The Atlas-Centaur was a United States expendable launch vehicle derived from the SM-65 Atlas D missile. The vehicle featured a Centaur upper stage, the first such stage to use high-performance liquid hydrogen as fuel. Launches were conducted from Launch Complex 36 at the Cape Canaveral Air Force Station (CCAFS) in Florida. After a strenuous flight test program, Atlas-Centaur went on to launch several crucial spaceflight missions for the United States, including Surveyor 1, Mariner 4, and Pioneer 10/11. The vehicle would be continuously developed and improved into the 1990s, with the last direct descendant being the highly successful Atlas II.
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 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 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 first flight in January 1961.
Research and development (R/D) flights
First flight
In October 1961, the first Atlas-Centaur (Vehicle Flight-1: Atlas 104D and Centaur F-1) arrived at Cape Canaveral and was erected at the newly completed and specifically built LC-36A. Technical problems caused the vehicle to sit on the launch pad for seven months, the most serious being leakage of liquid hydrogen through the intermediate bulkhead separating the propellant tanks combined with numerous lesser maladies with the guidance and propulsion systems.