http://nextbigfuture.com/2010/08/spacex-talks-falcon-x-heavy-for-125.html
I can’t wait for the Falcon X launcher to fly that’ll use the Raptor engines they are developing at the moment. I think it is supposed to be classified as a super-heavy class launch vehicle. Falcon XX is supposed to be ultra-heavy lift vehicle.
Same here. The speculation is, three of the nine-engine Falcon 9 boosters will be launched as the Falcon 9 Heavy sometime in 2015; the Merlin 4 engine was going to be a scaled-up kerosene burner, but the plug got pulled on that last year or so, and it’s going to be scaled-up, but a methane burner (same thing is going on at Blue Origin). This grew out of Musk’s goal of recycling the boosters which will eventually carry colonists to Mars — methane is available to refuel them, kerosene isn’t.
One Merlin 4 will replace the nine engines of the Falcon 9; a nine-engine booster using the Merlin 4 will be the next gen; a three-booster superheavy will be used for the Mars colonization. The timeframe is about a generation, twenty years. Meanwhile, barring political obstacles (corruption), SpaceX is likely to take over much of the world’s launch business.