An airplane, which is a “heavier-than-air” craft, is urged upwardly by a force generated by the relative movement between the airfoils and the airflow, while an airship, which is a “lighter-than-air” craft, makes use of buoyancy to “float” in the air, by filling the airship with a gas having specific gravity less than that of the air. An airship has many merits, which are impossible for an airplane or a helicopter, such as low fuel consumption, long term continuous flight, large payload, less noise pollution, calm flight, simple areas for take-off and landing, etc. Modern airships can fly in the air with little power, are relatively quiet, and do not generate turbulence. Moreover, modern airships can stay in the air for a long time, being able to suspend in a certain place for several days or even weeks. All of these illustrate the major advantages of an airship. Since velocity is not necessary for generating the upward force for an airship, a massive amount of energy can be saved. Nowadays, non-renewable resources are becoming scarcer, and the shortage of energy sources has become a threat to mankind. Accordingly, the use of an airship, which needs less energy than other aircrafts, will serve mankind for today and tomorrow. However, among various kinds of modern airships developed by different countries in the world, conventional rigid, semi-rigid or blimp designs are still adopted. Thus, it is difficult to avoid notable problems in these airships, such as, a need to provide a heavy-weight (water, sandbag, compressed air), which has to be increased or decreased to change altitude; the need to change the volume of an airship as the altitude is increased; slow velocity; poor wind resistance; relatively high effect-cost ratio even when an airship can carry out versatile tasks; and the difficulty for an airship to become balanced and level off when suspended in the air. Furthermore, since an airship designed for a certain altitude is only suitable for this specific altitude, different kinds of airships have to be designed for different altitudes, thereby making the use of airships costly. At the same time, the areas where solar cells can be installed on their exterior surface are quite limited for an airship adopting a semi-rigid or blimp design. Accordingly, when the incident angle of sunshine changes, solar cell panels may not be irradiated or sufficiently irradiated, thereby making it impossible to make full use of solar energy.