According to SpaceX CEO, founder, and chief designer Elon Musk, "This is another important milestone in our efforts to push the boundaries of space technology. With the Merlin 1D powering the Falcon 9 and Falcon Heavy rockets, SpaceX will be capable of carrying a full range of payloads to orbit.”
Watch the Merlin 1D full duration firing video (entitled "SpaceX Testing: Merlin 1D Engine Firing ") as shown on this webpage (courtesy of YouTube) (http://youtu.be/976LHTpnZkY).
The caption of the video reads, "The Merlin 1D builds on the proven technology of the Merlin engines used on the first three flights of Falcon 9, including the recent historic mission to the International Space Station."
On May 31 2012, SpaceX successfully launched and landed the historic mission that made Dragon the first commercial spacecraft in history to visit the International Space Station. Previously only four entities/governments -- the United States, Russia, Japan, and the European Space Agency -- had achieved this challenging technical feat.
The Merlin 1D will be needed on SpaceX's next Falcon 9 flight in 2013. Nine Merlin rockets will be blasting the Dragon spacecraft into space at that time.
For more on this story, please read the 6/25/2012 SpaceX press release "SPACEX'S MERLIN 1D ENGINE ACHIEVES FULL MISSION DURATION FIRING"