SLS on pad Aug. 26
Countdown clocks started on the morning of Aug. 27 for the first attempt to launch the SLS and Orion spacecraft on the Artemis 1 mission Aug. 29. Credit: NASA/Bill Ingalls

KENNEDY SPACE CENTER, Fla. — NASA started the countdown Aug. 27 for its first attempt to launch its Space Launch System rocket and Orion spacecraft for an uncrewed flight around the moon.

The countdown for the Artemis 1 launch formally started at 10:23 a.m. Eastern after a meeting of the mission management team. Liftoff is scheduled for 8:33 a.m. Eastern Aug. 29 at the beginning of a two-hour launch window.

At a briefing here shortly after the countdown started, agency officials said they were not working on any problems with the vehicle that could threaten the launch. In addition to a lack of technical issues, weather remains favorable, with a 70% chance of acceptable weather.

“We do feel good about our attempt on Monday in terms of our overall setup,” said Mike Sarafin, NASA Artemis mission manager.

He cautioned, though, that the launch could scrub for any number of reasons, including technical issues, weather, or range violations. But he and other agency officials expressed confidence in the prospects of a launch on the first attempt of the new launch vehicle.

“The vehicle is in great shape,” Sharon Cobb, NASA SLS associate program manager, said in an interview. “We have really tested everything we can test up until launch and we believe our systems are in really good shape, except for that one activity of chilling down the engines.”

That is a reference to a “hydrogen kickstart” that could not be conducted on the last wet dress rehearsal in June because of a leak in a hydrogen bleed line. That will be tested about five hours before liftoff, said Charlie Blackwell-Thompson, Artemis 1 launch director, at the briefing.

“We feel really good that, once we get through that, we’ll know everything we need to know about the vehicle,” Cobb said.

The launch is not without risk, though. At the briefing, Sarafin said NASA estimated a 1-in-125 chance of a loss of the Orion vehicle on Artemis 1. That figure comes from a probabilistic risk assessment that looks at the potential failure modes and the probability of them taking place.

“Some of our top risk drivers are common to any other program out there,” he said, such as damage from micrometeoroids and orbital debris as well as parachutes and the heat shield. The micrometeoroid risk is a function of the length of the mission, with a higher risk of damage for a longer mission.

Should NASA scrub the Aug. 29 launch, there are backup launch opportunities Sept. 2 and 5. However, Blackwell-Thompson said they have flexibility to target launches on Sept. 3, 4 and 6 instead depending on factors such weather and when a launch attempt is scrubbed. Key factors will be availability of liquid oxygen (LOX) and liquid hydrogen, with pad supplies scheduled to be topped off if the Aug. 29 launch is scrubbed.

“Because we go ahead and top off the LOX and hydrogen, we’re in a really great spot,” she said. “There are other opportunities. It doesn’t have to be the second or the fifth.”

A launch in early September, though, raises the odds of tropical weather systems based on long-term forecasts. Melody Lovin, weather officer at the Space Force’s Space Launch Delta 45, said it was too early to forecast weather for the next opportunity Sept. 2.

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...