Advanced Common Evolved Stage
Encyclopedia
The Advanced Common Evolved Stage, or ACES, is a proposed upper stage rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...

 for use on space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....

 launch vehicle
Launch vehicle
In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from the Earth's surface into outer space. A launch system includes the launch vehicle, the launch pad and other infrastructure....

s. The design concept is from the U.S.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 company United Launch Alliance
United Launch Alliance
United Launch Alliance is a joint venture of Lockheed Martin and Boeing. ULA was formed in December 2006 by combining the teams at these companies which provide spacecraft launch services to the government of the United States. U.S...

 (ULA). ACES is intended to boost satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

 payloads to geosynchronous orbit
Geosynchronous orbit
A geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...

 or, in the case of an interplanetary space probe
Space probe
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...

, to or near to escape velocity
Escape velocity
In physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...

. Other alternative uses include a proposal to provide in-space propellant depot
Propellant depot
An orbital propellant depot is a cache of propellant that is placed on an orbit about the Earth or another body to allow spacecraft to be fuelled in space. Launching a spacecraft separately from some of its propellant enables missions with more massive payloads...

s in LEO or at that could be used as way-stations for other rockets to stop and refuel on the way to beyond-LEO or interplanetary missions, and to provide the high-energy technical capacity for the cleanup of space debris
Space debris
Space debris, also known as orbital debris, space junk, and space waste, is the collection of objects in orbit around Earth that were created by humans but no longer serve any useful purpose. These objects consist of everything from spent rocket stages and defunct satellites to erosion, explosion...

.

Concept

The ACES is intended as a lower-cost, more-capable and more-flexible upper stage that would supplement, and perhaps replace, the existing ULA Centaur
Centaur (rocket stage)
Centaur is a rocket stage designed for use as the upper stage of space launch vehicles. Centaur boosts its satellite payload to geosynchronous orbit or, in the case of an interplanetary space probe, to or near to escape velocity...

 and Delta Cryogenic Second Stage (DCSS) upper stage vehicles.

Design

The vehicle is "based on a simple modular design" where the "use of multiple barrel panels, similar to Centaur, provides a straightforward means to building multiple-length (propellant
Rocket propellant
Rocket propellant is mass that is stored in some form of propellant tank, prior to being used as the propulsive mass that is ejected from a rocket engine in the form of a fluid jet to produce thrust. A fuel propellant is often burned with an oxidizer propellant to produce large volumes of very hot...

 load) stages that are otherwise common. The common equipment shelf accommodates one, two, or four RL10 engines. While ACES can start with existing Centaur and Delta pneumatic, avionics
Avionics
Avionics are electronic systems used on aircraft, artificial satellites and spacecraft.Avionic systems include communications, navigation, the display and management of multiple systems and the hundreds of systems that are fitted to aircraft to meet individual roles...

 and propulsion
Spacecraft propulsion
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...

 systems it is intended to transition to lower-cost and higher capability systems founded on our Integrated Vehicle Fluids (IVF) system concept. IVF eliminates all hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...

, helium, and nearly all batteries
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

 from the vehicle. It consumes waste hydrogen and oxygen to produce power, generate settling
Settling
Settling is the process by which particulates settle to the bottom of a liquid and form a sediment. Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a uniform manner in the direction exerted by that force...

 and attitude control thrust, and autogenously pressurize the vehicle tanks. IVF is optimal for depot
Propellant depot
An orbital propellant depot is a cache of propellant that is placed on an orbit about the Earth or another body to allow spacecraft to be fuelled in space. Launching a spacecraft separately from some of its propellant enables missions with more massive payloads...

 operations since only LH2
Liquid hydrogen
Liquid hydrogen 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 pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...

 and LO2
Liquid oxygen
Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...

 need be transferred, and it extends mission lifetimes from the present dozen hours to multiple days."

With the addition of a solar power system
Solar panels on spacecraft
Spacecraft operating in the inner solar system usually rely on the use of photovoltaic solar panels to derive electricity from sunlight. In the outer solar system, where the sunlight is too weak to produce sufficient power, radioisotope thermal generators are used as a power source.-History:The...

, the vehicle can remain in space and operate indefinitely.

, the upper-stage versions of ACES were proposed to be powered by enhanced RL-10
RL-10
The RL10 was USA's first liquid hydrogen fueled rocket engine. An updated version is used in several current launch vehicles. Six RL10 engines were used in the S-IV second stage of the Saturn I rocket. One or two RL10 engines are used in the Centaur upper stages of Atlas and Titan rockets...

 engines.

Variants

The ACES modular design supports the production of a number of standard propellant load stages, in a number of standard lengths, that are otherwise common, including the main propellant tank diameter of 5 metres (16.4 ft), "a size not seen since the 1970s":
  • ACES 41 upper stage — 41 tonne propellant capacity
  • ACES 73 upper stage — 73 tonne propellant capacity
  • ACES 41 tanker — no engine(s)
  • ACES 73 tanker — no engine(s)
  • ACES 121 depot — consists of an ACES 41 upper stage main vehicle (for L02 storage) and an ACES 73 tank (modified for LH2 storage) with 121 tonne of long-term, in-space, propellant depot capacity


Space debris cleanup

One explicit objective of the ACES design and the depot-based space architecture is to utilize the longer-stage endurance and the greater fuel capacity with in-space refueling
Propellant depot
An orbital propellant depot is a cache of propellant that is placed on an orbit about the Earth or another body to allow spacecraft to be fuelled in space. Launching a spacecraft separately from some of its propellant enables missions with more massive payloads...

 capability to retrieve derelict objects for near-space clean up and deorbit. More specifically, it is an explicitly stated goal that the technical potential for derelict capture/deorbit will be enabled to provide the large delta-V
Delta-v
In astrodynamics a Δv or delta-v is a scalar which takes units of speed. It is a measure of the amount of "effort" that is needed to change from one trajectory to another by making an orbital maneuver....

 required to deorbit even heavy objects from geosynchronous orbits. These new approaches offer the technical prospect of markedly reducing the costs of bey
Medium Earth Orbit
Medium Earth orbit , sometimes called intermediate circular orbit , is the region of space around the Earth above low Earth orbit and below geostationary orbit ....

ond
High Earth orbit
A High Earth Orbit is a geocentric orbit whose apogee lies above that of a geosynchronous orbit .Highly Elliptical Orbits are a subset of High Earth Orbits.-Examples of satellites in High Earth Orbit:...

-LEO
Geosynchronous orbit
A geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...

 object capture and deorbit with the implementation of a one-up/one-down launch license
License
The verb license or grant licence means to give permission. The noun license or licence refers to that permission as well as to the document recording that permission.A license may be granted by a party to another party as an element of an agreement...

 regime to Earth orbits.

See also

  • Solar-thermal monopropellant thrusters
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