NASA's Artemis I mission, scheduled to launch Monday to take an Orion capsule with three test dummies to the moon and back, was scrubbed because of chronic fuel leaks and an engine problem during final preparations.
The next flight window from Florida's Kennedy Space Center is Friday if NASA determines the rocket was ready.
"Safety is always first," NASA tweeted. "Following today's #Artemis I launch attempt, @NASAArtemis teams are working through an issue with engine number 3, and expect to give a news briefing later today."
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NASA struggled to fuel the rocket with nearly 1 million gallons of hydrogen and oxygen because of a leak of highly explosive hydrogen, a problem that also flared up during testing last spring.
The massive Space Launch System rocket will become the agency's most powerful when it ultimately takes flight. Teams had a two-hour launch window – from 8:33 a.m. until 10:33 a.m. Eastern – but elected not to go forward two hours before the window closed.
NASA's Artemis program is designed to take astronauts back to the moon sometime after 2025. This first test mission involves a roundtrip that will take about 42 days.
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NASA: 'You don't want to light the candle until it's ready to go'
The postponement was a disappointment to thousands of people who jammed the coastline to see the launch. Vice President Kamala Harris was among the VIPs in attendance. Launch commentator Derrol Nail said engineers were still analyzing the issues and “we must wait to see what shakes out from their test data" before announcing a new launch date and time. NASA Administrator Bill Nelson said delays are part of the "space business" and test flights, particularly when dealing with machines as complicated as Artemis1.
“All those things have to work, and you don’t want to light the candle until it’s ready to go,” he said.
NASA announces postponement, no word yet on next try
NASA said launch director Charlie Blackwell-Thompson halted the launch attempt at about 8:34 a.m. The Space Launch System rocket and Orion spacecraft "remain in a safe and stable configuration," NASA said in a statement.
Launch controllers were continuing to evaluate why a bleed test to get the engines on the bottom of the core stage to the proper temperature range for liftoff was not successful, and they ran out of time because of the two-hour launch window. Engineers were continuing to gather data.
NASA announces 'unplanned hold'
NASA tweeted that the launch was on hold: "#Artemis I update: Launch is currently in an unplanned hold as the team works on an issue with engine number 3 on the @NASA_SLS core stage. Operations commentary continues at http://nasa.gov/live."