Boeing Starliner's crew debut delayed again over spacecraft issue; What happens next?

Boeing's first Starliner mission carrying astronauts into space has been delayed again - until at least May 21 - over an issue with the spacecraft's propulsion system, the company said on Tuesday.

Starliner's mission carrying two NASA astronauts had been scheduled for liftoff from Florida last week until a technical issue with its Atlas 5 rocket prompted a delay to Friday, May 17, the latest postponement for a program years behind schedule and more than $1.5 billion over budget.

A new technical issue, now concerning Starliner itself, has prompted another postponement to at least next Tuesday, Boeing said in a statement.

"Starliner teams are working to resolve a small helium leak detected in the spacecraft's service module," Boeing said, adding that engineers traced the leak to a component on one of the propulsion system's 28 control thrusters that are used for maneuvering in Earth's orbit.

Boeing has been developing Starliner for more than a decade to provide NASA with a second U.S. spacecraft capable of ferrying astronauts to and from the International Space Station. SpaceX's Crew Dragon capsule, built under the same NASA program, first launched astronauts to space in 2020.

Starliner's latest mission, called the Crewed Flight Test, is due to be the final test before the spacecraft is certified by the U.S. space agency to fly routine astronaut missions to the ISS. Boeing completed an uncrewed Starliner trip to the ISS in 2022 following years of technical and management issues.

NASA officials and Boeing engineers will run tests and try to fix the helium leak before the next possible launch window on May 21 at 4:43 p.m. ET (2043 GMT). Helium is used on Starliner to pressurize the fuel that powers the spacecraft's thrusters for orbital maneuvering.

The Atlas 5 rocket, built by the Boeing and Lockheed Martin joint venture United Launch Alliance (ULA), launches Starliner into space. Before attempting to launch Starliner last week, ULA discovered a faulty valve on the Atlas 5 and rolled the rocket off the launchpad to replace the valve.

Sensors on Starliner first detected suspicious traces of helium inside the propulsion system while the spacecraft was on the launchpad last week, but those detections did not raise alarm to engineers at the time, according to a person briefed on the mission operations.

Boeing engineers investigated the helium detections while ULA was replacing the faulty valve on Atlas 5 and determined more testing and scrutiny was needed in order to meet the mission's strict launch safety criteria, the person said.