Tsiolkovsky, in elaborating his idea of a safe dirigible, critically examined all the known attempts at dirigible design and found them inadequate from the point of view of safety. He rigorously defined the essential reliability requirements for the guidance of inventors and designers and offered his own original design for an all-metal dirigible. Instead of merely designing an airship of no matter what kind, so long as it would fly, from the very outset Tsiolkovsky set himself the most difficult task, that of designing a vehicle that would be ideal from every point of view: safe, simple, operationally convenient, and economic. A pioneering Russian aeronautical theorist and writer, Konstantin Tsiolkovsky is the father of the Soviet space program. He built the first wind tunnel and solved fundamental problems about space travel, such as use of liquid rocket fuel, long before such activity was feasible. Although he was unappreciated in his lifetime, Sputnik's launch was made to coincide with his centennial.