... Credit: courtesy Marshall Space Flight Center , NASA Explanation: Inaugurating the era of space exploration for the US, the First Explorer , a thirty pound satellite, was launched into Earth orbit on February 1, 1958 by the Army Ballistic Missle Agency. Explorer I carried instruments to measure temperatures, micrometeorite impacts, and an experiment designed by James A. Van Allen to measure the density of electrons and ions in space. ... Publications with keywords: explorer 1 - satellite . ...