CAPE CANAVERAL—Stymied by a new liquid hydrogen leak, NASA on Sept. 3 called off its second attempt to launch the Space Launch System (SLS) rocket on the Artemis I flight test and will skip the rest of the current launch window, which closes on Sept. 6, while the team weighs repair options and future launch dates.

With the countdown clock ticking toward launch at 2:17 p.m. EDT, the Kennedy Space Center team overseeing preparations for the inaugural SLS flight wrestled with a leak at the base of the rocket where liquid hydrogen from the mobile launch platform flows through an 8-in. quick disconnect umbilical into the SLS.
 
Fueling for the second launch attempt began around 6:30 a.m. on Sept. 3. The first launch attempt on Aug. 29 was scrubbed due to a potentially faulty liquid hydrogen bleed system needed to thermally condition the SLS core stage main engines ahead of ignition. Follow-on analysis pointed to a suspect temperature sensor, clearing the way for the second launch attempt.

Just prior to the start of cryogenic loading operations on Sept. 3, a hydrogen transfer line was inadvertently over-pressurized, reaching 60 psi instead of the intended 20 psi. 

“It’s too early to tell … if that was the cause of the engine leak we had today,” Artemis Mission Manager Mike Sarafin later told reporters. “The flight hardware itself is fine—we did not exceed the maximum design pressure, but there’s a chance the seal in the quick disconnect saw some effects from that.”

“This was a manual sequence,” Sarafin added. “It may have been the fact that we didn’t automate this particular sequence that could have been part of the reason that we had the inadvertent overpress. 

“There are a whole host of other reasons when you are an operator and you are working through a command sequence that could have come into play,” Sarafin said. 

The launch team made three attempts to reseat the seal, to no avail. Loading of liquid hydrogen was halted at 7:15 a.m. to allow the fitting to warm up, with the hopes that the faulty seal would reseat itself when it was re-exposed to the -423F cryogenic propellant. 
 
When that failed, the launch team pressurized the fitting with helium, but that too failed to staunch the leak. 
 
Engineers made a third attempt to reseat the seal by again warming the fitting and then manually commanding liquid hydrogen to flow through it. “As soon as they resumed flow with any pressure, they saw the leak return,” Artemis I launch commentator Derrol Nail said. 
 
While troubleshooting efforts continued, the core stage was filled with 196,000 gal. of liquid oxygen and preparations were underway to begin loading propellants into the SLS upper stage.
 
Launch Director Charlie Blackwell-Thompson called a scrub at 11:18 a.m.

The current Artemis I launch period expires on Sept. 5, when the U.S. Space Force’s 25-day certification of the SLS flight termination system expires. The termination system is required for the destruction of the 322-ft. rocket should it veer off course after liftoff from NASA’s Kennedy Space Center.

The termination system can only be retested for recertification inside the Vehicle Assembly Building (VAB), which will require the SLS and Orion to be rolled back from Launch Complex 39B unless the Space Force’s Space Launch Delta 45, which oversees the Eastern Range, agrees to an extension.

The Space Force did so in early August, agreeing to an extension from 20 to 25 days. 

Sarafin and Jim Free, NASA’s associate administrator for exploration systems development, said they believe there is rationale for an extension beyond 25 days but acknowledged that the decision rests with the Space Force.

Even without an extension, the next launch period for sending the Artemis I’s Orion spacecraft on a flight test  around the Moon opens on Sept. 19 and closes on Oct. 4.

Meanwhile, NASA’s launch and Mission Management teams expect to complete an analysis of the repair options for the hydrogen leak, including whether the work could be done at the launchpad or if a rollback to the VAB is preferred.

If at the launchpad, NASA could be positioned to conduct a partial loading of hydrogen propellant into the SLS to determine if the repair has been successful. If for some reason an even longer delay became necessary, a third launch period for the Artemis I opens on Oct. 17 and closes on Oct. 31.

“We will go when we are ready,” said NASA Administrator Bill Nelson. ”This is part of the space business.”