The Apollo spacecraft, bound for the moon, consisted of a conical Command Module, in which the three U.S. astronauts would fly, connected to a cylindrical Service Module containing the power, propulsion, and life-support systems. Though marred by the tragedy of Apollo I (which led to many design improvements), the 10 following missions, including the first lunar landing, Apollo 11, may represent one of mankind's greatest achievements. Intimately bound up with the Apollo craft is the two-stage Lunar Module, the first true spaceship free of aerodynamic concerns, with its unmistakable spindly-legged aspect. Following the final lunar mission (Apollo 17) in 1972, 3 Apollo missions were flown to Skylab, and in 1975, the Apollo-Soyuz Test Mission concluded the program.