Advanced Cryogenic Evolved Stage

Two Advanced Cryogenic Evolved Stage (ACES) concepts were originally developed in 2005 by both Boeing and Lockheed Martin. By 2010, ULA had inherited the intellectual property of both proposals, and the ACES concept had evolved into a new high-performance upper stage to be used on both Atlas V and Delta IV/Delta IV Heavy launch vehicles. Now called the Advanced Common Evolved Stage, ACES was proposed to be a lower-cost, more-capable and more-flexible upper stage that would supplement, and perhaps replace, the existing ULA Centaur and Delta Cryogenic Second Stage (DCSS) upper stages. This upper stage was intended to incorporate improved insulation for improved cryogenic storage and longer coast durations. In April 2015, the name of the stage was reverted to the original Advanced Cryogenic Evolved Stage name, as the new ULA Vulcan design would be the only first stage rocket intended to use ACES, beginning no earlier than 2023. In September 2020, ULA stated they were no longer actively developing ACES. == Advanced Cryogenic Evolved Stage ==

, ACES was expected by ULA to debut on the Vulcan launch vehicle no earlier than 2023 In 2018, ULA gave multiple presentations that again showed an ACES debut in 2023. ACES was planned to use ULA's proprietary Integrated Vehicle Fluids (IVF) technology to significantly extend its lifetime in space. Vulcan Centaur upper stage In late 2017, ULA decided to bring the diameter and advanced insulation elements of the ACES upper stage forward. Under the new plan, Vulcan's upper stage is the Centaur V, with two LH2/LOX RL10 engines and no IVF or other ACES extended-duration technology On 11 May 2018, United Launch Alliance (ULA) announced that the Aerojet Rocketdyne RL10 engine was selected for Centaur V, following a competitive procurement process. Integrated Vehicle Fluids The IVF technology uses a lightweight internal combustion engine to use hydrogen and oxygen propellant boil-off (normally wasted when boil-off gases are vented to space) to operate the stage. The design included producing power, maintaining stage attitude and keeping the propellant tanks autogenously pressurized. Using these fluids was designed to eliminate the need for hydrazine fuel, helium for pressurization, , an internal combustion engine to be used to power the IVF system on ACES was to be produced by Roush Racing. == Possible applications ==

One potential application for ACES was stated by ULA in 2010 to be the use of the longer endurance and the greater fuel capacity as propellant depot with in-space refueling capability to retrieve derelict objects for near-space clean up and deorbit. These new approaches offer the technical prospect of markedly reducing the costs of beyond-low Earth Orbit object capture and deorbit with the implementation of a one-up/one-down launch license regime to Earth orbits. == See also ==