NASA’s leak-plagued Space Launch System lunar rocket suffered initially worrying problems during Wednesday’s refueling test, but engineers ‘managed’ a new leakAnd capable of filling a giant booster with a full 750,000 gallons of supercooled propellant.
They also conducted two other key tests, validating that they were able to properly cool the rocket’s four hydrogen-fueled engines for flight needs and successfully pressurize the core-stage hydrogen tanks to flight levels.
Launch director Charlie Blackwell-Thompson wouldn’t speculate on whether NASA will push the launch date to Sept. 27, as previously discussed, saying she wants her team to review the test data before drawing any conclusions. But she said she was “very encouraged by today’s test”.
“I don’t like knowing the data ahead of time, so I want the team to have a chance to go and look at it and see if we need to make changes to our loaders, our schedule, or if we’re going to go back to the way things were,” she said.
Discussions could prove challenging considering the seal that caused the early launch delay has been replaced and the same system leaked again (at least initially) Wednesday.
But even if the team believes September 27 is a viable target for the rocket’s maiden flight, it may not be enough. The Space Force Eastern Range, which oversees all military and civilian launches in Florida, has yet to rule on NASA’s request to waive inspections of batteries in the rocket’s self-destruct system.
The batteries cannot be used on the launch pad, and without the waiver, NASA would be forced to tow the 332-foot-tall SLS rocket back to the Kennedy Space Center’s iconic Vehicle Assembly Building, delaying the launch by a month or more.
The long-awaited Artemis 1 mission is designed to send an unmanned Orion crew module on a 40-day voyage around the moon and back, paving the way for the first manned Artemis mission in 2024. If all goes well, NASA plans to land two astronauts close to the moon’s south pole in the 2025-26 time frame, the first in a series of ongoing missions.
But engineers have been plagued by elusive hydrogen leaks and other problems as the rocket prepares to launch. On March 17, the SLS rocket, years behind schedule and billions over budget, was towed for the first time to launch pad 39B for a fuel test, clearing the way for a launch. But due to multiple unrelated issues, we ordered back-to-back scrubs on April 3rd and 4th.
The third test on April 14 was canceled due to a hydrogen leak near a quick disconnect in the core stage fuel line, and the rocket was returned to the VAB for repairs. It returned to the launch pad in early June, but encountered more problems during a fuel test on June 20, when engineers were unable to cool the rocket’s engines due to stuck valves in different systems.
The rocket returned to the VAB for repairs in early July and was towed back to the launch pad in mid-August, in what NASA hopes will be its maiden flight. But the Aug. 29 launch attempt was canceled due to more hydrogen problems, and on Sept. 3, the 8-inch quick-disconnect fitting leaked and the test flew again.
After the second launch scrub, NASA administrators opted to disassemble the components on the launch pad, replace the internal seals, reassemble the hardware and conduct a refueling test to verify the integrity of the seals. Hydrogen leaks usually only occur when the pipes are exposed to low temperatures (in this case minus 423 degrees Fahrenheit),
Repairs were completed last week, and testing began as normal on Wednesday, with oxygen and hydrogen flowing into separate core-level storage tanks at low velocities. To reduce thermal shock when transitioning to Fast Fill mode, slow down the load sequence and reduce the flow rate to reduce stress on the hardware.
However, when the flow rate and pressure increased, sensors detected gaseous hydrogen immediately accumulating in the containment casing around the just-repaired quick-disconnect fitting, indicating a leak. The sensor detected concentrations as high as 7%, well above the safe limit of 4%.
Engineers then opted to preheat the fittings before restarting the hydrogen flow, in hopes of allowing the internal seals to “re-seat” on their own. When flow resumed, the leak was still there, but well below the 4 percent threshold, and engineers were able to move on, eventually filling the hydrogen tank with a full 730,000 gallons.
Close examination of the sensor data revealed that, contrary to the initially observed behavior, the leak rate decreased with increasing pressure. That’s how the fitting is designed to operate, suggesting that efforts to reinstall the seal were at least partially successful.
After the core-stage hydrogen and oxygen tanks were filled, engineers proceeded to load the upper stage of the SLS rocket while performing boost and engine cooling tests.
Another hydrogen leak was reported near the 4-inch quick-disconnect fitting used for the cooling test. While engineers have agreed to continue the observed concentrations, it stops the actual launch countdown. There’s no word yet on what, if any, impact the issue might have on launch plans.