The Exploration Upper Stage (EUS) is being developed as a large second stage for Block 1B and Block 2 of the

Space Launch System The Space Launch System (SLS) is an American super heavy-lift expendable launch vehicle developed by NASA. As of 2022, SLS has the highest payload capacity of any rocket in operational service, as well as the greatest liftoff thrust of any r ...

(SLS), succeeding Block 1's

Interim Cryogenic Propulsion Stage The Space Launch System (SLS) is an American super heavy-lift expendable launch vehicle developed by NASA. As of 2022, SLS has the highest payload capacity of any rocket in operational service, as well as the greatest liftoff thrust of any r ...

. It will be powered by four RL10C-3 engines burning

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 applica ...

and

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 li ...

to produce a total thrust of . , the SLS Block 1B will have a payload capacity to

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 mor ...

of and Block 2 will have a payload capacity of . The EUS is expected to first fly on Artemis IV in March 2026.

Development

The Block 1 configuration of SLS has a core stage powered by four

RS-25 The Aerojet Rocketdyne 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 currently used on the Space Launch System (SLS). Designed and manufacture ...

engines, two

Space Shuttle The Space Shuttle is a retired, partially 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. Its official program na ...

-derived five-segment

solid rocket boosters A solid rocket booster (SRB) is a large solid propellant motor used to provide thrust in spacecraft launches from initial launch through the first ascent. Many launch vehicles, including the Atlas V, SLS and space shuttle, have used SRBs to giv ...

, and an

(ICPS)

upper stage A multistage rocket or step rocket is a launch vehicle that uses two or more rocket ''stages'', each of which contains its own engines and propellant. A ''tandem'' or ''serial'' stage is mounted on top of another stage; a ''parallel'' stage is ...

. NASA will develop the EUS to increase SLS performance beyond Block 1 specifications. The improved upper stage was originally named the Dual Use Upper Stage (DUUS, pronounced "duce") but was later renamed the Exploration Upper Stage (EUS) due to DUUS sounding like a profanity in Japanese. In 2014, NASA announced that it would proceed with development of Block 1B with the EUS and would use it on EM-2. In April 2016, it was reported that NASA has chosen to use a design based on four RL10-C3 engines for the EUS, and in October 2016 NASA confirmed they had ordered 10 of the engines. In 2018, it was decided to optimise EUS for payload to lunar missions, by using smaller tanks.''NASA completes Exploration Upper Stage CDR, focuses new office on SLS Block 1B development''
Feb 2021. By February 2020, the development contract for EUS had been delayed, and NASA was planning to use ICPS for the first three launches of SLS.''Upper Stage RL10s arrive at Stennis for upcoming SLS launches''
February 2020.

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 product ...

announced on 21 December 2020 that the Exploration Upper Stage (EUS) of the SLS completed a

critical design review In the United States military integrated acquisition lifecycle the Technical section has multiple acquisition "Technical Reviews". Technical reviews and audits assist the acquisition and the number and types are tailored to the acquisition. Over ...

(CDR) with

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

. That review confirmed the design of the EUS, allowing Boeing to proceed with development of the stage, including hardware fabrication.

Funding History

Cost concerns and alternatives

Due to the possible cost of EUS (about US$800 million each), NASA invited proposals for alternatives, but in May 2019 rejected Blue Origin's proposal.''NASA rejects Blue Origin's offer of a cheaper upper stage for the SLS rocket'' May 2019
/ref> NASA ordered eight EUSs from Boeing.

Notes

References

{{Upper stages Space Launch System Rocket stages

Development

Funding History

Cost concerns and alternatives

See also

Notes

References