NASA’s Artemis II Moon Mission Faces Crucial Wet Dress Rehearsal at Kennedy Space Center

Under the glare of floodlights at Florida’s Kennedy Space Center, NASA’s towering Space Launch System (SLS) rocket stands poised for a trial that will never leave the ground but could decide when—and how—astronauts next fly to the Moon.

As early as Saturday night, Jan. 31, engineers plan to begin pumping more than 700,000 gallons of supercold liquid hydrogen and liquid oxygen into the 322-foot-tall rocket and its Orion spacecraft at Launch Complex 39B. The wet dress rehearsal (WDR) will take the countdown to roughly half a minute before an imaginary liftoff—a high-stakes simulation NASA calls the final major integrated test before the first crewed Artemis mission.

If the fueling and countdown unfold as planned, the agency could soon set a firm date for Artemis II, a 10-day crewed flyby of the Moon launching no earlier than Feb. 6. If serious problems emerge, NASA may be forced to roll the rocket back to the Vehicle Assembly Building, delaying the first human trip to lunar space since 1972 and intensifying questions about the future of the country’s multibillion-dollar Moon program.

“This is the most daring, technically challenging, collaborative, international endeavor humanity has ever set out to do,” NASA Administrator Bill Nelson said in a briefing on Artemis progress, adding that crew safety remains the agency’s “top priority.”

Dress rehearsal for a lunar return

The WDR is designed to mimic launch day as realistically as possible without igniting engines or placing astronauts aboard.

About 49 hours before the simulated T-0, NASA’s launch team will report to stations at Kennedy’s Launch Control Center. Technicians will power up SLS and Orion, run through communications checks with ground systems and tracking networks, and prepare the pad’s propellant plumbing for cryogenic loading.

On Saturday evening, controllers intend to start flowing liquid hydrogen and liquid oxygen into the rocket’s core stage and upper stage, known as the Interim Cryogenic Propulsion Stage. Once the tanks are full and in stable replenish, the countdown will enter its final phase.

NASA plans two runs into the terminal count. In the first, controllers expect to work down to a built-in hold at 1 minute, 30 seconds, then resume to about T-minus 33 seconds—the point on a real launch day when control would pass to the automated launch sequencer. After recycling the clock to T-minus 10 minutes, the team will perform a second run to roughly the 30-second mark before intentionally cutting off, then practice draining the volatile propellants and “safing” the vehicle.

Launch Director Charlie Blackwell-Thompson has said the test is expected to reach around T-minus 29 to 30 seconds, depending on conditions and the day’s objectives.

No crew will be aboard Orion for the rehearsal, but four astronauts are waiting on the outcome. Commander Reid Wiseman, pilot Victor Glover, mission specialist Christina Hammock Koch, and Canadian Space Agency astronaut Jeremy Hansen are in preflight quarantine in Houston as they prepare to become the first people to travel to the Moon’s vicinity since Apollo 17.

Artemis II is planned as a roughly 10-day mission that will place Orion and its crew into Earth orbit before sending them on a looping trajectory around the Moon and back, following a hybrid free-return path designed to bring them home even if major systems fail.

If it launches on the current trajectory solution, Orion could carry the crew farther from Earth than any humans in history, potentially thousands of miles beyond the Moon’s far side.

Lessons from leaky dress rehearsals

The upcoming fueling test comes nearly four years after a troubled WDR campaign for Artemis I, the uncrewed precursor mission that first flew SLS and Orion.

In April 2022, NASA attempted the Artemis I wet dress rehearsal three times. Each attempt ended early—first due to faulty mobile launcher fans and gaseous nitrogen supply issues, then because of a liquid oxygen temperature problem and a malfunctioning core-stage vent valve, and finally after a liquid hydrogen leak was detected at one of the tail service mast umbilicals and a faulty helium check valve was found on the upper stage.

The rocket was rolled back to the Vehicle Assembly Building for repairs and ground facility upgrades. When SLS returned to the pad in June that year, NASA finally managed to fully fuel the rocket and count down to T-minus 29 seconds, short of an initial goal of around nine seconds. Engineers again battled a small hydrogen leak but deemed their primary test objectives met.

Those episodes prompted changes to fueling procedures—including a slower, more temperature-controlled loading process intended to reduce thermal shock to seals—as well as modifications to some ground systems. Artemis I ultimately launched successfully in November 2022, sending an uncrewed Orion around the Moon and back.

For Artemis II, the WDR is meant to demonstrate that the rocket and its support equipment can handle a full fueling and late countdown under even closer scrutiny, with human lives at stake on the next attempt.

Unfinished engineering questions

While the wet dress rehearsal focuses on fueling and countdown operations, key engineering issues on the spacecraft itself also loom over Artemis II.

