NASA's February rollback of the Artemis II stack looked like a launch campaign in trouble. Three months later, it reads differently: a late helium-system scare that forced the Space Launch System and Orion back into the Vehicle Assembly Building, then gave engineers one more hard test before the first crewed lunar flyby of the Artemis era. Artemis II launched on April 1, 2026 , splashed down on April 10 off San Diego, and completed a 9-day, 1-hour, 32-minute mission around the Moon. NASA's initial post-flight assessments now show the rocket, Orion, and ground systems met their core objectives, which changes the February rollback from a schedule failure into a useful stress test. AI-generated image Cutaway of the Interim Cryogenic Propulsion Stage helium pressurization system, where the flow interruption was detected. May 18 Update: Artemis II Flew, and the Hardware Passed the First Review NASA's Artemis II mission is now complete. The crewed Orion spacecraft traveled 694,481 miles around the Moon and back, reentered at nearly 35 times the speed of sound , and landed just 2.9 miles from its target point in the Pacific. The biggest post-flight item is encouraging for Artemis III. NASA says Orion's heat shield performed as expected, with the char-loss behavior seen on Artemis I significantly reduced in both quantity and size. The crew module is returning to Kennedy for de-servicing, then the heat shield will go to Marshall for sample extraction and internal x-ray scans. The only named open issue from the early assessment is a urine vent line problem. NASA is still working root cause and corrective actions before Artemis III, but the SLS insertion, pad systems, mobile launcher changes, and Orion recovery all cleared their first checks. Rolling Back From 39B At 9:28 a.m. EST on February 25, the Artemis II launch director gave the "go" for rollback. Ten minutes later, the crawler-transporter carrying the 322-foot-tall SLS rocket and Orion spacecraft began its crawl from Launch Complex 39B back to the Vehicle Assembly Building. NASA livestreamed the event on YouTube as the massive stack inched along the crawlerway at roughly one mile per hour. Once inside the VAB, technicians will establish work platforms around the upper stage to diagnose the exact cause of the helium flow interruption. The process of setting up access, performing the repair, and then reversing the sequence for another rollout will consume weeks, not days. Timeline of Events Feb 2: First wet dress rehearsal reveals hydrogen leaks at core stage interface. Feb 19: Second WDR completed successfully with no hydrogen leaks. Peak H2 concentration just 1.6%, well within limits. Feb 20: NASA targets March 6 for launch. Crew enters prelaunch quarantine. Feb 21: Helium flow interruption discovered in the ICPS upper stage. Rollback deemed "likely." Feb 25: SLS begins rolling back to the VAB at 9:38 a.m. EST. March window officially off the table. Workers at the pad had actually begun installing temporary work platforms for tasks like retesting the flight termination system. Those platforms had to be torn down before the rollback could proceed, and NASA pushed to complete the disassembly on February 21 before high winds arrived the following day. What Went Wrong With the Upper Stage The problem sits in the Interim Cryogenic Propulsion Stage (ICPS), a modified version of the Delta IV upper stage built by United Launch Alliance. Helium gas pressurizes the ICPS propellant tanks, and without steady helium flow, the stage cannot maintain the pressure needed to feed liquid hydrogen and liquid oxygen to the RL10 engine during its critical trans-lunar injection burn. AI-generated image The Vehicle Assembly Building at Kennedy Space Center, where technicians will access the upper stage for repairs. Isaacman noted that a similar helium issue appeared during the Artemis I mission in 2022. While NASA had not disclosed the precise fault, several potential causes were under consideration. "Regardless of the potential fault, accessing and remediating any of these issues can only be performed in the VAB," the administrator wrote on X. 322 ft SLS Stack Height 8.8M lbs Thrust at Liftoff ~12 hrs Rollback Duration 1 RL10 ICPS Engine 4 days From Target Date to Rollback 10+ days Mission Duration (Planned) The helium pressurization system is essential for the single most important burn of the entire Artemis II mission. After the SLS core stage and boosters propel the spacecraft into low Earth orbit, the ICPS fires its RL10 engine to send Orion on a trajectory around the Moon. Any uncertainty in the pressurization system is a non-starter for a crewed flight. A Successful Dress Rehearsal, Then a Gut Punch The frustration within NASA's workforce is palpable. Just days before the helium anomaly surfaced, the Artemis II team had pulled off a nearly flawless second wet dress rehearsal. On February 19, crews loaded the SLS core stage and upper stage with cryogenic propellants, ran a practice countdown to T-minus 33 seconds, recycled, and counted down again to T-minus 29 seconds. The hydrogen leaks that plagued the first WDR on February 2 were gone. Peak hydrogen gas concentration measured just 1.6%, and during fast-fill operations it dropped to 0.4%, a level launch director Charlie Blackwell-Thompson called "almost unheard of." AI-generated image The Artemis II crew had entered prelaunch quarantine on February 20, one day before the helium problem was discovered. Seal replacements on two liquid hydrogen fuel lines after the first WDR had solved the hydrogen issue. The fix mirrored what teams did during the Artemis I campaign in 2022. "On Artemis 1, we did the same thing. We changed the seals at the pad and we were successful," said John Honeycutt, chair of NASA's Artemis 2 mission management team, at the February 20 briefing. Honeycutt's confidence was high. "I've got a pretty high level of confidence in the configuration that we're in right now," he said at the time. "It's out there at the pad. It's going to be there at the pad until we go fly." Less than 24 hours later, that confidence collided with a data readout showing interrupted helium flow. Second WDR Results (Feb 19) • Hydrogen leaks: None detected. Peak concentration 1.6% (limit: higher). Fast-fill phase: 0.4%. • Countdown: Two terminal counts completed (T-33s and T-29s), both nominal. • Minor issues: Ground comms glitch in launch control; voltage anomaly in booster avionics (briefly paused countdown). • Seal repair: Two LH2 fuel line seals replaced after first WDR; no leaks with new seals. Launch Windows: April at the Earliest With the March 6-11 window gone, the next available launch period runs April 1 through April 6 . A second April window opens on April 30. NASA has not published launch opportunities beyond the end of April. Whether an April 1 launch is realistic depends entirely on what technicians find inside the ICPS. If the fix is straightforward, say a valve replacement or a line purge, the team could conceivably reassemble platforms, complete the repair, roll back out, and still hit early April. A more complex issue, such as a cracked helium line or a contamination problem inside the tank pressurization manifold, could push the timeline into late April or beyond. AI-generated image Launch Complex 39B, where Artemis II had been stationed since its initial rollout in late January. Launch Window Dates Status Window 1 March 6 - 11, 2026 Eliminated Window 2 April 1 - 6, 2026 Earliest possibility (dependent on repair) Window 3 April 30+, 2026 Backup if April 1 slips Isaacman addressed public frustration directly. "I understand people are disappointed by this development. That disappointment is felt most by the team at NASA, who have been working tirelessly to prepare for this great endeavor," he wrote, drawing a parallel to the Apollo program's setbacks before the first lunar landing in 1969. Scrutiny on SLS Grows After Starliner Report The timing of the rollback