Problems with Boeing’s Starliner capsule, which is still docked at the International Space Station (ISS), have upended original plans to return its two astronauts to Earth, as last-minute fixes and testing have upended a mission crucial to the future of Boeing’s space division.
NASA has rescheduled the planned return three times, and now has no date set for it. Since liftoff on June 5, the capsule has had five helium leaks, five maneuvering thrusters have shut down and a propellant valve failed to close completely, causing the crew in space and mission managers in Houston to spend more time than expected making repairs mid-mission.
Here’s a description of the possible paths forward for Starliner and its veteran NASA astronauts, Barry “Butch” Wilmore and Sunita “Suni” Williams.
present situation
The Starliner can stay docked at the ISS for up to 45 days, according to comments to reporters by NASA commercial crew manager Steve Stich. But if absolutely necessary, such as if another problem arises that mission officials can’t fix in time, it could stay docked for up to 72 days, relying on a variety of backup systems, according to a person familiar with the flight plan.
According to NASA internal sources, Starliner’s latest targeted return date is July 6, the source said on condition of anonymity. Such a return date would mean that the mission originally planned for eight days would last a month.
Starliner’s expendable propulsion system is part of the vehicle’s “service module.” Current problems are centered on this system, which is needed to propel the capsule away from the ISS and dive into Earth’s atmosphere. According to Stich, several of Starliner’s thrusters have overheated when fired, and leaks of helium – used to pressurize the thrusters – appear to be linked to the frequency of their use.
Stich said recent test-firings of the thrusters while Starliner was docked gave mission teams confidence in a safe return, though testing and review continue. The mission management team, made up of NASA and Boeing personnel, is examining data on propulsion issues, running simulations in Houston and considering ways to fix them, such as by updating software or changing the way the hardware is used.
Once NASA officials give the team the green light to return, Starliner’s thrusters will be used to dislodge the capsule from the ISS and begin its roughly six-hour journey back home, gradually lowering its orbit and entering Earth’s atmosphere for a parachute and airbag-assisted landing at one of several potential locations in the southwestern United States.
It is Starliner’s first mission to orbit carrying astronauts – the final test needed before NASA certifies it as the US space agency’s second trip to the ISS. It will join SpaceX’s Crew Dragon, which has dominated the government and nascent private markets for human spaceflight amid Starliner’s years-long delays.
If force majeure occurs
Despite the propulsion system issues, NASA has said that the Starliner will still be capable of returning astronauts to Earth if absolutely necessary — that is, if the capsule needs to serve as an escape pod from the ISS in an emergency or if any of Starliner’s perishable items — such as its solar panels — show signs of wearing out ahead of schedule.
Unlike Starliner’s current mission, NASA had no scheduled return date for Crew Dragon’s first mission carrying astronauts in 2020. That mission ultimately lasted 62 days because the astronauts were needed to help with ISS maintenance as the space station was understaffed at the time.
If Starliner cannot be used
If Starliner is deemed unable to return Wilmore and Williams safely to Earth, one option would be to send them home aboard Crew Dragon, which carried four astronauts to the station in March and is capable of carrying more people in an emergency.
This scenario, which is considered unlikely, would undoubtedly be embarrassing for Boeing. But NASA and Boeing officials, as well as engineers familiar with the program, told Reuters that there is nothing about Starliner’s current problems that indicates this would be necessary.
In such a situation, the fate of Starliner will depend on various factors, including the extent of its technical problems.
The last time a NASA astronaut needed an alternate ride to return home was in 2022, when a Russian Soyuz capsule carrying two astronauts and American astronaut Frank Rubio to the station suffered a coolant leak.
NASA had considered the Crew Dragon as an alternate ride for Rubio, but ultimately used an empty Soyuz capsule launched by Russia as a rescue vehicle. Rubio’s mission was extended from six months to a little over a year — 371 days — a record-breaking length of time for an American in space.
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