By Joey Roulette

WASHINGTON (Reuters) – The first two astronauts to fly Boeing’s Starliner capsule said from the International Space Station on Wednesday they were confident in the spacecraft‘s ability to return them home whenever the company and NASA solve thruster issues that have kept them in space far longer than expected.

“I have a real good feeling in my heart that this spacecraft will bring us home, no problem,” NASA astronaut Sunita “Suni” Williams said during the test crew’s first news conference since docking to the ISS more than a month ago.

Williams and Barry “Butch” Wilmore, both veteran NASA astronauts and former U.S. Navy test pilots, were launched aboard Starliner from Florida on June 5 and docked the next day at the ISS, where they were initially scheduled to spend roughly eight days.

Several issues with Starliner’s propulsion system have extended their mission indefinitely. Five of Starliner’s 28 maneuvering thrusters failed during its trek to the station, a propellant valve did not properly close and there have been five leaks of helium, which is used to pressurize the thrusters.

“We’re absolutely confident,” Wilmore told reporters. “That mantra you’ve heard, failure is not an option.”

“And that’s why we’re staying, because we’re going to test it. That’s what we do,” Wilmore said, acknowledging that an ongoing investigation by the U.S. space agency and Boeing involving thruster tests on Earth is key for their return.

The current test mission is Boeing’s final step before the spacecraft can clinch NASA certification for routine astronaut flights and become the second U.S. orbital capsule alongside SpaceX’s Crew Dragon, which has dominated the nascent human spaceflight market amid Starliner’s development delays.

TESTING IN NEW MEXICO AND ALABAMA

To understand why some thrusters overheated and stopped working during Starliner’s flight to the ISS, NASA officials and Boeing engineers began test-firing identical thrusters at New Mexico’s White Sands Missile Range to try to replicate the mishaps.

At the same time, an investigation at NASA’s Marshall Space Flight Center in Alabama aims to determine why a type of seal in Starliner’s propulsion system has let helium leak out.

The return of Wilmore and Williams to Earth on Starliner depends on the results of the thruster tests, according to NASA officials.

NASA’s commercial crew chief Steve Stich told reporters on Wednesday that “we’re taking our time” with the testing and that the results of the New Mexico thruster tests “are not quite what we would have hoped for.”

Stich said he hopes the testing will be completed by this weekend. Stich previously said this testing could last “a couple weeks,” followed by a detailed NASA review of the data to inform the agency’s decision on letting Starliner fly the astronauts home.

Also docked to the space station is SpaceX’s Crew Dragon capsule that ferried four astronauts to the ISS in March, and a Russian Soyuz capsule that delivered three others in September. Stich acknowledged that at least one of those vehicles could provide an alternative ride home for Wilmore and Williams.

“We have a little bit more time to go through the data, and then make a decision as to whether we need to do anything different” with the return plan, Stich said. “But the prime option today is to return Butch and Suni on Starliner. Right now, we don’t see any reason that wouldn’t be the case.”

Starliner is approved to stay docked to the ISS for 45 days – which would be July 21 – or up to 90 days using various backup systems and depending largely on the health of its lithium ion batteries, which have caused concerns in the past.

Though NASA and Boeing have said Starliner is capable of returning the astronauts to Earth in the event of an emergency on the ISS, the capsule is not approved to fly home under normal, non-emergency circumstances until its thruster issues are resolved or at least better understood.

A Russian satellite last month broke apart into some 180 pieces of debris near the space station’s orbit and forced astronauts into their various docked spacecraft, including Wilmore and Williams getting into Starliner, to prepare for a potential escape. Boeing cited the event as an example of Starliner’s readiness to return home if absolutely necessary.

Mark Nappi, Boeing’s Starliner chief, told reporters that such an emergency return scenario would simply involve Starliner undocking from the station and safely returning the crew to Earth, despite questions about the thrusters.

“I feel confident that if we had to, if there was a problem with the International Space Station, we can get in our spacecraft, and we can undock, talk to our team, and figure out the best way to come home,” Williams said.