The engine provides main propulsion on United Launch Alliance’s Delta IV rocket, which is used primarily by the U.S. Department of Defense. The Delta IV Heavy, featuring three vehicle cores in a side-by-side configuration, is capable of launching the Defense Department’s heaviest payloads.
The original variant of the engine, the RS-68, was developed with private company funds. The RS-68A represents an improvement over the RS-68 and provides 42,000 pounds of additional thrust. The upgraded RS-68A completed its first test firing in September 2008, was certified in April 2011 and made its inaugural flight in June 2012.