specific impulse of at sea level and in vacuum. The Merlin 1B was enhanced over the 1A with a turbine upgrade, increasing power output from to . The turbine upgrade was accomplished by adding additional nozzles, turning the previously partial-admission design to full admission. Slightly enlarged impellers for both RP-1 and LOX were part of the upgrade. This model turned at a faster 22,000 rpm and developed higher discharge pressures. Turbopump weight was unchanged at . Another notable change over the 1A was the move to TEA–TEB (pyrophoric) ignition over torch ignition. Initial use of the Merlin 1B was to be on the Falcon 9 launch vehicle, on whose first stage there would have been a cluster of nine of these engines. Due to experience from the Falcon 1's first flight, SpaceX moved its Merlin development to the Merlin 1C, which is regeneratively cooled. Therefore, the Merlin 1B was never used on a launch vehicle. Merlin 1C Three versions of the Merlin 1C engine were produced. The Merlin engine for Falcon 1 had a movable turbopump exhaust assembly, which was used to provide roll control by vectoring the exhaust. The Merlin 1C engine for the Falcon 9 first stage is nearly identical to the variant used for the Falcon 1, although the turbopump exhaust assembly is not movable. Finally, a Merlin 1C vacuum variant is used on the Falcon 9 second stage. This engine differs from the Falcon 9 first-stage variant in that it uses a larger exhaust nozzle optimized for vacuum operation and can be throttled between 60% and 100%. The Merlin 1C uses a regeneratively cooled nozzle and combustion chamber. The turbopump used is a Merlin 1B model with only slight alterations. It was fired with a full mission duty firing of 170 seconds in November 2007, first flew on a mission in August 2008, powered the "first developed liquid-fueled rocket to successfully reach orbit", Falcon 1 Flight 4, in September 2008, and powered the Falcon 9 on its maiden flight in June 2010. As configured for use on Falcon 1 vehicles, the Merlin 1C had a sea-level thrust of , a vacuum thrust of and a vacuum specific impulse of . In this configuration, the engine consumed of propellant per second. Tests have been conducted with a single Merlin 1C engine successfully running a total of 27 minutes (counting together the duration of the various tests), which