NASA is rolling the dice again. After a hydrogen fuel leak cut short the first wet dress rehearsal for the Artemis 2 moon rocket on February 3, the agency has launched a second attempt — with launch controllers reporting to their stations at Kennedy Space Center tonight to begin a grueling 50-hour countdown simulation. The stakes couldn't be higher. If this rehearsal succeeds, Artemis 2 could launch as early as March 6 , sending four astronauts on a historic 10-day journey around the Moon — the first crewed lunar mission since Apollo 17 in 1972. If it fails, the program faces yet another delay in an odyssey that has already tested the patience of space enthusiasts and lawmakers alike. AI-generated image The tail service mast umbilical — where hydrogen leaks have plagued both Artemis 1 and 2. July 1 update The rehearsal became the launch gate for a successful lunar flyby This article originally covered NASA's second Artemis 2 wet dress rehearsal as it was getting underway. The result is now clear: NASA completed the Feb. 19 rehearsal at T-29 seconds , after a planned countdown recycle and a resumed terminal count. The repaired hydrogen system reached core-stage replenish without exceeding the safety limit that ended the first attempt. That test fed directly into launch operations. Artemis 2 lifted off from Launch Complex 39B on April 1, 2026 , carried Reid Wiseman, Victor Glover, Christina Koch, and Jeremy Hansen around the Moon, and splashed down in the Pacific off San Diego on April 10 . NASA later reported a farthest distance of 252,756 miles from Earth and a total mission distance of 694,481 miles . WDR finish T-29 seconds Launch April 1, 2026 Splashdown April 10, 2026 Farthest point 252,756 miles What Changed After the Rehearsal The February question was whether NASA could tame SLS cryogenic loading enough to commit a crew to the rocket. The second rehearsal did not produce a perfectly silent countdown. Teams worked through a booster avionics voltage anomaly, extended a hold to bring the core-stage engine section into the required temperature range, and used backup communication methods during parts of the test. The important difference was that none of those issues stopped the sequence. The ground team completed the operations that mattered most for launch readiness: propellant loading, full replenish on the cryogenic tanks, closeout crew procedures at Orion, a terminal count to T-33 seconds, a recycle back to T-10 minutes, and a second terminal count that ended as planned at T-29 seconds. That turned the wet dress from another troubleshooting event into a launch qualification event. The completed mission also changes the Artemis program baseline. Artemis 2 proved Orion life support with astronauts aboard, demonstrated deep-space crew operations, validated recovery flow with the Navy, and gave NASA flight data before the next crewed lunar landing architecture. The wet dress rehearsal now reads less like a delay story and more like the last hard ground test before the first crewed Orion flight around the Moon. A Familiar Demon: Hydrogen Leaks and the TSMU The first wet dress rehearsal, conducted February 2-3, was supposed to be the final hurdle before launch. Teams loaded more than 700,000 gallons of liquid hydrogen and liquid oxygen into the Space Launch System's tanks and ran through a full countdown simulation. But a persistent hydrogen leak at the tail service mast umbilical (TSMU) — the critical interface connecting the rocket to its mobile launch tower — forced NASA to end the test early, never reaching the simulated T-0. The leak location was disturbingly familiar. During the Artemis 1 campaign in 2022, hydrogen leaks at the same TSMU interface delayed the uncrewed mission by roughly six months, pushing its launch from spring to November. Engineers had hoped three years of design improvements would resolve the issue. They were wrong. Timeline of Troubles Feb 2-3: First wet dress rehearsal ends early due to LH2 leak at TSMU and ground equipment issues. Feb 12: Confidence test with partial LH2 fill — ground equipment filter restricts flow, but seal repairs show promise. Feb 14-16: Suspect filter replaced in ground support equipment at Pad 39B. Feb 17: Launch controllers report to stations at 6:40 PM EST to begin second wet dress rehearsal. Feb 19: Targeted simulated launch at 8:30 PM EST (±4 hours). In the aftermath of the first attempt, engineers replaced two seals in the TSMU area. A follow-up "confidence test" on February 12 partially filled the core stage with liquid hydrogen to verify the fix. While a separate ground equipment problem restricted fuel flow during that test, NASA said the team "was able to gain confidence in several key objectives." The ground equipment issue was traced to a filter, which was replaced over the Presidents' Day weekend. Inside the 50-Hour Countdown The second wet dress rehearsal officially began tonight when team members arrived at the Launch Control Center at Kennedy Space Center at 6:40 PM EST. Over the next two days, they will execute a comprehensive countdown sequence that mirrors actual launch operations in almost every detail. AI-generated image Launch controllers at the Kennedy Space Center manage every phase of the wet dress rehearsal countdown. The sequence includes loading cryogenic propellants into the SLS tanks, conducting a full launch countdown, demonstrating the ability to recycle the countdown clock, and draining the tanks to practice scrub procedures. The test will culminate in two terminal countdown runs — simulations of the final 10 minutes before launch. Terminal Count Sequence • First Run: Count down from T-10 minutes, pause at T-1:30 for up to 3 minutes, resume to T-33 seconds, then hold. • Clock Recycle: Reset countdown to T-10 minutes to simulate a scrub scenario. • Second Run: Repeat terminal countdown to just inside T-30 seconds before ending the sequence. • Purpose: Validates real-world conditions including scrub-and-retry scenarios for weather or technical issues. The simulated launch is targeted for 8:30 PM EST on Thursday, February 19 , with a window extending approximately four hours in either direction. If hydrogen behaves this time, NASA will have cleared the last major technical gate before committing to a launch date. By the Numbers: SLS and Artemis 2 700K+ Gallons of Propellant 322 ft SLS Height 8.8M lbs Thrust at Liftoff 10 Days Mission Duration 4 Crew Members ~50 hrs Rehearsal Duration The SLS Block 1 configuration standing on Pad 39B is the most powerful rocket NASA has ever built. Its two solid rocket boosters and four RS-25 engines generate 8.8 million pounds of thrust at liftoff — 15% more than the Saturn V that carried Apollo astronauts to the Moon. The core stage alone holds over 537,000 gallons of liquid hydrogen and liquid oxygen, chilled to minus 423°F and minus 297°F respectively. AI-generated image The Artemis 2 crew: NASA astronauts Reid Wiseman, Victor Glover, Christina Koch, and CSA astronaut Jeremy Hansen. The Crew That's Been Waiting Four astronauts have been training for this mission for years, watching delays stack up while maintaining readiness. The Artemis 2 crew represents a historic lineup: Astronaut Agency Role Notable Reid Wiseman NASA Commander Former Navy test pilot, ISS veteran Victor Glover NASA Pilot First Black astronaut on a lunar mission Christina Koch NASA Mission Specialist First woman on a lunar mission; holds record for longest single spaceflight by a woman Jeremy Hansen CSA Mission Specialist First Canadian to fly beyond low Earth orbit The mission profile sends the Orion spacecraft on a free-return trajectory around the Moon, swinging within roughly 6,400 miles of the lunar far side before using the Moon's gravity to slingshot back toward Earth. While the crew won't enter lunar orbit or land, the flight will validate all of Orion's life-support, navigation, and communications systems in the deep space environment for the first tim