Atlas V’s RD-180 Shut Down Early on NASA Cargo Launch

Liftoff of Atlas V Carrying Cygnus Cargo Vessel
Credit: NASA

For anyone who was paying extraordinarily close attention to the ULA/Orbital ATK launch of an Atlas V rocket to the International Space Station on Tuesday night, a slight discrepancy in the timing of first stage main engine cutoff might have been noticeable. And if you caught that, then a burn of the Centaur upper stage’s RL-10 engine which lasted a full minute longer than anticipated would have been even more noticeable.

As it turned out, the ultra-reliable Atlas experienced a slight performance issue with its highly repected but politically controversial RD-180 main engine during the flight. Fortunately it was one for which the Centaur upper stage was able to compensate with a longer burn.

After initially suggesting the issue was simply a matter of a natural variation based on a launch carried out weeks after the “official” timeline was published, ULA confirmed today that first stage had indeed shut down six seconds prematurely. While the upper stage went on to perform very well, placing the Cygnus cargo ship almost exactly on target, it did result in a de-orbit burn being terminated early as well, presumably as it ran out of propellant. The net result was that any surviving debris landed in a slightly different, but still remote area of the Pacific than the one originally planned.

The anomaly will not detract from ULA’s sterling mission success record, but pending the outcome of further investigations into the precise cause, it may raise questions regarding the state of the RD-180 in a Russian space sector which has experienced a rash of technical failures in recent years, with the most recent possibly having occurred on the ExoMars launch, but has thus far not affected the export engine.

In other bad news for ULA, which might have hoped a successful launch and the announcement of a completed PDR for the Vulcan booster would help divert attention from last week’s PR nightmare, the Department of Defense Office of Inspector General has notified the company it is opening an investigation in comments made by former ULA executive Brett Tobey that conflict with its stated reason for refusing to participate in the first openly bid defense launch in more than a decade.