SLS before Aug. 29 scrub
Engineers spent more than two and a half hours trying to correct a problem with a hydrogen bleed line for one of four engines in the core stage of the SLS before calling off the launch Aug. 29. Credit: NASA TV

Updated 9:30 a.m. Eastern with Nelson remarks.

KENNEDY SPACE CENTER, Fla. — NASA scrubbed the first attempt to launch its Space Launch System rocket and Orion spacecraft Aug. 29 after a problem with a hydrogen bleed line with one of the rocket’s four core stage engines.

NASA called off the launch shortly after the scheduled 8:33 a.m. Eastern liftoff after spending more than two and a half hours attempting to resolve a problem flowing liquid hydrogen into one of four main engines in the rocket’s core stage to prepare them for the planned launch.

NASA encountered an issue with the “hydrogen kickstart” of the four RS-25 engines, where liquid hydrogen is flowed through the engines for thermal conditioning ahead of launch. That system was not tested in the final wet dress rehearsal in June because of a leak in a quick-disconnect fitting, and was something project officials said they would test earlier than planned in the launch countdown.

The hydrogen kickstart worked on three of the four engines, but on the fourth, designated engine #3, controllers did not see the flow of liquid hydrogen they expected. They took several measures to try to increase that flow, including shutting off the flow in the other three engines to increase the pressure for engine #3, without success.

NASA then called for an unplanned hold at T-40 minutes, originally scheduled to last 10 minutes, to work on a troubleshooting plan for the engine. After more than an hour, NASA scrubbed the launch but planned to collect additional data before unloading the liquid hydrogen and oxygen propellants from the core and upper stages.

NASA first ran into challenges with the launch shortly after managers gave their approval to load the rocket with liquid hydrogen and liquid oxygen propellants nearly nine hours before the scheduled liftoff. Thunderstorms in the vicinity of the launch site kept tanking from starting for about an hour until weather conditions improved.

“We don’t launch until it’s right,” NASA Administrator Bill Nelson said in remarks on NASA TV about half an hour after the scrub. “It’s just illustrative that this is a very complicated machine.”

“They’re going to work it. They’re going to get to the bottom of it,” he said of launch teams. “We’ll get it fixed and then we’ll fly.”

Nelson added that he had briefed Vice President Kamala Harris, who arrived at the Kennedy Space Center earlier in the morning, about the status of the launch. Harris was scheduled to tour the center, including hardware for Orion spacecraft under construction, and give a speech later in the day.

Launch officials reported no issues during earlier phases of the countdown, which formally started with a “call to stations” on the morning of Aug. 27. Lightning strikes in the vicinity of Launch Complex 39B the afternoon if Aug. 27, including some on towers surrounding the pad, did not cause any damage to the vehicle or ground systems.

“Everything to date looks good from a vehicle perspective,” Jeff Spaulding, NASA Artemis 1 senior test director, said at an Aug. 28 briefing. “My thoughts are that we look great for tomorrow,” he added when asked to give the odds for an Aug. 29 launch.

The next launch opportunity is no earlier than Sept. 2, because of Orion performance constraints that rule out launches on Aug. 30, 31 and Sept. 1. A two-hour launch window opens at 12:48 p.m. Eastern and would set up a 39-day mission for the Orion spacecraft. A third window, 90 minutes long is available Sept. 5 starting at 5:12 p.m. Eastern.

Spaulding said Aug. 28 there is some flexibility to attempt launches on Sept. 3, 4 or 6, the last day of the current launch period. “If we did not tank, for example, on the 2nd for some reason, we could potentially come back the next day and try again,” he said. However, if tanking of the rocket did take place on the Sept. 2 attempt, NASA would not be able to try again until Sept. 5.

Melody Lovin, weather officer for the Space Force’s Space Launch Delta 45, said at the Aug. 28 briefing the first weather forecast for a Sept. 2 launch attempt would come Aug. 29. She expected, though, that the probability of acceptable weather would be lower than for the initial launch attempt because the launch window is later in the day, with greater odds of storms.

Another factor, she said, would be the potential development of tropical weather systems that could affect the region by the end of the week. “The forecast is largely going to depend on the evolution of the tropics.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...