Bio: Shuttle Columbia Physician Cmdr. Dr. Laurel Clark

Before Columbia's launch, Dr. Laurel Clark, 41, said her family, including her 8-year-old son, Lain, sometimes worried about her being an astronaut.

"To me, there's a lot of different things that we do during life that could potentially harm us, and I choose not to stop doing those things," Clark said. "They've all come to accept that it's what I want to do."

The Columbia mission was the Racine, Wis., native's first.

Clark and her husband, Jonathan B. Clark, met in Scotland, where she dove with Navy divers and Navy Seals, performing medical evacuations from U.S. submarines. The Clarks lived in Houston.

Clark joined the Navy to pay her way through medical school, serving as a flight surgeon and performing medical evacuations from submarines until space beckoned and the adventurous scientist sought a new challenge.

"She had done something in a world usually reserved for men, and she was pleased at the opportunity," her aunt, Betty Haviland said.

"It had been an absolutely flawless flight," her brother, Daniel Salton, said in a telephone interview Saturday. "To have this happen with 15 minutes to go until it was over was just unbelievable."

Salton, who lives in Milwaukee and had been at Cape Canaveral for the Jan. 16 launch, got up at 5 a.m. Saturday to monitor Columbia's progress live on his computer.

When the shuttle lost communication with NASA, he didn't realize what was happening, he said.

"It took about 10 minutes for me to catch on that something was wrong," he said.

One day earlier, he had received an e-mail from his sister about how much she was enjoying her experience aboard the shuttle.

"She loved it," Salton said. "I'm just so glad she got to get up to space and got to see it because that had been a dream for a long time."

Clark's aunt and uncle, Betty and Doug Haviland, who live in Ames, Iowa, also received Clark's e-mail.

"She was, you know, thrilled, taking lots of pictures and could see the area in Wisconsin on one of their pass overs where they had lived for several years ... looking forward to sharing all this with her friends and family," Haviland said.

The Havilands, who lost their son, Timothy, in the attack on the World Trade Center, said they were in shock and grieving.

Clark was born in Ames while her father studied at Iowa State University. She lived in the central Iowa town for two years before moving with her family to Racine. She graduated from Horlick High School.

Clark was on board to help with Columbia's more than 80 science experiments, including studies of astronaut health and safety, advanced technology development and Earth and space sciences.

"The one thing that I'm looking forward to the most is being able to look down on the Earth from that height," Clark told the Racine Journal Times in 2001. "To see our entire planet Earth as one living unit."

She had already used her medical and scientific expertise to help create an astronaut treadmill in use on the international space station.

"She wasn't just intelligent," Salton said. "All the astronauts are just amazing people. She's just one of those people who made the right moves. She got along with people... She saw the path to be an astronaut was open -- she went at it full throttle all the way."

Clark joined NASA in 1996 and earned a flight assignment as a mission specialist after completing two years of training.

The Associated Press contributed to this report.