Gas leaks have compelled NASA to clean the launch of its new moon rocket on a no-crew check flight.
The subsequent launch try is not going to happen till Friday on the earliest.
The 98-metre Area Launch System rocket was set to raise off this morning (tonight AEST) with three check dummies aboard on its first flight, a mission to propel a capsule into orbit across the moon.
The shakedown flight, when it occurs, will probably be a giant step ahead in America's quest to place astronauts again on the moon for the primary time because the finish of the Apollo program 50 years in the past.
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NASA hopes to ship 4 astronauts across the moon in 2024 and land people there as early as 2025.