Earth orbit rendezvous

Earth orbit rendezvous (EOR) is a method for conducting round trip human flights to the Moon, involving the use of space rendezvous to assemble, and possibly fuel, components of a translunar vehicle in low Earth orbit. It was considered and ultimately rejected in favor of lunar orbit rendezvous (LOR) for NASA's Apollo program of the 1960s and 1970s, mainly because LOR does not require a spacecraft big enough to both make the return trip from Earth orbit to splashdown in the ocean, and a soft landing on the lunar surface. Three decades later, it was planned to be used for Project Constellation, until that program's cancellation in October 2010.