Trevor Mallman 11:15 am ET Saturday: NASA officially called off the Artemis I launch attempt on Saturday. The launch team was unable to resolve a leak in an 8-inch hydrogen inlet leading to the Space Launch System rocket. Launch managers attempted three troubleshooting measures, and none were able to substantially reduce the leak of cryogenic hydrogen as it flowed from ground systems on the rocket. It is unclear whether NASA will attempt to launch the Artemis I mission on Monday or Tuesday, or whether it will need to return the massive rocket to the Vehicle Assembly Building for restoration work. The latter seems likely, but no final decision has been made. Ars will have a full recap later Saturday. KENNEDY SPACE CENTER, Fla.—Five days after NASA’s first attempt to fly its massive Space Launch System rocket ended in technical problems, the space agency is ready to try again. A launch team began fueling the rocket Saturday morning just before the sun began to rise over the waters of the Atlantic Ocean that surround the spaceport. The SLS rocket, which launches the Artemis I mission around the Moon, has a two-hour launch window that opens at 2:17 p.m. ET (18:17 UTC). A successful launch will mark the beginning of a 42-day mission that will send the Orion spacecraft into lunar orbit and test critical technologies such as a heat shield that will protect the spacecraft during a fiery re-entry into Earth’s atmosphere. If the mission goes well, Artemis II would follow in a few years, carrying humans around the Moon. A lunar landing is planned for later this decade. A lot will have to go right for the rocket to launch on Saturday. There are three main reasons why a rocket launch cleans up: weather, range problems, and technical problems. The weather looks pretty good for a summer afternoon in Florida, with at least a 60 percent chance of favorable conditions. Launch range issues, such as a vessel traveling in confined waters, are a small possibility. That leaves technical issues, and since the SLS is a complex, towering rocket with leaking hydrogen fuel trying to launch for the first time—well, let’s just say a rub is more likely than not. Before launch, there are no fewer than 489 “launch commitment criteria” that must be met for the SLS rocket, such as propellant temperatures, tank pressures, and so on. Advertising
“There’s no guarantee we’ll land on Saturday, but we’ll try,” NASA engineer Mike Sarafin, who serves as mission manager for Artemis I, said during a press conference this week.

Monday’s scrub

The launch team decided to clean up Monday’s attempt even before the launch window opened after a series of problems delayed the countdown and plagued launch controllers. Storms delayed the start of feeding operations. then there was a leaking hydrogen inlet leading to the rocket and an ice problem in the booster foam insulation. But the biggest problem came when launch controllers tried to cool down the four main RS-25 engines, which must be at a very low temperature of -420 degrees Fahrenheit during launch to handle the extremely cold propellants during engine ignition. A sensor on one of the four engines indicated that it was not cooling to the correct temperature. Inside the Launch Control Center, some NASA engineers believed that the sensor must be to blame because there were other indications that the engine was cooling as required. But time was short, and given the other issues the launch team was working through, it became too much, Sarafin said. “One of the worst things you can do when you’re in a dangerous situation is to go off script,” Sarafin said. “The team did absolutely the right thing on Monday.” On Tuesday, technicians and engineers worked on the vehicle and its ground systems and became confident that it was indeed a faulty sensor and not a slack issue. Among the key indicators was that liquid hydrogen had flowed through the engine and exited at an expected temperature. So for Saturday’s effort, NASA has not replaced the sensor, which would require a return to the Vehicle Assembly Building and a delay of at least a month, if not longer. If there is a scrap for any reason on Saturday, NASA could have one more chance to launch the vehicle on Monday or Tuesday before it has to be returned for remedial work regardless. The official webcast for the mission will begin at 11:15 am. ET (15:15 UTC) on Saturday. It’s embedded below. NASA’s media channel will cover the feed operations, with live, intermittent commentary beginning at 5:45 a.m. ET (9:45 UTC) on Saturday. Official NASA webcast for the Artemis I mission.