On April 20th, NASA transferred the core stage of the third SLS rocket from the Michoud Assembly Facility in New Orleans to the Pegasus barge. This barge will transport the crucial component to the Kennedy Space Center in Florida for its final integration phases. The core stage is the primary and largest part of the launch vehicle, housing the liquid hydrogen and oxygen tanks, the intertank, and the forward skirt. Notably, the four RS-25 engines that will propel it into space were not yet attached during this transport.
According to NASA, this transfer signifies a major milestone in the preparation for the Artemis III mission, currently projected for 2027. Upon arrival in Florida, the core stage will be fitted with its engines and then vertically integrated with the other rocket elements: the side boosters, the interstage, the second stage, and the Orion capsule.
This massive stage stands approximately 64.6 meters tall and will hold nearly 3 million liters of cryogenic propellants (liquid oxygen and hydrogen) to fuel the four RS-25 engines. During launch, the core stage will power the engines for over eight minutes. Boeing is responsible for the design and assembly of the core stage, while L3Harris is in charge of the RS-25 engines.
For Artemis II, the first stage was moved from Michoud Assembly Facility on July 16, 2024, 624 days before the launch of the second Artemis mission. However, that timeline was influenced by the mission’s specific requirements and concerns regarding Orion’s heat shield, which led to multiple mission postponements in 2024 and 2025.
Uncertainties Surrounding Artemis III
The transfer of the SLS core stage is a particularly noteworthy and anticipated event following the completion of Artemis II. Initial assessments released by NASA indicated that both Orion and the SLS rocket performed as expected, which is not a given.
However, many questions remain unanswered regarding the role of Artemis III. On February 27th, NASA announced an update to the Artemis architecture: Artemis III will no longer be the mission for the first crewed lunar landing. Instead, it will be a demonstration flight in low Earth orbit to test rendezvous and docking maneuvers between Orion and one or more commercial landers. The first attempt at a crewed lunar landing is now assigned to Artemis IV, planned for 2028.
Details about Artemis III have not yet been fully clarified. It is unknown on which orbit the docking test between Orion and the landers will take place. Depending on this decision, it remains unclear whether the SLS will require a second stage, and if so, which one. NASA’s rocket is theoretically capable of taking Orion to a low Earth orbit at an altitude of 500 km even without a second stage. Furthermore, NASA possesses only one ICPS second stage (the one used for Artemis I and II) and may reserve it for the Artemis IV mission, where maximum safety will be paramount.
The adoption of an alternative second stage, the same one used by ULA’s Vulcan rocket, aligns with NASA’s strategy to increase mission frequency, standardize the SLS configuration, and expedite the preparation of subsequent flights.
