What Happens With NASA's Artemis Mega-Rocket Launch Now?

NASA is looking at Friday or next Monday for another go at launching its huge Space Launch System (SLS) rocket after the first attempt was scrapped. The highly anticipated launch follows more than a decade of development and will mark the start of NASA's Artemis program—a series of missions intended to return humans to the moon for the first time in over half a century. Monday's planned launch was due to kick off the Artemis I mission, during which the SLS will fire NASA's Orion spacecraft—with no crew inside—on a month-long journey around the moon to test its systems.

As engineers were gearing up the SLS for its first ever flight, they encountered an engine cooling issue that meant the rocket wouldn't have been ready within its two-hour launch window. The technical issue emerged when launch controllers were trying to cool the SLS's four main engines to the same temperature using what's known as an engine "bleed." The process involves releasing some liquid hydrogen, stored at less than -400 degrees Fahrenheit, from the rocket's propellant tanks. Unfortunately for NASA, engine 3 wasn't reaching the same temperature as the others. It's unclear why. It's important to get this right. The RS-25 engine—tried and tested during the Space Shuttle program—is what helps make the SLS the most powerful rocket NASA has ever built, providing over 500,000 pounds of thrust in a vacuum. As each engine operates, it must cope with temperatures ranging from -423 F to over 6,000 F. The countdown was paused with about 40 minutes to go until the launch. When this pause went beyond the start of the launch window, the decision was made to try again on another day, once the issue has been fixed.

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In a statement on its website, NASA said teams had trouble "getting one of the four RS-25 engines on the bottom of the rocket's core stage to the proper temperature range for liftoff." In a NASA broadcast following news of the scrubbed launch, NASA administrator Bill Nelson said: "It's just illustrative that this is a very complicated machine, a very complicated system, and all those things have to work—and you don't want to light the candle until it's ready to go." The next earliest possible launch window starts on September 2 at 12:48 p.m. ET and again lasts for two hours. After that, the next window would be September 5 at 5:12 p.m. until 6:42 p.m., CNN reported Monday.

However, all this depends on whether engineers can fix the cooling issue in time, while the rocket sits on the launch pad. They may decide that the rocket needs to be returned to NASA's huge Vehicle Assembly Building (VAB) to be fixed—a process that would take many days and could push the launch back quite a bit further. NASA is due to provide an update on the status of Artemis I in a media teleconference at 6 p.m. ET on Tuesday. It will be streamed on the NASA Live channel on YouTube. NASA hasn't said if the launch delay will affect the schedule of the Artemis program more widely. It aims to return astronauts to the moon in 2025 in the Artemis III mission. The program has already faced extensive delays, with the SLS initially expected to fly in 2016.