HONOLULU — NASA and Boeing will cooperate on an investigation into a timer anomaly that cut short December’s uncrewed test flight of Boeing’s CST-100 Starliner spacecraft as NASA weighs whether to require another such test flight.

In a Jan. 7 statement, NASA said the agency and Boeing were establishing a “joint, independent investigation team” to determine the primary cause of the timer problem the Starliner suffered immediately after its Dec. 20 launch on what was to be an eight-day mission to the International Space Station.

Boeing later said that the mission elapsed timer on the spacecraft was off by 11 hours, causing the spacecraft to think it was in the wrong phase of its mission immediately after separation from the upper stage of the Atlas 5 that launched it. The spacecraft fired its thrusters in reaction to the incorrect time, and by the time spacecraft controllers on the ground were able to take control, the spacecraft had expended too much propellant to allow it to dock with the station. The spacecraft instead landed safely at White Sands, New Mexico, Dec. 22.

The joint investigation, NASA said in the statement, will seek the root cause of the timer anomaly and also investigate any other software issues, and recommend corrective actions to implement prior to Starliner carrying people. NASA said it estimates the team will take two months to complete its work.

At the same time that investigation is underway, NASA will separately examine if a second uncrewed test flight will be needed before it allows astronauts to fly on the spacecraft. “NASA’s approach will be to determine if NASA and Boeing received enough data to validate the system’s overall performance, including launch, on-orbit operations, guidance, navigation and control, docking/undocking to the space station, reentry and landing,” the agency said in its statement, a process expected to take several weeks.

That uncrewed test flight, known as the Orbital Flight Test, did not approach or dock with the station. “Although data from the uncrewed test is important for certification, it may not be the only way that Boeing is able to demonstrate its system’s full capabilities,” NASA stated.

The Commercial Crew Transportation Capability contract that NASA awarded to Boeing did require an uncrewed test flight that included a docking. However, NASA Administrator Jim Bridenstine suggested at a post-landing briefing Dec. 22 that NASA might not hold Boeing to that requirement.

“There’s also a difference between what is a NASA requirement and what is a contractual requirement for this particular flight test,” Bridenstine said then. “The NASA requirement might not be the same as the contractual requirement for this particular flight test.”

“Although docking was planned, it may not have to be accomplished prior to the crew demonstration,” NASA said in the new statement. “Boeing would need NASA’s approval to proceed with a flight test with astronauts onboard.”

Neither NASA nor Boeing have released additional information about the timer anomaly since the mission. Boeing officials said during the mission that the timer is set on Starliner prior to launch by using data from the Atlas 5, but that the spacecraft have accessed the wrong data.

In a Dec. 28 update, Boeing said that the spacecraft itself was in good condition after the abbreviated flight, performing as expected or better while in orbit and during reentry and landing. Boeing announced Jan. 3 that the spacecraft was on its way back to the Kennedy Space Center in Florida for additional post-flight analysis and refurbishment for a future crewed test flight. That cross-country shipment was scheduled to last 10 days.