The fuel cell was originally conceived by a German scientist, Christian Schoenbein, in the middle of the 19th century. A Welsh physicist, William Grove, developed a working device in 1843. More than a century later in the 1950s, the American scientists Thomas Grubb and Leonard Niedrach improved on the design by incorporating an ion-exchange membrane and making use of hydrogen as the fuel source. Fuel cells of this type were used in some of the American space missions conducted by the National Aeronautics and Space Administration (NASA) during the 1960s.