KENNEDY SPACE CENTER, Fla. — Boeing’s CST-100 Starliner spacecraft passed another in a series of final reviews Dec. 17 as it proceeds towards a critical uncrewed test flight.

NASA announced the Orbital Flight Test (OFT) mission passed a launch readiness review Dec. 17, five days after a separate flight readiness review. Officials with both Boeing and launch vehicle manufacturer United Launch Alliance said the review uncovered no issues that would prevent a launch on Dec. 20 at 6:36 a.m. Eastern.

“We are tracking no spacecraft anomalies right now,” said John Mulholland, vice president and program manager for Boeing’s commercial crew program, at a press briefing here. “The spacecraft is in really good shape.”

If no new technical issues arise and weather cooperates — the latest forecast projected an 80% chance of acceptable weather at launch time — the Atlas 5 carrying Starliner will lift off shortly before sunrise Dec. 20. The flight will be the first for the Atlas 5 that uses a dual-engine Centaur upper stage and the first without a payload fairing.

That choice of upper stage is driven by the trajectory needed for Starliner’s future crewed flights. “The main reason for using the dual-engine Centaur is to flatten out the trajectory such that we can enable safe aborts if that should be necessary,” said John Elbon, chief operating officer of ULA. That reduces the g-forces should an abort and reentry be required, and also avoids a “blackout zone” in the north Atlantic.

The Atlas 5 will place Starliner into a suborbital trajectory, with an apogee of 181.5 kilometers and a perigee of just 72.8 kilometers. Starliner’s thrusters will then circularize the orbit and begin the maneuvers needed to reach the International Space Station.

Starliner will arrive at the ISS about a day after launch, with docking scheduled for 8:08 a.m. Eastern Dec. 21. Besides an anthropomorphic test dummy, nicknamed “Rosie,” the Starliner will carry about 270 kilograms of cargo for the station, said Joel Montalbano, deputy manager of the ISS program at NASA. Most of that is food, but the cargo also includes some crew clothing and radiation-monitoring equipment.

Starliner will remain on the station until early Dec. 28, undocking at 12:44 a.m. Eastern and landing at White Sands Missile Range in New Mexico about five hours later.

The Starliner that is flying the OFT mission is “nearly identical” to the spacecraft that will be used for the later crewed test flight, Mulholland said, with the major differences being a launch abort system that will be in passive mode for this flight and a lack of an emergency oxygen system since no astronauts will be on board to test it.

Despite the similarities, and the optimism expressed by NASA and Boeing officials about the OFT mission, they declined to estimate when that crewed test flight will take place even if there are no issues with the OFT flight. Kathy Lueders, NASA commercial crew program manager, said the factors that drive the schedule for the crewed flight include reviewing all the data collected during OFT and working through the various reviews and certifications for the crewed flight.

“John [Mulholland] and I are still working through those schedules and finalizing those,” she said. “Having this demonstration mission is going to be a key part of that schedule.”

Elbon said ULA was in discussions with Boeing about potential launch dates for that crewed flight, working around other Atlas 5 launches that have tight launch windows, like the Solar Orbiter mission launching in February and Mars 2020 in July.

“I think there’s a couple areas we can fit in on the manifest in that first part of the year,” Mulholland said. “We really wanted to stay away from any announcement of a Crew Flight Test launch date until we successfully complete OFT and we’re ready to lock in a launch date.”