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As part of its launch campaign for the first Artemis mission, the National Aeronautics and Space Administration (NASA) continued to experience problems with the support tower of the Space Launch System (SLS) rocket after aborting two launch attempts earlier this month and late August. . NASA’s SLS rocket was originally slated to fly the Orion spacecraft to the moon in August, but problems with fuel leaks and engine cooling forced the agency to abandon launch attempts. After the scrubs, NASA then moved full speed ahead to the next launch date and proceeded to repair the rocket’s quick-disconnect seal on the cushion for a quicker turnaround than possible if the rocket had been returned to the building. of vehicle assembly (VAB) of the agency.
NASA resumes hydrogen fuel flow in SLS rocket after halting refueling due to persistent leaks
After NASA replaced a seal on the SLS rocket’s quick-disconnect arm, the agency conducted a test operation today to test whether the changes stopped the leaks that caused a last-minute scrub of the Artemis 1 mission on September 3. The cryogenic demonstration test, which began at 7:32 a.m. Eastern today, saw liquid oxygen and hydrogen begin to flow into the rocket’s tanks just over an hour after the launch director gave the green light.
However, at 10:05 a.m., the flow of hydrogen into the rocket had to be stopped because the quick-disconnect arm seal could not prevent the liquid from leaking into the surrounding area. Hydrogen is charged into the rocket by a pressure differential mechanism, and as the fuel lines are first cooled before charging fuel, their materials contract, which then results in hydrogen leakage.
Describing the problem, NASA’s Derrol Nail pointed out that:
…the teams are discussing the detection of a hydrogen leak in the umbilical of the tail mast. It’s in the lower part of the rocket. They had a reading of 7% hydrogen in the cavity where the quick disconnect line is, that’s the one that got fixed. . . as soon as the flow stoppage occurred, the leak rate immediately decreased. The launch team is considering doing their warm-up procedure eventually.
The engineers decided to let the lines warm up and then resume filling the tanks. They had executed a similar plan during the launch attempt earlier this month, and the whole procedure took an hour and a half, after which the hydrogen began flowing through the rocket again.
This leak had the same signature as the previous one, leading to the concentration of hydrogen in the surrounding area at 7% – nearly twice the NASA safety threshold of 4%.
After refueling resumed, engineers then increased the pressure of the hydrogen flowing through the rocket to determine how much the leak rate increased, as initially they had increased the pressure much faster. The plan was to evaluate the seal when the hydrogen concentration touched 10% – and if it exceeded 10%, the flow would be stopped.
Engineers also reworked the “kickstart” test that cools the engines for a pre-launch procedure to condition them for super cold fuel to flow through them for ignition. This involved closing the hydrogen vents to supply hydrogen to the engines. Artemis 1’s first launch attempt in late August was canceled because a sensor showed incorrect temperatures for that test, and NASA officials later speculated that a faulty sensor was the most common cause. probable error.
During the start-up test, the leak increased from 1% to 3.4% as the pressure of the hydrogen flow increased. The start-up test was successful, and engineers continued to increase pressure to accelerate the fill rate, which would mirror the rate on launch day. The teams then decided to stop the flow if the leak exceeded 4%.
However, that’s where they “scratched their heads,” according to Nail, because six hours into the test, the peak leak percentage was 3.4%. The central stage hydrogen tank reached the “filling” stage without the leak increasing significantly. It is at this stage that the boiled fuel is refilled and the hydrogen flows out at slower speeds. Engineers confirmed that at the time refueling began, data showed that during the fast fill phase of refueling, when flow pressure is at its highest, the leak rate was only 0 .5%.
Right now, engineers are evaluating the joint, and it’s possible that the joint connecting the launch tower to the rocket just didn’t “set” properly when it was repaired. The latest data shows that as the pressure increased, the leakage decreased, which follows the design of the quick disconnect and its sealing. The rocket’s second stage has yet to begin filling operations, and teams are discussing whether to pressurize the first-stage tanks after the second-stage tanks enter filling.
For live coverage of the event, you can head over to NASA’s live stream: