[8][9] NASA will develop the EUS to increase SLS performance for trans-lunar injection beyond Block 1 specifications.

[11] In 2014, NASA announced that it would proceed with development of Block 1B with the EUS[12] and would use it on Exploration Mission 2, now referred to as Artemis II.

[16] Boeing announced on 21 December 2020 that the 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.

[17] In March 2022, Boeing discussed the possibility of using a carbon composite liquid oxygen tank on the EUS, offering mass savings of up to 30%.