NASA’s moon rocket rolls back to Vehicle Assembly Building for repairs

NASA’s Artemis 1 moon rocket arrives outside the Vehicle Assembly Building before dawn Tuesday. Credit: Stephen Clark / Spaceflight Now

NASA rolled the giant new rocket for the Artemis 1 moon mission off the launch pad back inside the Vehicle Assembly Building before dawn Tuesday at the Kennedy Space Center, moving into the hangar for repairs after technical problems prevented teams from completing a countdown dress rehearsal earlier this month.

Agency officials hope to complete the repairs and finish testing on the Space Launch System moon rocket in time for liftoff of the Artemis 1 mission no earlier than August, about two months later than previously scheduled. Artemis 1, an unpiloted mission, is the first test flight of the Space Launch System, the rocket NASA designed to send astronauts back to the moon.

“We’ve got the vehicle back in the Vehicle Assembly Building,” said Bob Cabana, NASA’s associate administrator, the third-most senior position at the space agency. “Obviously, we’re going solve that hydrogen leak issue in the tail service mast umbilical. We have a valve on the interim cryo propulsion upper stage that needs to be changed out. There’s some other work that needs to get done.”

The faulty helium check valve in the upper stage and the hydrogen leak, discovered in the interface between the core stage and the mobile launch platform, prevented NASA from fully loading the SLS moon rocket with more than 750,000 gallons of super-cold liquid hydrogen and liquid oxygen propellants during a series of countdown tests, or “wet dress rehearsals,” earlier this month.

“We will complete that work, and we still have a lot to do with wet dress rehearsal, so the team is evaluating options,” Cabana said. “We’ll make a decision here in the not too distant future of what the best path forward is.”

As for the soonest schedule when the SLS moon rocket might be ready for its first test flight, Cabana said: “August — there are options that still get us there.”

“The important thing now is we’ve got to do this right,” Cabana said. “It’s a big rocket, a lot of new equipment, new systems on the ground side and on the flight side.”

The Space Launch System passes by pad 39A, where a SpaceX Falcon 9 rocket is awaiting launch on the Crew-4 mission. Credit: Stephen Clark / Spaceflight Now

The 4.2-mile (6.8-kilometer) journey from pad 39B began at 7:54 p.m. EDT (2354 GMT) Monday, when NASA’s diesel-powered crawler-transporter rolled the SLS moon rocket and its mobile launch platform off the launch pad pedestals.

Reaching a top speed just shy of 1 mph, the crawler moved the rocket down the ramp at pad 39B, then along the rock-covered crawlerway leading to the Vehicle Assembly Building. The entire stack weighs about 21.4 million pounds.

After working through the night, NASA’s ground team parked the SLS moon rocket outside the VAB for about an hour, allowing time for the crew access arm near the top of the rocket’s mobile launcher tower to move into position next to the Orion crew capsule on top of the vehicle.

Then the 322-foot-tall (98-meter) rocket rolled through the vertical door and into High Bay 3 inside the Vehicle Assembly Building. The crawler’s jacking and leveling system lowered the mobile launch platform onto pedestals inside the hangar shortly after 6 a.m. EDT (1000 GMT), completing the 10-hour journey from pad 39B.

While repairs and troubleshooting begin inside the VAB, teams from Air Liquide, which runs a plant just outside the gates of the Kennedy Space Center, will upgrade the gaseous nitrogen supply that leads into the spaceport through a pipeline. NASA found that the nitrogen gas supply was not sufficient for the high demands of the Space Launch System, a rocket larger than any other currently flying from the Florida spaceport.

The large size of the SLS moon rocket means it needs more propellants and other fluids, including nitrogen gas, than other rockets.

“We are upgrading the vaporization system to optimally manage the increased nitrogen requirements during launches,” said Alyson Bartol, a spokesperson for Air Liquide, which also supplies nitrogen gas for commercial launch operations in Florida, including SpaceX missions. “The nitrogen supplied to Kennedy Space Center is not restricted for use by NASA only, therefore other parties utilizing the supply will also benefit from the upgrades to Air Liquide’s system.”

