NASA is preparing to replace a faulty seal linked to a hydrogen leak that resulted in the second scrubbed launch attempt of SLS on Saturday. The repairs will happen at the launch pad, which is ideal from a testing perspective, but NASA still needs to cart the jumbo rocket back to the assembly building to meet safety requirements.
Technicians will replace a seal on the quick disconnect, an interface that joins the liquid hydrogen fuel line on the mobile launcher to the Space Launch System core stage, according to a brief NASA statement. The teams will also check plate coverings on other umbilicals to rule out hydrogen leaks at those locations. “With seven main umbilical lines, each line may have multiple connection points,” NASA explained.
NASA is attempting an uncrewed mission to the Moon and back, in preparation for a human lunar landing later this decade. But during the early stages of the launch attempt on September 3, an inadvertent command briefly raised the pressure within the system, possibly damaging some components. An unmanageable hydrogen leak resulted in the scrub—the second in a week. The earlier scrub, on Monday, August 29, was also marred by a hydrogen leak, though engineers were able to resolve it. Ultimately, it was a faulty sensor that doomed the first launch attempt.
The unflown SLS rocket remains in a safe configuration, standing tall on Launch Pad 39B at Kennedy Space Center in Florida. NASA is seeking to launch the Artemis 1 mission, in which the rocket will send an uncrewed Orion spacecraft on a journey around the Moon and back. The first launch period, which ran from August 23 to September 6, has ended, forcing a pause in the action. The space agency must now prepare the 322-foot-tall (98-meter) rocket for the third Artemis 1 launch attempt, the date of which has not yet been announced.
Technicians are planning to set up a temporary enclosure around the base of the rocket to protect the hardware from the Florida weather. A benefit of working directly on the pad is that engineers will be able to test the fix under cryogenic conditions. During launch preparations, liquid hydrogen gets pumped through the system at ultra-cold temperatures reaching -423 degrees Fahrenheit (-253 degrees Celsius). This, plus the added high pressure, has the effect of contracting and warping components, which can lead to unwanted and dangerous leaks, particularly around seals.
As a propellant, hydrogen is efficient but notoriously difficult to reign in. Hydrogen leaks were an all-too-frequent source of scrubs during the Space Shuttle era, and now SLS, which is likewise powered by a liquid hydrogen and liquid oxygen mixture, appears to be suffering from the same technical hardship.
Engineers mulled returning SLS to the nearby Vehicle Assembly Building (VAB) for the required repairs but opted instead to work on the pad. The VAB would’ve presented a more controlled environment to work in, but without the ability to replicate the desired cryogenic conditions for testing (tests inside the VAB have to be run at ambient temperatures). “Performing the work at the pad also allows teams to gather as much data as possible to understand the cause of the issue,” NASA added.
SLS will likely have to return to the VAB, fix or no fix. The Eastern Range, a branch of the U.S. Space Force, requires periodic certification of the rocket’s flight termination system. NASA already received a waiver that extended certification from 20 to 25 days, but it’s not clear if the space agency will request a second waiver, which would be irregular. The Eastern Range oversees launches from Kennedy Space Center and Cape Canaveral Space Force Station, and works to ensure the public’s safety.
At a press briefing on Saturday, Mike Sarafin, Artemis mission manager, said “it’s not our decision—it’s the Range’s decision.” He added that a waiver from the Range could keep the rocket on the pad, “but that’s not likely.” So, under the Eastern Range restrictions, and until we hear otherwise from NASA about a second waiver, the rocket must return to the VAB prior to the next launch period.
A third launch attempt in late September or early October remains a distant possibility. The next period opens on September 19 and closes on October 4, with no opportunities to launch on September 29 and 30. For this to work, however, NASA would have to complete its latest fix, run tests, cart SLS back to the VAB for recertification (which involves a very short confidence test), and then cart it back to the launch pad. It’s possible, but ground teams will have to haul ass to make this happen.
Failing this, the third launch period opens on October 17 and closes on October 31, with launch exclusions on October 24, 25, 26, and 28. Two other periods, one in November and one in December, exist within the current calendar year.
There’s still plenty of time for SLS to launch in 2022, but it all depends on how quickly engineers can get a handle on this complex system. SLS is the most powerful rocket that NASA has ever built and is a key component of the space agency’s Artemis program, which seeks a sustained and prolonged human presence at and around the Moon.