Engineering:Exploration Upper Stage

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Short description: Rocket stage in NASA's Space Launch System
Exploration Upper Stage
2020 design of the Exploration Upper Stage
ManufacturerBoeing[1]
Country of originUnited States
Used onSpace Launch System (Block 1B/2)[2]
General characteristics
Height17.3 m (57 ft)[3]
Diameter
  • LH2 tank: 8.4 m (28 ft)
  • LOX tank: 5.5 m (18 ft)[4]
Propellant mass129,000 kg (284,000 lb)
Empty mass14,110 kg (31,110 lb)[5]
Engine details
Engines4 × RL10C-3[3]
Thrust433.1 kN (97,360 lbf)
Specific impulse460.1 s (4.512 km/s)[6]
Burn time1,275 seconds
FuelLH2 / LOX

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 Stage used on the Block 1 variant. The EUS will be powered by four RL10C-3 engines burning liquid oxygen and liquid hydrogen, generating a total thrust of 433.1 kN (97,360 lbf). Its first flight is planned for Artemis IV in 2028.[7] However, the Trump administration has proposed terminating the SLS program after Artemis III, which would eliminate the need for the EUS.

Development

The Block 1 configuration of the SLS, which first flew the Artemis I mission, has a core stage powered by four RS-25 engines, two Space Shuttle-derived five-segment solid rocket boosters, and an Interim Cryogenic Propulsion Stage (ICPS) upper stage.[8][9]

NASA is developing the EUS to increase SLS performance for trans-lunar injection beyond Block 1 specifications. The improved upper stage was originally named the Dual Use Upper Stage (DUUS, pronounced "duce"),[10] but was later renamed the Exploration Upper Stage (EUS) due to concerns that DUUS sounded like a profanity in Japanese.[11]

In 2014, NASA announced it would proceed with development of the Block 1B configuration using the EUS,[12] initially planning to use it on Exploration Mission 2, now referred to as Artemis II.[13] In April 2016, NASA selected a design using four RL10-C3 engines for the EUS,[6] and in October 2016 confirmed an order for 10 of the engines.[14]

In 2018, NASA decided to optimize the EUS for lunar missions by using smaller tanks.[15] By February 2020, delays in the development contract led NASA to plan on using the ICPS for the first three SLS launches.[16]

On 21 December 2020, Boeing announced that the EUS had completed a critical design review (CDR) with NASA, allowing hardware development to proceed.[17]

In March 2022, Boeing explored the use of a carbon composite liquid oxygen tank on the EUS, which could reduce mass by up to 30%.[18]

On 2 May 2025, the Trump administration released its fiscal year 2026 budget proposal, which called for terminating the SLS and Orion spacecraft programs after Artemis III.[19][20] The proposal described the SLS program as "grossly expensive" and exceeding its budget, and allocated funding to transition to "more cost-effective commercial systems".[21]

Funding history

Fiscal
year 		Nominal
(in millions) 		Inflation adjusted
(FY24, in millions)[22]
2016 $77 $98.9
2017 $300[23] $377.4
2018 $300[24] $368.1
2019 $150[25] $180.6
2020 $300[26] $353.4
2021 $400[27][lower-alpha 1] $454
2022 $636.7[28] $684.4
2023 $648.3[29] $669
2024 $600[30] $600
Total $3,412 $3,785.9

See also

Notes

  1. ↑ The spending plan indicates that this is for "Block 1B (non-add) (including EUS)"

