NASA’s Space Launch System lunar rocket ran into initially worrisome problems during a refueling test Wednesday, but engineers “worked out” a new leak in a coupling thatand were able to fill the huge booster with a full load of 750,000 gallons of supercooled fuel.
They also performed two more critical tests, confirming their ability to properly cool the rocket’s four hydrogen engines as required for flight and successfully pressurize the core’s hydrogen tank to flight levels.
Launch Director Charlie Blackwell-Thompson would not speculate on whether NASA might move forward with the Sept. 27 launch date as previously discussed, saying he wanted his team to review the test data before drawing any conclusions. But she said she was “extremely encouraged by today’s test”.
“I don’t like to go overboard with the data, so I’d like the team to have a chance to look at it and see if there are any changes we need to make to our loading procedures, our timelines, or if I’m good as is,” she said.
The discussion could prove challenging given that the seal blamed for the earlier launch delay has been replaced and the same system, at least initially, was leaked again on Wednesday.
But even if the team concludes that September 27 is a viable target for the rocket’s first flight, that may not be enough. The Space Force’s Eastern Range, which oversees all military and civilian launches from Florida, has not yet ruled on NASA’s request to waive the requirement to inspect the batteries in the rocket’s self-destruct system.
The batteries cannot be accessed on the launch pad, and without a waiver, NASA will be forced to tow the 332-foot-tall SLS rocket back to 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 capsule on a 40-day trip around the moon and back to pave the way for the first manned Artemis mission in 2024. If all goes well, NASA plans to land two astronauts near the moon’s south pole in in the 2025-26 timeframe, the first in an ongoing series of missions.
But engineers were baffled by elusive hydrogen leaks and other problems while preparing the rocket for launch. Years behind schedule and billions over budget, the SLS rocket first pulled up to launch pad 39B on March 17 for a fueling test to clear the way for launch. But the back scrub was ordered on April 3rd and 4th due to multiple unrelated issues.
A third test on April 14 was canceled due to a hydrogen leak near the core’s rapid separation fuel line, and the rocket was returned to VAB for servicing. It returned to the launch pad in early June only to suffer more problems during a fueling test on June 20, when engineers were unable to cool the rocket’s engines due to a stuck valve in another system.
The rocket was returned to VAB for repairs in early July and returned to the pad in mid-August for what NASA hoped would be its maiden flight. But a launch attempt on August 29 was canceled due to more hydrogen problems and again on September 3 when the 8-inch quick-detach fitting leaked.
After the second launch cleanup, NASA managers decided to disassemble the joint on the launch pad, replace the internal seal, reassemble the hardware, and perform a refueling test to confirm the integrity of the seal. Hydrogen leaks usually only appear when plumbing is exposed to cryogenic temperatures—in this case, minus 423 degrees Fahrenheit.
Repair work was completed last week and the test began as normal on Wednesday, with oxygen and hydrogen flowing into separate core tanks at low speeds. In an effort to mitigate thermal shock when switching to “quick charge” mode, the charging sequence is slowed down and flow rates are reduced to reduce the load on the hardware.
But when the flow and pressures increased, the sensors detected a momentary build-up of hydrogen gas in the protective housing around the just-repaired quick-disconnect coupling, indicating a leak. The sensors detected concentrations of up to 7%, well above the safety limit of 4%.
The engineers then decided to heat the joints before restarting the hydrogen flow in the hope of forcing the internal seal to “reset”. When flow resumed, the leak was still present, but was well below the 4% threshold and engineers were able to move forward, eventually filling the hydrogen tank with a full load of 730,000 gallons.
Careful examination of the sensor data showed that in a reversal of the behavior originally observed, the leak rate decreased as the pressure increased. That’s how the coupling was designed to work, suggesting that efforts to reseat the seal were at least partially successful.
With the base stage’s hydrogen and oxygen tanks full, engineers began fueling the SLS rocket’s upper stage while performing pressure and engine cooling tests.
Another hydrogen leak was reported near the 4-inch quick-disconnect fitting used for the cooling test. Although engineers had already agreed to proceed with the observed concentration, this would halt the actual launch countdown. No word yet on what impact, if any, the issue might have on launch planning.