NASA announced Tuesday it would pursue a launch of its $4.1 billion Artemis I rocket to the moon Saturday.
The two-hour launch window opens at 2:17 p.m. ET and teams will meet on Thursday for another review prior to an official countdown start.
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But the Space Launch Delta 45 weather squadron predicts only a 40% chance for good conditions.
“I’m optimistic that we’ll have some clear air to work with during the afternoon attempt on Saturday,” said 45th Weather Squadron Launch Officer Mark Burger at a Tuesday evening press conference. “However, again, the probability of a weather violation at any point in the countdown still looks to me rather high.”
If it scrubs Saturday, the next window falls on Labor Day, a 90-minute opportunity that opens at 5:12 p.m., that NASA said would still be feasible since NASA just needs a 48-hour time frame to replenish all the gases needed to refill the tank.
The massive combination of the Space Launch System topped with the Orion spacecraft steered through several roadblocks Monday morning on NASA’s first shot to send the Artemis I mission into space, but ultimately an engine issue forced a scrub.
The culprit was what is known as the bleed system, which feeds cryogenic propellant from the core stage into the four RS-25 engines at its base. Sensors showed during a bleed test leading up to Monday’s aborted liftoff that one of the engines did not cool down to acceptable levels.
All four need to have their temperature managed so they’re not stressed with the liquid hydrogen (LH2), which is chilled to minus 423 degrees Fahrenheit, when it starts flowing full throttle into the engines at liftoff.
The LH2 combined with liquid oxygen chilled to minus 297 degrees Fahrenheit provide 2.2 million pounds of thrust, which when combined with two solid rocket boosters, provide 8.8 million pounds of thrust for SLS on liftoff.
Other issues during Monday’s attempt involved the loading of the cryo propellants, which needed an adjustment when a potential hydrogen leak was detected in one of the umbilical feed lines. To deal with both issues, NASA is shifting how the Saturday countdown will proceed.
“We agreed on what was called option one, which was to operationally change the loading procedure and start our engine chill down earlier,” said Artemis mission manager Mike Sarafin. “We also agreed to do some work at the pad to address the leak that we saw in the hydrogen tail service mast umbilical.”
NASA SLS manager John Honeycutt said teams were not entirely certain if the engine temperature was really off target, and it could have been a faulty sensor based on readings from other equipment at the site.
“I think we understand the physics about how hydrogen performs and not the way the sensor is behaving,” he said noting it “doesn’t line up with the physics of the situation.”
He said replacing the sensor at the launch pad would be tricky and require a rollback, so instead they’re going to “go fly using the data we have access to today.”
The sensors from Monday’s attempt showed that three of the four engines came within 10 degrees of a target of minus 420 degrees Fahrenheit while the fourth, the one that convinced managers to scrub, was about 40 degrees warmer, Honeycutt said.
“We’re going to try to launch,” Sarafin said. “And you know coming into this prior attempt — (Monday’s) attempt — you know we said that if we couldn’t thermally condition the engines, we’re not gonna launch. And that’s the same posture that we’re going into Saturday. I don’t see it as any different.”
If and when it takes off, the rocket would become the most powerful to ever launch from Earth, besting the 7.6 million pounds of thrust produced by the Saturn V rockets of the Apollo missions to the moon.
Artemis I is supposed to send the uncrewed Orion capsule on a mutliweek mission to orbit the moon traveling 1.3 million miles and return home coming in as the fastest ever human-rated spacecraft at more than 24,500 mph generating close to 5,000 degrees Fahrenheit on re-entry.
The goal is to test the limits of the launch system and spacecraft so it can move on to human missions including Artemis II, an orbital moon mission slated for 2024, and Artemis III, that aims to return humans including the first woman to the lunar surface since 1972. That flight could come as early as 2025.
But first Artemis I has to get off the ground.
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