Atlas II

The Atlas II was the most reliable member of the Atlas rocket family — and by some measures the most reliable American expendable launch vehicle ever built. Across 63 launches of the II, IIA, and IIAS variants between December 1991 and August 2004, not a single mission failed. A perfect record across thirteen years of operations, covering military communications satellites, commercial broadcasting satellites, NASA science missions, and the final flight of the entire Rocketdyne-powered Atlas lineage that stretched back to the late 1950s.

The Atlas II was developed in the late 1980s at the direction of the US Air Force, which needed a reliable replacement launcher for the Defense Satellite Communications System after a string of Atlas I failures in the preceding years. General Dynamics — which would merge into Lockheed Martin in 1994 — was contracted to develop an upgraded Atlas with longer propellant tanks, higher-performing RL-10 engines on the Centaur upper stage, and improved avionics. The result was a rocket that combined the proven Atlas stage-and-a-half booster architecture with the powerful Centaur II upper stage running on liquid hydrogen and liquid oxygen — the same energetic combination that made the Atlas Centaur family so capable for high-energy missions.

The stage-and-a-half design was the last time it appeared on an Atlas vehicle. Unique to the Atlas lineage, this architecture ignited all three engines — two large booster engines and one sustainer engine — simultaneously at liftoff. The two booster engines, mounted in a skirt around the base of the core stage, were jettisoned partway through ascent while the sustainer engine continued burning, drawing from the same propellant tanks. The result was a rocket that shed mass during flight without the complication of a full stage separation, giving it efficiency characteristics between a true single-stage and a two-stage vehicle. The Atlas III and V that followed abandoned this design in favor of a cleaner two-stage architecture; the Atlas II was its last expression.

The IIA variant introduced engine upgrades that increased GTO capacity from 2,810 to 3,180 kilograms — a modest but commercially significant improvement that made it more competitive against Ariane 4 for the growing geostationary communications satellite market. The IIAS variant went further, adding four Castor 4A solid rocket boosters that ignited at liftoff alongside the Atlas main engines, providing additional thrust during the first phase of flight and pushing GTO capacity to 3,719 kilograms — the highest of any Atlas II configuration.

SOHO — the Solar and Heliospheric Observatory — launched on an Atlas IIAS on December 2, 1995, beginning a mission that is still operating in 2026. It was one of the most significant science payloads the Atlas II family carried, and one of the most enduring testaments to the vehicle's reliability: the rocket that put SOHO on its way to L1 performed flawlessly, and the spacecraft it launched has now outlived the rocket family that sent it there by more than two decades.

The final Atlas II launch came on August 31, 2004 — an Atlas IIAS carrying a classified national security payload. It was simultaneously the 63rd and last Atlas II launch and the 576th and final launch of any rocket powered by Rocketdyne's venerable Atlas engine series, closing out a propulsion lineage that had begun with the Atlas ICBM in the late 1950s. After 576 launches across multiple rocket families over nearly five decades, the original Atlas engine series was retired.