CAPE CANAVERAL, Fla. (AP) — Boeing is closer to understanding what went wrong with its astronaut capsule in orbit, now that testing is complete on a spare thruster here on Earth.

The Starliner capsule has been docked at the International Space Station since June 6. It should have returned with its NASA test pilots by mid-June, but thruster failures and helium leaks prompted NASA and Boeing to extend its stay.

Officials said Thursday there’s still no return date for astronauts Butch Wilmore and Suni Williams. Engineers will first disassemble the thruster that was test-fired in New Mexico over the past couple of weeks. Then they’ll analyze the data before clearing Starliner for the trip home.

“We collected an incredible amount of data on the thruster that could help us better understand what is going on in flight,” NASA’s commercial crew program manager Steve Stich said in a statement.

The testing managed to replicate the thruster conditions up until the capsule’s docking at the space station, as well as what the thrusters will experience between undocking and descent, according to NASA.

This is the Starliner’s first test flight with a crew aboard.

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