Exploration Upper Stage
{{short description|Rocket stage in NASA's Space Launch System}}
{{Use American English|date=July 2014}}
{{Use dmy dates|date=August 2024}}
{{Infobox rocket stage
| name = Exploration Upper Stage
| image = Exploration Upper Stage 2020 Design.png{{!}}upright
| caption = 2020 design of the Exploration Upper Stage
| manufacturer = Boeing{{Cite web |date=4 July 2014 |title=NASA, Boeing Finalize US$2.8 billion SLS Core Stage Contract |url=http://www.spacenews.com/article/civil-space/41139nasa-boeing-finalize-28b-sls-core-stage-contract |url-status=dead |archive-url=https://archive.today/20140727032517/http://www.spacenews.com/article/civil-space/41139nasa-boeing-finalize-28b-sls-core-stage-contract |archive-date=27 July 2014 |access-date=25 July 2014 |publisher=SpaceNews}}
| country = United States
| rockets = Space Launch System (Block 1B/2){{Cite web |title=Space Launch System Fact Sheet |url=https://www.nasa.gov/sites/default/files/atoms/files/sls_fact_sheet.pdf |access-date=16 May 2023 |publisher=NASA}}
| diameter = {{Unbulleted list
| LH2 tank: {{cvt|8.4|m}}
| LOX tank: {{cvt|5.5|m}}{{Cite web |title=1 year down, a galaxy to go |url=https://www.boeing.com/features/2024/02/one-year-down-a-galaxy-to-go |access-date=13 April 2024 |publisher=Boeing}}
}}
| propmass = {{cvt|129000|kg}}
| stagedata = {{Infobox rocket/stage
| name = Engine details
| engines = 4 × RL10C-3
| thrust = {{cvt|97360|lbf|kN|order=flip}}
| burntime = 1,275 seconds
}}
}}
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 {{cvt|97360|lbf|kN|order=flip}}. Its first flight is planned for Artemis IV in 2028.{{Cite web |last=Foust |first=Jeff |date=30 October 2022 |title=Lunar landing restored for Artemis IV mission |url=https://spacenews.com/lunar-landing-restored-for-artemis-4-mission/ |access-date=31 October 2022 |website=SpaceNews}} 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.{{Cite web |title=SLS |url=http://space.skyrocket.de/doc_lau/sls.htm |access-date=25 July 2014 |publisher=Gunter's Space Page}}{{Cite web |title=Space Launch System Data Sheet |url=http://www.spacelaunchreport.com/sls0.html |url-status=usurped |archive-url=https://archive.today/20130411204255/http://www.spacelaunchreport.com/sls0.html |archive-date=11 April 2013 |access-date=25 July 2014 |publisher=SpaceLaunchReport.com}}
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"),{{Cite web |date=June 2013 |title=SLS prepares for PDR – Evolution eyes Dual-Use Upper Stage |url=http://www.nasaspaceflight.com/2013/06/sls-pdr-evolved-rocket-dual-upper-stage/ |access-date=25 July 2014 |publisher=NASASpaceflight.com}} but was later renamed the Exploration Upper Stage (EUS) due to concerns that DUUS sounded like a profanity in Japanese.{{Cite web |last=Bergin |first=Chris |date=28 March 2014 |title=SLS positioning for ARRM and Europa missions |url=http://www.nasaspaceflight.com/2014/03/sls-positioning-arrm-europa-missions/ |access-date=8 November 2014 |publisher=NASASpaceflight.com}}
In 2014, NASA announced it would proceed with development of the Block 1B configuration using the EUS,{{Cite web |last=Bergin |first=Chris |date=30 July 2012 |title=Wind Tunnel testing conducted on SLS configurations, including Block 1B |url=http://www.nasaspaceflight.com/2012/07/wind-tunnel-testing-sls-configurations-block-1b/ |access-date=12 March 2015 |publisher=NASASpaceFlight.com}} initially planning to use it on Exploration Mission 2, now referred to as Artemis II.{{Cite web |date=6 June 2014 |title=NASA confirms EUS for SLS Block IB design and EM-2 flight |url=http://www.nasaspaceflight.com/2014/06/nasa-confirms-eus-sls-block-ib-design-em-2-flight/ |access-date=25 July 2014 |publisher=NASASpaceflight.com}} In April 2016, NASA selected a design using four RL10-C3 engines for the EUS, and in October 2016 confirmed an order for 10 of the engines.{{Cite web |date=21 October 2016 |title=Proven Engine Packs Big, In-Space Punch for NASA's SLS Rocket |url=https://www.nasa.gov/exploration/systems/sls/proven-engine-packs-big-in-space-punch-for-nasa-s-sls-rocket.html |access-date=18 November 2021 |publisher=NASA}}
In 2018, NASA decided to optimize the EUS for lunar missions by using smaller tanks.[https://www.nasaspaceflight.com/2021/02/nasa-completes-exploration-upper-stage-cdr-focuses-new-office-on-sls-block-1b-development/ NASA completes Exploration Upper Stage CDR, focuses new office on SLS Block 1B development]. Feb 2021. By February 2020, delays in the development contract led NASA to plan on using the ICPS for the first three SLS launches.[https://www.nasaspaceflight.com/2020/02/upper-stage-rl-10s-stennis-sls-launches/ Upper Stage RL10s arrive at Stennis for upcoming SLS launches]. February 2020.
