The most powerful version of Space Exploration Technologies (SpaceX) Merlin rocket engine yet developed has completed its first full-duration mission firing test at the company’s McGregor, Texas, development site.

The Merlin 1D engine fired for 185 sec. and generated 147,000 lb. of thrust during the full mission duration firing, which included multiple restarts at target thrust and specific impulse. The engine is destined to make its first flight on the sixth mission of a Falcon 9 in 2013, which is believed to be one mission earlier than originally planned.

Up until the debut of the 1D, all Falcon 9 flights will continue to be powered by the kerosene/liquid oxygen 95,000-lb. thrust Merlin 1C, with the Merlin 1C-Vac derivative powering the upper-stage. The newest details revealed by SpaceX appear to remain broadly in line with plans outlined last year.

At the time, SpaceX said the 1D is designed to produce 155,000 lb. vacuum thrust and a chamber pressure around 1,410 psia. The nozzle expansion ratio was increased from 14.5 on the Merlin 1C to 16, while the specific impulse was targeted at 310 sec. SpaceX also said the engine would have a lighter structure to help produce a thrust-to-weight ratio of 160:1. In its most recent statement, the company says “an enhanced design makes the Merlin 1D the most efficient booster engine ever built, with a vacuum thrust-to-weight ratio exceeding 150.”