The Constellation Program includes two separate launching vehicles: the Ares I, for the crew; and the Ares V, for cargo. Having two separate launching vehicles will allow for more specialized designs for the different purposes the rockets will fulfill.
The Ares I rocket is specifically being designed to boost the Orion Crew spacecraft. Orion is intended as a crew capsule, similar in design to the Project Apollo capsule, to transport astronauts to the International Space Station, the Moon, and perhaps Mars. The first stage of the Ares I is a more powerful and reusable solid fuel rocket derived from the current Space Shuttle Solid Rocket Booster. This fifth segment will enable the Ares I to produce more thrust and burn longer. Other changes made to the solid rocket booster are the removal of the Space Shuttle External Tank attachment points and the replacement of the solid rocket booster nosecone with a new forward adapter that will interface with the liquid-fueled second stage. The adapter will be equipped with solid-fueled separation motors to facilitate the disconnection of the stages during ascent.
The upper stage is to be propelled by one J-2X rocket engine fueled by liquid hydrogen (LH2) and liquid oxygen (LOX). The J-2X is derived from the J-2 engine used on the Saturn IB and Saturn V rockets. On July 16, 2007, NASA awarded Rocketdyne a sole-source contract for the J-2X engines to be used for ground and flight tests. Although its J-2X engine is derived from an established design, the upper stage itself is wholly new. Originally based on the internal structure of the Shuttle's External Tank, the original design called for separate fuel and oxidizer tanks, separated by an "intertank" structure. Using a concept going back to the Apollo era, the "intertank" structure was dropped to decrease mass, and instead, a common bulkhead would be used between the tanks.
The upper stage of Ares I is to be built at the NASA Michoud Assembly Facility, the current location of the fabrication and construction of the Shuttle's External Tank, and the former construction site of the Saturn V's first stage, the S-IC.