Homer J. Stewart, an early pioneer of rocket research who helped develop the first successful U.S. satellite, Explorer I, has died. He was 91. Stewart, an emeritus professor of aeronautics at the California Institute of Technology, died May 26 at his home in Altadena, the school said in a statement. Stewart came to Caltech in 1936, but in the late 1950s took a leave of absence to advise on the preparation of Explorer I. Following the launch of the Soviet satellite Sputnik I in October 1957, there was a frenzied effort by the United States to launch a satellite of...