The Advanced Cryogenic Evolved Stage (ACES) was a proposed

liquid oxygen Liquid oxygen, sometimes abbreviated as LOX or LOXygen, is a clear cyan liquid form of dioxygen . It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an application which is ongoing. Physical ...

liquid hydrogen Liquid hydrogen () is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecule, molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point (thermodynamics), critical point of 33 Kelvins, ...

upper-stage for use on a number of different

launch vehicle A launch vehicle is typically a rocket-powered vehicle designed to carry a payload (a crewed spacecraft or satellites) from Earth's surface or lower atmosphere to outer space. The most common form is the ballistic missile-shaped multistage ...

s produced by

Boeing The Boeing Company, or simply Boeing (), is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, and missiles worldwide. The company also provides leasing and product support s ...

Lockheed Martin The Lockheed Martin Corporation is an American Arms industry, defense and aerospace manufacturer with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta on March 15, 1995. It is headquartered in North ...

United Launch Alliance United Launch Alliance, LLC (ULA) is an American launch service provider formed in December 2006 as a joint venture between Lockheed Martin Space and Boeing Defense, Space & Security. The company designs, assembles, sells and launches rockets ...

(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 Delta commonly refers to: * Delta (letter) (Δ or δ), the fourth letter of the Greek alphabet * D (NATO phonetic alphabet: "Delta"), the fourth letter in the Latin alphabet * River delta, at a river mouth * Delta Air Lines, a major US carrier ...

Atlas An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...

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 (rocket family), Atlas launch vehicle family. It was developed by Lockheed Martin and has been operated by United Launch Alliance (ULA) since 2006. Primarily used to ...

and

Delta IV Delta IV was a group of five expendable launch systems in the Delta rocket family. It flew 45 missions from 2002 to 2024. Originally designed by Boeing's Defense, Space and Security division for the Evolved Expendable Launch Vehicle (EELV) p ...

Delta IV Heavy The Delta IV Heavy (Delta 9250H) was an expendable heavy-lift launch vehicle, the largest type of the Delta IV family. It had the highest capacity of any operational launch vehicle in the world after the retirement of the Space Shuttle in 20 ...

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 ( ; ; ), occasionally hippocentaur, also called Ixionidae (), is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse that was said to live in the mountains of Thessaly. In one version o ...

and

Delta Cryogenic Second Stage The Delta Cryogenic Second Stage (DCSS) is a family of cryogenic-fuelled rocket stages used on the Delta III, Delta IV, and on the Space Launch System Block 1 launch vehicles. The DCSS employs a unique two-tank architecture where the cylind ...

(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. RL10 version ...

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 a subsidiary of American Arms industry, defense company L3Harris that manufactures rocket, Hypersonic flight, hypersonic, and electric propulsive systems for space, defense, civil and commercial applications. Aerojet traces ...

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 comb ...

to use

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

and

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

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 hazardous unless handled in solution as, for example, hydraz ...

fuel,

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

for pressurization, and nearly all batteries in the vehicle. IVF was designed by ULA to be optimal for

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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 Fenway Keselowski Racing, doing business as RFK Racing, is an American professional stock car organization that currently competes in the NASCAR Cup Series. One of NASCAR's largest racing teams in the 2000s and early 2010s, Roush formerly ...

. 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 ha ...

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

deorbit Atmospheric entry (sometimes listed as Vimpact or Ventry) 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. Atmospheric entry may be ''uncontrolled entry ...

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

low Earth Orbit A low Earth orbit (LEO) is an geocentric orbit, orbit around Earth with a orbital period, period of 128 minutes or less (making at least 11.25 orbits per day) and an orbital eccentricity, eccentricity less than 0.25. Most of the artificial object ...

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 lau ...

regime to

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

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