Why are two Boeing astronauts stuck in space?

Two NASA-trained astronauts who were testing Boeing’s new CST-100 Starliner spacecraft have been forced to remain aboard the International Space Station (ISS) orbiting the Earth some 400km (250 miles) after experiencing technical difficulties with their spacecraft.
Astronauts Suni Williams and Butch Wilmore were originally scheduled to return to Earth on June 13, after their Boeing Starliner capsule launched its first crewed flight from Florida’s Cape Canaveral Space Force Station on June 5. But the Starliner has been plagued with issues, even before the June 5 launch. A previous launch attempt was scrapped on June 1 just moments before launch because of a ground control computer performance issue.
During the 25-hour flight to the International Space Station, the spacecraft experienced several helium leaks and a malfunctioning thruster. Then, when the Starliner arrived on June 6 and attempted to dock at the ISS, four more of the 28 thrusters malfunctioned causing the ship’s arrival to be delayed.
According to a Boeing spokesperson, four of the five thrusters that previously malfunctioned are now operating normally. “This means only one thruster out of 27 is currently offline. This does not present an issue for the return mission,” the spokesperson added.
Sunita “Suni” Williams is an American astronaut and US Navy officer who joined NASA in 1998. Williams made her first spaceflight to the ISS to service electricity-generating solar array panels on the Space Shuttle Discovery (STS-116) in December 2006, when she was a flight engineer. Her second mission in May 2012 as a flight engineer was on Expedition 32 to the ISS to test a new microsatellite deployment system. After completing other missions, Williams was one of the first astronauts selected to train for NASA’s Commercial Crew Program in 2015.
Williams has spent a total of 322 days in space so far and is best known for her missions aboard the ISS, where she set records for the longest spaceflight by a woman (195 days) and is the former record holder of seven spacewalks, when astronauts go outside a craft in space, by a female astronaut. This was only broken by Peggy Whitson in 2017. Whitson has now completed 10 spacewalks.
Williams has received several awards, including the Legion of Merit, Navy Commendation Medal, Navy and Marine Corps Achievement Medal and Humanitarian Service Medal.
Barry “Butch” Wilmore flew on the Space Shuttle Atlantis to deliver parts to the ISS in November 2009 and served as commander of the ISS from November 2014 to March 2015.
Wilmore’s first spaceflight was aboard Space Shuttle Atlantis (STS-129) in November 2009 as part of a mission to deliver spare parts to the ISS. He served as a flight engineer for Expedition 41 in May 2014 to study the effects on the body and the growth of plants during weightlessness. He was also commander of Expedition 42 to study how space affects immune cells and to observe pollution in Earth’s atmosphere in 2014.
Wilmore has also received numerous awards, including the Defense Superior Service Medal, the Legion of Merit and the NASA Space Flight Medal.
NASA and Boeing are making use of the astronauts’ extra time aboard the ISS time to further assess the problems with the thrusters which disrupted the Starliner’s initial attempt to dock with the ISS on June 6.
Steven Hirshorn, NASA chief aeronautics engineer took to his LinkedIn page to clarify some of the issues on the Starliner. “The problems being reported on the Starliner, namely reaction control thruster and helium leaks in the propulsion system, are all located on the spacecraft’s service module,” he explained. “When the crew departs the ISS and deorbits, the service module is discarded and burns up in the atmosphere on reentry. Thus, the helium systems and thrusters will not return to earth for failure analysis. They’re gone. As such, the only way to get insight into what might be going on there is in space.”
According to NASA, the Starliner can be docked to the ISS for up to 45 days, or a maximum of 72 days if using a backup system.
Last week, NASA stated it is aiming for a return sometime in early July. NASA stated that additional time was required for the mission teams on the ISS to thoroughly investigate the issues with the propulsion system.
“We are taking our time and following our standard mission management team process,” said NASA’s Commercial Crew Program manager, Steve Stich, in a statement earlier this week. “We are letting the data drive our decision-making relative to managing the small helium system leaks and thruster performance we observed during rendezvous and docking.”