After months of testing, troubleshooting and repairs, engineers began fueling the Space Launch System rocket for blast off Monday on NASA’s long-delayed Artemis 1 test flight, but a hydrogen leak, similar to the one that derailed a previous power test, interrupted the complicated process.
The leak developed in a launch pad service structure where propellants are fed into the rocket’s core stage through umbilicals designed to ensure a watertight seal until the moment of launch when they are retracted. The build-up was located in the casing around these umbilicals, known as the “scavenger pot”.
Spills are potentially dangerous, and sensors monitor concentrations to make sure safety limits aren’t breached. During Monday’s fueling process, higher than permitted hydrogen concentrations were observed when the flow rate was changed from “slow” to “fast fill” at a rate 10 times higher, subjecting the plumbing to higher pressures.
After returning to the slow fill and evaluating the readings, the engineers decided to continue the fast fill to see if the hydrogen concentration in the tail umbilical cylinder rose again. Concentrations higher than 4 percent are a violation of safety criteria, which prohibits launching.
Liftoff was originally scheduled for 8:33 AM. EDT. It was not immediately clear what impact the weather-related fueling delay and dealing with hydrogen problems might have on the final launch time, assuming the problem can be resolved before the end of a two-hour launch window.
The SLS rocket’s core stage must be filled with 196,000 gallons of liquid oxygen and 537,000 gallons of hydrogen for liftoff. The upper stage requires another 22,000 gallons of oxygen and hydrogen, for a total of 750,000 gallons of propellant.
All of this propellant will power the core stage’s four bus-era engines. Coupled with two strap-on solid fuel boosters, the rocket will generate a ground-shaking 8.8 million pounds of thrust upon launch to propel the 5.7 million pound rocket away from pad 39B at the Kennedy Space Center.
The initial Artemis 1 test flight is intended to verify the rocket’s ability to propel Orion capsules into Earth orbit and then to the Moon. Engineers will also test the crew ship’s myriad systems in deep space and make sure its heat shield can protect returning astronauts from the 5,000-degree heat of reentry.
NASA plans to follow up on the unfunded Artemis 1 mission by launching four astronauts on a lunar orbit in 2024, setting the stage for the first astronaut landing in nearly 50 years, when the first woman and the next man step onto the surface . the 2025-26 timetable.
But first, NASA must prove that the rocket and capsule will perform as planned, and that starts with the launch of Artemis 1 on Monday.
NASA conducted four reverse measurements and dress power tests earlier this year, and all four encountered problems. Most difficult to resolve were hydrogen leaks in the service tail mast umbilical system that derailed the initial test and in a 4-inch quick-disconnect fitting that appeared during the most recent test on June 20.
Hydrogen leaks are notoriously difficult to find and repair because they tend to only appear when the material is subjected to cryogenic temperatures. For hydrogen, this is minus 423 degrees Fahrenheit.
The umbilical system leak during the first rocket fueling test was repaired at ambient temperatures in the Vehicle Assembly Building and functioned normally during a subsequent pad fueling test.
Whether the problem that developed Monday is a repeat of the original issue was not immediately clear, but it was located in the same area.
The 4-inch quick disconnect was repaired during a subsequent trip back to the VAB, but the fitting had not yet been exposed to hydrogen when the umbilical leak was detected, interrupting the fueling process.
NASA engineers were confident that the rocket was finally ready to fly, but the latest leak raises concerns that another VAB reset may be required.
Due to the constantly changing positions of the Earth and the Moon, NASA can only launch the SLS rocket during limited launch periods.
The current run, No. 25, opened on August 23 and runs through September 6. Launch Season 26 opens on September 19th and runs through October 4th. The season after that, No. 27, opens on October 17th and runs through October 31st.
Due to the requirement to service self-destruct system batteries, which cannot be accessed on the launch pad, the SLS rocket must lift off by September 6 or be towed back to the Vehicle Assembly Building.
Fixing another hydrogen leak would also require a trip back to the VAB, which would almost certainly delay the launch until late September or October at the earliest.
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