The Earth Departure Stage (EDS) was the name given to the proposed second

stage Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...

of the Block 2

Space Launch System The Space Launch System (SLS) is an American Super heavy-lift launch vehicle, super heavy-lift Expendable launch system, expendable launch vehicle used by NASA. As the primary launch vehicle of the Artemis program, Artemis Moon landing progra ...

. The EDS was intended to boost the rocket's payload into a

parking orbit A parking orbit is a temporary orbit used during the launch of a spacecraft. A launch vehicle follows a trajectory to the parking orbit, then coasts for a while, then engines fire again to enter the final desired trajectory. An alternative trajec ...

around the Earth and from there send the payload out of

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 ...

to its destination in a manner similar to that of the

S-IVB The S-IVB (pronounced "S-four-B") was the third stage on the Saturn V and second stage on the Saturn IB launch vehicles. Built by the Douglas Aircraft Company, it had one J-2 rocket engine. For lunar missions it was fired twice: first for Earth ...

rocket stage used on the

Saturn V The Saturn V is a retired American super heavy-lift launch vehicle developed by NASA under the Apollo program for human exploration of the Moon. The rocket was human-rated, had multistage rocket, three stages, and was powered by liquid-propel ...

rockets that propelled the

Apollo Apollo is one of the Twelve Olympians, Olympian deities in Ancient Greek religion, ancient Greek and Ancient Roman religion, Roman religion and Greek mythology, Greek and Roman mythology. Apollo has been recognized as a god of archery, mu ...

spacecraft to the Moon. Its development was initially put on hold until stages capable for Mars are required. It was eventually cancelled in favor of

Exploration Upper Stage The Exploration Upper Stage (EUS) is a rocket stage under development for future flights of NASA’s Space Launch System (SLS). Designed for use on the SLS Block 1B and Block 2 configurations, it will replace the Interim Cryogenic Propulsion ...

Ares V

Design

The EDS used on the cancelled

Ares V The Ares V (formerly known as the Cargo Launch Vehicle or CaLV) was the planned cargo launch component of the cancelled NASA Constellation program, which was to have replaced the Space Shuttle after its retirement in 2011. Ares V was also plan ...

would have been propelled by a single J-2X main engine fuelled with

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 ...

(LOX) and

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, ...

(LH₂), and was to have been designed at

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

Marshall Space Flight Center Marshall Space Flight Center (officially the George C. Marshall Space Flight Center; MSFC), located in Redstone Arsenal, Alabama (Huntsville, Alabama, Huntsville postal address), is the Federal government of the United States, U.S. government's ...

Huntsville, Alabama Huntsville is the List of municipalities in Alabama, most populous city in the U.S. state of Alabama. The population of the city is estimated to be 241,114 in 2024, making it the List of United States cities by population, 100th-most populous ...

as part of Project Constellation. Originally, the stage would have been based on the

Space Shuttle The Space Shuttle is a retired, partially reusable launch system, reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. ...

's external tank, and would have used two J-2X engines, while the

core booster would have used five

RS-25 The RS-25, also known as the Space Shuttle Main Engine (SSME), is a liquid-fuel cryogenic rocket engine that was used on NASA's Space Shuttle and is used on the Space Launch System. Designed and manufactured in the United States by Rocketd ...

engines and two 5-segment Solid Rocket Boosters during the first eight minutes of flight. When the Ares V was then redesigned around the use of five (later six) RS-68B rocket engines used on the

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 ...

as of 2019, the EDS was then redesigned using only a single J-2X engine and a common bulkhead, thus in its final design, the EDS resembled an oversized S-IVB, but with the capability of on-site storage (using new propellant storage techniques along with a "loiter skirt" containing solar panels for electricity) for up to 4 days, something impossible with the old S-IVB.

Mission

Launched on the Ares V rocket, the EDS with its

Altair Altair is the brightest star in the constellation of Aquila (constellation), Aquila and the list of brightest stars, twelfth-brightest star in the night sky. It has the Bayer designation Alpha Aquilae, which is Latinisation of name ...

payload would not have become active until the six RS-68 engines cut off, and the Ares V core was jettisoned to burn up in Earth's atmosphere. Upon separation using the on-board staging and

ullage motor Ullage motors (also known as ullage engines or ullage rockets) are relatively small, independently fueled rocket engines that may be fired prior to main engine ignition, when the vehicle is in a zero-g situation. The resulting acceleration causes ...

s, the single J-2X engine would then have fired at full thrust to place itself and the Altair into a

until it was retrieved, via a separate launch on an

Ares I Ares I was the crew launch vehicle that was being developed by NASA as part of the Constellation program. The name "Ares" refers to the Greek deity Ares, who is interpretatio graeca, identified with the Roman god Mars (mythology), Mars. Ares I w ...

, by the Orion MPCV and its four-person astronaut crew. Once the Orion was docked with the Altair and its systems were checked out, the crew was to jettison the loiter skirt and then fire the J-2X engine for a second time, this time at 80% rated thrust, for

trans-lunar injection A trans-lunar injection (TLI) is a propulsive maneuver, which is used to send a spacecraft to the Moon. Typical lunar transfer trajectories approximate Hohmann transfers, although low-energy transfers have also been used in some cases, as with ...

(TLI). Unlike the S-IVB, which propelled the

Apollo spacecraft The Apollo spacecraft was composed of three parts designed to accomplish the American Apollo program's goal of landing astronauts on the Moon by the end of the 1960s and returning them safely to Earth. The expendable (single-use) spacecraft ...

and its three-man crew in a forward-facing motion, the EDS would have fired with the crew ''facing'' the EDS. This "eyeballs out" type of flying would be similar to the flight profile of the proposed, but never flown Manned Venus Flyby, from the cancelled

Apollo Applications Program The Apollo Applications Program (AAP) was created as early as 1966 by NASA headquarters to develop science-based human spaceflight missions using hardware developed for the Apollo program. AAP was the ultimate development of a number of official ...

of the late 1960s. When TLI was completed and the EDS was shut down for the last time, it would then have been jettisoned to fly into a

heliocentric orbit A heliocentric orbit (also called circumsolar orbit) is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun ...

, or in a manner similar to that employed by NASA from

Apollo 13 Apollo 13 (April 1117, 1970) was the seventh crewed mission in the Apollo program, Apollo space program and would have been the third Moon landing. The craft was launched from Kennedy Space Center on April 11, 1970, but the landing was abort ...

Apollo 17 Apollo 17 (December 7–19, 1972) was the eleventh and final mission of NASA's Apollo program, the sixth and most recent time humans have set foot on the Moon. Commander Gene Cernan and Lunar Module Pilot Harrison Schmitt walked on the Moon, ...

, it may have been deliberately crashed into the lunar surface to help scientists calibrate sensitive seismometers placed on the lunar surface by either astronauts on lunar sortie flights or by uncrewed robotic probes.

Space Launch System

When the Ares program was cancelled in favor of the

, the EDS was considered as a second stage for the Block 1B SLS. This version of the stage would have been about long and equipped with one to three J-2X engines. Technological development of the J-2X was expected to take considerably more time, so the EDS was dropped in favor of the

, which will use the much lower-thrust but already-developed

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 ...

. According to NASA, the J-2X will be overpowered for the

Artemis program The Artemis program is a Exploration of the Moon, Moon exploration program led by the United States' National Aeronautics and Space Administration (NASA), formally established in 2017 via Space Policy Directive 1. The program's stated long-ter ...

; its development has been put on hold until stages capable of transferring heavy payloads to Mars are required (expected in the 2030s).

References

{{Use American English, date=January 2014 Ares (rocket family) Rocket stages Space Launch System