Boeing’s leak-prone Starliner capsule will remain docked to the International Space Station an additional four days, NASA announced Tuesday, returning to Earth with a pre-dawn landing at White Sands, New Mexico, on June 26 to close out an extended 20-day test flight, the first with astronauts aboard.

The additional docked time will give Starliner commander Barry “Butch” Wilmore and co-pilot Sunita Williams more time to help out aboard the station while flight controllers and engineers continue scrutinizing telemetry and finalizing plans for re-entry with five known helium leaks in the capsule’s propulsion system and unexpected, presumably now-resolved issues with multiple maneuvering jets.

One jet will not be used for the remainder of the flight, but the other suspect thrusters were successfully “hot fired” during a test Saturday, giving managers confidence they will work as needed for post-undocking maneuvers and to drop the Starliner out of orbit for re-entry and landing.

As for the helium leaks, engineers say the spacecraft has more than seven times the amount needed for the remainder of the flight. During the hot-fire test Saturday the leak rates were less than what telemetry indicated earlier in the mission, but engineers are still assessing data to better understand the behavior of the system.

“We’ve learned that our helium system is not performing as designed. Albeit manageable, it’s still not working like we designed it,” said Mark Nappi, Boeing’s Starliner program manager. “So we’ve got to go figure that out.”

As for the thrusters, “there’s some things about our flight profile and/or our parameters … where our thrusters aren’t performing (as expected). So we’ve got to go figure that out.” But he said Boeing intends to “fully eliminate” both issues, which he described as “nuisances,” before the Starliner flies again.

“The good thing about the situation,” he said, “is that we can stay up on ISS a little bit longer and get as much data as we possibly can so that we can fully understand this to the best of our ability.”

In the meantime, Steve Stich, NASA’s Commercial Crew Program manager, said the Starliner can safely carry Wilmore and Williams back to Earth as is if some issue crops up that requires an immediate departure.

But as it now stands, Wilmore and Williams will undock from the space station’s forward port at 10:10 p.m. EDT on June 25 and fire the ship’s aft-facing thrusters to drop out of orbit early the next day, setting up a parachute-and-airbag-assisted landing at White Sands, N.M., at 4:51 a.m. EDT.

The day before Wilmore and Williams depart, ISS astronauts Tracy Dyson and Mike Barratt plan to venture outside the station for a spacewalk, or EVA, to retrieve a faulty radio transmitter and to collect swabs near vents and the station’s airlock to find out if any microorganisms have managed to make it outside and survive in the harsh environment of space.

During an initial attempt June 13, in what was to have been the first of three planned spacewalks, Dyson and Matthew Dominick, her original partner, never got out of the airlock. Dominick reported a spacesuit “discomfort issue,” and the EVA was called off.

Rather than take the time to investigate and correct the problem with Dominick’s suit, and given the amount of airlock oxygen available, NASA managers decided to re-try the original spacewalk with Dyson and Barratt and to combine tasks planned for the second and third outings in a single excursion on July 2.

But the spacewalk schedule is dependent on the Starliner undocking, which is the top near-term priority.

Already running four years behind schedule, the Starliner was launched June 5, a month later than planned due to problems with its Atlas 5 rocket, trouble with a countdown computer and because of an initial helium leak in the system used to pressurize the capsule’s thrusters.

NASA and Boeing managers decided the leak was too small to pose a safety threat and the ship was cleared for launch. Once in orbit and on the way to the space station, however, four more helium leaks developed and the Starliner’s flight computer took seven maneuvering jets off line when the telemetry did not match pre-launch expectations.

Stich said the hot-fire test Saturday showed the jets needed for post-undocking maneuvers and the critical de-orbit “burn” will work as needed to take the ship out of orbit for re-entry. Likewise, he said engineers were confident the helium leaks can be managed even if one or more gets worse after undocking.

But the additional days docked with the space station will give engineers more time to review data and monitor telemetry from the Starliner’s service module, which is where the thrusters and the helium pressurization plumbing are located. Engineers will not be able to study the actual hardware because the service module is discarded prior to re-entry and will burn up in the atmosphere.

“We’re taking extra time given that this is a crewed vehicle, we want to make sure that we haven’t left any stone unturned,” Stich said. “We also want to look at the systems and potential interaction between the systems and make sure we haven’t missed something before we return.

“I like the fact that the vehicle is staying a little longer. I like the fact that we’re watching how the vehicle performs thermally, how the space station charges the batteries. We’re getting to see those kinds of cycles, which we absolutely need for the subsequent missions. … So I think there’s a silver lining in staying a little (longer at the space station).”

Before launch, NASA managers had hoped the Starliner test flight would pave the way toward certifying the spacecraft for operational space station crew rotation missions starting early next year. But given the problems encountered earlier in the flight, certification could be delayed depending on what is required to address the issues identified to date.