Editing Atlas-Centaur (section)

== Early development ==
[[Convair]], the manufacturer of the Atlas, developed the [[Centaur (rocket stage)|Centaur]] upper stage specifically for that booster, sharing its pressure-stabilized tank structure.

=== Technical ===
[[File:Centaur stage during assembly 1962.jpg|thumb|A Centaur stage during assembly at General Dynamics in 1962]]
[[File:Centaur-propellant-system.jpg|thumb|Diagram of a Centaur stage]]
Centaur was the first rocket stage to utilize [[liquid hydrogen]] (LH2) and [[liquid oxygen]] (LOX) as propellants. Despite boasting high performance, LH2 had to be chilled to 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 [[United States Air Force|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 (rocket stage)|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 ===
Originally under [[DARPA|ARPA]] supervision, Centaur was transferred to [[NASA]] in July 1959, eleven months after the program's inception. 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 program|Mariner]] and [[Surveyor program|Surveyor]].

An initial lack of funds caused the project to take far longer than intended. Under original timetables, Centaur was to make its first flight in January 1961.