Artemis II teams step through full-scale launch rehearsal at Kennedy

by Clarence Oxford
Los Angeles CA (SPX) Feb 02, 2026

The countdown for NASA's Artemis II wet dress rehearsal is underway at the agency's Kennedy Space Center in Florida, marking a key test before the first crewed flight of the Space Launch System rocket and Orion spacecraft in the Artemis campaign to return astronauts to the Moon.

The Space Launch System (SLS) rocket and Orion spacecraft, secured to the mobile launcher at Launch Pad 39B, will support a test that runs the integrated launch team and supporting centers through a full range of launch day operations, including loading cryogenic propellants, executing terminal countdown sequences, recycling the clock, and draining the tanks to practice scrub procedures. NASA's Artemis II test flight will carry Commander Reid Wiseman, Pilot Victor Glover, and Mission Specialist Christina Koch from NASA, along with Mission Specialist Jeremy Hansen from the Canadian Space Agency, on a mission around the Moon and back to Earth no later than April 2026.

The wet dress rehearsal countdown clock began at 8:13 p.m. EST at L-48 hours, 40 minutes before the opening of a simulated launch window at 9 p.m. on Monday, Feb. 2, with the test expected to continue until approximately 1 a.m. on Feb. 3. The exercise is designed to verify launch vehicle and ground systems performance and to ensure the launch team is fully prepared for the actual Artemis II liftoff.

During the rehearsal, controllers at Kennedy, mission control teams at NASA's Johnson Space Center in Houston, and personnel at other supporting NASA centers will conduct a detailed countdown sequence to two separate terminal count holds. The team will first pause at T-1 minute 30 seconds for up to three minutes, resume the count to T-33 seconds before launch, then recycle the clock back to T-10 minutes and perform a second terminal countdown to approximately T-33 seconds before ending the sequence.

A continuous live stream is following the SLS rocket and Orion spacecraft at the pad, and NASA is providing a separate feed during tanking operations along with real-time blog updates as the fueling day progresses. The test includes loading liquid oxygen (LOX) and liquid hydrogen (LH2) into the core stage and the interim cryogenic propulsion stage (ICPS), along with chilling, slow fill, fast fill, topping, and replenish operations that mirror launch day procedures.

The countdown is structured around both L-minus and T-minus times. L-minus time tracks the overall time remaining before the planned liftoff window, while T-minus time governs the event-driven sequence of operations built into the countdown. The plan includes built-in holds during which the T-minus clock is intentionally stopped while L-minus time continues to advance, allowing teams to synchronize with the target launch window and manage tasks without affecting the larger schedule.

Key early milestones include launch team arrival on console and start of countdown at about L-49 hours 15 minutes, filling the sound suppression system water tank, and preparing LOX and LH2 systems for vehicle loading between roughly L-48 hours 45 minutes and L-39 hours 45 minutes. The core stage and ICPS are powered up in the L-39 hour to L-38 hour range, followed by final preparations of the four RS-25 core stage engines.

Later in the flow, technicians power down the ICPS temporarily, charge Orion and core stage flight batteries, and then power the ICPS back up for launch operations while leak checks are conducted on Orion crew suit regulators. As the timeline advances toward L-15 hours, all non-essential personnel depart Launch Complex 39B, the Ground Launch Sequencer is activated, and air systems transition to gaseous nitrogen to inert vehicle cavities in preparation for cryogenic tanking.

Around L-11 hours 40 minutes, a built-in 2-hour 15-minute hold begins, during which the launch team conducts weather and tanking briefings and decides whether they are go or no-go to begin fueling the rocket. Subsequent steps include chilldown of core stage LOX and LH2 transfer lines, chilldown of the core stage main propulsion system, initiation of slow and fast fills for both propellants, and cold soak operations for Orion to condition the spacecraft for the cryogenic environment.

As the propellant loading sequence progresses, the core stage and ICPS tanks transition from fast fill to topping and then to replenish modes to maintain proper levels and pressures through the remainder of the countdown. ICPS LH2 and LOX lines are chilled and vent and relief tests are performed, while Orion communications systems are activated and checked with mission control via radio frequency links.

In the L-6 hour to L-4 hour window, ICPS LOX fast fill operations are completed, core stage LOX replenishment continues, and ICPS LOX topping and replenish activities begin. NASA teams also conduct stage pad rescue readiness checks, assemble the closeout crew, and start a 40-minute built-in hold at L-4 hours 40 minutes, during which the closeout crew moves to the white room at the pad.

During this period, technicians complete Orion crew module hatch preparations and closure, perform counterbalance mechanism hatch seal pressure decay checks, and install and close out the crew module service panel. The Launch Abort System (LAS) hatch is then closed for flight, ensuring the integrated Orion spacecraft is sealed for the simulated launch configuration.

As the final phases approach, the launch director receives briefings on the integrated flight vehicle and thermal protection system scan results, while the closeout crew departs Launch Complex 39B roughly 1 hour 45 minutes to 1 hour 40 minutes before the simulated liftoff. A built-in 30-minute countdown hold begins at L-40 minutes, which is used to finalize configuration and communications loops.

At L-25 minutes, teams transition to the Orion-to-Earth communication loop following the final NASA Test Director briefing, and at L-16 minutes the launch director polls the team to confirm they are go for launch. At T-10 minutes, the Ground Launch Sequencer initiates the terminal count, beginning a tightly choreographed series of automated events.

During the terminal count, the crew access arm retracts at T-8 minutes, and the Ground Launch Sequencer gives the go for core stage tank pressurization at T-6 minutes, when Orion is also switched to internal power. Core stage LH2 replenish is terminated at T-5 minutes 57 seconds, followed by a go for core stage auxiliary power unit start at T-4 minutes, at which time the auxiliary power units start and core stage LOX replenish terminates.

As the sequence continues, ICPS LOX replenish ends at T-3 minutes 30 seconds, and the Ground Launch Sequencer issues a go for purge sequence 4 at T-3 minutes 10 seconds. ICPS switches to internal battery power at T-2 minutes 2 seconds, followed by the boosters switching to internal power at T-2 minutes, while a planned hold at T-1 minute 30 seconds of up to three minutes is used to verify core stage certification hold time and confirm vehicle readiness.

At T-1 minute 30 seconds, the core stage transitions to internal power, and ICPS enters terminal countdown mode at T-1 minute 20 seconds. ICPS LH2 replenish terminates at T-50 seconds, and at T-33 seconds the Ground Launch Sequencer sends the go for automated launch sequencer command before issuing a cutoff and recycle at the same mark to conclude the rehearsal with the clock paused just before the point at which the automated system would take over for an actual launch.

Inside the terminal countdown, teams have several options to hold the clock if needed. They can stop at T-6 minutes for the duration of the launch window, less the six minutes required to launch, without recycling back to T-10 minutes. If an issue arises between T-6 minutes and T-1 minute 30 seconds, they can hold for up to three minutes and then resume the count; any longer delay in that range requires recycling to T-10 minutes.

If the clock stops after T-1 minute 30 seconds but before handover to the automated launch sequencer, teams can recycle back to T-10 minutes and attempt another run, provided sufficient launch window remains. On an actual launch day, once control passes to the automated launch sequencer, any problem that would halt the countdown would end the launch attempt for that day.

While the Artemis II astronauts are not directly participating in the wet dress rehearsal, key crew-related milestones that will occur on launch day are built into the test timeline. The Artemis closeout crew is using this opportunity to rehearse their closeout operations, including closing and securing the Orion crew module and launch abort system hatches, which are critical steps in preparing the spacecraft for its mission around the Moon.