They walked hand in hand, father and son, at a steady pace under a cloudless blue sky. While a stiff breeze snapped flags to attention, Jon Clark took his 8-year-old boy, Iain, for one last walk with his mother.

Ahead of them was a horse-drawn caisson carrying her flag-draped coffin, and behind them was a contrail of family, friends and mourners who had come to say goodbye to Laurel Blair Salton Clark, one of the seven astronauts who died Feb. 1 aboard the space shuttle Columbia.

They buried her at Arlington National Cemetery yesterday on what would have been her 42nd birthday -- next to one of her crew mates, Air Force Lt. Col. Michael P. Anderson. A third Columbia crew member, Navy Capt. David M. Brown, will be laid to rest tomorrow at the same site.

Before yesterday's solemn procession along the narrow cemetery lanes, Jon Clark delivered his wife's eulogy at a service held in the Memorial Chapel at Fort Myer. His remarks mirrored her life -- filled with passion, promise, love and humor.

She was an explorer of the first order; a submarine officer, a diver, a helicopter pilot, a medical doctor and, her last job, a mission specialist performing scientific experiments on her first shuttle flight.

Jon Clark said that explorer mentality was present even during simple family hikes: While he and Iain would race to the top of the trail, Laurel would invariably stop along the way, more interested in the journey than its end.

From her family, he said, she learned compassion and acquired her thirst for knowledge and realization of the importance of family and friends. What she learned from him, he said, laughing, was tolerance.

"I used to say that I was like the sand in an oyster," he said, as those filling the chapel laughed gently, "and she would make a pearl out of me."

Laurel Salton was born in Iowa but called Racine, Wis., home. She was the oldest of four, two girls and two boys. Her parents, Margory and Robert Salton, were divorced when she was a teenager. Her mother later married Richard Brown, who had five children of his own, and the family moved to Racine in 1975.

Jon Clark is also a Navy commander and NASA flight surgeon. The couple met at dive school, and he asked her to marry him while they were stationed in Scotland. They were wed in 1993 and, when their son was born, they named him Iain in honor of her Scottish roots.

She joined the Navy after college because she wanted to go to medical school and, with three siblings and five step-siblings, there wasn't much money.

The Navy got much more than a doctor in the deal. Clark became an undersea medical officer, dove with the elite Navy SEALs, became a flight surgeon and, later, an astronaut.

"When she applied to become an astronaut," her husband recalled, "I asked her what she would do if she didn't get in. And she said she would be a stay-at-home mom. They were both great jobs!"

Six women from her 1996 astronaut class served as honorary pallbearers yesterday.

"Columbia was a proud spacecraft," Jon Clark said. "She came to know and love her fellow crew mates . . . as if they were brothers and sisters."

Among the messages his wife sent home from space, he said, was this one: "Hello from above our magnificent Earth. Let me beam good, positive energy to all who I love."

He recalled how he chose her "wake-up" music for the Columbia voyage; on the final morning of her life, she awakened to the stirring strains of "Scotland the Brave." Yesterday, as the mourners placed farewell roses on her coffin, a bagpiper played.

Laurel Clark loved the outdoors, her husband recalled, which made the family's final walk yesterday all the more poignant. They arrived at the grave site about noon. There was a flyover of F-18s from U.S. Marine Fighter Attack Squadron 321. The Navy Band played "America the Beautiful."

The father sat next to the son, the coffin in front of them. They were presented with three medals honoring Laurel Clark's service to her country.

Jon Clark said his wife would have wanted U.S. space exploration to continue, despite the Columbia tragedy. The loss of its crew, he said, should serve as an inspiration for exploration.

Clark said his wife recognized the inherent danger. "She used to say, 'A ship in the harbor is safe, but that is not what ships are for,' " he said, referring to her favorite quote.

At the end of the service for Laurel Clark, her husband, Jon, and son, Iain, lay a rose on the coffin in their final goodbye.Vice Adm. Michael L. Cowan, Navy surgeon general, presents a flag to Jon Clark, with son Iain, at Arlington National Cemetery. "She came to know and love her fellow crew mates . . . as if they were brothers and sisters," Clark said.