Explorer 1

Late on the night of 31 January 1958, a slender white rocket stood floodlit at Cape Canaveral's Launch Complex 26. America had watched Sputnik cross its skies for four months and had watched its own Vanguard rocket explode on the pad in December on live television. At 10:48 p.m. Eastern time the Juno I booster lit and climbed into the dark, and after ninety anxious minutes a tracking station in California confirmed a signal coming back around the world. The United States was in orbit.

The satellite itself was a two-meter pencil of instruments weighing just 13.9 kilograms, designed and built by the Jet Propulsion Laboratory in 84 days. NASA did not yet exist; this was the Army Ballistic Missile Agency's rocket, Wernher von Braun's modified Jupiter-C, mated to a payload carrying James Van Allen's cosmic ray experiment, a single Geiger-Müller tube from the University of Iowa. At about 1:30 a.m., Pickering, Van Allen, and von Braun hoisted a full-scale model overhead at a Washington press conference, creating one of the Space Race's defining photographs.

Then the instrument started behaving strangely. At low altitudes the counter clicked along as expected, but at the high points of the orbit it sometimes fell silent. Van Allen's team realized the tube was not failing, it was saturating, overwhelmed by radiation far more intense than anyone had predicted. Earth, they concluded, is wrapped in belts of charged particles trapped by its magnetic field. Explorer 3 confirmed the theory two months later, and the Van Allen radiation belts became the first scientific discovery of the Space Age.

Explorer 1 transmitted until 23 May 1958, then circled silently for twelve more years before burning up on 31 March 1970 after roughly 58,000 orbits. Even its flaws taught lessons: the satellite's flexible whip antennas drained rotational energy and flipped it into an end-over-end tumble, an accident that rewrote the rules of spacecraft spin stability and is still cited in aerospace textbooks today.