KENNEDY SPACE CENTER, Fla. — Boeing’s CST-100 Starliner will not dock with the International Space Station after suffering a problem that caused the spacecraft to use too much propellant when entering orbit.

At a briefing here three hours after Starliner lifted off on an uncrewed test flight Dec. 20 called the Orbital Flight Test (OFT), NASA and Boeing officials said a problem with a timer on the spacecraft that tracks what’s known as Mission Elapsed Time meant that the spacecraft’s internal time was off, disrupting an orbital insertion burn 31 minutes after liftoff to place the spacecraft into orbit.

“It appears as though the mission elapsed timing system had an error, and that anomaly resulted in the vehicle believing that the time was different than it actually was,” NASA Administrator Jim Bridenstine said.

That caused reaction control thrusters on the spacecraft to fire to maintain a precise alignment at the wrong time, using up propellant. “When that prop got burnt, it looked like we weren’t going to be able to go ahead and rendezvous with the International Space Station,” Bridenstine said. He confirmed later in the briefing that a Starliner docking with the ISS had been ruled out.

Flight controllers recognized that the problem was taking place and tried to send commands to take over the spacecraft, said Jim Chilton, senior vice president of Boeing Space and Launch. The problem, though, may have been exacerbated by a handover from one Tracking and Data Relay Satellite to another, creating a gap in communications around the time controllers were trying to correct the problem.

Controllers were able to later execute an orbital insertion burn and put the spacecraft into a stable orbit. The spacecraft was, at the time of the briefing, in an orbit of 216 by 186 kilometers. Steve Stich, deputy manager of the commercial crew program, said two additional maneuvers are scheduled for later Dec. 20 to refine that orbit.

That orbit will allow Starliner to perform a landing at White Sands Missile Range in New Mexico Dec. 22, about 48 hours after launch. NASA and Boeing officials said they were still studying the state of the spacecraft and determining what test objectives they could carry out before deciding whether to land on Dec. 22 or stay in orbit for a longer mission.

The root cause of the timer problem is not yet known. “We don’t know if it started that way, or if some event caused it to be that way,” Chilton said, adding his team’s “most important job” is to diagnose the problem and to make sure it won’t reoccur in other phases of the mission, such as reentry and landing.

The problem doesn’t appear to be linked to the launch of the spacecraft itself. Tory Bruno, president and chief executive of United Launch Alliance, said they had a “nominal flight” of the Atlas 5 that launched Starliner, including the first use of a dual-engine Centaur upper stage on that rocket. “We achieve those separation parameters and, in fact, literally hit a bullseye,” at the time of spacecraft separation.

Bridenstine declined to speculate whether Boeing would need to fly another uncrewed test flight, this time docking with the ISS, before flying crew. “I think it’s too early to make that assessment,” he said, citing the lack of knowledge on the root cause of the timer problem. Neither Chilton nor Stich said they immediately knew what fraction of the OFT mission objectives won’t be achieved.

However, Bridenstine would not rule out going directly to a crewed flight after this mission despite the problems encountered. “That’s something we’ve got to look at,” he said.

It’s possible, he and others added, that had astronauts been on board the spacecraft, they could have been able to take manual control when the problem arose and preserved the opportunity to dock with the station. “In some cases, having a crew on board gives you some better, different, enhanced capability to responding to some failures,” said Stich.

The two NASA astronauts currently training for that Starliner crewed test flight agreed. “Starliner has a robust manual capability,” said Mike Fincke. “We like to think that, had we been on board, we could have given the flight control team more options on what to do in this situation.”

“Had we been on board, there could have been actions that we could have taken,” said Nicole Mann. “We are looking forward to flying on Starliner. We don’t have any safety concerns.”