NASA Tests SLS Umbilicals, Prepares for Second Wet Dress Rehearsal
Following the incomplete first Wet Dress Rehearsal (WDR) for the Artemis II mission earlier this month due to hydrogen leaks, the Exploration Ground Systems team decided that more testing was needed before trying again. To test repairs made to liquid hydrogen seals at the pad, the launch team decided to perform a limited tanking test. The Core Stage Liquid Hydrogen (LH2) tank would be partially filled, only enough to test that the repaired seals were functioning well enough to handle a full tanking. A positive result would allow them to conduct a second WDR, while a negative result would show they needed to do more intensive repairs.
A complete launch rehearsal requires teams to be on station continually for nearly 50 hours and involves many preparations and steps that are not required if the only objective is to fill a tank. Committing to that effort without knowing if the seals were sound can easily turn into a debacle in terms of wasted time, money, morale, and bad publicity, so a limited test is a much lower risk way to test the waters.
Accordingly, on February 12th, the limited test was performed. The desired fill percentage could not be reached due to a ground equipment filter reducing the flow of liquid hydrogen, but the tank was filled enough to give confidence to proceed to a second WDR. Call to Stations will come at approximate 6:40pm EST on Tuesday, February 17th with a simulated T-0 at approximately 8:30pm on February 19th. This WDR will focus on unmet objectives from the last WDR, primarily focusing on getting through two “runs” of terminal count.
Terminal count is the final phase of the countdown, putting the vehicle in a liftoff configuration before handing off control to the onboard computers at T-30 seconds. Once terminal count begins at T-10:00 and until the Core Stage goes to internal power at T-1:30, SLS has the ability to hold for up to three minutes inside terminal count before resuming. After those 3 minutes, or if a hold is called after T-1:30, the count must reset to T-10:00 and do another full run through terminal count. To date, terminal count has only been entered three times: the fourth WDR for Artemis I proceeded to T-28 seconds (after significant masking of violated parameters due to hydrogen leaks) before the onboard computer aborted; the final launch attempt of Artemis I on November 16th, 2022 made a single full run without issues; and Artemis II’s first rehearsal made it to T-5:15 before being manually aborted due to leaks.
The primary objective of Thursday’s attempt will be to run through terminal count twice. Teams will proceed through terminal count to T-1:30, hold for three minutes, and proceed to T-33 seconds before aborting and recycling to T-10:00. They will then re-enter terminal count and go straight down to T-30 seconds before aborting just after handoff to the Automated Launch Sequencer (ALS) onboard SLS.
If the second WDR is a success, Artemis II will launch no earlier than March 6th, 2026 at 8:29:00 PM Eastern Standard Time (March 7th, 2026 at 1:29:00 AM UTC). A date earlier in March was under consideration, but a likely cause of its unavailability is that the delay from February requires NASA to re-test the Flight Termination System (FTS). This requires an access kit to be attached to the intertank section of the rocket and then removed before launch. This extra time may not have left enough of a buffer before the earlier window for NASA’s comfort. An unsuccessful WDR or other factors causing Artemis II to miss the March window will necessitate a rollback to the VAB for ICPS servicing and a delay to late April/early May.
Edited by Beverly Casillas
