The countdown pause at 5 minutes 15 seconds remaining was not due to the mission time limitation, but was caused by ground systems determining that the leak rate had reached a limit. That automatic stop on the initial wet-dress rehearsal of Artemis II put NASA ruled out a February launch and shifted focus to March launch opportunities, following a practice campaign that was intended to uncover precisely this mode of failure.
Artemis II will be configured to accommodate four astronauts on a flyby and return trip to the moon to restore a human capability of deep-space flight not seen since Apollo. The new posture of NASA is based on a two-day simulated flow of launch at the Launch Complex 39B in Kennedy Space Center that started on Jan. 31, with team consoles conducting a complete full-up dress rehearsal: powering and configuring the Space Launch System and Orion and then graduating to the delicate business of loading cryogenic propellants and stabilizing conditions when the vehicle is on the pad.
The technical limitation that characterized the rehearsal was the behavior of liquid hydrogen within the interface which opened the direct passage to propellant entering the SLS core stage. It was later found that during tanking, leaks occurred in an area linked with the tail service mast umbilical which is the connection to the ground on the rocket feed side. The crew used methods developed during the Artemis I 2022 mission, such as halting flow, heating the interface to allow seals to reseat, and re-setting propellant flow, which returned concentrations within reasonable limits and allowed the core-stage to be filled and the topping to begin. This timing was significant since it was evidence of a gradual recovery, as well as of the possibility of stabilizing at the interface late in the sequence, when conditions and pressures vary and the ground launch sequencer starts to tighten the choreography. Finally, the leak rate of hydrogen shot up prompting the sequencer to terminate the test prematurely and NASA was thrown back into a second rehearsal to capture more data on a cleaner day under “launch day” conditions.
The program message was simple: rehearsals are not formalities. Jared Isaacman directly presented that fact on the social media: “With more than three years between SLS launches, we fully anticipated encountering challenges. That is precisely why we conduct a wet dress rehearsal.”
Although the headline was given by hydrogen, the pad run also revealed smaller friction points, which are schedule multipliers during a crewed campaign. A new valve that was connected with the hatch pressurization of the Orion crew module needed to be retorqued, and this slowed down closeout work. Independently, cold weather affected cameras and other equipment and crews had to work out audio communications dropouts, a problem that does not impair the thrust or control of the vehicle, but can complicate real-time coordination when the clock is running.
Wet systems rehearsal is also human-system exercise. NASA conducted Orion closeout operations, and a 5-member pad crew practiced closeout, and the flight crew was not within the flow. The astronauts, who were commanded by Reid Wiseman, Pilot Victor Glover, Mission Specialist Christina Koch and Canadian Space Agency astronaut Jeremy Hansen had been under preflight quarantine but were released due to the delay until around two weeks prior to the next targeted launch opportunity.
In the case of Artemis II, the planning of NASA is currently based on the March dates, such as March 6-9 and March 11. The calendar is not the schedule hinge, but the second wet dress rehearsal and the data review that follows, in which the pacesetter is hydrogen sealing performance and ground-side reliability rather than any single mission manifest milestone.
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