Video: Scientists explain why twin Nasa spacecraft were deliberately crashed into the moon Its twin, Flow, followed about 30 seconds later and aimed for the same target. After the double impacts, the mission's principal investigator, Maria Zuber of the Massachusetts Institute of Technology said: "Ebb and Flow have removed a veil from the moon, and removing this veil will enable discoveries about the way the moon formed and evolved for many years to come." Ebb and Flow was launched into space in September 2011 and took a roundabout journey to the moon, arriving over the New Year on a gravity-mapping mission. They focused exclusively on measuring the moon's lumpy gravity field in a bid to learn more about its interior and early history. By design, their final resting place is far away from the Apollo landing sites and other historical spots on the moon.