NASA’s exploration systems architecture study will this month propose two new launch vehicles to replace the Space Shuttle. The study will also confirm that development of the Crew Exploration Vehicle (CEV) must be accelerated to reduce the gap after the Shuttle retires.
One proposal is for a heavylift vehicle having a first stage of a modified Shuttle external tank with six Shuttle main engines, plus two solid rocket boosters (SRB), as used on the Shuttle. A second stage will be mounted on top. A later booster, to launch the CEV, is expected to comprise a five-segment Shuttle SRB-based solid-propellant first stage with a liquid-propellant second stage.
Source: Flight International