Konstantin Tsiolkovsky, a self-taught rural schoolteacher deaf since age ten, publishes in 1903 in the journal Nauchnoye Obozreniye the fundamental equation of rocket motion in a vacuum (the Tsiolkovsky equation): Δv = Isp·g·ln(m₀/mf), establishing the relationship between exhaust velocity, specific impulse, and mass ratio. He proposes liquid-propellant rockets, multiple stages, the orbital escape hatch, and the concepts of space stations and colonization of the solar system. He died in 1935 without seeing any of his concepts realized. He was rediscovered by Soviet space-program engineers in the 1940s and posthumously recognized as the father of cosmonautics. The first artificial satellite (Sputnik, 1957) and the first human in space (Gagarin, 1961) are direct applications of his theoretical work.