Two American astronauts stranded waiting to leave the International Space Station said on Wednesday they were confident the problematic Boeing Starliner they boarded would bring them back soon, though much uncertainty remained.
Butch Wilmore and Sunita Williams blasted off June 5 aboard a new spacecraft that NASA hopes to certify to carry astronauts to and from the Space Shuttle.
They arrived at the ship the next day, where they were supposed to stay for about a week, but their return was postponed due to thruster malfunctions and helium leaks during the voyage.
No date has been set for the return, but NASA officials said Wednesday they are eyeing “late July.”
When asked during a live press call from the station if he still had confidence in the Starliner team and the spacecraft, mission commander Wilmore replied: “We have complete confidence.”
“I have a good feeling in my heart that the spacecraft will bring us home, no problem,” Sunita Williams said.
He said he is enjoying his time on the ISS, replacing the pump on a machine that turns urine into drinkable water, and conducting scientific experiments such as gene sequencing in a microgravity environment.
They also tested Starliner as a “safe haven” vehicle in case of a problem on the ISS, and examined how its life support systems perform with four people inside.
The uncertainty that remains
However, before Wilmore and Williams return home, engineering teams need to run more simulations of similar thrusters and helium seals on the ground to better understand the root causes of some of the technical problems Starliner encountered — and make changes to the way it flies if necessary.
It was known before launch that the spacecraft had a helium leak, but further leaks were discovered during the flight. Helium, although non-combustible, provides pressure to the propulsion system.
In addition, some of Starliner’s thrusters, which provide excellent handling, initially failed to operate while approaching the station, causing a delay in docking.
Engineers don’t know why the spacecraft’s computer “deselected” these thrusters, though they were able to restart all but one of them.
In a later press briefing, Boeing executive Mark Nappi told reporters that the “working theory” for the thruster malfunction was overheating due to excessive firing.
There were various theories about the cause of the helium leak, including debris entering the propulsion system, and Boeing possibly installing undersized seals for that purpose.
NASA and Boeing say the Starliner can be returned to orbit in an emergency, particularly because the problem affects only a few thrusters that control orientation.
He has no concerns about the more powerful thrusters responsible for the “deorbit burn” that will bring the spacecraft back down.
But much remains unclear — including whether the worn-out orientation control thrusters have malfunctioned, making it necessary to rely on other thrusters during descent, said NASA official Steve Stich.
He stressed that NASA is not yet considering bringing Williams and Wilmore back on the SpaceX Crew Dragon, which would be a major snub to aerospace giant Boeing, whose reputation has suffered in recent years because of a safety crisis affecting its commercial jets.
“The primary option today is to send Butch and Suni back on Starliner,” Stich said, though he acknowledged that a return flight on a SpaceX spacecraft couldn’t be ruled out.
In 2014, both SpaceX and Boeing were awarded multibillion-dollar contracts by NASA to develop crewed spacecraft following the retirement of the Space Shuttle program. SpaceX conducted a successful crew test in 2020 and has flown dozens of people since then.
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