The Atlas-Centaur was a United States expendable launch vehicle derived from the SM-65 Atlas D missile. Launches were conducted from Launch Complex 36 at the Cape Canaveral Air Force Station (CCAFS) in Florida. Early development Convair, the manufacturer of the Atlas, developed the Centaur upper stage specifically for that booster, sharing its pressure stabilized tank structure. Technical Centaur was the first rocket stage to utilize liquid hydrogen (LH2) and liquid oxygen (LOX) as propellants. Despite high performance, LH2 had to be chilled at extremely low temperatures (lower than LOX) and its low density meant that large fuel tanks were needed. The first attempt at using an LH2/LOX-fueled engine was the U.S. Air Force's top-secret Lockheed CL-400 Suntan reconnaissance aircraft program in the mid-1950s. The progress made during the aborted venture was picked up by Convair and others for rocket stage use. Originally, Centaur was conceived of as a purely experimental project to develop an experience for larger, more powerful rocket stages so as not to distract Convair's focus on the all-important SM-65 Atlas missile program. Convair developed a specially-enhanced version of the Atlas D vehicle for mating with Centaur stages; the Atlas was equipped with an uprated booster section, the MA-5, which had twin turbopumps on each booster engine, and the structure reinforced for the large upper stage, along with elongated fuel tanks. Centaur development was made somewhat difficult by the insistence on modifying Atlas components rather than developing totally new ones. This was done for time and budget reasons and because it allowed the Centaur to be manufactured on the existing Atlas assembly line at Convair. The engines were manufactured by Pratt & Whitney. Program Although originally under ARPA supervision, Centaur was transferred to NASA in July 1959, eleven months after the program's inception. However, the Air Force retained overall supervision in part because they intended to use Centaur to launch a network of military communications satellites known as ADVENT. A constellation of ten satellites would provide round-the-clock instant communications for the three main branches of the US military. The first three would be launched on an Atlas-Agena, then the remainder on Centaur. ADVENT never got off the drawing board, but Centaur quickly found a use for several NASA planetary probe projects, namely Mariner and Surveyor. An initial lack of funds caused the project to drag on far longer than intended. Under original timetables, Centaur was to make its