Advanced Cryogenic Evolved Stage

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The Advanced Cryogenic Evolved Stage (ACES) is a proposed liquid oxygen/liquid hydrogen upper-stage rocket for use on the Vulcan space launch vehicle designed by the U.S. company United Launch Alliance (ULA).[1]

The ACES concept is currently intended to improve the on-orbit lifespan of current upper stages, enabling a variety of applications as discussed below.[1]

In 2016, ULA announced conceptual plans to transition the Vulcan rocket to the ACES second stage after approximately 2024. Vulcan will initially launch with the Centaur V upper stage.[2]

History (Advanced Common Evolved Stage)[edit]

Two Advanced Cryogenic Evolved Stage (ACES) concepts were originally proposed in 2006 by both Boeing and Lockheed Martin.[3][4]

By 2010, ULA had inherited the intellectual property of both proposals, and ACES 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 intended 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.[1] This upper stage was intended to incorporate improved insulation for improved cryogenic storage and longer coast durations.[5]

In April 2015, the stage was reverted to the original Advanced Cryogenic Evolved Stage name, as the new Vulcan will be the only application, beginning no earlier than 2023.[6]

Advanced Cryogenic Evolved Stage[edit]

The current ACES is expected to fly on the Vulcan launch vehicle no earlier than 2023[6] and planned for 2024–25.[7]

ACES will use ULA's proprietary Integrated Vehicle Fluids (IVF) technology to significantly extend its lifetime in space.[8]

ACES is planned to include common bulkhead propellant tanks with a diameter of 5.4 meters, capable of carrying 68 tonnes (150,000 lb) of propellant.[9]

Vulcan Centaur Upper Stage[edit]

In late 2017, ULA decided to bring the 5.4 m 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 RL-10 engines and no IVF. ACES is now expected to have the same tanks as Centaur V, but with the possible addition of two more RL-10s and IVF.[citation needed]

Bringing critical items from ACES into the Centaur V development workstream in 2017 was expected to increase the lift capacity of the first generation Vulcan, so it could carry planned high mass, high energy national security reference payloads. The Centaur V was projected to permit ULA to retire both the Atlas V and Delta IV earlier than planned.[citation needed]

On May 11, 2018 United Launch Alliance (ULA) announced that the Aerojet Rocketdyne RL-10 engine was selected for Centaur V, following a competitive procurement process.[10]

Integrated Vehicle Fluids[edit]

The IVF technology utilizes a lightweight internal combustion engine to use hydrogen and oxygen propellant boiloff (normally wasted when boiloff gasses are vented to space) to operate the stage including production of power, maintaining stage attitude,[8][11] and keeping the propellant tanks autogenously pressurized, eliminating the need for hydrazine fuel and helium,[6][12]:4, 5 and nearly all batteries from the vehicle.

IVF is optimal for depot operations, since only LH2 and LO2 need be transferred, and it extends mission lifetimes from the present dozen hours to multiple days.[1][12]:2–4[13]:4

As of April 2015, the internal combustion engine to be used to power the IVF system on ACES will be produced by Roush Racing.[6]

In August 2016 ULA's President and CEO Tory Bruno said both Vulcan and ACES were intended to be human rated.[14]

Possible applications[edit]

One possible application for ACES is 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-LEO object capture and deorbit with the implementation of a one-up/one-down launch license regime to Earth orbits.[15]

See also[edit]


