National Aeronautics and Space Administration 

Space Launch System 

Exploration Upper Stage (EUS) 

The Exploration Upper Stage (EUS) will 

enable the Space Launch System (SLS) 

rocket’s future configurations to launch 

NASA’s most ambitious human and robotic 

deep space missions. The EUS will serve 

as the upper, or in-space, stage for all 

Block 1B and Block 2 SLS flights in both 

crew and cargo (with payload fairing) 

configurations. 

SLS is an advanced super heavy-lift rocket 

that serves as the backbone for the agency’s 

Artemis human exploration missions 

beyond Earth orbit. Compared to available 

commercial rockets and the initial SLS 

Block 1 rocket, the EUS enables SLS 

Block 1B and Block 2 to send heavier and 

larger payloads to deep space, provides 

daily launch opportunities for flexibility in 

mission execution, and incorporates many 

features for astronaut safety. 

Built by Boeing at NASA’s Michoud Assembly 

Facility in New Orleans, the EUS is a 

modern design that leverages state-of-theart tools and processes already developed 

and in place for manufacturing the SLS 

core stage. The core stage with four RS-25 

engines and the twin solid rocket boosters 

provide the power to send SLS along with 

its crew and/or cargo to Earth orbit. After 

reaching Earth orbit, the EUS continues 

the job of sending Orion and cargo to the 

Moon or other destinations. 

The Exploration Upper Stage (EUS) is a four-engine liquid hydrogen/liquid oxygen in-space stage on 

the Space Launch System (SLS) Block 1B and Block 2 rockets. The EUS provides numerous advantages, such as increased payload mass to deep space destinations, daily launch opportunities, and 

enhanced safety features. 

NASAfacts 
The EUS replaces the single-engine Interim 

Cryogenic Propulsion Stage (ICPS) that serves as 

the in-space stage on the initial SLS Block 1 

configuration of the rocket. With its larger liquid 

hydrogen and liquid oxygen propellant tanks feeding 

four Aerojet Rocketdyne RL10 C-3 engines, the EUS 

generates nearly four times the thrust of the ICPS, 

providing unrivaled lift capability to the SLS Block 1B 

and Block 2 rockets and making a new generation of 

crewed lunar missions possible. 

SLS Block 1B will increase payload to the Moon 

by 40%, from 27 metric tons (t) or 59,525 pounds 

(lbs.) with Block 1 to 38 t or 83,776 lbs. in the crew 

configuration and 42 t or 92,594 lbs. in the cargo 

configuration. In addition, the Block 1B 

and Block 2 rockets in the crew configuration 

can carry a large-volume 10 t (22,046 lbs.) comanifested payload to the Moon, along with the 

Orion spacecraft and crew, as part of their overall 

capability. Launching crewed missions along with 

other large payloads enables multiple large scale 

objectives to be accomplished in a single mission. 

Human involvement with space systems, such 

as habitats, improve mission success of safely 

deploying and using these systems in space or on 

the surface of the Moon or Mars. 

Designed from the ground up to support human 

missions to deep space, the EUS engines will 

burn on ascent to help place Orion in a 100 x 100 

nautical mile (nmi) circular orbit to avoid the dense 

micrometeroid and orbital debris field in lower orbits, 

allowing astronauts to safely stay longer in Earth 

orbit and check out critical systems before heading 

to the Moon. The EUS also gives mission operations 

the flexibility of daily or near-daily launch windows 

to the Moon, depending on the desired orbit. With 

Orion in a higher parking orbit and the additional 

energy available from the EUS, the stage can 

perform a burn to put Orion on a lunar trajectory one 

or more times per day. 

The EUS is composed of eight major elements: 

forward adapter, liquid hydrogen tank, aft adapter, 

midbody, liquid oxygen tank, equipment shelf, thrust 

structure, and RL10 C-3 engines. The four RL10 C-3 

engines provide redundancy so the stage can insert 

Orion on its trajectory with only three engines in the 

event there is an issue with one engine. Exposed 

sections of the EUS are enclosed by an interstage 

structure during launch. 

In contrast to the Block 1 rocket, the flight computers 

in the Block 1B and Block 2 rockets are located in 

the EUS equipment shelf instead of the core stage 

forward skirt. The three flight computers provide 

redundancy for safe operations; the rocket can 

continue to operate normally with one computer out. 

In addition, locating the flight computers in the EUS

allows them to control the entire flight, from liftoff to

separation from Orion, streamlining operations and 

reducing opportunities for failure.The stage also 

provides dual S-band communication to and from 

Orion and ground operations, giving astronauts 

greater control of the stage during rendezvous and 

docking/proximity operations with co-manifested 

payloads. 

Additional key features that the EUS provides the 

Block 1B and Block 2 rockets:

 • Fixed engine nozzles

 • Thicker structures, such as propellant

 tanks, rated to a higher safety factor

 than those on the ICPS for protection 

 from micrometeoroids and orbital debris

 • Redundant guidance, navigation, and

 control systems

 • Redundant batteries so the EUS can still safely

 complete missions with loss of a battery string

 • An advanced, automated flight safety system

that eliminates the need for an individual in the 

loop to make a flight termination decision

Forward adapter 

Liquid hydrogen tank

Aft adapter 

Midbody 

Liquid oxygen tank

Equipment shelf

Thrust structure 

RL10 C-3 engines 

 

 

The EUS for SLS Block 1B and Block 2 is a powerful, fourengine upper stage comprised of eight major components. 
 

Solid Rocket 

1Booster (2) ............_ , '. 

' 

Lat.1nch Abort Sy&-lem 

Crew Module -......., 

Seivice MOdtile ----...., 

Encapsulated Service· Module Panels -......., 

Spaoecraifl Adapter~ 

Co-Manifested Payload 

- ............. ?ayloadl A.d'apter IPlA) 

E~loralion 'Upper Stage -........ 

............. AL 10 IEngifie, (4) 

............. 

Universal Sla.ge Mapter 

= ' 

0 

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Exploration Upper Stage 

Interstage 

Expanded view of SLS Block 1B, in crew configuration (external markings under review) with Orion. The EUS is a powerful

upper stage, providing additional energy to launch strategic payloads to deep space, as well as opening daily launch 

Exploration Upper Stage Facts 

Mission Duration: 8 hrs 

Height: 54.5 ft 

Diameter: 27.6 ft 

Fueled Weight: 279,000 lbs.

Propulsion: Four Aerojet Rocketdyne 

RL10 C-3 engines 

Propellants: Liquid hydrogen and liquid oxygen

Maximum thrust: 97,360 lbs. 

windows for Artemis Moon missions. 

The EUS is a key capability in NASA’s plan to return 

astronauts to the Moon as part of the agency’s 

Artemis missions. With the ability to lift three times

more mass than available commercial launchers as 

well as a large co-manifested payload in a single 

launch, the Block 1B and Block 2 rockets enable the 

agency to reduce the number of launches required

to build infrastructure for long-term lunar exploration. 

Through NASA’s Artemis lunar exploration missions, 

the agency will use new technologies and systems to 

explore more of the Moon than ever before. Lessons 

learned from lunar missions will inform human 

missions to Mars. 
Weld confidence panels for the EUS interstage produced at NASA’s Michoud Assembly Facility.

National Aeronautics and Space Administration For more information about SLS, visit: 

George C. Marshall Space Flight Center http://www.nasa.gov/sls Huntsville, AL 35812 

www.nasa.gov/marshall http://www.twitter.com/NASA_SLS 

www.nasa.gov http://www.facebook.com/NASASLS 

http://www.instagram.com/NASAArtemis 

FS-2023-02-109-MSFC NASA Facts