The return to Earth of Boeing's Starliner capsule will be delayed a few more days due to thruster troubleshooting and a scheduled spacewalk.

NASA announced today (June 18) that Starliner will conclude its first human mission to the International Space Station (ISS) no earlier than June 26, nearly three weeks after it launched. Landing that day is scheduled to occur at White SandsSpace Harbor in New Mexico at 4:51 a.m. EDT (0851 GMT). We'll carry it live here at Space.com, via NASA Television.

The two-astronaut mission, known as Crew Flight Test (CFT), was originally supposed to spend about a week at the ISS, but its ISS departure has been pushed back considerably. NASA and Boeing are using the extra time to continue evaluating thruster issues that interfered with Starliner's first ISS docking attempt on June 6. Additionally, a postponed ISS maintenance spacewalk will now take place on June 24, two days before Starliner's scheduled departure.

"We want to give our teams a little bit more time to look at the data, do some analysis and make sure we're really ready to come home," Steve Stich, manager of NASA's Commercial Crew Program, said during a livestreamed teleconference with reporters today. Starliner can undock in case of emergency, but otherwise, testing is ongoing to learn more about the vehicle's systems.

Related: Thruster glitches and helium leaks can't stop Boeing's Starliner astronaut test flight but why are they happening?

Stich reiterated that five of Starliner's 28 reaction control thrusters failed during the final phase of the ISS rendezvous on June 6, though four of them eventually came back online. (Starliner succeeded on its second docking try, which occurred several hours later on June 6.) Evaluation of what happened is ongoing. As part of that effort, Boeing and NASA ground team members performed a thruster hot-fire test over the weekend alongside the astronauts, and, after that, Stich said, everyone "feels very confident."

One thruster was not fired during the test due to abnormally low pressure first observed during docking, and it will remain offline during the return to Earth. (Canadarm2, the robotic arm on the space station, was also used to view the thrusters via robotic camera, according to ISS Program Manager Dana Weigel, who also participated in the teleconference.)

Breaking space news, the latest updates on rocket launches, skywatching events and more!

CFT's docking was a bit more complex than the only other time Starliner approached the ISS, which was done during an uncrewed test flight in May 2022. That uncrewed mission, called Orbital Flight Test 2 (OFT-2), also faced thruster issues that interfered with docking.

But "the rendezvous [for CFT] was a little bit more demanding on the propulsion system. In other words, it fired its thrusters a bit more frequently," Stich said. Additionally, teams are doing hardware simulations at NASA's Marshall Space Flight Center in Alabama to model ongoing helium leaks on Starliner.

A small helium leak in one of Starliner's reaction control system (RCS) thrusters was first discovered on the pad in early May, after a launch attempt was waved off due to a valve issue with the capsule's United Launch Alliance Atlas V rocket.

Several new helium leaks arose during the mission, and a fault tree analysis is ongoing to find out what happened. Stich said the helium leaks and RCS thruster issues appear to have different causes, while Mark Nappi, vice president and program manager ofBoeing's commercial crew program, said data review is continuing to reveal more about what is happening.

The helium leak on the launch pad was not an immediate safety issue, but in investigating it further, NASA and Boeing uncovered a design vulnerability in the RCS system that could affect Starliner's reentry. Agency officials subsequently certified a new reentry mode after testing the idea on the ground in simulations with the CFT crew, veteran NASA astronauts Barry Wilmore and Suni Williams, both of whom are former U.S. Navy test pilots.

Wilmore and Williams have been testing Starliner's various systems in orbit, and ground teams have continued to analyze data to get a better handle on the thruster and helium-leak issues.

Stich emphasized that testing in orbit on Saturday (June 15) gave the team confidence that Starliner is recovering. "Saturday was a big day of understanding that helium leaks have gone down, and also understanding the thrusters have recovered, and that we can count on the thrusters for the remainder of the flight," he said.

Although evaluation of what is happening continues, he said the tone of the conversation has changed. "I think now we're doing the normal business we do of, What are the contingencies that could happen [with] the undock timeframe? And when we get to these, how we manage each of those contingencies, should something happen, and then look at the procedures we have in place. Are we ready to execute those?"

The delayed mission return also accommodates a planned June 13 spacewalk that was postponed due to a "spacesuit discomfort" issue during suit-up. NASA astronaut Matt Dominick, the ISS crew member experiencing discomfort, will not go outside during the rescheduled spacewalk on June 24 to prevent this from happening again, Weigel said during today's press conference.

Weigel told Space.com that, if the June 24 spacewalk is delayed again, Starliner's undocking would be the priority and spacewalking NASA astronauts Tracy Caldwell Dyson and Mike Barratt would wait until after Starliner leaves to perform the extravehicular activity.

CFT is a developmental mission. Throughout the launch and flight campaign, Boeing and NASA have emphasized that mission timelines are therefore very much in flux as Starliner flies its first-ever mission with humans on board. Wilmore and Williams said much the same, based on their experience with the U.S. Navy flying complex aircraft.

"We've always said this is a test flight, and we're going to learn some things. So here we are," Nappi said during today's press conference. "We've learned that our helium system is not performing, albeit manageable. It's still working like we had designed it. So, we got to go figure that out."

Nappi emphasized that the performance of most of the RCS thrusters is good, trending toward nominal, while the helium leaks "show that they're stable and less than measured [before]." The team is working to learn more about Starliner while the service module, which provides most of the spacecraft's fuel and power, is still attached to the spacecraft, as it will be discarded just before landing.

"This is an opportunity to fully understand the system's performance and without the pressure of schedule or time," Nappi said. Aside from the technical issues, the mission has satisfied 77 of the original 87 flight test objectives, he noted; the remaining 10 will be evaluated during undocking and landing.

Related: NASA weighs potential impacts of helium leaks and more on Boeing's Starliner astronaut test flight

Starliner, along with SpaceX's Dragon capsule, are tasked by NASA to send agency-led crews to the ISS from American soil. (Russia also leads and launches cosmonaut-led crews on its long-running Soyuz spacecraft.) CFT aims to certify Starliner for the first operational ISS rotation mission, called Starliner-1, expected to launch in 2025.

Dragon and Starliner were first tasked in 2014 to send NASA astronauts aloft by 2017, but funding and technical issues extended the timeline by several years. SpaceX, whose Crew Dragon spacecraft is based on the company's ISS cargo capsule, launched its first astronaut test mission in 2020 following just one uncrewed test flight. Starliner's first human mission came four years after that and required two uncrewed tests, in part because the spacecraft is a new design.

Starliner's path to CFT was delayed after the capsule experienced problems on its first uncrewed test mission in December 2019 and failed to reach the ISS as planned. (Astronauts often say, however, that in developmental programs such as Starliner, timelines are difficult to estimate as the unexpected can always arise.)

Boeing addressed those glitches, which took time. The outbreak of the coronavirus pandemic in early 2020 delayed the launch of the second uncrewed ISS mission further, pushing it into May 2022. CFT was next expected to launch in 2023, but that flight was delayed after issues with parachute loading and flammable tape were uncovered last year.

CFT then underwent two scrubs on the pad due to issues with the Atlas V and ground equipment. The first, on May 6, occurred roughly two hours before launch due to a "buzzing valve" that required rolling back to a company facility for replacement. The second launch attempt on June 1 was scrubbed due to an issue with a ground launch sequencer less than four minutes before liftoff.

Read the original post:

NASA, Boeing delay Starliner astronaut landing to June 26 amid thruster issues - Space.com