NASA's moon rocket is about to be loaded with 700,000 gallons of propellant

In its first "wet dress rehearsal".
Grant Currin

Got any big plans this weekend? NASA's behmoth SLS rocket sure does.

Two weeks after making its debut on a launchpad at the Kennedy Space Center, the most powerful rocket in history is preparing to undergo a 45-hour-long test slated to begin at 5:00 PM EDT on Friday. During this "wet dress rehearsal," the launch control team and other workers will prepare the 322-foot-tall rocket for launch, stopping just short of igniting its RS-25 engines.

Results from the test will help launch planners set a date for the SLS's first real launch, when the rocket will propel an uncrewed Orion spacecraft toward the Moon in the first mission of the agency's Artemis program. 

Here's the schedule for the two-day test 

NASA engineers and technicians have spent weeks preparing for this test, which got the final go-ahead from Mission Control on Monday. The test will officially begin once members of the launch team have arrived to their stations at the Kennedy Space Center’s Launch Control Center. Before that happens, the crew module hatch of the Orion spacecraft sitting atop the SLS rocket will be closed, the crew access arm will be retracted, and the Orion Spacecraft will be checked for leaks one last time. 

Soon after the countdown begins, the tank for the sound suppression system will be filled with nearly half-a-million gallons of water that dampens the huge wave of accoustic energy from the SLS engines. Later in the evening, the Orion Spacecraft and SLS core stage will be powered up, and the side flame deflectors will be moved into place. Next, technicians will power up a rocket stage that will propel Orion once its in space. At that point, all non-essential personnel will be cleared from the launch complex. 

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The real action begins Sunday morning

Early on Sunday, the launch director and chair of the mission management team will conduct briefings and decide whether to begin the complex proccess of loading liquid oxygen and liquid nitrogen into the SLS. Assuming they are a "go," that process will last roughly five hours. At 2:00 PM ET on Sunday, the test director will hold a final briefing and a 30-minute countdown will begin.

At T-33 seconds, the ground-based computer orchestrating the launch will send a "cut off" command just a few seconds before it would typically hand off launch control to computers inside the rocket. But that isn't the end of the test. After an hour or so, the countdown will be reset to T-10 minutes for another test run. This time, the launch sequence will go right up to T-9.34 seconds, when a manual command will stop the launch. After the rehearsal is done, technicians will drain and inspect the equipment before moving it back into the Vehicle Assembly Building. 

This test paves the way for NASA's big lunar plans

Two countdowns to almost-launch sounds anticlimactic, but the agency says these tests are essential to ensuring the success of the Artemis progrm, which aims to land humans on the Moon and build infrastructure there in the late 2020s and beyond. The wet dress rehearsal is an important step in preparing for Artemis I, an uncrewed mission that will see the Orion spacecraft orbit the Moon for six days before splashing down in the Pacific Ocean.

In a move that has surprised many onlookers, NASA will not be broadcasting its internal communications or providing live commentary during the test. The agency says unfriendly countries could use that information to develop weapons. 

“Typically, what they’re looking for is timing and sequencing data, flow rates, temperatures, how long it takes to do certain tasks,” NASA deputy associate administrator Tom Whitmeyer said at a press conference.

“That’s considered to be important information by other countries. And so we have to be very careful when we share data, particularly for the first time.”

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