Engineers are ready to reload NASA's Artemis moon rocket with supercold fuel Wednesday to make sure a repaired liquid hydrogen quick-disconnect fitting is leak free, one of two requirements that must be met before the agency can make a third attempt to launch the huge booster September 27 on a maiden moonshot.
The other is a needed waiver from the Space Force Eastern Range, which oversees all military and civilian launches from Florida, allowing the unpiloted launch to proceed without first inspecting and servicing batteries in the booster's self-destruct system.
The batteries initially were certified for 20 days, a limit that later was extended by five days to give NASA three launch opportunities between August 29 and September 5. That extended waiver expired September 6, three days after the SLS rocket's second launch attempt wasbecause of a hydrogen leak during fueling.
The batteries in question cannot be accessed at the launch pad, and without another extension from the Eastern Range, the Space Launch System rocket would have to be hauled back to NASA's Vehicle Assembly Building, delaying the Artemis 1 mission to late October or early November.
"They've got the responsibility of public safety, and so they've asked for additional information (about the batteries)," said John Blevins, chief engineer of the Space Launch System rocket.
The fueling test does not require a waiver and "we really haven't been focused, other than answering their questions, on any kind of deadline to get that news back," Blevins said of the waiver request. "And so we'll let them do what they do and see if the data we provided them answers the questions they've got."
NASA carried out four fueling tests between April 3 and June 20, encountering a variety of problems that triggered repeated interruptions and modifications. The first actual launch attempt on August 29 was called off primarily because of trouble cooling the rocket's engines.
That problem was the result of a faulty sensor and NASA pressed ahead for a second launch attempt. But during fueling on September 3, high concentrations of gaseous hydrogen were detected in a housing around an 8-inch quick-disconnect fitting at the base of the SLS core stage where liquid hydrogen, at minus 423 degree Fahrenheit, flows into the rocket.
Sensors detected hydrogen concentrations of up to 8%, twice the allowable level, surging every time flow rates and pressures were increased. With clear indications of a leak, the launching was called off.
In the wake of the second scrub, NASA ordered engineers to detach the quick-disconnect fitting at the launch pad and to replace internal seals. That work was completed last week, clearing the way for Wednesday's fueling test.
During a teleconference with reporters Monday, managers said the seal taken out of the quick-disconnect fitting showed signs of deformation suggestive of an impact from "foreign object debris" of some sort. The indentation only measured about .01 inch across, but that may have been enough to explain the leak.
"We found a witness mark, or an indentation, on the soft goods associated with foreign object debris," said Mike Sarafin, the Artemis 1 mission manager. "We did not recover a piece of foreign object debris, but there was clearly an indentation in that seal that showed us there was a problem ... that contributed to the hydrogen leak."
Hydrogen leaks are notoriously difficult to pin down and fix because they typically only show up when the hardware is exposed to supercold, or cryogenic, temperatures. That's why NASA managers opted to attempt a repair at the launch pad, enabling a "cryo test" to verify the seal is leak free.
The allowable hydrogen concentration in the housing around the quick-disconnect fitting is 4%, the level at which the gas can spontaneously burn when mixed with oxygen. During the SLS rocket's second launch attempt September 3, sensors detected concentrations surging to 8% when flow rates and pressures were increased.
For the tanking test Wednesday, engineers are using a "kindler, gentler" approach, filling the core stage tank a bit slower and at slightly lower pressures to ease the shock when transitioning from "slow fill" to "fast fill" operations.
The "cryo test" countdown was expected to start at 5:30 p.m. Monday and conclude at 3 p.m. Wednesday at the T-minus 10-minute mark.
Assuming Wednesday's test goes well - and assuming clearance to proceed from the Eastern Range - NASA plans to restart a fresh countdown at 1:27 p.m. EDT Sunday, setting up a launch at 11:37 a.m. Tuesday.
The primary goals of the Artemis 1 mission are to use the SLS rocket to send an unpiloted Orion crew capsule into a distant orbit around the moon before returning to Earth on November 5, closing out a 39-day mission with a high-speed re-entry to splashdown in the Pacific Ocean west of San Diego.
NASA hopes to follow the Artemis 1 mission by launching four astronauts atop the second SLS rocket in late 2024 on an around-the-moon shakedown flight. And that will set the stage for two astronauts to land on the moon in the 2025-26 timeframe.
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