According to NASA, the plans for a new Shuttle and Heavy Lift Booster will look a lot like the Saturn V rockets of the Apollo era. NASA has decided to build two new launch systems - both will draw upon existing Space Shuttle hardware. One vehicle will be a cargo-only heavy lifter, the other will be used to launch the Crew Exploration Vehicle.
According to a NASA source , the study team focused on four primary areas:
Complete assessment of the top-level Crew Exploration Vehicle (CEV) requirements and plans to enable the CEV to provide crew transport to the ISS and to accelerate the development of the CEV and crew launch system to reduce the gap between Shuttle retirement and CEV IOC.
Definition of top-level requirements and configurations for crew and cargo launch systems to support the lunar and Mars exploration programs.
Development of a reference lunar exploration architecture concept to support sustained human and robotic lunar exploration operations.
Identification of key technologies required to enable and significantly enhance these reference exploration systems and reprioritization of near-term and far-term technology investments.
The Heavy Lifter
According to on-line reports, the heavy lifter will be a "stacked" or "in line" configuration (one stage atop another) and not a "side-mounted" configuration as is currently used to launch the space shuttle. The first stage will be a modified shuttle external tank with rocket engines mounted underneath. The first configuration will use 6 existing shuttle (SSME Block II) engines.
A growth version for lifting heavier cargos will use three RS-68 engines. The RS-68, manufactured by Boeing, are currently used in its Delta IV family of launch vehicles. Additional engines would be clustered for launching heavier loads such as those needed for Mars missions.