Houston ? Lisa Nowak chose a juggling act of dauntingly high difficulty: to be an astronaut and a mother of three.

Her background – high school valedictorian, Naval Academy graduate, test pilot – seemed to equip her for the challenge. Yet as she and some of her acquaintances acknowledged, the stresses on her and her family were extraordinarily intense.

On Wednesday, transformed from space hero to criminal suspect, Nowak returned to Houston for a medical assessment, a day after she was charged in Florida with attempted murder and attempted kidnapping in what police depicted as a love triangle involving a fellow astronaut.

The woman viewed as a role model by the schoolchildren she often addressed was met on the tarmac by police and escorted into a waiting squad car after her release on bail. Her head was covered by a jacket. She faced a medical exam at Johnson Space Center.

NASA, at a loss to explain what went wrong, said it would revamp its psychological screening process in light of Nowak’s arrest. The review will look at how astronauts are screened for psychological problems and whether Nowak’s dealings with co-workers signaled complications.

Nowak’s children were with her husband, Richard, who works for a NASA contractor. She was being replaced as a ground communicator for the next space shuttle mission in March, a job in which she would talk to the astronauts from Houston during their flight.

Some part of any breakdown may defy rational explanation, but those who know Nowak and NASA could sense the stress she was under.

Dr. Jon Clark, a former NASA flight surgeon who lost his wife, astronaut Laurel Clark, in the 2003 Columbia disaster, said Nowak provided invaluable support to his family then, at the cost of losing time with her own family.

“She was the epitome of managing a very hectic career, making sacrifices to accommodate her family,” Clark said in a telephone interview. “All those stresses can conspire to be overwhelming. … Clearly she suffered a lot of mental anguish.

Lisa Nowak, was charged with attempted murder and attempted kidnapping in a love triangle involving William Oefelein.

“There is a lot of marital stress in the astronaut corps in general – a huge amount,” Clark said. “It’s not unheard of for things to change into relationships that are beyond professional.”

Clark also said there can be extra pressure on NASA’s female astronauts – and the men, like himself, who marry them.

“They made more sacrifices than the ‘Right Stuff’ guys,” he said, comparing women astronauts to the original all-male astronaut corps. “They have to balance two careers – to be a mom and wife and an astronaut. … You don’t come home at night, like most of the male astronauts, and have everything ready for you.”

Clark expressed empathy with Richard Nowak, who separated from his wife a few weeks ago after 19 years of marriage.

“He was a real low-key, go-with-the flow, unobtrusive person,” Clark said. “You almost have to be to survive in the realm. … It was hard on our marriage to have my wife gone all the time, and eventually have her career surpass mine.”

Lisa Nowak grew up in Rockville, Md., where she was co-valedictorian and member of the track team in high school. After graduating from the Naval Academy, she received a master’s degree in aeronautical engineering, flew as a test pilot in the mid-1990s while caring for an infant son, and became a full-fledged astronaut in 1998.

“It’s definitely a challenge to do the flying and take care of even one child and do all the other things you have to do. But I learned that you can do it,” she said in a recent interview with Ladies Home Journal.

A Houston police officer stands watch outside the Houston home of astronaut Lisa Nowak. Nowak returned Wednesday to Texas and Johnson Space Center for a medical assessment a day after being charged in Florida with trying to murder the woman she believed was her romantic rival for a space shuttle pilot's affections.

In July, in the climax of her career, she flew on the space shuttle Discovery, helping operate its robotic arm and winning praise for her performance.

However, there were signs of turmoil in her life as she tried to balance her career with raising a teenage son and 5-year-old twin girls.

In November, a neighbor reported hearing the sounds of dishes being thrown inside Nowak’s Houston home. And she had begun to form a relationship with William Oefelein, a fellow astronaut and father of two whose own marriage ended in divorce in 2005.

Nowak told police Monday that the relationship was “more than a working relationship but less than a romantic relationship.”

Charlene Davis, the mother of Oefelein’s ex-wife, Michaella, said Wednesday that Nowak – although friends with Oefelein for years – had nothing to do with his marriage breakup.

“I think there were a lot of bad choices being made, and Lisa just made a horrible one,” Davis said in a telephone interview. “And I just feel sorry for her. What the hell was she thinking?”

The final unraveling came this week when police arrested Nowak for allegedly trying to kidnap Colleen Shipman, an Air Force captain from Florida whom she believed was her rival for Oefelein’s affections.

Police charged Nowak with attempting to murder Shipman based on weapons and other items found with Nowak or in her car: pepper spray, a BB-gun, a new steel mallet, knife and rubber tubing.

Those who know Nowak away from the high-pressure atmosphere of NASA were stunned.

“I was very surprised … She always seemed very normal to me,” said Candis Silva, who lives three houses down from the Nowaks. “She was a good role model for our daughters.”

Thomas Nagy, a Palo Alto, Calif., psychologist who has studied the stresses facing dual-career couples, hesitated to offer any specific diagnosis of Nowak, but said such seemingly desperate acts could result from a chronic personality disorder or from a period of high stress that clouds one’s judgment.

“When people are in that role of trying to do everything to the Nth degree, they don’t get enough sleep, they don’t do enough activities that are fun, they don’t get enough exercise,” he said.

“If we ignore those because we’re trying to do it all, we pay a price – more anxiety, more depression.”

Jon Clark expressed hope that Americans would empathize with Nowak, rather than condemning her.

“Obviously, she had some things that didn’t go well,” he said. “Any of us could be there. All of us have a dark side.”