Second Stage Needed to Reach Deeper Space

First launched in 1960, Agena was an expendable upper-stage launch system (ELS) developed by Lockheed Aircraft Corporation. Agena sat atop an Atlas D lower “stage and a half” configuration and, combined, provided two and a half stages of rocket power. Atlas Agena was launched 109 times during its 18-year career, with an 85 percent success rate. It addition to the first five Mariner unmanned probes to Venus and Mars, the first interplanetary fly-bys, and the Ranger and Lunar Orbiter unmanned moon probes, Atlas Agena was used even more extensively for launching classified DoD payloads. After Agena’s retirement in the summer of 1978, all Atlases were subsequently flown with the Centaur upper stage.

“See, we’re doing it, too!” Poker-faced rocketeer Krafft Ehricke with futuristic GD Astronautics satellite models on 10 October 1957. This carefully staged publicity shot was probably conceived as PR “damage control” in the wake of Russia’s shocking success with Sputnik I, the world’s first artificial satellite, less than one week before this photo was taken. Like Wernher von Braun, Ehricke was an alumnus of Hitler’s V-2 program but today is remembered as the father of the Atlas Centaur, a second-stage vehicle so versatile, reliable and efficient that variants are still in use 55 years later. (Piction ID: 48063106 - Catalog: 14_025440)

Back in 1954, Convair hired an ex-German V-2 rocket engineer named Krafft Arnold Ehricke (1917-1984) to perform conceptual studies of Atlas performance. Ehricke, who had worked with Wernher von Braun at Peenemünde and later at Red Stone Arsenal, concluded that Atlas, based on the data, was capable of boosting itself into orbit, which it later did with the Project SCORE satellite. Ehricke also opined that Atlas would need a second-stage rocket in order to be useful for deeper space missions, so in 1956 he and a small group of Convair engineers began to study the problem in earnest. They all agreed that liquid oxygen (LOX) / liquid hydrogen (LA2) rocket engines were the most promising solution to the propellant question for “higher-end” applications.

Convair’s second-stage concept, ushered into hardware by Ehricke, was basically a smaller version of the Atlas rocket itself, using the same pressurized balloon-tank concept. One or two Rocketdyne RL10 engines burning liquid oxygen (LOX) and liquid hydrogen (LH2) made Centaur the world’s first high-energy upper-stage rocket, one which enabled NASA to launch some of its most important scientific missions over the next 50 years. Ehricke, known as the father of Centaur, named his creation for the halfman / half-horse creature of Greek mythology. The horse symbolized the Atlas 1-1/2 stage lower “workhorse” booster, while the man portion symbolized the “intelligent” upper stage.

30 May 1966, Atlas Centaur AC-10 launches the Surveyor 1 spacecraft from Pad 36A at Cape Canaveral. The first of seven Surveyor robotic spacecraft sent to collect data (in-cluding 11,000 photographs) over a period of 30 days for the proposed Apollo moon landing, Surveyor 1 was the first spacecraft to make a soft lunar landing, using retro-rockets to slow the lander from 6,000 to 3 mph for a soft touch-down. Surveyor was one of NASA’s greatest achievements of the early lunar and interplanetary exploration period.

Funded since January 1959, the first Atlas Centaur, AC-1, was launched on 8 May 1962 on Atlas 104D and was spectacularly unsuccessful. The second launch six months later succeeded, but a rash of additional failures very nearly derailed the program. Wernher von Braun himself disliked Atlas and Centaur’s “balloon” concept and the use of cryogenic fuels, which he considered too dangerous. During congressional hearings on the initial Centaur failures he even recommended that Atlas-Centaur be defunded in favor of his preference, the (much more costly) Saturn platform.

Fortunately, cooler heads prevailed and Centaur went on to earn its spurs in seven Surveyor missions to the moon in preparation for the manned Apollo lunar landing. At the front end of that program, which ran from 1966-1968, Atlas Centaur boosted Surveyor 1 to a soft landing in the lunar Ocean of Storms – NASA’s first landing on an extraterrestrial body.

Other Centaur successes followed, including most of the Mars-bound Mariner missions (also used with the Titan booster family, another story). Other notable Atlas Centaur successes included the TRW-built Pioneer 10 and Pioneer 11 space probes of 1972 and 1973 that, respectively, completed the first missions to Jupiter and Saturn, and achieved the escape velocity necessary to exit the solar system and, presumably, fly on forever.

After a long and storied career, the last Rocketdyne MA5-powered Convair “balloon tank” rocket, AC-167, successfully flew on 31 August 2004. In operation, Atlas Centaur (i.e., the Convair balloon-tank version) was launched 142 times with 13 failures, for an overall success rate of 91%.

San Diego Air & Space Museum

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