Boeings Starliner spacecraft, which was supposed to remain docked to the International Space Station for about a week, is getting some extra time in space, NASA said Tuesday, as officials troubleshoot helium leaks and study why some thrusters failed during the test flight.

The capsule is now scheduled to fly a pair of NASA astronauts, Suni Williams and Barry Butch Wilmore, back to Earth and land in the New Mexico desert at 4:51 a.m. Eastern time June 26, which would mark a 20-day mission. The return leg, with a fiery plunge through the atmosphere, is a key part of the test flight that will stress the spacecrafts heat shield with temperatures reaching about 3,000 degrees Fahrenheit.

Officials will also be examining whether the parachute system, which Boeing had to redesign after an earlier test flight without anyone on board, provides a safe landing in what would be the final act of Starliners first flight with humans on board.

After delays caused by a faulty valve on the rocket and helium leaks in the spacecraft, Starliner launched from Cape Canaveral, Fla. on June 5 and reached the station a day later. As Starliner approached the station, five of its thrusters, used to make small adjustments to its trajectory, went offline, forcing Boeing to back the vehicle away from the station and troubleshoot the issue.

NASA and Boeing were able to bring four of the five back online and dock successfully.

The teams test fired the thrusters on Saturday while the spacecraft was attached to the station, and all of them worked well, NASA said. They did not try to test fire the one thruster that didnt come back online during the flight and wont try to use it during Starliners return flight out of an abundance of caution, Steve Stich, NASAs commercial crew program manager, said during a briefing Tuesday.

In addition to the thruster problems, Starliner has suffered a series of helium leaks in its propulsion system. NASA and Boeing discovered a new one the fifth since Starliner has been on the station. That leak is small and wont pose a problem for the return, NASA said. Helium is used to pressurize the propellants through the propulsion system.

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NASA originally said Starliner would come home June 18, then pushed the landing back to June 22. The thruster problems and helium leaks are contained in the spacecrafts service module, which is used to maneuver the capsule during flight. Before the capsule reenters Earths atmosphere, the service module is jettisoned and burns up. That means engineers wont be able to study it after the flight, which is one of the reasons they said they were taking more time to understand the issues now.

Were taking our extra time given that this is a crewed vehicle, and we want to make sure that we havent left any stone unturned, Stich said. We also want to look at the systems, and potential interaction between the systems, and make sure we havent missed something before we return. And were getting a lot of great data while were at the space station for not only this flight but for the next flight.

NASA and Boeing think the thrusters went offline because of the extreme heat generated while they were firing in rapid succession to keep the capsule on course with the space station, Stich said.

In some cases, we think the heating may have caused the propellants to vaporize a little bit and we didnt get good mixing [of the propellants], and thats why the thrust was a little bit lower, he said. Engineers still dont understand what is causing the helium leaks, he said.

While on the station, Williams and Wilmore have prepared for their return, as well as rehearsed using Starliner as a safe haven in the event of an emergency on the space station. Theyve also worked alongside the other astronauts installing research equipment, maintaining the labs hardware, and helping station crew members Matt Dominick and Tracy Dyson prepare for a spacewalk, NASA said in a statement.

Despite the problems, NASA expressed confidence in Starliner. Officials said they expected to discover issues during the mission, a test flight designed to see how Starliner operates with humans on board.

Weve always said this as a test flight and were going to learn some things, said Mark Nappi, a Boeing vice president who oversees the Starliner program. So here we are. Weve learned that our helium system is not performing as designed, albeit manageable. So weve got to go figure that out.

Once the mission is complete, NASA would certify Starliner for regular crew rotation flights of a full contingent of four astronauts to the space station. SpaceX, the other participant in NASAs commercial crew program, which outsourced human spaceflight to the private sector after the space shuttle was retired, has been flying astronauts for NASA since 2020.

Given the problems Starliner has faced on this test flight, its not clear when Boeing, which was awarded a $4.2 billion NASA contract in 2014, would fly its first regular crew rotation mission.

Weve got to go address the helium leaks, Stich said. Were not going to go fly another mission like this with the helium leaks. The teams also need to find out whats causing the thrusters to have low thrust, he added. So weve got some of that work to do after this flight.

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NASA says Boeing Starliner spacecraft return delayed to June 26 - The Washington Post