A married mother of three, Nowak was in love with Navy Cmdr. William Oefelein, 41, who trained alongside her in NASA's space shuttle program and piloted the Discovery in a mission last December. At the same time, Oefelein, the divorced father of two children, was apparently romantically involved with Shipman,.

Nowak has told police she raced in her car nearly 1,000 miles from Houston to catch up with Shipman after learning she was flying back to her home near Orlando from the Texas city.

She said put on diapers, as astronauts do during launch and landing, so she would not have to stop for a bathroom break.

Nowak covered her head with a jacket as she arrived at the Houston airport. She then got into a police car that drove her across town to the space center where NASA's astronaut corps is based.

"We're perplexed and concerned and trying to determine what really happened," said Doug Peterson, spokesman at Johnson Space Center in Houston. "Everything I've ever seen gave evidence to me that Lisa was one of our good astronauts; she had all the right background credentials, skills and abilities. We don't know what happened here."

Nowak made her first space flight in July.

"I didn't expect it to be 10 years when I first got here," she said at the time.

On her first flight, she spent 13 days in space. Her flying pony tail encouraged laughter among the crew.

"Whoever was standing behind me was very annoyed," Nowak said.

Nowak's family said she and her husband, who also works at the space center, had recently separated.

Neighbors in the affluent Houston suburb of Clear Lake had no idea anything was wrong with the couple's 19-year marriage.

"As far as I knew, everything was fine," David Silva, who lives across from the Nowaks' two-story brick home in a cul-de-sac, tells PEOPLE. "They're good people."

Even Nowak's parents weren't aware her situation was so dire. "Her mother says she wishes she would have known that Lisa was so confused," says Nowak's cousin Tony Caputo, 58. "Her family doesn't know what to do. They are completely devastated by this."