LOS ANGELES – After the Soviet Union launched Sputnik, the United States gave a 90-day deadline to the Army and a little-known research lab in California to send up its own satellite. Seemingly against all odds, the project was completed in 84 days. On Jan. 31, 1958, a knot of rocket scientists and engineers waited anxiously as the satellite, Explorer 1, blasted into orbit, launching the U.S. into the space race. Historians see the 50th anniversary of Explorer 1 Thursday as a chance to go beyond the Reader's Digest version of events. “It's been cemented in all the popular accounts,”...