepared and tested. Adhesively-bonded Kapton® samples have been tested only for durability at high temperatures (200°C), since the Kapton® layer undergoes no structural loads. Zylon® samples (both bonded and sewn) have been tested under load at high temperatures (200°C). The samples were in the form of cylinders inflated at 250 kPa, which is the maximum expected gas pressure during re-entry. A prototype of the inflatable capsule has been manufactured and assembly technologies are discussed in the paper. The model will be submitted to aerodynamic tests for shape stability (fluttering). The capsule is designed specifically for Earth entry (sample return), but the advantages of the innovative inflatable concept introduced can readily be exploited for future interplanetary missions