NASA made the public call this week to remove the planned lunar landing from Artemis III, as both SpaceX’s Starship derived Human Landing System and Blue Origin’s Blue Moon continued to fall behind. However alongside that decision came a surprising call to replace the under construction Exploration Upper Stage with yet another new rocket stage for Artemis IV and V. NASA Administrator Jared Isaacman claimed this move was to accelerate these missions, but many within the industry are questioning whether this will actually accelerate things.

HLS and Scaling Back Artemis III

The Human Landing System program has continued to fall behind. The first lander contracted, SpaceX’s Starship derived lunar lander, was supposed to reach the lunar surface in 2024. That date very quickly came and went but at the same time so did the planned dates for Artemis II and III. However as the schedule began to settle down for Artemis II and Artemis III, delays continued to add up for the HLS program and the viability of flying a crewed landing on Artemis III became a questionable task at best.

In October of 2025, then acting administrator Sean Duffy elected to open up the contract for the Artemis III landing attempt to allow either SpaceX or Blue Origin, who had been on boarded with their Blue Moon lander to the HLS program in 2023, to provide the services for this mission. Despite this, neither lander looked to be ready by 2027.

After a few more months of waiting and continued delays to both HLS options, a decision was made to make Artemis III a test flight akin to that of Apollo 9. This new profile will have the Orion spacecraft rendezvous with a prototype of one or both HLS landers in Earth orbit. This mission is a needed change of pace for Artemis and allows for a combined effectiveness test of the vehicles before performing operations in deep space.

This new mission profile also allows NASA to fly out the final Block 1 version of the SLS rocket as soon as possible, something manufacturer Boeing has been keen on doing. This fly out would allow them to implement the Block 1B vehicle as soon as possible and enable smoother launch to launch operations with the more cohesive vehicle than the interim Block 1. However NASA administrator Jared Isaacman had a different plan.

Isaacman’s Surprise Announcement

During the press conference to announce the new plan for Artemis III, Jared Isaacman announced that Artemis IV and V would be a pair of lunar landings both in 2028. This plan to accelerate these missions was ambitious, but one that the providers of the SLS rocket and Orion spacecraft were prepared to step up to when asked if they could earlier in the year.

However what these companies were not prepared for was the sudden announcement that these missions would not use the SLS Block 1B vehicle they had been developing, and instead use an entirely new upper stage for Artemis IV and V he dubbed the “Standardized Upper Stage”.

This new variant of the SLS rocket would be similar in performance to the current Block 1 vehicle, and be primarily focused on delivering just Orion to the Moon for Artemis missions. In the conference he claimed this rocket could be ready to fly twice in 2028, approximately 10 months apart from each other. This gives teams less than two years to go from nothing to a flight ready, crew rated stage on the launch pad in Florida.

“Just” A New Upper Stage

The first major issue is, of course, designing this new upper stage itself. While details are sparse on the stage, a render shared by NASA implied that this stage would be derived from United Launch Alliance’s Centaur V. Converting an upper stage to use on a different rocket is not an impossible task, it’s how the ICPS was built based off of the DCSS, however it is not a simple task. The work needed to convert the DCSS to the ICPS took five years and included stretching the hydrogen tank, adding additional hydrazine bottles for control, and strengthening the stage to handle the different loads from the SLS rocket. Centaur V would need to go through a similar upgrade path before being flight ready, and that’s before touching the vehicle interfaces.

There are three main components this new stage needs to interface with. The SLS Core Stage, Orion Spacecraft, and the Mobile Launcher. Centaur V cannot reuse the systems built for ICPS, as the stage’s dimension differ significantly from the ICPS. The simplest of these new adapters would be to connect the Centaur V to Orion, as they share a common diameter. This allows for a relatively simple structure similar to payload adapters used in the past. The adapter between Centaur V and the SLS core itself however presents a far more complex issue.

This new adapter would be significantly flatter than the LVSA currently used by Block 1 to keep Orion in line with the Crew Access Arm and Umbilical on Mobile Launcher 1. This structure would also need to be significantly stronger than the current LVSA to handle the higher aerodynamic loading, and further work would need to be done to verify that the new profile does not significantly change the aerodynamic effects on components located below the adapter.

The connections with the launch pad would also need to be completely redone. While the basic structure of the ICPS Umbilical might be able to be salvaged, most of the plumbing would need to be reworked to support the umbilical connections used by a new stage. This process of retrofitting would however need to wait until after Artemis III to begin, as that flight is still planned to use the ICPS.

Another problem is on the Core Stages themselves, the current in progress builds of Core Stages 4 and 5 would need to be retrofitted back to the Block 1 configuration. While structurally these systems are identical, the avionics suite on board is significantly less complicated on the Block 1B core stage, as it is designed to fly with EUS commanding the entire ascent. On Block 1 and presumably with the new upper stage, the core operates fully independently, with the rocket effectively flying as two different rockets at the same time.

What About EUS?

Despite all of the issues above in creating a new upper stage for another SLS configuration, perhaps the most pressing one is why not use EUS? If the goal as Isaacman claimed was to accelerate SLS, why pivot away from a stage that is already moving through manufacturing and testing.

EUS has not had a smooth development, with support for it being tepid for most of its early days. It finally was fully supported with the NASA Authorization Act of 2022, which laid out that the stage would be used no later than Artemis IV. Since then development of the stage and its associated components have continued across the SLS facilities.

The most apparent of these is the near completion of Mobile Launcher 2 near the Vehicle Assembly Building. The structure was designed with lessons learned from Mobile Launcher 1 and the SLS program as a whole to reduce turnaround time between launches and reduce long term operating costs. It has also already been fully outfitted with the umbilical suite to support the SLS Block 1B rocket from day one, completing one of the major tasks in developing the upgraded rocket.

However at the Michoud Asssembly Facility, work on the first EUS Units, the Structural Test Article and the first flight unit, has steadily gone from a design to full sets of hardware. Ironically, during the press conference to announce the Standard Upper Stage, the liquid hydrogen tank for the STA completed its final weld, the final weld of the entire STA.

The flight unit is not far behind, with barrels and domes being welded for integration later this year. The flight unit will also be tested at the Stennis Space Center on the B2 test stand, the same one used by the Core Stage in 2020 and 2021 for its Green Run campaign. That stand has just finished being modified to accept the EUS and conduct full mission environment testing including a nearly 20 minute long burn of its main engines.

The state of EUS production has raised a simple but huge question about this pivot. How is starting from square one going to be faster or cheaper than using what you’ve already made to do the same job?

In a statement published by NASA, Associate Administrator Amit Kshatriya attempted to answer this and said “It is needlessly complicated to alter the configuration of the SLS and Orion stack to undertake subsequent Artemis missions,”. However, the new Standard Upper Stage is still a drastic design departure from the current Block 1 vehicle, and would be treated as a first time operation, just as the first EUS flight would be.

Time will tell if this plan will at all be implemented, but with so many questions unanswered and less than two years to develop, test, crew rate, and fly a new upper stage, the odds are certainly against it working.