In a surprising turn of events, NASA has announced that Boeing's Starliner spacecraft will return to Earth without any astronauts onboard. The decision comes as a result of ongoing propulsion problems with the spacecraft that could not be resolved to meet NASA's safety requirements.

Originally, the plan was for NASA astronauts Butch Wilmore and Suni Williams to fly to the International Space Station (ISS) aboard Starliner and return home on the same spacecraft. However, the issues with the spacecraft's thrusters posed a significant risk, forcing NASA to reconsider its plans.

During a teleconference on Wednesday, Steve Stich, program manager for NASA's commercial crew program, shed light on the decision-making process. He mentioned the tension in the room during the discussion to return Starliner without astronauts, with Boeing standing firm in their belief in their predictive model for thruster degradation.

"The NASA team had concerns about the limitations of Boeing's model and their confidence in predicting thruster degradation from undock through the deorbit burn," Stich explained.

The spacecraft is scheduled to leave the ISS on September 6 and return to Earth on September 7, ending a mission that commenced on June 5. Originally intended as a 10-day mission, the flexibility for an extended stay was granted due to its developmental nature.

However, the Starliner's historic first test mission encountered setbacks from the start. Upon docking with the ISS on June 6, five thrusters out of the 28 in its reaction control system misbehaved. Months of rigorous space testing, ground testing, and modeling followed, but the exact cause of the issues – potentially overheating and shedding insulation that obstructs propulsion lines – could not be definitively identified.

Considering the risks involved, NASA concluded it was too great a risk to place the two astronauts back on board the Starliner. Consequently, NASA has revised its ISS manifest to include an alternate plan for Wilmore and Williams to return home with the SpaceX Crew-9 mission in February 2025 for an extended stay on the ISS.

Stich acknowledged that the difference in opinion between NASA and Boeing regarding risk assessment stems from varying levels of understanding and available alternatives. Boeing's commercial crew manager, Mark Nappi, did not comment on the meeting where the decision was made.

In a statement released earlier, Boeing emphasized their unwavering focus on crew and spacecraft safety, affirming their commitment to execute the mission as directed by NASA.

As Starliner readies for its uncrewed return, all eyes will be on NASA and Boeing as they closely monitor the spacecraft's performance. The outcome of this mission will undoubtedly have implications for future endeavors and collaborations in space exploration.

Continued efforts will be made to address the propulsion issues faced by Starliner and ensure that future missions can operate seamlessly and safely in the vast expanse of space.