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As part of its launch campaign for the first Artemis mission, the National Aeronautics and Space Administration (NASA) continued to run into problems with the Space Launch System (SLS) rocket's supporting tower after it aborted two launch attempts earlier this month and in late August. NASA's SLS rocket was initially set to fly the Orion spacecraft to the Moon in August, but problems with fuel leaks and engine chill forced the agency to stand down from its launch attempts. Following the scrubs, NASA then moved full speed ahead towards the next launch date and proceeded to repair the rocket's quick disconnect seal on the pad for a quicker turnaround than possible if the rocket had been shipped back to the agency's Vehicle Assembly Building (VAB).
NASA Resumes Hydrogen Fuel Flow In SLS Rocket After Stopping Fuelling Due To Persistent Leaks
After NASA replaced a seal on the SLS rocket's quick disconnect arm, the agency proceeded to go ahead with a test operation today to check whether the changes stopped the leaks that caused a last moment scrub of the Artemis 1 mission on September 3rd. The cryogenic demonstration test, which started at 7:32 am Eastern Time today, saw liquid oxygen and hydrogen start flowing into the rocket's tanks a little over an hour after the launch director gave the go ahead.
However, at 10:05 am, the flow of hydrogen into the rocket had to be stopped as the quick disconnect arm's seal could not stop the liquid from leaking into the surroundings. Hydrogen is loaded into the rocket through a pressure differential mechanism, and since the fuel lines are first cooled before loading the fuel, their materials contract - which then results in hydrogen leaking out.
Describing the problem, NASA's Derrol Nail outlined that:
...teamns are discussing the detection of a hydrogen leak in the tail service mast umbilical. It's in the lower portion of the rocket. They had a 7% reading of hydrogen in the cavity where the quick disconnect line is, this was the one that was repaired. . . as soon as stop flow happened, the leak rate immediately came down. The launch team is discussing possibly doing their warm up procedure.
The engineers decided to let the lines warm up and then resume filling the tanks once again. They had carried out a similar plan during the launch attempt earlier this month, and the entire procedure took an hour and a half, after which hydrogen began to flow again into the rocket.
This leak had the same signature as the previous one, leading to the concentration of hydrogen in the surrounding area to 7% - nearly twice as much as NASA's safety threshold of 4%.
After the fuelling resumed, engineers then raised the pressure of hydrogen flowing into the rocket to determine at which point the leak rate increased, as initially, they had increased pressure much faster. The plan was to evaluate the seal when the hydrogen concentration touched 10% - and if it crossed 10%, the flow would be stopped.
The engineers also resumed the 'kickstart' test that cools the engines for a pre-launch procedure to condition them for the super cold fuel to flow into them for ignition. This involved closing the hydrogen vents to feed hydrogen into the engines. The first Artemis 1 launch attempt in late August was canceled as a sensor showed incorrect temperatures for this test, and NASA officials later speculated that a faulty sensor was the most likely cause for the error.
During the kickstart test, the leak increased from 1% to 3.4% as the hydrogen flow pressure increased. The kickstart test was successful, and engineers continued to increase the pressure to fast fill flow, which would mirror the flow rate on launch day. At that point, the teams decided to stop the flow if the leak went above 4%.
However, this is where they were left "scratching their heads," according to Nail, as six hours into the test, the maximum leak percentage stood at 3.4%. The core stage hydrogen tank reached the 'replenish' stage without the leak increasing significantly. This stage is where the fuel that has boiled off is refilled, and it sees hydrogen flow at slower rates. Engineers confirmed that just as replenish started, data showed that during the fast fill phase of fuelling, where the flow pressure is at its highest, the leak rate was only 0.5%.
As of now, engineers are proceeding to evaluate the seal, and it is possible that the seal connecting the launch tower to the rocket simply did not 'set' properly during its repair. The latest data shows that as the pressure increased, the leak decreased, which follows the design of the quick disconnect and its seal. The second stage of the rocket is yet to begin its filling operations, and the teams are discussing whether to proceed to pressurize the first stage's tanks after the second stage tanks have entered replenish.
For live coverage of the event, you can head on to NASA's live stream: