NASA will attempt again this week to fully load its Space Launch System rocket with more than 700,000 gallons of liquid hydrogen and liquid oxygen at the conclusion of the full launch countdown rehearsal.
The operation, called Wet Dress Rehearsal, or WDR, will begin Tuesday, Feb. 17, at 6:40 p.m. EST (2340 UTC) with a call to stations inside Firing Room 1 at the Launch Control Center. It will conclude with actual refueling of the rocket on Thursday, February 19, aiming for a simulated T-0 at 8:30 p.m. EST (0130 UTC).
This second, full-length refueling demonstration comes a week after NASA conducted the confidence test on Thursday, Feb. 12. During that operation, teams loaded an unspecified amount of liquid hydrogen (LH2) into the rocket’s core stage “to assess the newly replaced seal in the area used to fill the rocket with propellant.”
However, a new ground equipment issue emerged that “reduced the flow of liquid hydrogen to the rocket,” according to a blog post shared Friday night. NASA said it managed to get enough data from “key test objectives” and was able to get good data from the core stage interface – called the Tail Service Mast Umbilical (TSMU) – during the same period where the leaks were revealed during the first WDR on February 3.
“The confidence test provided a tremendous amount of data on the seals we repaired and replaced after WDR-1, and we saw significantly lower leakage rates than prior observations during WDR-1,” NASA Administrator Jared Isaacman said in a social media post Saturday. ‘I wouldn’t say that something was broken that caused the test to end prematurely, because we did enough inspection and reached a point where it was unnecessary to wait for additional troubleshooting.’
During the first WDR, which concluded on February 3, NASA encountered a hydrogen leak as they transitioned from the slow fill rate of LH2 to fast fill on the core stage, requiring loading to be halted several times. Hydrogen is highly combustible and so NASA has restrictions on how concentrated it can be once it is airborne.
During the process of pressurizing the tanks amid the terminal count on WDR-1, teams exceeded the 16 percent LH2 limit and the clock stopped at T-5 minutes and 15 seconds.
“We wanted to go inside the terminal count, we wanted to hold and we wanted to verify our three-minute hold capability, meaning all of your cryo prop systems are in the launch ready position and you can hold them there for three minutes and we wanted to demonstrate the capability,” Artemis launch director Charlie Blackwell-Thompson said during a WDR-1 press conference.
He said, “We wanted to demonstrate a recycle, when you go down and you have a planned cutoff in the countdown, come back, and re-target a new T-0 and be able to demonstrate that within the launch window.” “Didn’t get a chance to do that. And then we would come down, do the handoff to the ALS (Automated Launch Sequencer), and cutoff immediately after that. So I would say those were probably the three things that we intended to do. [on Feb. 3] “We didn’t get the opportunity to do that.”
Those objectives are back on the table for the WDR-2. Launch controllers intended to advance the count to T-1 minutes and 30 seconds, pause for three minutes, advance the terminal count to T-33 seconds, and then pause again. They will then take the clock back to T-10 minutes and make another run through the terminal count.
Before problems were encountered inside the terminal count during WDR-1, Blackwell-Thompson had abandoned the possibility of conducting a second terminal count attempt due to problems previously observed during the refueling campaign.
Like WDR-1, WDR-2 will also have the closeout crew performing their launch day activities even though the crew will not be present. At one time, NASA was not going to include a closeout crew in the loop for WDR-2, but later changed its mind.
NASA leaders have repeatedly said that a more formal launch date would not be established until after a successful wet dress rehearsal campaign. March 6 remains the earliest possible launch date within the March window.
“There is still much work left to do to prepare for this historic mission,” Isaacman wrote on social media. “We will not launch until we are ready and the safety of our astronauts remains the top priority.”
