The test is an essential step before NASA can set a launch date for its Artemis II mission, which will send four astronauts around the moon.

The Space Launch System and Orion spacecraft at Launch Pad 39B at NASA`s Kennedy Space Center, Fla., on Jan. 28.Sam Lott / NASA

NASA on Thursday will again attempt to fuel up its giant lunar rocket and complete a launch-day walkthrough ahead of its highly anticipated mission to send four astronauts around the moon.

The hourslong test, known as a "wet dress rehearsal," is an essential step before NASA can set a targeted launch date for the mission, known as Artemis II. The crew could lift off as soon as March 6 - the start of a 10-day journey during which they will orbit Earth then make a figure eight around the moon.

It will be the first time humans travel to the moon in more than 50 years, and the crew is expected to reach a greater distance from Earth than anyone has before. The mission will also mark the first time that NASA`s Space Launch System rocket and Orion capsule carry people.

Thursday`s rehearsal at NASA`s Kennedy Space Center in Florida will help mission managers assess recent repairs made to the rocket, after they found a hydrogen leak during the first wet dress rehearsal. The leak forced NASA to stop that Feb. 2 test early and forgo all launch opportunities this month.

During the fueling test, engineers will study the effectiveness of the repairs, with NASA officials weighing the overall readiness of the rocket and its various systems. If all goes smoothly, the agency has said it has launch opportunities from March 6 through 9, and again on March 11.

The Space Launch System rocket and the Orion spacecraft at Kennedy Space Center on Jan. 30. Miguel J. Rodriguez Carrillo / AFP - Getty Images

The wet dress rehearsal formally began on Wednesday evening and continued into Thursday morning, as teams powered up parts of the rocket and spacecraft and charged flight batteries. The main part of the test, however, will start once mission managers give the go-ahead to fuel the Space Launch System rocket.

The booster will then be filled with more than 700,000 gallons of cryogenic propellant, and mission managers will practice counting down to a simulated launch time of 8:30 p.m. ET.

As part of the test, NASA plans to conduct two walkthroughs of the final 10 minutes of the countdown, with a pause at T-minus 1 minute and 30 seconds. At T-minus 33 seconds, NASA plans to reset the clock back to T-minus 10 minutes and run through again.

These stops and starts are designed to demonstrate that the rocket`s systems are performing as expected during the final part of the countdown, when automated systems take over control of the booster. The pauses and resets also give mission managers a chance to practice different scenarios, such as situations in which issues crop up that need investigation or in which a launch has to be called off due to technical issues or bad weather.

The Artemis II crew, from left, astronauts Reid Wiseman, Christina Koch, Jeremy Hansen and Victor Glover, in front of an Orion simulator at NASA`s Johnson Space Center in Houston on Jan. 23.Robert Markowitz / NASA

The four Artemis II crew members - NASA astronauts Reid Wiseman, Christina Koch and Victor Glover, and Canadian astronaut Jeremy Hansen - will not participate in the wet dress rehearsal, though NASA will still practice closing the Orion spacecraft`s hatches and running through other pre-flight activities.

After NASA discovered leaking hydrogen fuel at the tail end of the rocket during the prior rehearsal, the agency replaced two seals on fueling lines and conducted a partial fueling test to assess the repairs. That test, in turn, turned up other issues with ground support equipment, which appeared to reduce the flow of liquid hydrogen into the booster. NASA said earlier this week that it had replaced a filter in the affected equipment.

The Artemis II astronauts are expected to enter quarantine in Houston for around two weeks before their launch. That could be as early as Friday if the rehearsal goes well, though NASA has said it "will not set a formal launch date until after a successful rehearsal and data reviews."

A full moon shines over NASA`s Space Launch System and Orion spacecraft, atop the mobile launcher, at Kennedy Space Center on Feb. 1.Sam Lott / NASA

Artemis II is a key step for NASA as it works to return astronauts to the lunar surface. Just like it did during the Apollo program of the 1960s and `70s, NASA is testing its systems with a trip around the moon before it attempts to land astronauts on the lunar surface - that milestone is planned for the Artemis III mission in 2028.

The upcoming flight follows the uncrewed Artemis I mission in 2022, when NASA sent the SLS rocket and Orion capsule on a trip around the moon without any people onboard.

During the first wet dress rehearsal for that earlier flight, NASA identified hydrogen leaks that wound up delaying the mission six months.

 

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By Denise Chow