Boeing's Starliner won't launch Wednesday as had been planned following problems with its propulsion system that prevented a key uncrewed test flight to the international space station a day earlier—and it's not clear when the troubled spaceship will fly next.

The aerospace giant said in a statement that valves in Starliner's engine were in "unexpected" positions, forcing the mission team to halt the countdown.

NASA added that engineering teams have ruled out several potential causes, including a software glitch, but need more time to understand the issue.

"We're going to let the data lead our work," said John Vollmer, vice president and program manager of Boeing's Commercial Crew Program.

I'm currently training to become Australia's first woman astronaut. I expect to fly my first suborbital mission sometime in 2023 as a payload specialist on a commercial mission. In other words, I'll be one of few certified crew members who can handle specialized scientific equipment aboard a suborbital spacecraft.

Once we're up there, my team and I expect to conduct research on Earth's atmosphere. It's an opportunity I consider out of this world. But it has taken a lot of effort for this dream to be realized.

My path to PoSSUM

As a female STEM and legal professional, my past jobs included working as a research scientist in mining and metals for BHP-Billiton, Rio Tinto and the Australian Nuclear Science and Technology Organisation (ANSTO)—but I always loved space.