NASA will move its first giant Space Launch System moon rocket off the launch pad and back to its hangar at the Kennedy Space Center as soon as next Tuesday, giving teams an opportunity to resolve several problems discovered during three attempts to load super-cold propellants into the launcher earlier this month.
Rolling the 322-foot-tall (98-meter) rocket off of pad 39B and back to the Vehicle Assembly Building — a move tentatively set for next Tuesday, April 26 — will delay the first flight of the Space Launch System with an unpiloted Orion crew capsule on the Artemis 1 demonstration mission, a precursor for future astronaut flights to the moon.
A 10-day launch period in early June is “challenged” because of the delays in the Artemis 1 countdown dress rehearsal, said Tom Whitmeyer, a NASA manager who oversees development of the SLS moon rocket and other exploration systems.
“The next launch period opportunity is from June 29 through July 12, and then there’s another opportunity after that,” said Mike Sarafin, NASA’s Artemis 1 mission manager, in a media teleconference Monday. Another two-week launch period opens July 26 and runs until Aug. 9.
The launch periods are constrained by a number of considerations, including the position of the moon in its orbit around Earth, limits on how long the Orion spacecraft can fly in shadow without direct sunlight on its solar arrays, and re-entry and splashdown rules, including a requirement for daytime return to Earth to aid in recovery operations in the Pacific Ocean.
NASA officials don’t want to set an official target launch date for the oft-delayed maiden flight of the Space Launch System rocket until completing the countdown test, known as a wet dress rehearsal.
The test involves loading some 755,000 gallons of super-cold liquid hydrogen and liquid oxygen into the rocket. On the third countdown attempt last Thursday, NASA’s launch team got as far as filling about half of the core stage’s liquid oxygen tank, and about 5% of the liquid hydrogen tank — and never tried to pump cryogenic propellants into the upper stage.
Technicians inside the Vehicle Assembly Building will replace a faulty helium check valve on the rocket’s upper stage, and try to locate and repair a hydrogen leak discovered in the interface between the moon rocket’s core stage and its mobile launch platform. The valve failure prevented loading of propellant into the upper stage, and the hydrogen leak cut short tanking of the core stage Thursday.
Meanwhile, crews at an off-site plant operated by Air Liquide will upgrade gaseous nitrogen infrastructure needed to better support the demands of the SLS moon rocket, the largest launcher to fly from Florida’s Space Coast in nearly 50 years. The nitrogen is pipelined into the space center to help purge flammable gases from spaces inside rockets, but the SLS needs more of the nitrogen than other rockets based at the Kennedy Space Center or neighboring Cape Canaveral Space Force Station.
Upgrades at the Air Liquide facility will provide a “more robust capability” needed for SLS pre-launch operations, Whitmeyer said. The upgrades will not impact launch operations from other pads that use the same facility, such as SpaceX’s missions from pad 39A, NASA officials said.
NASA rolled the SLS moon rocket out to pad 39B on March 17 to prepare for the wet dress rehearsal. Teams at the pad are now configuring the launcher for the 4.2-mile (6.8-kilometer) journey back to the Vehicle Assembly Building, said Charlie Blackwell-Thompson, NASA’s Artemis 1 launch director.
The move could begin as soon as next Tuesday, she said.
Once the rocket is back in High Bay 3 inside the iconic 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 have 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. Blackwell-Thompson said 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.
Whitmeyer, NASA’s exploration systems manager, said Monday 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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