NASA is entering one of the most consequential tests of its modern moon program, a full wet dress rehearsal on Monday that will show whether the Space Launch System and Orion are ready to fly a crew. Engineers plan to fully tank the rocket, run the countdown as they would on launch day, and stop roughly 30 seconds before ignition.
The results will drive the schedule for the first crewed Artemis mission, which the agency has said could launch no earlier than Sunday for a 10-day trip around the moon.
Mission managers have been clear that the test, not the calendar, will decide the final date. After the rehearsal, teams will comb through data, verify performance, and only then set a target. If everything looks nominal, a launch attempt could be announced within days.
If issues surface, the agency is prepared to troubleshoot, which could include rolling the vehicle back to the Vehicle Assembly Building for access and repairs.
What a wet dress rehearsal proves
A full-up fueling test is the closest thing to launch without committing the engines. Controllers will load more than 700,000 gallons of supercold propellant into the core stage and upper stage, chill down lines and valves, and transition the stack into the automated phase when onboard software takes control.
They will practice planned holds and rapid recycles in the final minutes to confirm the team can pause, resolve a problem, and pick up the count without introducing new risks.
This is the second flight of the Space Launch System and the first time it will carry astronauts inside Orion. Before the uncrewed flight in 2022, engineers ran multiple fueling tests to chase down hydrogen leaks and ground system quirks. Those lessons prompted hardware and procedure updates that are now on the vehicle.
Monday’s rehearsal is designed to validate those changes under real conditions, including pressure swings and thermal loads that only occur during tanking.
Countdown timeline and Monday’s objectives
The rehearsal is keyed to a simulated launch time of 9 p.m. ET Monday. In the hours leading up to that mark, teams will begin chilldown of the propellant systems and start slow fill, then fast fill, for the liquid hydrogen and liquid oxygen tanks.
The operations sequence also includes checks on vents and relief systems, verification of umbilical plate loads, and tests of the ground launch sequencer that orchestrates the last minutes of the countdown.
Mission control intends to demonstrate several hold points in the final 10 minutes, then run to an automatic cutoff that mirrors the handoff to flight software.
A clean performance would confirm that valves respond within tolerance, that sensors track temperatures and pressures accurately, and that ground and vehicle computers stay synchronized during the most dynamic phase of the count.
Launch window, weather, and why the schedule is tight
The rehearsal was originally set for Saturday, but a strong cold snap across the Southeast prompted managers to wait for milder conditions at the pad.
The shift forced NASA to stand down from the first two opportunities in this month’s window and concentrate on the late-week attempts.
The current window extends through Feb. 11. If the rocket does not fly by then, managers have identified opportunities in March and April.
Cold air matters, even for a cryogenic rocket. Materials contract, seals can harden, and icing can develop on structures and lines. Teams also consider pad crew safety during long outdoor operations. Moving the test to Monday allows the agency to gather live data in conditions closer to those expected on launch night and preserves time to analyze the results before committing the crew to flight.
