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Critical Test of NASA’s Megarocket Resumes After Lightning Strikes and Technical Glitches [Updated]

The multi-day rehearsal is the final step as NASA readies its gigantic Moon rocket for a possible launch in June.

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SLS on the launch pad at Kennedy Space Center, Florida.
SLS on the launch pad at Kennedy Space Center, Florida.
Photo: NASA/Joel Kowsky

The wet dress rehearsal of NASA’s Space Launch System has restarted following an eventful weekend at Kennedy Space Center in Florida. In addition to dealing with multiple lightning strikes, mission managers had to contend with malfunctioning ventilation fans and a problem with the gaseous nitrogen system.

Update: 5:30 p.m. EDT: NASA called off the wet dress rehearsal at 5:00 p.m. EDT today citing a valve issue. “Just prior to sending liquid hydrogen (LH2) into the vehicle the team was unable to open a necessary vent valve on the 160 level of the mobile launcher,” explained NASA’s Exploration Ground Systems in a tweet. The issue “is on an actuation and purge panel on the mobile launcher that supplies pressure to for the core stage vent valve,” according to the ground team.

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The liquid oxygen (LOX) that was loaded earlier in the day will now have to be offloaded. The team is currently discussing how quickly the rocket can be turned around for a subsequent attempt, and the space agency plans to hold a press conference tomorrow to discuss the situation.

Original post follows.

The decision to resume the wet dress rehearsal came at dawn today, with NASA Ground Systems saying the launch director would soon give the “go” for tanking and that weather shouldn’t be a problem. The 322-foot-tall (98-meter) rocket is currently standing on Launch Pad 39B at Kennedy Space Center in Florida, as NASA teams execute a full-fledged launch rehearsal that will stop 10 seconds prior to the ignition of four RS-25 engines.

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Live video coverage of the wet dress rehearsal is available at the Kennedy Space Center YouTube channel, but commentary is light given security concerns.

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SLS is a critical component of the upcoming Artemis missions to the Moon, but the program has suffered from budget overruns and scheduling delays. The wet dress rehearsal is in preparation for the rocket’s inaugural launch, the Artemis 1 mission, in which an uncrewed Orion capsule will travel to the Moon and back. A crewed mission to the Moon is expected no earlier than 2025.

The wet dress was supposed to have ended yesterday, but controllers were forced to press pause on account of two malfunctioning fans, which ventilate the rocket’s 370-foot-tall (113-meter) mobile launcher. The fans “are needed to provide positive pressure to the enclosed areas within the mobile launcher and keep out hazardous gases,” and “without this capability, technicians were unable to safely proceed with remotely loading the propellants into the rocket’s core stage and interim cryogenic propulsion stage,” according to a NASA update.

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The scrub came shortly before noon on April 3, preventing teams from loading cryogenic liquid hydrogen and liquid oxygen into the rocket’s core and upper stages. NASA stopped the clock at T-minus 6 hours and 40 minutes to give its ground teams the time needed to troubleshoot the anomaly.

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The malfunctioning fans were not related to four lightning strikes that hit the launch pad late Saturday afternoon, resulting in a slight delay. Lightning towers at the pad were hit three times during the electrical storm, while a fourth struck the catenary wiring system that channels electricity away from the rocket while it stands exposed. NASA checked the rocket and all systems, determining that it was safe to proceed with the wet dress.

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The countdown clock resumed at 10:52 a.m. EDT today. NASA is now targeting a T-0 at 6:02 p.m. EDT. NASA’s Exploration Ground Systems says the team resolved the issue with the fans as well as an earlier issue with the system that supplies gaseous nitrogen. The tanking of the rocket’s two stages, which happens sequentially, should take around 4.5 hours to complete. As this is happening, the team will perform checks to make sure the propellant is loading as expected and that the rocket hasn’t sprung any leaks.

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Ground controllers also plan to rehearse launch recycling, in which the clock is deliberately stopped and restarted. Once testing is complete, the tanks will be drained of propellant and the rocket will be carted back to the Vehicle Assembly Building for final modifications and check-outs.

Assuming the successful completion of a wet dress rehearsal, NASA will review the results, and, depending on how things went, announce a formal launch date for the Artemis 1 mission. Current expectations are that the megarocket will launch in early June, but since that the wet dress didn’t go exactly as planned, this will likely be pushed forward.