Enlarge / The Merlin vacuum engine on SpaceX's Falcon 9 rocket fired for six minutes to place the Crew-9 mission into low-Earth orbit. (credit: NASA/SpaceX) SpaceX is investigating a problem with the Falcon 9 rocket's upper stage that caused it to reenter the atmosphere and fall into the sea outside of its intended disposal area after a Saturday launch with a two-man crew heading to the International Space Station. The upper stage malfunction apparently occurred after the Falcon 9 successfully deployed SpaceX's Crew Dragon spacecraft carrying NASA astronaut Nick Hague and Russian cosmonaut Aleksandr Gorbunov on SpaceX's Crew-9 mission.