OrbitalHub

Wikipedia dixit:

“ULA plans an “incremental approach” to rolling out the vehicle and its technologies. Deployment will begin with the first stage, based on the Delta IV’s fuselage diameter and production process and is expected to use two BE-4 engines. Aerojet Rocketdyne’s AR-1 engine is being retained by ULA as a contingency option, with a final decision to be made in 2016. The first stage can have from zero to six solid rocket boosters (SRBs), and in the maximal configuration could launch a heavier payload than the highest-rated Atlas V, though still less than the Delta IV Heavy. A later feature is planned to make the first stage partly reusable. ULA plans to develop the technology to allow the engines to detach from the vehicle after cutoff, descend through the atmosphere with a heat shield and parachute, and finally be captured by a helicopter in mid-air. In April 2015, ULA estimated that reusing the engines would reduce the cost of the first stage propulsion by 90%, with propulsion being 65% of the total first stage build cost.

Initial configurations of Vulcan will use the same Centaur upper stage as the Atlas V, with its existing RL-10 engines. A later advanced cryogenic upper stage — called the Advanced Cryogenic Evolved Stage (ACES) — is conceptually planned for full development by ULA in the late 2010s. ACES would be LOX and liquid hydrogen (LH2) powered by one to four rocket engines yet to be selected. This upper stage will include the Integrated Vehicle Fluids technology that could allow long on-orbit life of the upper stage, measured in weeks rather than hours.”

Video credit: ULA