Atlas (familia) Atlas III

The Atlas III was first called Atlas II-AR, and the R gave the change away: the three-engine cluster that had defined the family since the 1950s made way for a single Russian-built RD-180 with two thrust chambers, more powerful and more efficient than anything before it. It was the first Atlas since the A model to stage conventionally.

The first stage came from the Atlas II with its tanks stretched by three metres, and it was still thin stainless steel that had to be held under helium pressure to keep from buckling. The roll control module went away: by gimballing its chambers, the RD-180 handled pitch, yaw and roll on its own.

The extra first-stage performance allowed something no Atlas had done before: flying with a single-engine Centaur. The lone RL10 sat on a beam bolted to the existing twin-engine mounts and carried an extendible nozzle.

The IIIA flew the single-engine Centaur II. The IIIB introduced Centaur III, the Common Centaur, with tanks stretched by about a metre and a half and available with one or two engines; the twin-engine version was worth roughly four hundred kilograms more towards geostationary transfer orbit. That is the stage the Atlas V inherited.

The first flight, in May 2000, placed a European communications satellite into geosynchronous orbit. The sixth and last, in February 2005, carried a classified payload for the National Reconnaissance Office. Six missions, no failures, and a role close to that of a prototype: the Atlas III proved in flight the engine and the upper stage the Atlas V would use for the next two decades.

There were plans to give it a second life. Japan's GX rocket was to use its first stage under a new upper stage, but the Japanese government cancelled the programme in 2009.