SLS Rolls Back to VAB for Repairs

NASA’s first SLS moon rocket rolls atop its Crawler Transporter at Kennedy Space Center. Photo: Mike Killian / AmericaSpace

NASA has moved their new SLS moon rocket back into its Vehicle Assembly Building (VAB) at Kennedy Space Center in Florida, after a series of issues prevented completion of a wet dress rehearsal (WDR) on launch pad 39B.

The two-day WDR test is intended to demonstrate the vehicle and launch team’s ability to load propellants into the rocket, conduct a full launch countdown (minus engine ignition), demonstrate the ability to recycle the countdown clock, and practice safely draining propellants at the launch pad. It’s a critical opportunity to refine countdown procedures and validate models and software interfaces, giving the team valuable experience before the real countdown and launch day.

SLS rocket approaching VAB for repairs needed to continue WDR
Photo Credit : Jeff Seibert / AmericaSpace

The rocket and its Orion spacecraft will not be cleared for launch on the Artemis-1 mission to the moon until a WDR is complete.

The 6 million pound fully stacked vehicle, which stands taller than the Statue of Liberty at 322 feet, made the 4-mile / 10-hour trip back to the VAB last night atop. Workers will now spend several days extending platforms to allow access to it and Orion in high bay 3, before starting weeks of work to replace a faulty upper stage helium check valve and fix a small hydrogen leak within the tail service mast umbilical ground plate housing on the mobile launcher, which is located at the base of the mobile launcher and connects to the rocket’s core stage.

NASA sent the rocket to the launch pad on March 18, where it was connected to various ground service equipment and powered up to ensure all the systems would operate as planned.

The first countdown began April 1, followed by the first tanking operations on April 3 to load liquid oxygen (LOX) and liquid hydrogen (LH2) into the into the rocket’s core stage and interim cryogenic propulsion stage (ICPS) tanks. Those operations however were scrubbed when fans needed to provide positive pressure to the enclosed areas within the mobile launcher and keep out hazardous gases lost their ability to pressurize.

The malfunction was resolved and the countdown resumed on April 4. Teams had to troubleshoot a temperature limit issue for the LOX, which delayed the countdown before they developed a new procedure for loading the LOX and filling the tank to 50 percent. But the day’s operations were later scrubbed after partially loading LOX into the core stage when teams encountered an issue with a panel on the mobile launcher that controls the core stage vent valve, which relieves pressure from the stage during tanking.

Artemis-1 on pad 39B for the first wet dress rehearsal. Photo: Mike Killian / AmericaSpace

Inspections after showed the valve was configured physically in a closed position, which prevented it from being commanded remotely to open. The issue was corrected, but then engineers found an issue maintaining helium purge pressure on the rocket’s upper stage RL10 engine after change-out of a regulator on the mobile launcher. After initial troubleshooting, the team reestablished normal helium purge, but identified a 3-inch helium check valve not functioning correctly, which prevents helium from flowing back out of the rocket.

Adjustments in the procedures and modifications in test objectives were made as necessary, and the test schedule refined to account for insights gained during the previous runs and activities. NASA then targeted April 12 to resume a modified WDR, followed by tanking on April 14, primarily focused on fueling the core stage, and not the ICPS, because the problematic helium check valve couldn’t be fixed at the launch pad.

Fueling of LOX into the core stage encountered another minor temperature issue, but it was resolved, and teams then proceeded to begin fueling the core stage LH2 tank. But a surge in pressure automatically stopped the flow of LH2, at which point teams also paused loading any more LOX to ensure the tanking operations for both propellants remained synchronized.

That’s when engineers detected a small LH2 leak on the tail service mast, which is located at the base of the mobile launcher and connects to the core stage. When teams paused propellant loading, there was about 49% of LOX and about 5% of LH2 loaded on the core stage.

Once the repairs and checkouts in the VAB are complete, the rocket will be rolled out again to finish the WDR.

The SLS Artemis-1 atop pad 39B, with a SpaceX Falcon 9 and Crew Dragon atop pad 39A in the distance. Photo: Jeff Seibert / AmericaSpace

A WDR is meant to find issues such these, especially on a vehicle that has never flown. And while a couple repairs are needed, the engineers accomplished several test objectives that will prepare the teams and integrated systems for launch, including:

  • Configuring Launch Pad 39B and the mobile launcher for the test, just as it will have to be prepared for launch
  • Clearing personnel and equipment from the launch pad after configuration in order to proceed with propellant loading
  • Powering up Orion and the SLS rocket systems in launch configuration, including the solid rocket boosters, the core stage, and the interim cryogenic propulsion stage
  • Checking out and verifying the Orion spacecraft countdown and commanding by flight controllers at NASA Johnson Space Flight in Houston
The SLS Artemis-1 stack being moved at night. Photo: Mike Killian / AmericaSpace
  • Checking out the guidance, navigation and control system and all the integrated software that operates across the rocket, Orion, ground systems and ground support centers including the Launch Control Center
  • Verifying and checking out all the range safety and systems with the range
  • Draining the liquid oxygen and liquid hydrogen after the test
  • Powering down the rocket, the spacecraft and ground systems and putting them in a safe configuration

We will update once NASA has completed the work and establishes a new date to roll the rocket back to pad 39B for the next WDR.

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