  1. ^ a b c d Zegler, Frank; Kutter, Bernard (2 September 2010). Evolving to a Depot-Based Space Transportation Architecture (PDF). AIAA SPACE 2010 Conference & Exposition. American Institute of Aeronautics and Astronautics. Retrieved 25 January 2011. ACES design conceptualization has been underway at ULA for many years. It leverages design features of both the Centaur and Delta Cryogenic Second Stage (DCSS) upper stages and intends to supplement and perhaps replace these stages in the future. The baseline ACES will contain twice the Centaur or 4m DCSS propellant load, providing a significant performance boost compared to our existing upper stages. The baseline 41-mT propellant load is contained in a 5m diameter, common bulkhead stage that is about the same length as ULA's existing upper stages.
  2. ^ @jeff_foust (18 January 2018). "Tom Tshudy, ULA: with Vulcan we plan to maintain reliability and on-time performance of our existing rockets, but at a very affordable price. First launch mid-2020" (Tweet) – via Twitter.
  3. ^ LeBar, JF; Cady, EC (2006). "The Advanced Cryogenic Evolved Stage (ACES) - A Low-Cost, Low-Risk Approach to Space Exploration Launch" (PDF). Retrieved 2016-01-02.
  4. ^ 2006: Centaur Extensibility For Long Duration, Gerard Szatkoski, et al, NASA/KSC and Lockheed Martin Space Systems Company, (AIAA Space 2006 Conference Paper no. 60196), accessed 20 October 2015.
  5. ^ 2005: Atlas Centaur Extensibility to Long-Duration In-Space Applications, Bernard F. Kutter, Frank Zegler, et al, Lockheed Martin Space Systems Company, (AIAA 2005-6738), accessed 20 October 2015.
  6. ^ a b c d Gruss, Mike (2015-04-13). "ULA's Vulcan Rocket To be Rolled out in Stages". SpaceNews. Retrieved 2015-04-18.
  7. ^ Bruno, Tory (28 July 2015). "@MrMonster911 @PopSci @ulalaunch enabler will be ACES, our ultra long duration upper stage. Planned to fly in the 2024-5 time frame". Retrieved 11 August 2017.
  8. ^ a b Ray, Justin (14 April 2015). "ULA chief explains reusability and innovation of new rocket". Spaceflight Now. Retrieved 2015-04-18.
  9. ^ "2-1 Transportation & Propellant Resources in the Cislunar Economy-Kutter.pdf" (PDF). 12 June 2018. Retrieved 20 January 2019.
  10. ^ "United Launch Alliance Selects Aerojet Rocketdyne's RL10 Engine". ULA. May 11, 2018. Retrieved May 13, 2018.
  11. ^ Boyle, Alan (2015-04-13). "United Launch Alliance Boldly Names Its Next Rocket: Vulcan!". NBC. Retrieved 2015-04-18.
  12. ^ a b Barr, Jonathan (2015). ACES Stage Concept: Higher Performance, New Capabilities, at a Lower Recurring Cost (PDF). AIAA SPACE 2015 Conference & Exposition. American Institute of Aeronautics and Astronautics. Archived from the original (pdf) on 13 March 2016. Retrieved 18 March 2016.
  13. ^ Barr, Jonathan; Kutter, Bernard (2010). Phase 2 EELV - An Old Configuration Option with New Relevance to Future Heavy Lift Cargo (PDF). AIAA SPACE 2010 Conference & Exposition. American Institute of Aeronautics and Astronautics. Retrieved 17 April 2016.
  14. ^ Tory Bruno. ""@A_M_Swallow @ULA_ACES We intend to human rate Vulcan/ACES"". Retrieved August 30, 2016.
  15. ^ Zegler, Frank; Bernard Kutter (2010-09-02). "Evolving to a Depot-Based Space Transportation Architecture" (PDF). AIAA SPACE 2010 Conference & Exposition. AIAA. pp. 13–14. Archived (PDF) from the original on 2011-10-20. Retrieved 2011-01-25. for disposing of these obsolete or derelict spacecraft all [approaches] involve the expenditure of substantially more delta V than what has been traditional. It may well be required that old spacecraft be removed at the same time new spacecraft are being emplaced. ... [this architecture] anticipates the task of removing derelict spacecraft by providing an infrastructure to permit these high ΔV missions and enables the likely new paradigm of removing a spacecraft for each one deployed.

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