Exploration Upper Stage

The Exploration Upper Stage (EUS) is being developed as a large second stage for Block 1B of the Space Launch System (SLS), succeeding Block 1's Interim Cryogenic Propulsion Stage. It will be powered by four RL10-C3 [4] engines burning liquid oxygen and liquid hydrogen to produce a total of 440 kN (99,000 lbf) thrust. As of February 2015, the SLS Block 1B will provide thrust of 105 t (103 long tons; 116 short tons).[5] The EUS is expected to first fly on Artemis IV in March 2026.[6][7]

Exploration Upper Stage
Diagram of the Exploration Upper Stage
ManufacturerBoeing[1]
Country of originUnited States
Used onSLS Block 1B[2]
General characteristics
Heightnot to exceed 18 m (59 ft)
Diameter8.4 m (28 ft)
Propellant massup to 129,000 kg (284,000 lb)
Engine details
Engines4 RL10-C3[3][4]
Thrust440 kN (99,000 lbf)
FuelLOX / LH2

Development

The Block 1 configuration of SLS will have 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 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")[10] but was later renamed the Exploration Upper Stage (EUS) due to DUUS sounding like a profanity in Japanese.[11]

In 2014, NASA announced that it would proceed with development of Block 1B with the EUS,[12] and would use it on EM-2.[2] In April 2016, it was reported that NASA has chosen to use a design based on four RL10-C3 engines for the EUS,[3] and in October 2016 NASA confirmed they had ordered 10 of the engines.[4]

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.[13]

Boeing announced on 21 December 2020 that the Exploration Upper Stage (EUS) of the SLS completed a critical design review (CDR) with NASA. That review confirmed the design of the EUS, allowing Boeing to proceed with development of the stage, including hardware fabrication.[14]

Role and comparable stages
A comparison of the EUS with the S-IVB stage of the Saturn V

The EUS is to complete the SLS's ascent phase and then re-ignite to send its payload to destinations beyond low Earth orbit. This is a similar function to the S-IVB stage of the old Saturn V rocket.

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.[15] NASA ordered eight EUS's from Boeing.[15]

See also

References
  1. "NASA, Boeing Finalize US$2.8 billion SLS Core Stage Contract". SpaceNews. 4 July 2014. Retrieved 25 July 2014.
  2. "NASA confirms EUS for SLS Block IB design and EM-2 flight". NASASpaceflight.com. 6 June 2014. Retrieved 25 July 2014.
  3. Bergin, Chris (7 April 2016). "MSFC propose Aerojet Rocketdyne supply EUS engines". NASASpaceflight.com. Retrieved 8 April 2016.
  4. Proven Engine Packs Big, In-Space Punch for NASA's SLS Rocket. October 2016 This article incorporates text from this source, which is in the public domain.
  5. "Advanced Boosters progress towards a solid future for SLS". NasaSpaceflight.com. 20 February 2015. Retrieved 12 March 2015.
  6. "NASA's Management of the Gateway Program for Artemis Missions" (PDF). OIG. NASA. 10 November 2020. p. 3. Retrieved 4 January 2021. Artemis IV is scheduled to launch in March 2026 (as of August 2020).
  7. Loff, Sarah (16 October 2019). "NASA Commits to Future Artemis Missions With More SLS Rocket Stages". NASA. Retrieved 4 January 2021. NASA aims to use the first EUS on the Artemis IV mission.
  8. "SLS". Gunter's Space Page. Retrieved 25 July 2014.
  9. "Space Launch System Data Sheet". SpaceLaunchReport.com. Retrieved 25 July 2014.
  10. "SLS prepares for PDR – Evolution eyes Dual-Use Upper Stage". NASASpaceflight.com. June 2013. Retrieved 25 July 2014.
  11. Bergin, Chris (28 March 2014). "SLS positioning for ARRM and Europa missions". NASASpaceflight.com. Retrieved 8 November 2014.
  12. Bergin, Chris (30 July 2012). "Wind Tunnel testing conducted on SLS configurations, including Block 1B". NASASpaceFlight.com. Retrieved 12 March 2015.
  13. Upper Stage RL10s arrive at Stennis for upcoming SLS launches February 2020
  14. "SLS Exploration Upper Stage passes review". SpaceNews. 22 December 2020. Retrieved 22 December 2020.
  15. NASA rejects Blue Origin's offer of a cheaper upper stage for the SLS rocket May 2019
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