Abstract: A container for a flight craft such as a gas balloon is provided. Part of the walls of the container is constituted of three separated plates. The first plate has one or more holes that causes gas to flow in and out of two spaces so that the pressure difference between a first space and a second space separated by the first plate is resolved but does not cause gas convection between those two spaces. As the flight craft ascends, a relationship T1<T2<T3<T4 occurs among the temperatures inside the first to a fourth space. The temperature gradient between the inside and outside of the container becomes less pronounced. Condensation is unlikely to form on any of the three plates. The first plate with the holes buffers the force that the second plate is subjected to due to a pressure difference between the inside and outside of the container.

Abstract: When lighter-than-air gas compressed and filled in a pressure-resistant container is injected into an envelope, buoyancy created in the envelope causes an aircraft to ascend. When the aircraft finishes its flight role, a lid of an opening/closing mechanism is opened to exhaust from a port lighter-than-air gas from the envelope. When the buoyancy of the envelope is insufficient to counter the weight of the aircraft, the aircraft begins to descend. The lid of the opening/closing mechanism is closed on the port, and exhaust of lighter-than-air gas from the envelope stops. After the aircraft reaches a surface of land or water, an operator connects a duct to a gas suction device. The gas suction device collects the lighter-than-air gas remaining in the air sac into a container. The lighter-than-air gas collected into the container is transported to a gas collection facility, compressed by a compressor, and filled into a pressure-resistant container.