Artemis I launch rescheduled after scrub: What to Know

NASA will move forward with a second launch attempt of Artemis I on Saturday, with the megarocket's two-hour launch window set to open at 2:17 p.m. Eastern Time. 

On Monday, the launch was scrubbed after one of the Space Launch System's (SLS) four RS-25 engines on the bottom of its core stage failed to reach the proper temperature range for liftoff. 

During the first launch attempt, readings showed SLS' engine 3 appeared to be as much as 40 degrees Fahrenheit warmer than the desired minus 420 degrees Fahrenheit, according to SLS program manager John Honeycutt. The three other engines came up just a little short.

Other issues encountered during Monday's launch window included storms in the area that delayed the start of propellant loading operations, a leak at the quick disconnect on the 8-inch line used to fill and drain core stage liquid hydrogen and a hydrogen leak from a valve used to vent the propellant from the core stage intertank.

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On Thursday, SLS engineers said that all four of the rocket's main engines were good and that a faulty temperature sensor caused engine 3 to appear as though it were too warm. Honeycutt has said that the sensor would be "tricky" to fix at the launch pad and that rolling SLS back into Kennedy Space Center's Vehicle Assembly Building could result in weeks of delay. 

In preparation for Saturday, Artemis program manager Michael Sarafin said that the team would change its operational procedure for loading propellant into the rocket and try chilling the engines about 30 to 45 minutes earlier in the countdown. Even if the suspect temperature sensor indicates the one engine is too warm, other sensors can be relied on to ensure everything is working correctly and to halt the countdown if there’s a problem, Honeycutt told reporters.

The team will also do some work at the launch pad to prevent another leak from occurring in the rocket's hydrogen tail service mast umbilical. 

The U.S. Space Force Space Launch Delta 45 is predicting a 60% chance of favorable weather conditions at the beginning of the two-hour launch window and an 80% chance of favorable weather conditions toward the later part of the window.

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If the launch is successful, SLS' Orion capsule will travel into space for about six-weeks before splashing down in the Pacific Ocean on October 11. Assuming the test goes well, astronauts would climb aboard for Artemis II and fly around the moon and back as soon as 2024. A two-person lunar landing could follow by the end of 2025. 

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The SLS and Orion have been under development for more than a decade, with years of delays and ballooning costs that have run to at least $37 billion as of last year. NASA Administrator Bill Nelson has called the Artemis program an "economic engine," noting that in 2019 alone, for example, it generated $14 billion in commerce and supported 70,000 American jobs.

Contractors who have worked on SLS and Orion include Boeing, Northrop Grumman, Lockheed Martin and Aerojet Rocketdyne. 

The 322-foot rocket is the most powerful ever built by NASA, out-muscling even the Saturn V that took the Apollo astronauts to the moon. Astronauts last walked on the moon in 1972.

The Associated Press and Reuters contributed to this report