NASA's leak-plagued Space Launch System moon rocket ran into initially worrisome problems during a fueling test Wednesday, but engineers “managed” a fresh leak in a fitting thatand were able to fill the huge booster with a full load of 750,000 gallons of supercold propellants.
They also carried out two other critical tests, verifying their ability to properly chill the rocket's four hydrogen-fueled engines as required for flight and successfully pressurizing the core stage hydrogen tank to flight levels.
Launch Director Charlie Blackwell-Thompson would not speculate on whether NASA might press ahead toward a September 27 launch date as earlier discussed, saying she wanted her team to review data from the test before drawing any conclusions. But she said she was “extremely encouraged by the test today.”
“I don't like to get ahead of the data, so I'd like the team to have the opportunity to go look at it to see if there are changes we need to make to our loading procedures, our timelines or if we're good as is,” she said.
The discussion could prove challenging given the seal blamed for the earlier launch delay was replaced and the same system, at least initially, leaked again Wednesday.
But even if the team concludes September 27 is a viable target for the rocket's maiden flight, it might not be enough. The Space Force Eastern Range, which oversees all military and civilian launches from Florida, has not yet ruled on a request from NASA to waive a requirement to inspect batteries in the rocket's self-destruct system.
The batteries cannot be accessed at the launch pad and without a waiver, NASA will be forced to haul the 332-foot-tall SLS rocket back to the Kennedy Space Center's iconic Vehicle Assembly Building, delaying launch for a month or more.
The long-awaited Artemis 1 mission is designed to send an unpiloted Orion crew capsule on a 40-day voyage around the moon and back to pave the way for the first piloted Artemis mission in 2024. If all goes well, NASA plans to land two astronauts near the moon's south pole in the 2025-26 timeframe, the first in a sustained series of missions.
But engineers have been bedeviled by elusive hydrogen leaks and other issues during the rocket's run-up to launch. Already years behind schedule and billions over budget, the SLS rocket was first hauled out to launch pad 39B on March 17 for a fueling test to clear the way for launch. But back-to-back scrubs were ordered April 3 and 4 because of multiple unrelated problems.
A third test on April 14 was called off because of a hydrogen leak near the core stage fuel line quick-disconnect, and the rocket was rolled back to the VAB for servicing. It returned to the launch pad in early June only to suffer more problems during a June 20 fueling test, when engineers were unable to cool the rocket's engines because of a stuck valve in a different system.
The rocket was returned to the VAB for repairs in early July and hauled back to the pad in mid-August for what NASA hoped would be its maiden flight. But a launch try on August 29 was called off because of more hydrogen issues and again on September 3 when the 8-inch quick-disconnect fitting leaked.
In the wake of the second launch scrub, NASA managers opted to take the fitting apart at the launch pad, replace an internal seal, re-assemble the hardware and carry out a fueling test to verify the seal's integrity. Hydrogen leaks typically show up only when the plumbing is exposed to cryogenic temperature — minus 423 degrees Fahrenheit in this case,
The repair work was completed last week and the test began normally enough Wednesday, with oxygen and hydrogen flowing into separate core stage tanks at low rates. In an effort to ease the thermal shock when transitioning to “fast fill” mode, the loading sequence was slowed down and flow rates reduced to ease stresses on the hardware.
But when the flow rate and pressures increased, sensors detected an immediate buildup of gaseous hydrogen in a containment housing around the just-repaired quick-disconnect fitting, indicating a leak. Sensors detected concentrations of up to 7%, well above the 4% safety limit.
Engineers then opted to warm up the fittings before restarting the hydrogen flow in hopes of coaxing the internal seal to “re-seat” itself. When flow resumed, a leak was still present, but it was well below the 4% threshold and engineers were able to press ahead, eventually topping off the hydrogen tank with a full load of 730,000 gallons.
A close examination of sensor data showed that in a reversal of the initially observed behavior, the leak rate went down as pressure increased. That's how the fitting is designed to operate, suggesting efforts to re-seat the seal were at least partially successful.
With the core stage hydrogen and oxygen tanks full, engineers pressed ahead with loading the SLS rocket's upper stage and in the meantime carried out the pressurization and engine cooling tests.
Another hydrogen leak was reported near a 4-inch quick-disconnect fitting used for the cooling test. While engineers already had agreed to press ahead with the observed concentration, it would have halted an actual launch countdown. No word yet on what impact, if any, that issue might have on launch planning.