References

  1. ↑ "NASA, Boeing Finalize US$2.8 billion SLS Core Stage Contract". SpaceNews. 4 July 2014. http://www.spacenews.com/article/civil-space/41139nasa-boeing-finalize-28b-sls-core-stage-contract. 
  2. ↑ "Space Launch System Fact Sheet". NASA. https://www.nasa.gov/sites/default/files/atoms/files/sls_fact_sheet.pdf. 
  3. ↑ 3.0 3.1 "Space Launch System". Spaceflight Insider. 9 September 2018. https://www.spaceflightinsider.com/hangar/sls/. 
  4. ↑ "1 year down, a galaxy to go". Boeing. https://www.boeing.com/features/2024/02/one-year-down-a-galaxy-to-go. 
  5. ↑ Donahue, Benjamin; Sigmon, Sheldon; Cooper, Darby (9 July 2018). "The NASA SLS Exploration Upper Stage Development & Mission Opportunities" (in en). 2018 Joint Propulsion Conference. Cincinnati, Ohio: American Institute of Aeronautics and Astronautics. doi:10.2514/6.2018-4639. ISBN 978-1-62410-570-8. https://arc.aiaa.org/doi/10.2514/6.2018-4639. 
  6. ↑ 6.0 6.1 "RL10 Engine". https://www.rocket.com/space/liquid-engines/rl10-engine. 
  7. ↑ Foust, Jeff (30 October 2022). "Lunar landing restored for Artemis IV mission". https://spacenews.com/lunar-landing-restored-for-artemis-4-mission/. 
  8. ↑ "SLS". Gunter's Space Page. http://space.skyrocket.de/doc_lau/sls.htm. 
  9. ↑ "Space Launch System Data Sheet". SpaceLaunchReport.com. http://www.spacelaunchreport.com/sls0.html. 
  10. ↑ "SLS prepares for PDR – Evolution eyes Dual-Use Upper Stage". NASASpaceflight.com. June 2013. http://www.nasaspaceflight.com/2013/06/sls-pdr-evolved-rocket-dual-upper-stage/. 
  11. ↑ Bergin, Chris (28 March 2014). "SLS positioning for ARRM and Europa missions". NASASpaceflight.com. http://www.nasaspaceflight.com/2014/03/sls-positioning-arrm-europa-missions/. 
  12. ↑ Bergin, Chris (30 July 2012). "Wind Tunnel testing conducted on SLS configurations, including Block 1B". NASASpaceFlight.com. http://www.nasaspaceflight.com/2012/07/wind-tunnel-testing-sls-configurations-block-1b/. 
  13. ↑ "NASA confirms EUS for SLS Block IB design and EM-2 flight". NASASpaceflight.com. 6 June 2014. http://www.nasaspaceflight.com/2014/06/nasa-confirms-eus-sls-block-ib-design-em-2-flight/. 
  14. ↑ "Proven Engine Packs Big, In-Space Punch for NASA's SLS Rocket". NASA. 21 October 2016. https://www.nasa.gov/exploration/systems/sls/proven-engine-packs-big-in-space-punch-for-nasa-s-sls-rocket.html. 
  15. ↑ NASA completes Exploration Upper Stage CDR, focuses new office on SLS Block 1B development. Feb 2021.
  16. ↑ Upper Stage RL10s arrive at Stennis for upcoming SLS launches. February 2020.
  17. ↑ "SLS Exploration Upper Stage passes review". SpaceNews. 22 December 2020. https://spacenews.com/sls-exploration-upper-stage-passes-review/. 
  18. ↑ "With all-composite cryogenic tank, Boeing eyes mass-reducing space, aviation applications". 28 January 2016. https://www.compositesworld.com/articles/nasaboeing-composite-launch-vehicle-fuel-tank-scores-firsts. 
  19. ↑ Berger, Eric (2 May 2025). "White House budget seeks to end SLS, Orion, and Lunar Gateway programs". Ars Technica. https://arstechnica.com/space/2025/05/white-house-budget-seeks-to-end-sls-orion-and-lunar-gateway-programs/. 
  20. ↑ Dooren, Jennifer M.; Stevens, Bethany (2 May 2025). "President Trump's FY26 Budget Revitalizes Human Space Exploration" (Press release). NASA. 25-035. Retrieved 2 May 2025.
  21. ↑ "Fiscal Year 2026 Discretionary Budget Request". 2 May 2025. p. 37. https://www.whitehouse.gov/wp-content/uploads/2025/05/Fiscal-Year-2026-Discretionary-Budget-Request.pdf. 
  22. ↑ "NASA FY24 Inflation Tables – to be utilized in FY24". NASA. p. Inflation Table. https://www.nasa.gov/wp-content/uploads/2024/02/2023-nasa-new-start-inflation-index-for-fy24-final.xlsx.  Public Domain This article incorporates text from this source, which is in the public domain.
  23. ↑ "NASA outlines plan for 2024 lunar landing". SpaceNews. 1 May 2019. https://spacenews.com/nasa-outlines-plan-for-2024-lunar-landing/. 
  24. ↑ Berger, Eric (20 May 2019). "NASA's full Artemis plan revealed: 37 launches and a lunar outpost". Ars Technica. https://arstechnica.com/science/2019/05/nasas-full-artemis-plan-revealed-37-launches-and-a-lunar-outpost/. 
  25. ↑ Sloss, Philip (18 December 2019). "Amid competing priorities, Boeing redesigns NASA SLS Exploration Upper Stage". NASASpaceFlight.com. https://www.nasaspaceflight.com/2019/12/amid-priorities-boeing-redesigns-nasa-sls-eus/. 
  26. ↑ "NATIONAL AERONAUTICS AND SPACE ADMINISTRATION FY 2020 SPENDING PLAN FOR APPROPRIATIONS PROVIDED BY P.L. 116-93 and P.L. 116-136". July 2020. https://www.nasa.gov/wp-content/uploads/2023/06/fy-2020-spend-plan-update.pdf. 
  27. ↑ "NATIONAL AERONAUTICS AND SPACE ADMINISTRATION FY 2021 SPENDING PLAN FOR APPROPRIATIONS PURSUANT TO P.L. 116-260". June 2021. https://www.nasa.gov/wp-content/uploads/2021/04/updated_fy_2021_spend_plan_june_2021.pdf. 
  28. ↑ "NATIONAL AERONAUTICS AND SPACE ADMINISTRATION FY 2022 SPENDING PLAN FOR APPROPRIATIONS PROVIDED BY P.L. 117-103". July 2022. https://www.nasa.gov/wp-content/uploads/2022/03/fy_2022_spend_plan_july_2022.pdf. 
  29. ↑ "NATIONAL AERONAUTICS AND SPACE ADMINISTRATION FY 2023 SPENDING PLAN FOR APPROPRIATIONS PROVIDED BY P.L. 117-328". March 2023. https://www.nasa.gov/wp-content/uploads/2023/10/nasa-fy-2023-spending-plan.pdf. 
  30. ↑ "COMMERCE, JUSTICE, SCIENCE, AND RELATED AGENCIES APPROPRIATIONS ACT, 2024". March 2024. https://docs.house.gov/billsthisweek/20240304/FY24%20CJS%20Conference%20JES%20scan%203.3.24.pdf. 



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