NASA rolled the SLS moon rocket out to pad 39B on March 17 to prepare for the rocket’s first full-up countdown rehearsal and fueling test, culminating in a cutoff of the countdown clock at T-minus 9 seconds, just before main engine ignition.

NASA’s launch team attempted to pump propellants into the rocket April 3, April 4, and April 14. The final wet dress rehearsal test ended with the discovery of the hydrogen leak in the tail service mast umbilical, where propellants flow from the mobile launch platform into the SLS core stage.

The furthest the launch team got in the dress rehearsal was filling about 5% of the core stage’s liquid hydrogen tank and loading about half of its liquid oxygen.

Initial inspections at the launch pad revealed no sign of the hydrogen leak.

Exposure to super-cold propellants contracts components in the mobile launch platform and the rocket itself, manifesting leaks not apparent at ambient temperatures. Charlie Blackwell-Thompson, NASA’s Artemis 1 launch director, said last week engineers and technicians in the VAB will use probes and instrumentation to scan for a leak. They will also inspect seals, and re-torque flange connections in the umbilical, she said.

The Space Launch System passes by pad 39A, where a SpaceX Falcon 9 rocket is awaiting launch on the Crew-4 mission. Credit: Stephen Clark / Spaceflight Now

NASA officials originally planned to roll the SLS moon rocket back to the hangar after completing the wet dress rehearsal, allowing ground crews to complete closeouts on the rocket, test the vehicle’s flight termination system, and install final equipment into the Orion crew capsule.

Then the rocket would roll out again to pad 39B for launch preparations and the real countdown for the Artemis 1 mission, perhaps as soon as early June.

Blackwell-Thompson said NASA managers are evaluating three options for how to complete the work required before clearing the Artemis 1 mission for liftoff.

One is a “VAB quick turn” option that would focus engineers on completing the minimum work to ready the rocket for another wet dress rehearsal run. That work would include replacing the upper stage helium valve and fixing the hydrogen leak, but the rocket would still need to come back to the VAB for final pre-flight preps.

“There’s a second option that looks at doing a great amount of work in the VAB, maybe getting closer to your rollout for flight configuration,” Blackwell-Thompson said. This option would also require another rollback to the hangar, but would involve a relatively shorter stay in the VAB focused on flight termination system testing.

NASA’s Orion spacecraft perched atop the Space Launch System. Credit: Stephen Clark / Spaceflight Now

The third option under consideration would keep the SLS moon rocket in the VAB for a longer period of time after rolling back from the pad next week, allowing teams to complete all the work needed to outfit the launcher for flight. Then the rocket would roll out again to pad 39B, allowing NASA to run through a wet dress rehearsal and then the real launch attempt during one campaign.

The third option would include a 20-day limit from the time the rocket rolls out of the VAB until the mission must launch. The restriction is associated with the flight termination system, which would be activated to destroy the rocket if it flew off course.

The U.S. Space Force’s Eastern Range, responsible for public safety, only certifies the SLS flight termination system for 20 days after it completes an end-to-end test inside the Vehicle Assembly Building.

The comprehensive flight termination system check can only be run inside the VAB, so the rocket would have to return to the hangar for another end-to-end test after 20 days, potentially leaving little margin for error to resolve problems during a wet dress rehearsal, and still proceed with the Artemis 1 launch.

The Space Launch System moves into High Bay 3. Credit: Stephen Clark / Spaceflight Now

Tom Whitmeyer, NASA’s exploration systems manager, said last week the agency is committed to completing the wet dress rehearsal before launching the SLS moon rocket.

“We will absolutely go back out,” he said. “We are absolutely going to do a dress rehearsal. We’ll demonstrate cryo loading, and we will also demonstrate terminal countdown.

“It’s just a matter of what’s the right time and what’s the right way to do that, and how that might fit in our forward scheduling.”

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