On 21 December 2020, Boeing announced that the EUS had completed a critical design review (CDR) with NASA, allowing hardware development to proceed.{{Cite web |date=22 December 2020 |title=SLS Exploration Upper Stage passes review |url=https://spacenews.com/sls-exploration-upper-stage-passes-review/ |access-date=22 December 2020 |publisher=SpaceNews}}
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%.{{Cite web |date=28 January 2016 |title=With all-composite cryogenic tank, Boeing eyes mass-reducing space, aviation applications |url=https://www.compositesworld.com/articles/nasaboeing-composite-launch-vehicle-fuel-tank-scores-firsts |access-date=2 June 2024}}
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.{{Cite news |last=Berger |first=Eric |author-link=Eric Berger (journalist) |date=2 May 2025 |title=White House budget seeks to end SLS, Orion, and Lunar Gateway programs |url=https://arstechnica.com/space/2025/05/white-house-budget-seeks-to-end-sls-orion-and-lunar-gateway-programs/ |access-date=2 May 2025 |work=Ars Technica}}{{Cite press release |title=President Trump's FY26 Budget Revitalizes Human Space Exploration |date=2 May 2025 |publisher=NASA |url=https://www.nasa.gov/news-release/president-trumps-fy26-budget-revitalizes-human-space-exploration/ |last1=Dooren |first1=Jennifer M. |last2=Stevens |first2=Bethany |access-date=2 May 2025 |id=25-035}} The proposal described the SLS program as "grossly expensive" and exceeding its budget, and allocated funding to transition to "more cost-effective commercial systems".{{Cite web |date=2 May 2025 |title=Fiscal Year 2026 Discretionary Budget Request |url=https://www.whitehouse.gov/wp-content/uploads/2025/05/Fiscal-Year-2026-Discretionary-Budget-Request.pdf |access-date=2 May 2025 |website=United States Office of Management and Budget |page=37}}
= Funding history =
| class="wikitable" |
| Fiscal year
! Nominal ! Inflation adjusted |
|---|
| 2016
| $77.0 | $98.9 |
| 2017
| $377.4 |
| 2018
| $368.1 |
| 2019
| $180.6 |
| 2020
| $353.4 |
| 2021
| $400.0{{Cite web |date=June 2021 |title=NATIONAL AERONAUTICS AND SPACE ADMINISTRATION FY 2021 SPENDING PLAN FOR APPROPRIATIONS PURSUANT TO P.L. 116-260 |url=https://www.nasa.gov/wp-content/uploads/2021/04/updated_fy_2021_spend_plan_june_2021.pdf |access-date=2 June 2024}}{{efn|The spending plan indicates that this is for "Block 1B (non-add) (including EUS)"}} | $454.0 |
| 2022
| $684.4 |
| 2023
| $669.0 |
| 2024
| $600.0 |
| Total
! $3,412.0 ! $3,785.9 |
See also
Notes
{{Notelist}}