Imagine an astronaut exiting a pressurized habitat through a rigid hatch to enter an airlock, which is a tube of fabric inflated to the same pressure as inside the habitat. At the end of the tube is not a traditional hatch, but an inward-facing seal. As long as there is pressure in the airlock, the opening holds itself closed. Multiple redundant restraint lines resist the 20-ton pressure force to keep the seal facing inward so it can't evert itself. A pressure-sealing zipper holds the lips of the seal closed, but the zipper is not needed to keep the air inside. In a sense, the softgoods airlock has simply been extended and curved back inside the airlock to form this self-sealing opening that can't be opened until the pressure inside the airlock equals the outside pressure, typically vacuum. The inverted seal hatch concept retains the safety aspect of rigid hatches since there is no way to open it early with catastrophic consequences. The advantage of using a softgoods hatch is that it stows in a very small volume for launch and is lighter than a rigid hatch. The volume and mass savings are further amplified for the integrated softgoods airlock-hatch combination.
Global Aerospace Corporation developed a concept for a Deployable Inward-facing Seal Hatch (DISH) for manned inflatable structures. The key features of DISH are a safe, pressure-reinforcing duckbill seal; use of nearly 100% soft materials for packing ease and reduced launch mass; compatibility with a variety of rigid or inflatable airlock designs; and the provision of a fast, simple, safe, and reliable method for entry or exit. The DISH concept is inspired by the design of duckbill valves. A duckbill valve is an elastomer valve which seals against fluid flow from its flattened end, thus acting as a check valve.
Rigid airlocks and hatches take up a large amount of volume and are higher in mass, which are both at a premium when designing systems to be launched into space. An airlock and hatch made from soft materials are lighter and can be stowed much more compactly. As a result, more payload (for example, scientific instruments) can be taken along inside the launch vehicle faring while still keeping launch costs lower. The soft-material airlock and hatch can be deployed externally to rigid structures once the system is in place.
Soft-material airlocks and hatches can be used anywhere there is a pressure difference between the habitable zone and the external environment, such as in space, on planets, moons, asteroids, space stations, as well as on fixed or mobile planetary platforms. Future missions will require habitats in space and on these bodies and crewed rovers that will need airlocks and hatches.
The potential market includes companies planning low Earth orbit (LEO) tourist habitats, as well as industries and government organizations that need airlocks and hatches for isolation of hazardous materials or biologicals, and protection for pharmaceuticals or for cleanrooms. For private companies, the savings in launch costs and volume associated with soft-material airlocks and deployable hatches can make these options especially attractive.