 Agena was primarily the domain of the U.S. Air Force, who intended to use it for military payloads, and NASA had originally assumed it would begin flying in late 1960 or early 1961 by which time any developmental issues with the stage could be weeded out.However, Agena B ended up taking longer to put into service than originally anticipated and its performance also turned out to be somewhat less than expected, which forced some of the planned experiments on the Block II Rangers to be cancelled.While the Thor-Agena B had begun flying in October 1960, the Atlas-Agena B did not make its maiden voyage until July 1961, meaning that Ranger 1 was only the second time this launch vehicle combination been flown.