Artemis I's biggest test yet: What to know about the modified plans

NASA is preparing to finally host a “wet dress rehearsal” for its Artemis I mission — if it isn’t delayed again.

The mission’s Orion crew capsule, mounted atop the Space Launch System, rolled out of the Vehicle Assembly Building at Kennedy Space Center in Florida on March 17 for the slow four-mile trip to the launch pad aboard one of NASA’s gargantuan crawlers.

One of the first items on Artemis I’s agenda at the launch pad — and one of many steps between Artemis I and launch day — is called a wet dress rehearsal. While far from a launch, it’s an important step in finding out if the mission is ready to go.

On March 28, the agency announced that the rehearsal would take place April 1 to 3. But a series of subsequent NASA delays place fueling starting on the afternoon of April 14 — with a test that won’t involve entirely fueling the upper stage.

The problems included problems with a vent valve, leaving the wet dress rehearsal team scrambling after the latest setback.

The rollout gave fans a first glimpse of the impressive construction that will power the mission. Under daylight and later moonlight, the gargantuan Space Launch System rocket rolled down the road, at a height of around 100 meters — taller than the Statue of Liberty.

The rocket moved from High Bay 3 at the Vehicle Assembly Building down to Launch Complex 39B. The move took so long at the crawler moved at a top speed of just 0.82 mph.

Now at its final position for tests, here’s what comes next.

What is a wet dress rehearsal?

A wet dress rehearsal is a practice launch countdown in which the spacecraft’s liquid propellant tanks are filled. In Artemis I’s case, that means the core stage of the Space Launch System is full of supercooled liquid hydrogen fuel, and its oxidizer tanks are full of supercooled liquid oxygen — hence the “wet” in “wet dress rehearsal.”

The rocket will take a lot of fueling — in total, NASA’s rocket takes around 700,000 gallons of cryogenic fuel into the rocket.

The launch team at Kennedy Space Center will fuel the rocket, then run through a launch countdown.

The rehearsal timer will count down to one minute and 30 seconds before pausing. This will demonstrate the ability to stop for a period of up to three minutes. They will then resume the countdown, before pausing again around 33 seconds before liftoff.

The countdown will resume again before stopping completely around 9.3 seconds before liftoff. In particular, the launch team will practice scrubbing a launch at the last moment, resetting the countdown to T-10 minutes, and “de-tanking” or emptying the fuel from the main rocket. Although the SLS rocket will be fueled up during the wet dress rehearsal, it won’t actually fire — that part comes later, during a test called a static fire.

The team was originally expected to completely fuel the rocket. On April 9, however, NASA announced that it would follow a modified wet dress rehearsal that mostly focused on tanking the core stage. That means the interim cryogenic propulsion stage, or ICPS, will only see “minimal propellant operations.”

The reason for this tweak is that NASA’s engineers have discovered a helium check valve is not functioning correctly. The three-inch-long valve ensures helium only flows in one direction.

Charlie Blackwell-Thompson, NASA Artemis launch director, defended the decision in a conference call attended by SpaceNews.

“We believe that this is the best option moving forward,” Blackwell-Thompson said. “We believe that we’ll be able to meet the majority of our test objectives and provide us with a reasonably good set of data prior to rollback.”

The wet dress rehearsal is just one of a whole battery of tests and drills that the launch team will run over the next few months. Right up until the day before launch, the teams responsible for launching Artemis I will run tests and simulations — checking out their equipment, practicing procedures, and rehearsing every emergency scenario mission planners can think of.

How to watch Artemis I wet dress rehearsal

The live video stream for the wet dress rehearsal is underway, and you can watch that process on Kennedy Newsroom’s YouTube channel courtesy of the launchpad cameras.

The rehearsal has experienced multiple delays. Originally slated for April 1, the team paused the test during rehearsal due to technical issues. Space.com notes that NASA eventually delayed the test entirely due to the planned Axiom-1 launch nearby. The test was expected to resume on April 11, but issues with the helium valve led to further delays.

Because the core booster on SLS is so large, and because it has an upper-stage engine that also needs fueling, fueling the entire rocket is about an eight-hour process. The former Space Shuttle’s external tank, on the other hand, took about two hours to fuel up. The wet dress rehearsal itself is about a two-day process.

Once the wet dress rehearsal wraps up successfully, NASA plans to announce a launch date for Artemis I. The team will analyze the data from the tests to determine the final launch date.

The launch won’t happen before June, according to NASA, but when the time comes, you can watch the launch live on NASA Television.

Artemis I mission goals

When it launches this summer, the Artemis I mission will be the first-ever flight of the spacecraft-and-rocket combination that will eventually carry astronauts to the Moon and beyond. The uncrewed mission’s main goal is to ensure that the Space Launch System rocket and Orion crew capsule can carry future crews to the Moon and return them to Earth safely.

After liftoff from NASA’s Kennedy Space Center, Artemis I will make a quick lap around Earth before setting out for the Moon. There, the Orion capsule will whiz past just 62 kilometers above the lunar surface, using the Moon’s gravity to help the spacecraft’s boosters maneuver it into lunar orbit. The Orion capsule will orbit the Moon for 6 days while NASA engineers study its performance.

“Although there will not be actual crew aboard this flight test, we will have some 'passengers' aboard,” Tiffany Fairley, a spokesperson for Kennedy Space Center, tells Inverse.

A mannequin will make the trip to the Moon strapped into the capsule commander’s seat, fully decked out in a spacesuit designed specifically for future Orion crews. Sensors in the seat will measure acceleration and vibration, and radiation sensors will measure the mannequin’s radiation exposure in deep space. All of that data will help design future flight simulations for crews and double-check the capsule’s safety parameters.

On the return trip, the Orion capsule will test a re-entry technique called skip entry. A skip entry means that the spacecraft dips into the upper edge of Earth’s atmosphere just long enough to slow down a little, then skips back out into space again before making its final descent.

It looks a bit like a rock skipping across the surface of a pond, and according to NASA, it spreads out the heat and G-forces of re-entry enough to make the process safer and smoother for astronauts (who won’t be aboard Artemis I but will eventually appreciate the smoother ride). Skip entry also lets the spacecraft fly farther on its way down, which means it can splash down off the coast of San Diego no matter when and where it actually enters the atmosphere.

Artemis II details and launch date

If all goes well with Artemis I, NASA plans to send astronauts to the Moon sometime in 2024. That mission, Artemis II, will be the first time humans have visited our nearest neighbor in space since the Apollo 17 mission in 1972. Artemis II will test the entire launch vehicle and spacecraft system again, with one last key component added: people.

Though no official astronaut selection has been made, NASA has selected an astronaut corps training for their chance for an Orion seat. The agency has also stated its intent to put the first woman and the first person of color on the Moon.

The missions could lead to impressive findings for the new team. Earlier this month, NASA researchers opened up a 50-year-old Moon rock sample that returned to Earth following the Apollo 17 mission. Analyzed on March 21 and 22, the samples demonstrate how the Artemis missions could fuel scientific discovery for a new generation.