Engineers are set to reload NASA’s Artemis moon rocket with supercooled fuel on Wednesday to make sure a repaired liquid hydrogen fast disconnect is free of leaks, one of two requirements that must be met before the agency can make a third attempt to launch the massive booster on September 27 at a virgin moon.
The other is a necessary waiver from Space Force Eastern Range, which oversees all military and civilian launches from Florida, allowing the unmanned launch to proceed without first inspecting and repairing the batteries in the booster’s self-destruct system.
The batteries were originally certified for 20 days, a limit that was later extended by five days to give NASA three launch opportunities between August 29 and September 5. That extended waiver ended on September 6, three days after the SLS rocket’s second launch attemptdue to hydrogen leakage during refueling.
Unable to access those batteries from the launch pad, and without another extension from the Eastern Range, the Space Launch System rocket will have to be moved back to NASA’s Vehicle Assembly Building, delaying the Artemis 1 mission to late October or early November.
“They have a public safety responsibility, and that’s why they asked for additional information (about the batteries),” said John Blevins, chief engineer of the Space Launch System rocket.
The feed test does not require a waiver, and “we really haven’t focused, other than answering their questions, on any deadline to get that news back,” Blevins said of the waiver request. “And so we’re going to let them do what they’re doing and see if the data we give them answers the questions they have.”
NASA conducted four power-up tests between April 3 and June 20, dealing with a variety of problems that caused repeated interruptions and modifications. The first real launch attempt on August 29 was canceled mainly due to cooling problems of the rocket engines.
That problem was the result of a faulty sensor, and NASA pushed ahead with a second launch attempt. But during fueling on Sept. 3, high concentrations of hydrogen gas were detected in a sheath around an 8-inch quick-detach fitting at the base of the SLS core, where liquid hydrogen, at minus 423 degrees Fahrenheit, flows into the rocket.
The sensors detected hydrogen concentrations of up to 8%, twice the permitted level, increasing as flow rates and pressures increased. With clear indications of a leak, the launch was aborted.
After the second rub, NASA ordered engineers to disconnect the quick disconnect on the launch pad and replace the internal seals. That work was completed last week, paving the way for Wednesday’s feed test.
During a conference call with reporters Monday, administrators said the seal removed from the quick-disconnect fitting showed signs of deformation that suggested an impact from “foreign object debris” of some kind. The indentation was only about 0.01 inch in diameter, but that might have been enough to explain the leak.
“We found a witness mark, or an indentation, in the soft material associated with foreign object debris,” said Mike Sarafin, the Artemis 1 mission manager. “We didn’t recover a piece of foreign object debris, but there was clearly an indentation in this seal that showed us there was a problem … that contributed to the hydrogen leak.”
Hydrogen leaks are very difficult to detect and fix because they usually only appear when the material is exposed to supercold or cryogenic temperatures. That’s why NASA managers chose to attempt a repair on the launch pad, allowing a “cryo test” to verify that the seal is not leaking.
The allowable concentration of hydrogen in the enclosure around the quick-disconnect fitting is 4%, the level at which the gas can spontaneously combust when mixed with oxygen. During the SLS rocket’s second launch attempt on September 3, sensors detected concentrations rising to 8% when flow rates and pressures increased.
For Wednesday’s tank test, engineers are using a “softer” approach, filling the core tank a little more slowly and at slightly lower pressures to soften the shock of going from “slow-fill” to “fast-fill” mode .
The countdown to the “cryo test” was expected to begin at 5:30 p.m. on Monday and end at 3 p.m. of Wednesday at the T-minus 10 minute point.
Assuming Wednesday’s test goes well — and assuming clearance goes through from the Eastern Range — NASA plans to restart a new countdown at 1:27 p.m. EDT Sunday, setting up an 11:37 a.m. launch. of Tuesday.
The Artemis 1 mission’s primary goals are to use the SLS rocket to send an unmanned Orion crew capsule into a distant orbit around the moon before returning to Earth on Nov. 5, capping a 39-day high-speed repeat mission. splashdown entry into the Pacific Ocean west of San Diego.
NASA hopes to follow up the Artemis 1 mission by launching four astronauts atop the second SLS rocket in late 2024 on a shakedown flight around the moon. And this will set the stage for two astronauts to land on the moon in the 2025-26 time frame.
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