The SLS program continues with preparations for the first human spaceflight to the Moon’s vicinity since 1972. Currently scheduled for April 2026, the mission’s date could be moved up to as early as February if no major issues arise. Meanwhile, the program’s future faces uncertainties as the proposed NASA budget for Fiscal Year 2026 aims to end the SLS and Orion programs after the Artemis III lunar landing.
The SLS for Artemis II is now fully stacked on Mobile Launcher 1, missing only the Orion and its ascent abort motor fairing. NASA started stacking Artemis II’s two five-segment solid rocket boosters in November 2024. Workers completed the boosters’ stacking on Feb. 19 when the forward assemblies — containing the nose cones, avionics, and separation motors — were attached to the boosters.
The solid rocket boosters, derived from the boosters that powered 135 Space Shuttle flights, originally were certified to be stacked no more than one year before flight. NASA studied the problem and approved waivers prior to the Artemis I launch based on its analysis of how the boosters handled the stresses of being stacked upright for long periods of time.
The Artemis II SLS Launch Vehicle Stage Adapter installation onto the core stage. (Credit: NASA)
The SLS core stage, undergoing processing in the Vehicle Assembly Building (VAB)’s High Bay 2, was stacked between the boosters on March 23 at the VAB High Bay 3, where Mobile Launcher 1 stands. On April 3, teams lifted the Launch Vehicle Stage Adapter (LVSA), which connects the core stage to the second stage, or Interim Cryogenic Propulsion Stage (ICPS). Connecting the two elements finished on April 12, when hard mate was completed.
However, some unexpected work was needed after NASA stacked the core stage. A hydraulic leak in a main oxidizer valve actuator in one of the SLS core stage’s four RS-25 engines caused NASA to order an engine replacement. The number four engine, E2063, is now off the stack, with E2061 installed in its place by the end of April.
E2063 was assembled in 2015 using some parts that had flown on previous Shuttle missions but had never flown. After the engine’s repair, it will fly on a future flight if the SLS program continues. Its replacement, E2061, received its certification for flight in 2008 and flew on the STS-130 and STS-134 missions, some of the last before Shuttle’s retirement. E2061 was originally assigned for the Artemis III lunar landing mission.
Artemis II mission concept and engine information graphic. (Credit: L3Harris)
Workers swapped the engines while the core stage was in the vertical position on Mobile Launcher 1, marking the first-ever RS-25 replacement in the SLS program. Previously, RS-25s — then known as Space Shuttle Main Engines — were replaced vertically during the Space Shuttle program.
The engine replacement, finished by the end of April, is not expected to affect the timeline for Artemis II’s flight readiness. With the core stage for Artemis II completed, the mission’s second stage became the next item to be stacked. Following its arrival on at the VAB April 15, NASA mated the ICPS, derived from the Delta family’s upper stage, to the Artemis II stack’s LVSA on Thursday, May 1.
The next lift activity involving Artemis II will not take place for several months. During the intervening period, systems are to undergo checkout on the stacked vehicle and its ground launch control systems. The Mobile Launcher 1 umbilicals and plates need connecting to the SLS; the umbilicals provide the SLS with power, cooling, and fluids while also allowing data to be exchanged between the rocket and launch control.
The Orion spacecraft for Artemis II moving to the Multi-Payload Processing Facility. (Credit: NASA)
The Orion spacecraft for Artemis II finished final assembly by the end of April before being handed over by Lockheed Martin to NASA Exploration Ground Systems on May 1. On Saturday, May 3, Orion moved from the Operations and Checkout Building at the Kennedy Space Center (KSC) to the Multi-Payload Processing Facility (MPPF). While at the MPPF, hypergolic propellant and other consumables are scheduled for loading onto Orion.
Once loading Orion’s commodities finishes at the MPPF, the capsule will move to the Launch Abort System Facility (LASF) for assembly and installation of the launch abort motor and shroud. The launch abort system is critical for allowing the crew to survive if an off-nominal event occurs during ascent that endangers the vehicle and spacecraft.
Orion’s move to the LASF may happen around the August timeframe, and the spacecraft’s stacking is the next major task after that. A stacking of Orion atop SLS in fall could allow a rollout of the Artemis II SLS and Mobile Launcher 1 to the launch complex around the very end of 2025 or the start of 2026.
The Artemis II crew. L to R: Jeremy Hansen, Victor Glover, Reid Wiseman, Christina Koch. (Credit: NASA)
While Artemis II’s elements were being assembled, NASA agreed to fly a South Korean CubeSat aboard the mission. NASA and the Korean space agency KASA signed an agreement on May 2 to fly the K-Rad Cube, a satellite designed to measure radiation’s effect on human tissue during the passage of the Van Allen radiation belts.
NASA is also discussing the possibility of additional CubeSat payloads, which would fly aboard the adapter connecting Orion to the ICPS upper stage. The agency signed a similar agreement with the German space agency DLR in September 2024, and recently announced the addition of a space weather CubeSat for the Saudi Space Agency.
While Artemis II is being processed in the VAB, mission elements for Artemis III are also being prepared. Artemis III’s liquid oxygen tank moved into the spray-on insulation cell at the Michoud Assembly Facility in Louisiana on April 25. The liquid hydrogen tank for this mission already had its insulation foam sprayed on, and both tanks for the core stage will be mated to the interstage before transport to KSC. The core stage’s completion is realistically possible in 2026.
Elements necessary for post-Artemis III missions are still in work for the moment. The Mobile Launcher 2, required for the SLS Block 1B and Block 2, is under construction at KSC. The sixth and seventh modules of the tower were added to the structure on April 22. In Promontory, Utah, Northrop Grumman has been preparing the first static test firing of the upgraded Booster Obsolescence and Life Extension (BOLE) solid rocket booster, although no date for this test has been announced at this time.
The Artemis III hydrogen tank moving on April 22, 2025, after application of its insulation. (Credit: NASA/Steven B. Seidel/Michael DeMocker)
The recent NASA Fiscal Year 2026 budget request would fund Artemis II and III but cancel all SLS missions from Artemis IV onward, as well as the SLS Block 1B and Block 2 vehicles. Elements of these vehicles, like the Exploration Upper Stage and BOLE face cancelation, as well as the human-tended cis-lunar Gateway space station, if the budget becomes law.
The release of the “skinny” budget request to the United States Congress is just the start of a months-long process, and both houses of Congress will need to pass the budget before it can become law. The budget cuts NASA’s top line from close to $25 billion to close to $19 billion, and the line item details will be released at a later time.
The final budget passage will depend on whether Congress supports the potential cuts, and representatives from states with SLS facilities, as well as states with other NASA activities in danger, will no doubt have their opinions on these reductions.
NASA Administrator nominee Jared Isaacman appearing before the Senate Commerce Committee on April 9. (Credit: NASA/Bill Ingalls)
Meanwhile, the Senate is in the process of installing Jared Isaacman as the next NASA Administrator. The full Senate will vote on his nomination after the Senate Commerce Committee passed the nomination on April 30 with 19 votes in favor and 9 against. Isaacman’s confirmation is expected, and he will be heavily involved in the budget process going forward.
Isaacman stated his support for not only lunar operations to be continuous, enduring, and routine, but also for the current federal law to conduct human landings on the Moon before any human Mars exploration. Committee chair Ted Cruz and Ranking Member Maria Cantwell supported the Isaacman nomination on that basis.
The next six months will likely determine the fate of the SLS, Orion, Gateway, and Artemis programs as well as the future of U.S. space exploration in general.
(Lead image: Artemis II upper stage installation atop the SLS core stage. Credit: NASA)
