NASA has made a strategic decision to terminate the long-standing and problematic Exploration Upper Stage (EUS) project, an advanced upper stage for the lunar SLS rocket, which was being developed by Boeing. As reported by news agencies, including Reuters and Bloomberg, the U.S. space agency will instead turn to the United Launch Alliance (ULA) consortium to request a modified version of the Vulcan Centaur rocket to serve as the upper stage for heavier Artemis program missions. This decision represents a serious blow to Boeing, which loses a key contract in NASA's flagship endeavor, and a significant acceleration of the schedule through the use of existing, commercial technology.
End of Boeing's Project
NASA has officially terminated work on the Exploration Upper Stage (EUS), the advanced upper stage of the SLS rocket, which had been under development by Boeing for years. The project was criticized for massive delays and cost overruns, becoming a bottleneck for the Artemis program.
New Supplier: ULA Vulcan
In place of the EUS, NASA intends to use a modified version of the Vulcan Centaur rocket, produced by the United Launch Alliance consortium (a joint venture of Boeing and Lockheed Martin). This rocket is to be adapted to serve as the upper stage for the SLS Block 1B configuration, starting with the Artemis IV mission.
Reasons for the Change
The decision was driven by the need to accelerate the schedule of lunar missions. The ready and already tested Vulcan rocket offers a faster implementation path than continuing the delayed EUS project. This will allow NASA to focus on other elements of the Artemis program.
Consequences for Boeing and the Program
For Boeing, losing the EUS contract is a serious reputational and financial blow in a key space program. For NASA, however, it represents a chance to unlock the schedule and reduce dependence on a single, unreliable supplier of a critical component.
The U.S. space agency NASA has made a radical decision to abandon the long-standing and problematic advanced upper stage project Exploration Upper Stage (EUS), which was being developed by Boeing for the flagship lunar rocket Space Launch System (SLS). The information about the project's termination, based on sources within the agency, was first reported in a metaphorical manner by the Ars Technica website. This decision officially closes a chapter that for years had been a bottleneck for the entire program. The Artemis program, officially announced in 2017, is the successor to the legendary Apollo program of the 1960s and 70s. Its goal is not only to return humans to the Moon but also to establish a sustained presence through the construction of the Gateway orbital station and a surface base, which requires regular, advanced supply and crewed missions. The direct cause of this radical change was the chronic delays and uncontrolled cost overruns of the EUS project. This stage was essential for missions Artemis IV and beyond, as it was supposed to provide significantly greater payload capacity and trajectory precision than the currently used temporary Interim Cryogenic Propulsion Stage (ICPS). In response, NASA turned to the commercial sector, where proven technologies are already available. As reported by Bloomberg and Reuters, the agency chose a solution from the United Launch Alliance (ULA) consortium. This involves delivering a modified version of the Vulcan Centaur rocket to serve as the upper stage for the SLS Block 1B configuration. The Vulcan rocket already had a successful maiden flight in 2023, and its use is expected to allow NASA to bypass years of delays associated with the EUS. For Boeing, which is one of the main contractors for the entire SLS rocket, losing the contract for a key component is a serious blow. The company has struggled for years with technical and financial problems in developing the EUS. Meanwhile, ULA, a joint venture of Boeing and Lockheed Martin, paradoxically benefits from this decision, strengthening its position in the Artemis program. This change reflects a broader trend at NASA, involving greater use of commercial, off-the-shelf solutions instead of long-term and costly development programs led by traditional agency contractors. The decision has not yet been officially announced by NASA, but according to sources cited by press agencies, it is already a done deal and is expected to be finalized soon.