 The Gemini-Agena Target Vehicle had a specially modified Range Safety destruct system designed to fire slugs into the propellant tanks rather than the conventional method of rupturing them externally, since an inadvertent activation of the RSO system in orbit could endanger the Gemini astronauts.The very first Atlas-Agena flight, Midas 1 in February 1960, failed when the unproven ISDS system mistakenly activated at staging, rupturing the Atlas's LOX tank and causing the breakup of the Agena.The ISDS system was redesigned afterwards and this failure mode did not repeat itself.