A demonstration to confirm a repaired hydrogen leak appears to have gone well, with NASA declaring Wednesday’s cryogenic tanking test a success. Engineers still need to review the results, but the space agency could be on track to perform its third launch attempt of its SLS megarocket in just six days—a mission that would officially kick off the Artemis lunar program.
Launch director Charlie Blackwell-Thompson declared a “go” for tanking at 7:30 am (all times Eastern), around 30 minutes after the intended start time. Ground teams began the process of loading more than 700,000 gallons of propellant into the megarocket, beginning with the core stage. Today’s cryogenic tanking test, as it was called, happened as the 321-foot-tall (98-meter) rocket stood at Launch Pad 39B at the Kennedy Space Center in Florida.
The test follows two previous launch attempts, both of which ended in scrubs, for different reasons. The first scrubon August 29, was the result of a faulty sensor that recorded erroneous engine temperature readingswhile the second scrub, on September 3, was the result of a significant hydrogen leak, which NASA subsequently traced to damaged seals at the quick disconnect fitting between a liquid hydrogen fuel line and the core stage. SLS uses a mixture of oxygen and liquid hydrogen, the latter of which has a propensity to leak due to its small atomic stature.
Not willing to attempt a third launch attempt just yet, NASA officials decided to run a cryogenic tanking test, the primary objective of which was to “look at the two new seals,” as Tom Whitmeyer, deputy associate administrator for common exploration systems development at NASA, told reporters on Monday. NASA officials refrained from calling today’s test a wet dress rehearsal, as key wet dress objectives, such as going into the terminal count phase of the countdown and powering the Orion spacecraft and side boosters, were not included in Wednesday‘s test.
For today’s test, a key strategy was for ground teams to employ a “kinder, gentler” approach to tanking. Engineers felt that a slower approach would lessen the chance of thermal shock, as components come into contact with ultra-cold propellants at temperatures reaching -423 degrees Fahrenheit (-217 degrees Celsius). It’s possible that thermal shock, or an unintended over-pressurization, resulted in the hydrogen leak on September 3, but the true cause of the faulty 8-inch seal, which exhibited a possible indentation mark less than 0.01 inches in size, is not yet known.
At around 9:45 am, ground teams transitioned from slow fill to fast fill. An hour later, the teams reported a hydrogen leak at the quick disconnect between the rocket and the tail service mast umbilical, in what was an ominous sign. Blackwell-Thompson signed off on the ensuing plan to warm the line and reset the connection point, and the teams were back in business about an hour later. Speaking to Blackwell-Thompson after the test, Derrol Nail, launch commentator for NASA, said, “you could kind of feel the room deflate a bit, but as [the ground teams] got past it, you could feel a certain lifting of the room.”
The tanking moved quickly and smoothly after that, with the completion of the thermal conditioning of the rocket’s four RS-25 engines happening shortly before 1:00 pm The teams managed to fully fill the core stage and the Interim Cryogenic Propulsion Stage (ICPS), otherwise known as the upper stage, with propellants. By 3:45 pm, launch controllers had completed the pre-pressurization test, with de-tanking activities starting shortly thereafter. “All objectives for the Artemis 1 cryogenic demonstration have been met,” tweeted NASA’s Exploration Ground Systems at 4:33 pm, and the test was declared complete 20 minutes later.
“I think the test went really well,” Blackwell-Thompson told Nail. “We wanted to learn, we wanted to evaluate the [tail service mast umbilicals] under cryogenic conditions.” She said teams were also working with a new loading operation, the so-called kinder, gentler approach, which Blackwell-Thompson described as being “very purposeful.” Ultimately, “all test objectives were accomplished today,” she said.
NASA will need to review today’s test results and decide how to move forward. Ideally, the engineers will like what they saw, setting the stage for launch in just six days. Assuming the test is as much of a success as it appears to be, NASA could launch SLS as early as September 27, with a 70-minute launch window opening at 11:37 am ET. For that to happen, however, the space agency still needs to receive a waiver from the Space Force’s Eastern Range, which manages launches along the Florida east coast. NASA is currently attempting to launch the Artemis 1 missionin which the SLS rocket will deliver an uncrewed Orion capsule on a journey to the Moon and back.
A successful launch would be the start of the Artemis era, in which NASA is seeking a sustainable and sustained presence in the lunar environment. Artemis 1 is a demonstration mission that would set the stage for Artemis 2, in which a crewed Orion spacecraft will attempt a similar journey in late 2024.