Postflight analysis of Orion after Artemis I revealed unexpected erosion and “char loss” in more than 100 localized areas of the capsule’s Avcoat heat shield. Engineers concluded that pyrolysis gases generated within the ablative material could not vent as predicted, building pressure that caused cracking and shedding of char layers during the high-speed plunge through Earth’s atmosphere.

The NASA Office of Inspector General has described the anomaly as a significant risk that needed resolution before a crewed mission. Rather than replacing Orion’s already bonded heat shield for Artemis II—a step that would have required major disassembly—NASA has opted to keep the hardware, refine its thermal models and adjust the spacecraft’s planned return profile, including the use of a skip-entry trajectory designed to manage heating loads.

Agency officials maintain that the redesigned flight path and updated analyses provide adequate safety margin for the crew, and have reserved manufacturing changes to the heat shield material for later missions.

Separately, Orion’s Environmental Control and Life Support System underwent design corrections after testing identified problems with valve control and seal deformation in its carbon dioxide removal system. Engineers say those issues have been fixed and the system has since been pushed through aggressive, off-nominal testing.

At Kennedy, ground crews recently addressed concerns with the pad’s emergency egress baskets—open-air gondolas linked to a highline that would allow astronauts and pad workers to escape quickly in an emergency. In a test, some baskets stopped short of the intended terminus; NASA adjusted the braking system and plans further verifications while the rocket is at the pad. Sampling of Orion’s onboard water supply also found higher-than-expected levels of total organic carbon, prompting additional testing and potential mitigation steps before flight.

Adding complexity, an unusual cold spell forecast for Florida around Jan. 27 has required engineers to pay close attention to heaters and environmental control systems to ensure the rocket, spacecraft, and propellant lines remain within their temperature limits before and during the WDR.

A costly test for a costly rocket

Beyond the technical stakes, the wet dress rehearsal comes amid scrutiny of Artemis costs and long-term plans for SLS.

NASA’s inspector general has estimated that spending on Artemis-related systems—including SLS, Orion, exploration ground systems, the planned Gateway lunar outpost, and other elements—will reach about $93 billion by the end of fiscal 2025. The watchdog has pegged the production and operations cost for the first four SLS/Orion launches at roughly $4.1 billion each, calling that price tag “unsustainable.”

The Government Accountability Office has similarly warned that the current approach to SLS may not be affordable over the long term, even as Congress has continued to fund the program. In parallel, commercial heavy-lift rockets such as SpaceX’s Starship are being developed under separate contracts for future Artemis lander and cargo roles.

Although any decision to retire or replace SLS rests with policymakers, the rocket’s performance in key events like the WDR and the Artemis II launch campaign is likely to influence that debate. A clean rehearsal and relatively smooth countdown to launch would strengthen NASA’s case that SLS is maturing. Major leaks, valve failures, or pad rollbacks could fuel arguments for accelerating a shift to commercial alternatives.

A diverse crew and a global audience

Artemis II also carries symbolic weight.

If the mission flies as planned, Koch is expected to become the first woman to travel beyond low Earth orbit, Glover the first person of color, and Hansen the first Canadian—and first non-American—to journey to the Moon’s neighborhood. Wiseman would be the first astronaut since Apollo’s Gene Cernan to command a lunar voyage.

NASA in recent years emphasized such “firsts” in its public messaging but has since removed explicit diversity, equity, and inclusion language from high-level Artemis descriptions and some internal structures, following changes in federal policy. The makeup of the crew has not changed, however, and international participation remains central to the program.

Sixty-one nations have now signed the U.S.-led Artemis Accords, a set of principles for peaceful exploration and responsible behavior in space. Hansen’s seat is closely tied to Canada’s commitment to provide the Canadarm3 robotic system for the future Gateway station, while the European Space Agency is supplying Orion’s service module.

Those partners, along with competitors such as China, which is pursuing its own International Lunar Research Station initiative, will be watching what happens at Pad 39B.

Countdown to a decision

NASA’s official Artemis II page continues to list launch as “no earlier than Feb. 6,” with available opportunities in early February and additional launch periods later in the spring. Officials have repeatedly said they will not assign a specific date until the WDR is complete and engineers have combed through the data.

If the rocket fuels smoothly, the countdown reaches its planned cutoff point, and systems behave as expected, Artemis II could be just days away from flight. If not, the night’s rehearsal may instead mark the beginning of another round of troubleshooting, repairs, and rescheduled windows.

For now, the focus is on a single simulated launch in the Florida night: a countdown to nowhere that will help determine when four astronauts can climb aboard for real, and how confidently NASA can say its path back to the Moon is ready for people.