The Advanced Cryogenic Evolved Stage (ACES) was a proposed

liquid oxygen Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an app ...

liquid hydrogen Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point of 33 K. However, for it to be in a fully l ...

upper-stage from 2005 to 2020 for use on a number of different

launch vehicle A launch vehicle or carrier rocket is a rocket designed to carry a payload ( spacecraft or satellites) from the Earth's surface to outer space. Most launch vehicles operate from a launch pads, supported by a launch control center and sys ...

s produced by

Boeing The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and ...

Lockheed Martin The Lockheed Martin Corporation is an American aerospace, arms, defense, information security, and technology corporation with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It ...

, and after a late-2006 merger,

United Launch Alliance United Launch Alliance (ULA), legally United Launch Alliance, LLC, is an American spacecraft launch service provider that manufactures and operates a number of rocket vehicles that are capable of launching spacecraft into orbits around Earth, a ...

(ULA). During the last five years of the program, ACES was proposed for eventual use on the Vulcan space launch vehicle designed by the U.S. company United Launch Alliance. The ACES concept had the objective to improve the on-orbit lifespan of current upper stages. In 2015, ULA announced conceptual plans to transition the Vulcan rocket to the ACES second stage, also referred to as Centaur Heavy, after 2024. Vulcan will initially launch with the Centaur V upper stage. Both Boeing and Lockheed Martin had separate but similar ACES concepts prior to the formation of the jointly-owned (50% Boeing/50% Lockheed Martin) ULA in late 2006. In the event, the long- duration upper stage concept was never able to obtain top-line attention from any of the companies as it never won full development funding from the US government, the primary source of funding for the Delta,

Atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geogra ...

and Vulcan rockets. However, some aspects of changes planned for ACES, such as the larger tank-diameter, were eventually used in the Centaur V upper stage.

Advanced Common Evolved Stage

Two Advanced Cryogenic Evolved Stage (ACES) concepts were originally developed in 2005 by both

and

.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 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 Atlas V is an expendable launch system and the fifth major version in the Atlas launch vehicle family. It was originally designed by Lockheed Martin, now being operated by United Launch Alliance (ULA), a joint venture between Lockheed Mart ...

and

Delta IV Delta IV is a group of five expendable launch systems in the Delta rocket family introduced in the early 2000s. Originally designed by Boeing's Defense, Space and Security division for the Evolved Expendable Launch Vehicle (EELV) program, th ...

Delta IV Heavy The Delta IV Heavy (Delta 9250H) is an expendable heavy-lift launch vehicle, the largest type of the Delta IV family. It is the world's third highest-capacity launch vehicle in operation, behind NASA's Space Launch System and SpaceX's Falcon H ...

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 A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. Centaurs are thought of in many Greek myths as bein ...

and

Delta Cryogenic Second Stage The Delta Cryogenic Second Stage (DCSS) is a family of cryogenic rocket stages used on the Delta III and Delta IV rockets, and on the Space Launch System Block 1. The stage consists of a cylindrical liquid hydrogen (LH2) tank structurally separate ...

(DCSS) upper stages. This upper stage was intended to incorporate improved insulation for improved cryogenic storage and longer coast durations.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 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 but in July 2015 the timeframe was clarified to not likely fly until 2024–2025. In 2018, ULA gave multiple presentations that again showed an ACES debut in 2023. In 2019 however, ULA said that while they still planned to develop ACES, they no longer had a specific date for when that would be. ACES was planned to use ULA's proprietary Integrated Vehicle Fluids (IVF) technology to significantly extend its lifetime in space. ACES was planned to include common bulkhead propellant tanks with a diameter of , capable of carrying of propellant.

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 The RL10 is a liquid-fuel cryogenic rocket engine built in the United States by Aerojet Rocketdyne that burns cryogenic liquid hydrogen and liquid oxygen propellants. Modern versions produce up to of thrust per engine in vacuum. Three RL ...

engines and no IVF or other ACES extended- duration technology as had been planned for ACES. ACES was then expected to have the same tank diameter as Centaur V, but stretched (longer tank length), with the possible addition of two more RL10s and IVF. On 11 May 2018, United Launch Alliance (ULA) announced that the

Aerojet Rocketdyne Aerojet Rocketdyne is an American manufacturer of rocket, hypersonic, and electric propulsive systems for space, defense, civil and commercial applications. Headquartered in Sacramento, California, the company is owned by Aerojet Rocketdyne Hold ...

engine was selected for Centaur V, following a competitive procurement process.

Integrated Vehicle Fluids

The IVF technology uses a lightweight

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...

to use

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

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 Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...

fuel,

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...

for pressurization, and nearly all

batteries Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...

in the vehicle. IVF was designed by ULA to be optimal for depot operations, since only

and

would need be transferred, and it could, if built, conceivably extend mission lifetimes from the present dozens of hours to multiple days. , an internal combustion engine to be used to power the IVF system on ACES was to be produced by

Roush Racing Roush is a surname. Notable people with the surname include: Politics *Glenn Roush (1934–2020), American politician in Montana * J. Edward Roush (1920–2004), United States Representative for Indiana, namesake of: ** J. Edward Roush Lake, a re ...

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

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 An orbital propellant depot is a cache of propellant that is placed in orbit around Earth or another body to allow spacecraft or the transfer stage of the spacecraft to be fueled in space. It is one of the types of space resource depots that ...

with in-space refueling capability to retrieve derelict objects for near-space clean up and

deorbit Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the entr ...

. These new approaches offer the technical prospect of markedly reducing the costs of beyond-

low Earth Orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never m ...

object capture and deorbit with the implementation of a one-up/one-down

launch license The Office of Commercial Space Transportation (generally referred to as FAA/AST or simply AST) is the branch of the United States Federal Aviation Administration (FAA) that approves any commercial rocket launch operations — that is, any laun ...

regime to

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...

orbits.

References

External links

United Launch Alliance
official site
ULA Upper Stage Evolution
Mark Wilkins, United Launch Alliance, 2009
ULA Integrated Vehicle Fluids
video, released by ULA on 2 April 2015
ULA Innovation: Advanced Cryogenic Evolved Stage, Part 1
video, released by ULA on 4 March 2016 {{United Launch Alliance Proposed spacecraft Rocket stages United Launch Alliance