A crucial pre-flight milestone will be reached on Wednesday with the Artemis moon rocket fueling test.

 

A crucial pre-flight milestone will be reached on Wednesday with the Artemis moon rocket fueling test.

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 second is a necessary waiver from the Space Force Eastern Range, which monitors all commercial and military launches from Florida and allows the unpiloted launch to occur without first assessing and maintaining batteries in the booster's self-destruct mechanism.
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 was called off because 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.
According to John Blevins, chief engineer of the Space Launch System rocket, "They have the responsibility of ensuring public safety, thus they have requested additional information (regarding the batteries). 
The fueling test does not call for a waiver, and regarding the waiver request, Blevins said, "we really haven't been focused, other than answering their questions, on any kind of timetable to deliver that news back." "So we'll let them do what they do and see if the information we gave them addresses the questions they have," the statement continued.
Between April 3 and June 20, NASA conducted four fuelling tests, but a number of issues necessitated frequent alterations and suspensions. The main reason why the first actual launch attempt on August 29 was aborted was due of issues with the rocket's engines cooling. 
A defective sensor was to blame for that issue, so NASA moved forward with a second launch attempt. However, on September 3, as the SLS core stage was being fueled, significant amounts of gaseous hydrogen were found in a housing near an 8-inch quick-disconnect fitting where liquid hydrogen, at minus 423 degrees Fahrenheit, flows into the rocket.
Sensors recorded hydrogen concentrations of up to 8%, which is double the permitted amount. These concentrations spiked whenever flow rates and pressures were raised. The launch was postponed due to obvious signs of a leak. 
After the second scrub, NASA gave engineers the go-ahead to replace the internal seals and unhook the quick-disconnect fitting at the launch pad. Last week's work was finished, making Wednesday's fueling test possible.
Managers said the seal removed from the quick-disconnect fitting revealed traces of deformation indicative of an impact by "foreign object debris" of some sort during a teleconference with media on Monday. Even though the indentation was just about.01 inch wide, it might have been sufficient to account for the leak.

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The mission manager of Artemis 1 Mike Sarafin stated, "We found a witness mark, or an indentation, on the soft commodities associated with foreign object debris." Although we were unable to locate any foreign item debris, the seal had an obvious indentation that indicated an issue that may have contributed to the hydrogen leak. 
Because they often only manifest when the hardware is exposed to extremely cold temperatures, or cryogenic temperatures, hydrogen leaks are notoriously challenging to locate and repair. To enable a "cryo test" to confirm the seal is leak-free, NASA managers decided to try a repair at the launch pad.
In order to prevent the hydrogen gas from spontaneously igniting when combined with oxygen, the hydrogen concentration in the housing around the quick-disconnect fitting must not exceed 4%. On September 3, sensors discovered concentrations rising to 8% as flow rates and pressures were raised during the SLS rocket's second launch attempt. 
Engineers are taking a "kinder, softer" approach for the tanking test on Wednesday, filling the core stage tank a little bit more slowly and at a little lower pressure to lessen the shock when switching from "slow fill" to "rapid fill" operations.
The "cryo test" countdown was scheduled to begin at 5:30 p.m. on Monday and end at T-minus 10 minutes on Wednesday at 3 p.m. 
If the test on Wednesday goes well and the Eastern Range gives the go-ahead, NASA intends to start a new countdown at 1:27 p.m. EDT on Sunday, setting up a launch for 11:37 a.m. on Tuesday. 
The main objectives of the Artemis 1 mission are to launch an unmanned Orion crew capsule into a far-off orbit around the moon using the SLS rocket and then return to Earth on November 5 with a high-speed re-entry to splashdown in the Pacific Ocean west of San Diego.
NASA plans to deploy four humans on the second SLS rocket in late 2024 for an around-the-moon shakedown flight to follow the Artemis 1 mission. And that will prepare the way for two astronauts to visit the moon between 2025 and 2026.