The ‘sticky valve’ on Boeing’s rocket ship that left astronauts stuck in space

Boeing launched the Starliner on June 6 despite a host of issues– a decision it may come to regret
Boeing launched the Starliner on June 6 despite a host of issues– a decision it may come to regret - REUTERS/Joe Skipper

Boeing’s Starliner was sitting on Cape Canaveral’s launchpad in Florida when a small but crucial issue with the spacecraft’s 191ft booster rocket brought the countdown to a halt.

The US aerospace giant had been hired by Nasa to ferry two astronauts – Sunita Williams and Barry “Butch” Wilmore – to the International Space Station (ISS) under a contract worth $4.2bn (£3.3bn).

But on May 6, engineers found that a valve used to regulate the rocket’s flow of oxidizer – which is mixed with fuel in a combustion chamber to create thrust – was creating an audible buzzing sound, forcing them abort the mission.

This first “sticky valve” has been followed by a cascade of further issues. Yet on June 5, Nasa and Boeing pushed ahead with the launch anyway.

Now, with the malfunctioning Starliner and its passengers stranded in orbit for two weeks longer than planned, it is a decision they may regret.

Barry "Butch" Wilmore and Sunita Williams
Barry "Butch" Wilmore and Sunita Williams are stuck in orbit for two weeks longer than planned - Cristobal Herrera-Ulashkevich/EPA-EFE/Shutterstock

“The company is in a deep crisis. The optics of it are terrible,” says Rob Adlard, the chief executive of British space launch company Gravitilab. “Space is super hard, but it does contrast with SpaceX’s successes.”

The Starliner problems are a fresh blow to Boeing, which has been battling a reputational crisis since a major safety failure on one of its 737 Max 9 passenger planes in January.

At 16,000ft, about nine minutes into an Alaska Airlines flight that took off from Portland, Oregon, pilots were forced to turn around and make an emergency landing after a door plug blew out – depressurising the cabin and leaving a hole in the side of the aircraft.

In the wake of the incident, Boeing has faced tough scrutiny from regulators and calls from customers to overall its approach to safety.

The seemingly small valve issue found on May 6, which affected the Starliner’s Atlas V booster rocket (built in a joint venture between Boeing and Lockheed Martin), is typical of the minuscule problems that can play havoc with complex rocket launches.

Boeing 737 Max 9 passenger plane that lost a door mid-flight in January 2024
Boeing has been battling a reputational crisis since a door blew out mid-flight on one of its planes in January - National Transportation Safety Board via AP

On spacecraft, these valves control the flow of important gases such as helium as well as oxygen and other propellants. Boeing was previously forced to fix corroded valves in the Starliner which were found in 2021 after 13 failed on the launch pad.

Starliner, which was originally commissioned for a crewed mission in 2017, has been plagued with issues that have cost Boeing more than $1bn, from software glitches to parachute problems.

The setbacks mean Boeing has fallen behind Elon Musk’s rocket company, SpaceX, which has also partnered with Nasa to ferry astronauts into space. SpaceX’s Dragon spacecraft has been carrying out regular trips to the ISS since 2020.

After May’s discovery of Atlas V’s faulty rocket valve, more problems followed. As engineers tackled the problem, they realised Starliner was suffering from a helium leak.

The gas is used as a pressurant to push propellant into the thrusters, meaning a leak can cause them to fail. Worryingly, during the resulting testing, the leak – which was traced to a bad seal – appeared to get worse, Steve Stitch, Nasa’s crew programme manager, said at the time.

Fixing the leak would have required separating Starliner from the Atlas rocket, causing longer delays, and Nasa and Boeing decided it was possible to proceed safely anyway. Boeing’s Starliner manager, Mark Nappi, even said the delay had a “silver lining” because the company had discovered the helium issue ahead of the mission.

Boeing's setbacks have allowed Elon Musk's rocket company, SpaceX, to race ahead
Boeing's setbacks have allowed Elon Musk's rocket company, SpaceX, to race ahead - SpaceX via AP

Starliner eventually launched at 10.52am on June 5. But mid-flight, with its crew sleeping, more helium leaks were detected and five of the spacecraft’s 28 thrusters failed as it approached the ISS. Wilmore and Sunita were forced to undertake manual manoeuvres in space in a docking sequence that took an hour longer than planned.

A further valve issue was also uncovered, with one valve in the “reaction control system”, which helps steer the spacecraft, failing to shut properly. Starliner is now relying on a backup “B valve” instead.

Now, Nasa and Boeing have the complicated task of double-checking Starliner’s systems and troubleshooting as many of the in-orbit issues as possible to ensure a safe return home.

In a news conference on June 18, Stitch said one thruster, B1A3, only fired at 11pc of its expected power during a “hot fire” test, and will remain switched off for the remainder of the mission. He said the helium leaks and the thruster problems “seem to be related”.

Starliner had been scheduled to return on June 14, but now will not undock until June 26.

On the ground at the Marshall Space Flight Centre, experts are also testing copies of Starliner’s helium seals by “purposely damaging a seal, cutting a seal, looking at leak rates” to assess the impact, Stitch said.

Boeing and Nasa are confident the craft can return, but they are being kept in orbit to conduct more tests on why the problems keep occurring. Stitch said the team wanted to “make sure we’re really ready to come home”. Nappi, of Boeing, told journalists on Tuesday: “We have a good, safe spacecraft.”

Adlard, of Gravitilab, said the issues sounded “fixable”, adding that some problems may have emerged as components “perform differently in the absence of gravity”.

Chris Welch, a consultant and former professor of space engineering at the International Space University in Strasbourg, said: “All these components are like links in a chain that all have to work in synchrony.

“Valves in particular are very little, fiddly things that have to operate very precisely, under a wide temperature range and under challenging conditions.

“You can simulate them as much as you’d like, but you can never really be sure how they are going to work until you actually put them out in the field.”

Should Starliner experience further delays, the ISS has months’ worth of food supplies, while the craft can remain docked for up to 45 days.

While helium has been gradually leaking out of the craft, it still has enough for 70 hours of flight – and it only needs seven to make it home.

Nasa, at least, insists its astronauts have confidence in Boeing’s craft, with hopes that its next flight can go ahead early 2025. “You can tell every time they get in the vehicle,” said Stitch on a call with reporters, “they love Starliner.”