Today SpaceX formally announced development of the Falcon Heavy. Outwardly it looks like three of the human-rated Falcon 9 strapped together. With 27 Merlin engines in the lower stages, Falcon Heavy is designed to complete its mission even if multiple engines fail. Inside it has propellant-crossfeed capability, so when the boosters separate the inner stage will have nearly full tanks. Falcon is Heavy enough to launch small spacecraft to Mars.
The launcher will lift a surprisingly large 53 metric tons to Low Earth Orbit. The Space Shuttle can carry only about 28 tons. If Falcon were much heavier, it would compete with NASA's undefined heavy lift launcher. Washington is still arguing whether their booster should launch 70 or 130 tons. According to their website, "SpaceX agrees with the need to develop a vehicle of that class as the best way to conduct a large number of human missions to Mars." Meanwhile they have plans for an advanced engine that will take the place of 9 Merlins, and still larger Falcon X and Falcon XX. If the US government dithers, private industry may lead the way to the planets.