Space Odyssey: Why are two US astronauts stranded on the ISS

When veteran astronauts Sunita Williams and Butch Wilmore departed for the International Space Station (ISS) in early June on the Starliner—Boeing’s space capsule meant for transporting people to and from low-earth orbit—they expected to be back to their families in about a week.

But a couple of months later, they’re still stuck in outer space. Worse, their space odyssey won’t likely be over until at least February 2025.

The reason for the inordinate delay in their journey back home is that Boeing’s Starliner capsule is “unsafe” to return to Earth.

Why did they go to the ISS?

The two astronauts were part of the first crewed launch of the Starliner, a new capsule designed by Boeing to transform human exploration of space.

As the final flight test for the Starliner, the Boeing Crew Flight Test was meant to “validate” the transportation system, including the launch pad, rocket, spacecraft, in-orbit operational capabilities and finally return to earth with the astronauts aboard.

During the flight, the spacecraft and its crew were supposed to perform flight test objectives, supporting the certification ahead of regular rotation missions for the Starliner.

What’s Boeing Starliner?

Boeing has developed the Starliner in collaboration with NASA’s Commercial Crew Programme, which aims to deliver safe, reliable and cost-effective human transportation to and from the ISS from the US through a partnership with American private-sector firms.

The Starliner was designed to accommodate seven passengers, or a mix of crew and cargo, for missions to low-earth orbit. The capsule has a weldless structure and is reusable up to 10 times with a six-month turnaround time.

The spacecraft’s maiden journey started roughly seven years after its scheduled launch, thanks to supply and production hold-ups, hardware and software issues, and the failure of an uncrewed test flight five years ago.

What went wrong?

Engineers from NASA and Boeing detected a “small helium leak” in the spacecraft's propulsion system before the launch of the Starliner. Yet they decided to greenlight the launch, thinking it posed no material danger.

But following the launch, four more helium leaks developed and five rear-facing manoeuvring thrusters failed to operate as expected.

NASA earlier reported that excess heat around some of the Starliner thrusters was causing teflon seals to bulge, restricting the flow of propellant and triggering the thruster issues.

But more recently, officials within NASA have debated whether those bulging seals are indeed the root cause of the issue and if using the Starliner after repairs to bring back the two astronauts was a foolproof idea.

Starliner’s alternate

NASA is leaning towards engaging SpaceX, Elon Musk’s space company that’s proven itself a formidable rival to Boeing under NASA’s Commercial Crew Programme, to bring the two astronauts back.

But engaging SpaceX means the astronauts will have to stay on the ISS for another six months.

According to CNN, the space agency has made a “stunning change of tone” regarding the preferred spacecraft for the flight back from the ISS. Until now, officials repeatedly indicated that the two astronauts were likely to return home on the Starliner.

Crew Dragon featured only in a “backup scenario” that was a “mere possibility”. But recent statements by NASA officials suggest the SpaceX vehicle is “rapidly becoming a serious option”.

NASA has already discussed plans with SpaceX to leave two seats empty on an upcoming Crew Dragon launch so that astronauts can be brought back on the journey back to Earth.

Using the SpaceX spacecraft to bring back astronauts instead of the one by Boeing as per the original plan would be a major blow to an aerospace giant that has struggled for years to outshine the Elon Musk-led company.

Life on the ISS

Earlier this week, NASA used a SpaceX rocket to deliver food and supplies to the ISS, including extra clothes for the two astronauts.

The two astronauts are currently staying on the ISS only as “guests”. But overstaying their scheduled visit to outer space means they’ll transition to being full-time expedition members by joining the international crew of seven astronauts who’re already serving as ISS staff.

NASA has said they’ve seamlessly integrated with the group, picking up everyday tasks aboard the orbiting laboratory.