The Advanced Cryogenic Evolved Stage (ACES) was a proposed liquid oxygen/liquid hydrogen upper-stage for use on a number of different launch vehicles produced by Boeing, Lockheed Martin, United Launch Alliance (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. [1] The ACES concept had the objective to improve the on-orbit lifespan of current upper stages. [1]
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. [2] 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 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. [3]
Two Advanced Cryogenic Evolved Stage (ACES) concepts were originally developed in 2005 by both Boeing and Lockheed Martin. [4] [5] [ clarification needed ]
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. [1] This upper stage was intended to incorporate improved insulation for improved cryogenic storage and longer coast durations. [6]
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. [7]
In September 2020, ULA stated they were no longer actively developing ACES. [3]
As of April 2015 [update] , ACES was expected by ULA to debut on the Vulcan launch vehicle no earlier than 2023 [7] but in July 2015 the timeframe was clarified to not likely fly until 2024–2025. [8] In 2018, ULA gave multiple presentations that again showed an ACES debut in 2023. [9] 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. [9]
ACES was planned to use ULA's proprietary Integrated Vehicle Fluids (IVF) technology to significantly extend its lifetime in space. [10]
ACES was planned to include common bulkhead propellant tanks with a diameter of 5.4 m (18 ft), capable of carrying 68,000 kg (150,000 lb) of propellant. [11]
In late 2017, ULA decided to bring the 5.4 m (18 ft) 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 [1] 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. [12]
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. [13]
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 [10] [14] and keeping the propellant tanks autogenously pressurized. Using these fluids was designed to eliminate the need for hydrazine fuel, helium for pressurization, [7] [15] : 4, 5 and nearly all batteries in the vehicle.
IVF was designed by ULA to be optimal for depot operations, since only liquid hydrogen and liquid oxygen would need be transferred, and it could, if built, conceivably extend mission lifetimes from the present dozens of hours to multiple days. [1] [15] : 2–4 [16] : 4
As of April 2015 [update] , an internal combustion engine to be used to power the IVF system on ACES was to be produced by Roush Racing. [7]
In August 2016, ULA's President and CEO Tory Bruno said both Vulcan and ACES were intended to be human rated. [17]
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. [18]
A monopropellant rocket is a rocket that uses a single chemical as its propellant.
The Centaur is a family of rocket propelled upper stages produced by U.S. launch service provider United Launch Alliance, with one main active version and one version under development. The 3.05 m (10.0 ft) diameter Common Centaur/Centaur III flies as the upper stage of the Atlas V launch vehicle, and the 5.4 m (18 ft) diameter Centaur V is being developed as the upper stage of ULA's new Vulcan rocket. Centaur was the first rocket stage to use liquid hydrogen (LH2) and liquid oxygen (LOX) propellants, a high-energy combination that is ideal for upper stages but has significant handling difficulties.
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National Security Space Launch (NSSL) is a program of the United States Space Force (USSF) intended to assure access to space for United States Department of Defense and other United States government payloads. The program is managed by the Assured Access to Space Directorate (SSC/AA) of the Space Force's Space Systems Command (SSC), in partnership with the National Reconnaissance Office.
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 110 kN (24,729 lbf) of thrust per engine in vacuum. Three RL10 versions are in production for the Centaur upper stage of the Atlas V and the DCSS of the Delta IV. Three more versions are in development for the Exploration Upper Stage of the Space Launch System and the Centaur V of the Vulcan rocket.
Atlas II was a member of the Atlas family of launch vehicles, which evolved from the successful Atlas missile program of the 1950s. The Atlas II was a direct evolution of the Atlas I, featuring longer first stage tanks, higher-performing engines, and the option for strap-on solid rocket boosters. It was designed to launch payloads into low Earth orbit, geosynchronous transfer orbit or geosynchronous orbit. Sixty-three launches of the Atlas II, IIA and IIAS models were carried out between 1991 and 2004; all sixty-three launches were successes, making the Atlas II a highly reliable space launch system. The Atlas line was continued by the Atlas III, used between 2000 and 2005, and the Atlas V which is still in use.
Delta III was an expendable launch vehicle made by McDonnell Douglas. The vehicle was developed from the highly-successful Delta II to help meet the launch demand of larger satellites. The first Delta III launch was on August 26, 1998. Of its three flights, the first two were failures, and the third, though declared successful, reached the low end of its targeted orbit range and carried only a dummy (inert) payload. The Delta III could deliver up to 3,810 kg (8,400 lb) to geostationary transfer orbit, twice the payload of its predecessor, the Delta II. Under the four-digit designation system from earlier Delta rockets, the Delta III is classified as the Delta 8930.
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United Launch Alliance, LLC (ULA), commonly referred to as ULA, is an American aerospace manufacturer, defense contractor and launch service provider that manufactures and operates a number of rocket vehicles that launch spacecraft into orbits around Earth and other bodies in the Solar System.
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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.
Peller described ACES as a concept that ULA is no longer actively pursuing. "We did a lot of studies, we invested in a lot of technology development to assess the feasibility of some of the innovative features of ACES", he said. "That has served us well, because a lot of that original ACES work has its fingerprints in our new version of Centaur, the Centaur 5 we're fielding with Vulcan. Those studies five, eight years ago certainly served us well, and it put us on a good path forward here for the evolution of our upper stages. We will continue to evolve our upper stage to meet the needs of the market going forward".
The increased capability of the upper stage is somewhere in there in the future
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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