In February, 2010, President Obama announced the cancellation of Project Constellation. In October, 2010, Congress came up with a compromise - keep the Orion capsule but launch it on a commercial launcher. Ares I and V were cancelled. To provide a heavy lift capability, congress ordered NASA to build a rocket that specifically used Space Shuttle technology.
Nasa has defined two parts to the new system. The MPCV (multi purpose crew vehicle, formerly Orion) and the SLS (space launch system). The MPCV will launch a crew of 2-4 people into orbit in a partially reusable capsule on top of a Delta IV Heavy rocket. Current proposals for the SLS leans toward launching a Saturn V style rocket, with two five segment solid rocket boosters, with a 70 ton version to lift the capsule, or 130 ton cargo variant. Only the solid rocket boosters would be "re-usable".
The second complete Orion Spacecraft will be flown unmanned on top of a Delta IV Heavy rocket in 2014. The mission involves placing the capsule in a 3,600 mile high orbit and then accelerating it to re-entry speeds that are encountered when returning from the moon (20,000 mph). Originally Orion was going to travel to the International Space Station on its maiden flight, but this ferrying task will be assumed by private industry, most likely the SpaceX Falcon 9 and the Dragon capsule. Orion will be designed for manned, deep space missions.
NASA formally abandoned the development of the Ares I and Ares V rockets in October, 2010. Congress mandated that NASA develop a "Multi Purpose Crew Vehicle" to be launched on a private industry rocket, capable of travelling beyond low earth orbit to the moon or nearby asteroids. NASA is tentatively planning to develop the MPCV from the Orion capsule.
For the first space launch of Orion, a Delta IV heavy will be used. People aren't allowed to ride on a Delta, so crews will have to wait for the man-rated SLS in 2020 or so.
The new SLS design is a sort of Space Shuttle refactor with a Saturn V mix-in. The tank now has engines on the bottom. The SRB's are still on the side, but have 5 instead of the shuttle's 4 segments. Then it will have a Saturn-like third stage with an updated J2 engine. It will be man-rated, so the orion capsule can ride on it with people inside, unlike when it is on the commercial grade Delta IV.
Proposed build tools for the SLS rocket. These will be installed at Michoud in New Orleans, LA where the SLS will be manufactured.
1987, NASA commissioned a design study for cargo-variant of the Space Shuttle. Called
Shuttle C, the design replaced the reusable orbiter with an empty cargo cylinder that
could lift 103,000 lb load (15 feet in diameter by 72 feet long) into a 250 mile orbit.
Ironically, the Soviet Union actually used this configuration for the first flight of their Energia Space Shuttle stack. In May, 1987 the 180,000 lb Polyus Weapons Platform was launched into orbit. Unfortunately, after separation, Polyus oriented itself in the wrong direction and fired its rockets so that it promptly burned up in the atmosphere. The Energia stack only flew one more time, to launch the Buran Space Shuttle. The Buran landed successfully, but suffered severe heat damage which was beyond economic repair.
After the cancellation of the Ares V rocket, the "Shuttle-C" concept was reprised as the Shuttle Heavy Lift but was eventually rejected.
Lockheed Martin (who graciously provided these pictures & video) has a Space Operations Simulation Center in Denver, Colorado. The first Orion spacecraft, which is a ground test article and manufacturing pathfinder, was transported from New Orleans in March, 2011 to begin testing in simulated space like conditions, including navigating to and docking with the International Space Station. Read Lockheed Martin's press release for more details.