NASA Artemis I Wet Dress Rehearsal Slated For Today - Here's What That Means

It's been a couple of weeks since NASA's gigantic Space Launch System rocket rolled its way to the launch pad and, in the time since, NASA scientists have been preparing to carry out something called a "wet dress rehearsal" for the Artemis I mission. That wet dress rehearsal involves activating the necessary launch facilities, working through the core propellant load phase, and then simulating a mission scrub in which the launch is halted and the previously-loaded propellant is removed from the rocket.

Essentially, a wet dress rehearsal works through all of the potential stages of a launch — including a scrub — so NASA scientists can practice before the real deal. The Artemis I wet dress rehearsal was slated to happen over the weekend, but yesterday NASA scientists decided to delay the test because of "loss of ability to pressurize the mobile launcher," according to the Artemis blog. That meant technicians were unable to safely load the propellant, so the wet dress rehearsal was delayed until today.

It seems that NASA engineers and scientists fixed the pressurization issue overnight, because this morning, the wet dress rehearsal once again has been given the green light to proceed from the mission management team chair. That approval came this morning at 7:40 AM EDT, and from now until this evening, NASA will be working its way through the wet dress rehearsal. "At approximately 10 a.m. EDT, the launch director gave the 'go' to begin tanking the rocket. Cryogenic loading operations are scheduled to begin with chilling down the liquid oxygen lines for the core stage," NASA writes in a separate post on the Artemis blog. "Once propellant loading operations begin, liquid oxygen (LOX) and liquid hydrogen (LH2) will flow into the rocket's core stage and interim cryogenic propulsion stage tanks and be topped off and replenished as some of cryogenic propellant boils off. The team will also conduct leak checks to ensure propellant loading is proceeding as expected."

The countdown resumed this morning at T-6 hours, 40 minutes, which will bring us to a T-0 time of 6:02 PM EDT. You can watch the test happen at the livestream embedded above or follow NASA's Exploration Ground Systems on Twitter for updates on the wet dress rehearsal. Once the wet dress rehearsal is done, NASA says that the Space Launch System rocket and Orion spacecraft will travel back to the Vehicle Assembly Building to charge batteries, take on additional cargo, and allow engineers to run final checks before launch. We don't have a precise launch date for the Artemis I mission yet, but it's expected to happen sometime this summer.