Ground teams moved a diesel-powered crawler-transporter underneath the Space Launch System moon rocket Sunday on pad 39B at NASA’s Kennedy Space Center, preparing the towering launcher for a return to the Vehicle Assembly Building for repairs.
The rollback to the Vehicle Assembly Building is set to begin as soon as Monday afternoon, giving the SLS team plenty of time to bring the rocket back to the hangar before the scheduled launch of a SpaceX crew mission to the International Space Station early Wednesday.
The 4.2-mile (6.8-kilometer) journey along the dual-lane crawlerway is expected to last approximately 10 hours, but that could vary based on how many stops the crawler makes on the return trip to the assembly building.
NASA is moving the 322-foot-tall (98-meter) moon rocket off pad 39B after failing to fully load the vehicle with cryogenic propellants during testing earlier this month. On three fueling attempts, NASA’s launch team was blocked by ground equipment problems, a faulty helium valve, and finally a hydrogen leak in the interface between the rocket and its mobile launch platform.
The problems are expected to delay the first flight of the powerful new Space Launch System rocket — a vehicle NASA intends for future astronaut voyages to the moon — from the previous target schedule in early June. NASA has not identified a new timetable for the first SLS launch.
The launch will carry NASA’s Orion crew capsule on a multi-week journey into lunar orbit and back to Earth. The mission, known as Artemis 1, is a shakedown cruise before NASA aims to launch a crew around the moon on the second SLS/Orion flight.
Managers decided to return the Space Launch System to the Vehicle Assembly Building to replace the faulty helium check valve on the rocket’s upper stage, and to allow technicians an opportunity to locate and repair the hydrogen leak in the umbilical that leads into the core stage.
Meanwhile, 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.”
The upgrades are not expected to impact other launches from the Kennedy Space Center or Cape Canaveral Space Force Station, according to NASA.
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, when the core stage had been filled with about 5% of its liquid hydrogen load and about half of its liquid oxygen.
Once the SLS moon rocket is back in High Bay 3 inside the iconic Vehicle Assembly Building, ground teams will begin work to swap out the faulty helium valve and search for the source of a hydrogen leak in the tail service mast umbilical, where propellants flow from the mobile launch platform into the core stage.
Initial inspections at the launch pad revealed no sign of the leak, which appeared when NASA’s launch team began flowing liquid hydrogen — chilled to minus 423 degrees Fahrenheit (minus 253 degrees Celsius) — into the rocket in a “fast fill” mode.
Exposure to super-cold propellants contracts components in the mobile launch platform and the rocket itself, revealing 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.
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.
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.
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.
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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