There is a new engine firing or a theatrical stage separation is not the last big hurdle on the way of a stacked Artemis II rocket and a crewed departure. It entails a lengthy, procedural, dress exercise where ground crews demonstrate their ability to freeze, load, control, and empty an ocean of super-cold propellants in a vehicle that once astronauts are on board cannot use improvisation.
The Space Launch System and Orion are undergoing a wet dress rehearsal at Kennedy Space Center that includes the countdown procedures on the ground, including the startup of the integrated vehicle and the fueling procedure that will lead up to the lunar flyby of Artemis II. The checkpoint will be able to qualify the flight hardware and the choreography of the launch team, and operators are invited to stations about 49 hours before a simulated liftoff time.
The focus of the entire exercise is fueling. The test has shown that it can load over 700,000 gallons of cryogenic propellants and cleanly pass through the late-countdown decision points where a launch can pause, recycle or resume without losing control of the temperatures, pressures and timing. NASA will have several “runs” as it counts through the terminals, which will set the team back through holds and restarts until the last few seconds when the automatic sequencer of the rocket would be activated. This is important since the greatest failures experienced during a launch campaign are usually at interfaces: valves, quick-disconnects, purge cavities, sensors, and procedures which must co-operate under extreme thermal conditions.
The interface work has been accumulating since rollout, when the integrated stack was slowly ferrying to the crawler-transporter at under a mile per hour making its slow trip to Launch Pad 39B. As soon as the vehicle got to the pad, technicians started hooking the vehicle to the lifelines of the launch site, electrical, environmental control, cryogenic feeds and communications, and turned on key components to perform integrated checkouts. Pad flow also involves swing tests of the crew access arm and exercises of the emergency egress baskets which part the personnel off the mobile launcher during an anomaly.
Minor mechanical and environmental aspects are considered as mission level concerns during a crewed campaign. Recent pad preparations have involved activities like booster servicing using hydrazine in the aft skirt, radio-frequency communication test with the Eastern Range and late stowage of crew and medical equipment in Orion. The technicians have also done things to maintain Orion and SLS components within necessary environmental limits under colder than normal Florida weather. Those normal jobs have been accompanied with the teams working on systems that can only really be called non-negotiable when people are on the plane: the emergency egress baskets had been checked after falling short of their intended destination, and more testing of potable water on board Orion was scheduled after initial tests indicated that the total carbon of organic origin was higher than expected.
Wet dress rehearsal performance also predetermines the course of further action. In case of issues that arise and necessitate a deeper access, the integrated vehicle may be retracted to the Vehicle Assembly Building and worked on it before returning to the pad to make another attempt. The program has clearly created an allowance of more wet dress rehearsals in case the initial run fails to cover all checklist items.
Artemis II is expected to have four astronauts on board including Reid Wiseman, Victor Glover, Christina Koch and Canadian Space Agency astronaut Jeremy Hansen on a mission around the Moon and back over a period of about 10 days. The flight is supposed to test the full life-support and crew systems, which Artemis I did not require, and inject the data into the architecture desired to operate on the moon. Practically, it is at the wet dress rehearsal, where the long arc intersects the launch pad, that the ground test is done, which will answer the question: Does the hardware, the people and the procedures act like one machine when the tanks begin to fill?