SLS enters pad flow ahead of historic Artemis II mission

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NASA’s Artemis II Space Launch System (SLS) rocket and Orion spacecraft arrived at Launch Pad 39B after an approximately 10-hour journey from the Vehicle Assembly Building (VAB) at the agency’s Kennedy Space Center.

Crawler Transporter 2 (CT-2) carried the Moon rocket and its Mobile Launcher-1 (ML-1) back to the historic launch site after a slightly delayed rollout due to high winds. All eyes are now on the final pad flow ahead of a potential NET (No Earlier Than) launch on April 1 in what is the biggest NASA mission in decades.

The rollout was planned for the evening of March 19 but shifted due to conditions; the planned 8 p.m. local first motion time was delayed by high winds.

This was less related to the huge rocket and its ML-1, and more to the laying of plywood on the exit of the Vehicle Assembly Building (VAB) High Bay, where several planks went flying during the process.

The planks are required as the huge weight of the CT passes over onto the bedrock of the Crawlerway over the tracks that are used for the VAB doors.

Once the winds died down, the CT began its rollout onto the Crawlerway and made the overnight trip to 39B.

SLS’s return marks the second time it’s been hosted at 39B, following its first rollout in January for a series of launch rehearsals, including a fully successful wet dress rehearsal in February during which the vehicle was loaded with its cryogenic propellants.
However, engineers later identified an issue in the upper stage helium pressurization system—specifically, a dislodged seal inside a Quick Disconnect (QD) connection between the upper stage and the ground umbilical. The seal had blocked helium flow under pressure, preventing proper tank pressurization.

NASA opted to roll the stack back to the VAB for inspection and repairs, allowing access for engineers to remove the problematic seal, redesign a secondary seal to perform its function, conduct extensive validation testing—including reduced-flow helium trials—and fully flight-certify the repaired assembly before reinstalling it.

They also replaced flight termination system batteries and refreshed several other systems.
In mid-March, following these resolutions, NASA conducted the Artemis II Flight Readiness Review (FRR) on March 12. All teams unanimously polled “go” for launch in early April.

Acting Associate Administrator Lori Glaze, Exploration Systems Development Mission Directorate, described the two-day FRR as “extremely thorough,” with “very open, transparent” discussions focused on risk posture and mitigation.

All participants—including engineering, mission management, ground systems, and flight operations teams—reported no dissenting concerns.

John Honeycutt, Chair of the Artemis II Mission Management Team, emphasized caution: “A clean FRR is not the time to celebrate. That will be when the astronauts are home safely,” before providing an honest assessment on the risk matrix procedure that made headlines and deeper conversations on LOM (Loss Of Mission) vs LOC (Loss Of Crew).

Somewhat surprisingly, Shawn Quinn, Manager of the Exploration Ground Systems Program, noted the helium fix did not require teams to conduct an additional wet dress rehearsal once back at the pad. This decision will ultimately be proven out during the launch day countdown.

With FRR approval secured, the rocket’s return to Pad 39B now kicks off the final prelaunch campaign. Launch opportunities begin as soon as Wednesday, April 1, and extend through at least April 6 (with backup dates later in the month).

Commander Reid Wiseman, Pilot Victor Glover, and Mission Specialist Christina Koch of NASA, together with CSA Mission Specialist Jeremy Hansen of the Canadian Space Agency, will fly the 10-day mission. The crew entered quarantine earlier this week and will soon travel to Kennedy to continue preparations in the astronaut crew quarters.

Along with Canada, Europe is represented via ESA’s second European Service Module (ESM-2) that will power Orion around the Moon. This critical element supplies propulsion, electrical power, thermal control, air, water, and temperature regulation for the four astronauts in deep space.

This test flight will validate Orion’s deep-space performance, paving the way for Artemis III’s crewed lunar landing and eventual sustained presence on the Moon.

Lead photo: Sawyer Rosenstien for NSF.

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