Astronauts are stuck on the International Space Station after yet more problems with Boeing’s beleaguered Starliner

The spacecraft’s return has been delayed while experts study helium leaks and thruster problems.

For the past few weeks, Nasa astronauts Butch Wilmore and Suni Williams have been stuck on the International Space Station (ISS) after the first crewed voyage of Boeing’s new Starliner spacecraft hit a snag. Concerns raised by Boeing and Nasa over thruster problems and several helium leaks (helium is used in Starliner’s engine system) have prevented the craft from making the return journey as scheduled. Nasa has now said the astronauts may have to stay put until the next scheduled crew switchover in August – potentially on another ship.

Boeing and Nasa are trying to put a positive spin on the extension by saying they are testing systems required for longer Starliner missions. But the project has already suffered several delays, having originally been set to lift off for the first time with crew in 2017. This, combined with the latest problems raise questions over the whole Starliner programme.

Starliner was noted as having a small helium leak before it even launched. Helium is an inert gas (much like neon or xenon), meaning that it is very unreactive with other materials.

This makes it ideal when coming into contact with rocket fuel and high temperatures, although producing it is an expensive process. It is pressurised and used to push fuel into the engines at the correct rate. Helium leaks can mean that not enough fuel will reach a thruster.

The leak spotted while Starliner was on the launch pad was determined to be negligible and the spacecraft was sent to orbit regardless. However, this turned into a larger problem when additional helium leaks were identified following launch, meaning that several of the spacecraft’s small manoeuvring thrusters couldn’t be used.

Four of the five thrusters have been repaired while Starliner has been docked to the ISS, but it raises concern for other thrusters cutting out during the return journey to Earth. On Starliner’s return, re-entering Earth’s atmosphere requires a very specific “angle of attack” to ensure there is not too much friction heating up the vessel.

An inability to adjust the orientation of the craft or the orbital parameters for re-entry could in the worst-case scenario result in massive heat build up and the destruction of the spacecraft with two astronauts on board.

There are additional thrusters and other so-called “redundancies” – back up systems – designed into the spacecraft, so this is a very unlikely scenario. However, so were the helium leaks. While Boeing and Nasa have considered it safe to return on Starliner, it’s perfectly conceivable that the astronauts might have some trepidation and anxiety – especially as these issues did not occur with the uncrewed test flights.

The next particular problem is that Starliner returns and jettisons its service module on re-entry as it returns to the surface on land rather than at sea (like Russian spacecraft Soyuz did and the SpaceX Dragon capsules do). This means that the bit of the spacecraft with all the vital information on will be burned up, making it very difficult to determine what actually went wrong.

Investigations in space

Currently ground tests are being run by Nasa and investigations are being conducted on the ISS to gather as much information as possible before the return.

The astronauts made it up to the ISS and are safe there. While it is likely that Starliner will return to Earth, should a major fault be discovered while it is docked to the ISS, there are other return vehicles that can be used to ferry the two crew members back home.

The astronauts’ safety will no doubt be paramount in the minds of both agency and industry. But this is not the first problem with Starliner. The vehicle has suffered from major delays since conception as part of the Commercial Crew Program in 2010.

The contract indicated that Starliner should be ready by 2017 with a two-year delay before the first successful unmanned launch in 2022 (there was a failed attempt in 2019). The main crewed launch was then delayed by a month.

These delays indicate that Boeing is falling behind its main commercial competitor SpaceX, which won a contract at the same time as Boeing in 2010 to build vehicles that could transport crew to the ISS. SpaceX successfully launched a crewed mission with the Dragon capsule in 2020. To give an indication of the success, Crew Dragon is currently completing its fifth manned mission to the ISS, and has also completed 30 cargo missions.

Boeing has been a major player in space missions with Nasa for decades, playing a major role in the space shuttle programme, for example. This relationship continues with the company’s role in the Space Launch System (SLS) rocket that will send astronauts on their way to the Moon.

The company has been one of the biggest and most admired contractors in the aerospace industry. However, the problems with the Starliner come not long after widely publicised incidents with Boeing aircraft, so the corporation could do without any further problems with its crewed spacecraft to add to its woes.

Ian Whittaker does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.