The uncrewed test flight - called off for a second time - aims to ensure NASA's new SLS rocket is capable of putting astronauts back on the Moon.
NASA aborted its second attempt to launch its new giant rocket to the Moon on Saturday due to another dangerous fuel leak, five days after a pair of technical issues forced it to postpone its widely anticipated maiden lift-off.
Launch controllers were forced to call off this second attempt to send a crew capsule into lunar orbit with test dummies after discovering a new liquid hydrogen leak while loading the propellant into the rocket.
Fuel leaks and a bad engine sensor also foiled Monday's attempt, although the leaks were in a different location on the rocket, the most powerful ever built by the US space agency.
NASA Administrator Bill Nelson said repair work could bump the launch into October.
"We’ll go when it’s ready. We don’t go until then and especially now on a test flight, because we’re going to stress this and test it... and make sure it’s right before we put four humans up on the top of it,” Nelson said.
"This is part of our space program: Be ready for the scrubs," he added.
When it launches, the 98-metre, 32-story-tall Space Launch System (SLS) rocket will propel test dummies on an unmanned flight which will aim to ensure it's capable of eventually putting astronauts back on the Moon for the first time in 50 years.
At a media briefing on Tuesday, NASA officials said Monday's first attempt was useful in troubleshooting some problems and that additional difficulties could be worked through in the midst of a second launch try.
In that way, the launch exercise was serving essentially as a real-time dress rehearsal that hopefully would conclude with an actual, successful lift-off.
If all goes as hoped on the proposed third attempt, the SLS and its Orion astronaut capsule will blast off from the Kennedy Space Center in Cape Canaveral, Florida, sending the Orion on an uncrewed, six-week test flight around the Moon and back.
The long-awaited voyage would kick off NASA's Moon-to-Mars Artemis program, the successor to the Apollo lunar project of the 1960s and '70s, before US human spaceflight efforts shifted to low-Earth orbit with space shuttles and the International Space Station.
Why was the rocket launch scrubbed?
NASA's initial Artemis I launch attempt on Monday ended after data showed that one of the rocket's main-stage engines failed to reach the proper pre-launch temperature required for ignition, forcing a halt to the countdown and a postponement.
Speaking to reporters, mission managers said they believe a faulty sensor in the rocket's engine section was the culprit for the engine cooling issue.
As a remedy for Saturday's attempt, mission managers plan to begin that engine-cooling process roughly 30 minutes earlier in the launch countdown, NASA's Artemis launch director Charlie Blackwell-Thompson said. But a full explanation for the faulty sensor requires more data analysis by engineers.
"The way the sensor is behaving doesn't line up with the physics of the situation," said John Honeycutt, NASA's SLS program manager.
The sensor was last checked and calibrated months ago in the rocket factory, Honeycutt said. Replacing the sensor would require rolling the rocket back to its assembly building, a process that could delay the mission for months.
Why is the Artemis 1 mission so important?
The first voyage of the SLS-Orion, a mission dubbed Artemis I, aims to put the giant rocket through its paces in a rigorous demonstration flight pushing its design limits, before NASA deems it reliable enough to carry astronauts.
Named for the goddess who was Apollo's twin sister in ancient Greek mythology, Artemis seeks to return astronauts to the Moon's surface as early as 2025, though many experts believe that time frame will likely slip by a few years.
The last humans to walk on the Moon were the two-man descent team of Apollo 17 in 1972, following in the footsteps of 10 other astronauts during five earlier missions beginning with Apollo 11 in 1969.
Artemis also is enlisting commercial and international help to eventually establish a long-term lunar base as a stepping stone to even more ambitious human voyages to Mars, a goal NASA officials say would probably take until at least the late 2030s to achieve.
But NASA has many steps to take along the way, starting with getting the SLS-Orion vehicle into space.