The seven astronauts who died in the space shuttle Columbia disaster can best be memorialized by carrying on their work, speakers at a memorial service said Tuesday.

About 200 students, staff members and faculty members at the Naval Postgraduate School filled King Hall on Tuesday afternoon to commemorate Air Force Col. Rick Husband and Lt. Col. Michael Anderson, Navy Capt. David Brown and Cmdrs. William McCool and Laurel Clark, Israeli Air Force Col. Ilan Ramon, and civilian scientist Kalpana Chawla, who were aboard Columbia when it disintegrated over Texas on Saturday morning.

"We gather to share a national grief as well as a personal grief," said Navy chaplain Lt. Cmdr. Mark Smith, who noted that the astronauts "paid with their lives, not that we would stop, but that we would continue on."

Especially remembered was McCool. He was one of 35 astronauts to pass through the Navy school over the years, graduating from its cooperative test pilot program with a degree in aeronautical engineering in 1992 and being chosen for the astronaut program in 1996.

That "was the fulfillment of a lifelong dream," said Rudy Panholzer, chairman of the NPS space systems academic group.

Noting that the school's latest astronaut-graduate, Marcos Pontes, is from Brazil, Panholzer commented that "space exploration binds together nations as spacefarers and explorers... we share the excitement of discovery, we share the fruits of space exploration, we share the knowledge gained on new frontiers, we share the burden of cost, but we also share the risk that comes with reaching for the stars."

Navy Capt. Frank Petho, chief of staff for the school, said the astronauts "took calculated risks to follow their dream" and that their example "admonishes us to dream the dream, fight the fight."

There is an inherent risk in the space program, and the Columbia tragedy won't end it, said retired Navy Rear Adm. Thomas Betterton, NPS chair professor of space technology, after the ceremony.

Betterton spent many years with NASA and helped investigate the loss of the Mars Observer spacecraft.

Although Columbia was the oldest space shuttle, it hadn't flown the most missions, and age wasn't likely a factor in the events that led to its disintegration, he said.

McCool was not the stereotypical "top gun" jet jockey, though he was a fighter pilot and "a very sharp one," said Rob Bourke, NPS alumni director.

"He had a philosophical outlook you don't see in most astronauts. He felt humankind should advance, push forward, and he felt lucky to be one of the people pushing the boundaries."

Navy Lt. Layne McDowell of Lubbock, Texas, a student in the test pilot program at NPS, programmed his career to follow those of fellow Texans Husband and McCool.

"I never met them, but I followed their careers, and I was able to follow their career paths," he said.

Married and the father of a 4-month-old son, McDowell said he is undeterred by the losses of Columbia and Challenger in pursuing a chance to go into space.

A veteran of combat tours over Kosovo, Iraq and Afghanistan, where he flew F-14 fighter jets off aircraft carriers, McDowell remarked that "there are risks in everything you do; driving to work, carrier aviation.

"I lost more friends in F-14 and F-18 carrier flying. The risks are there. The goal is worthwhile."

His wife supports him, he said, adding that they both consider a NASA assignment less risky than an operational deployment with a carrier fighter squadron.