WASHINGTON — Boeing’s CST-100 Starliner is now installed on the Atlas 5 rocket that will launch the spacecraft on a crewed test flight to the International Space Station next month.

The spacecraft rolled out from Boeing’s Commercial Crew and Cargo Processing Facility at the Kennedy Space Center to Space Launch Complex 41 in the early morning hours April 16. The spacecraft was hoisted into place atop the Atlas 5 rocket in the Vertical Integration Facility building there later in the day.

The rollout is the latest milestone in preparations for the Crew Flight Test (CFT) mission, which will launch no earlier than the evening of May 6. NASA astronauts Butch Wilmore and Suni Williams will be on board, flying Starliner to the International Space Station. They will remain on the station for about eight days before boarding Starliner for a return to Earth, landing in the southwestern United States.

The launch was previously planned for May 1 but delayed because of activities at the ISS, including revised schedules for the departure of a cargo Dragon vehicle and the relocation of the Crew Dragon spacecraft there to free up the forward docking port on the Harmony module for Starliner.

The CFT mission will take place almost exactly two years since a second uncrewed test flight, designated OFT-2, that successfully docked to the station and returned to Earth. The original uncrewed test flight, in December 2019, suffered malfunctions that prevented the spacecraft from reaching the station and forced it to return to Earth after only a couple days.

At a March 22 briefing, Mark Nappi, vice president and program manager for Starliner at Boeing, said the key purpose of CFT is to see how spacecraft systems perform with a crew on board. “We flew OFT-2, and that was the uncrewed mission for the Starliner vehicle, and it was very successful. Now we introduce humans.”

Most of the flight test objectives, he said, are devoted to answering “does the vehicle perform with the human in the loop as expected?” That includes various environmental systems, control interfaces and the ability of the astronauts to take manual control of the spacecraft if needed.

A successful CFT would allow NASA to complete certification of Starliner for regular crew rotation missions, starting with Starliner-1 in early 2025. At the March briefing, Steve Stich, NASA commercial crew program manager, said that certification needed to be completed by November of December to keep Starliner-1 on schedule. “I think we have a good shot” of achieving that schedule, he said then. “We just need to stay on track.”

The next milestone for the CFT mission is a flight test readiness review, scheduled for April 25. Wilmore and Williams are also scheduled to arrive at KSC the same day for final preparations for the mission.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...