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The breakup of Columbia over Texas stunned relatives of the crew and people waiting to watch the space shuttle's landing at Cape Canaveral, and it revived sorrowful memories for relatives and friends of the astronauts killed in the loss of the shuttle Challenger 17 years ago.

"To have this happen with 15 minutes to go until it was over was just unbelievable," said Daniel Salton, whose sister, Laurel Clark, was aboard Columbia.

Salton, of Milwaukee, had received an e-mail from his sister just the day before saying how much she was enjoying her experience aboard the shuttle.

"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," Salton said.

Betty Haviland, Clark's aunt, of Ames, Iowa, said she and her husband, Doug, and other members of the family were in shock.

"It sort of brought back our son Timothy [who] had perished in the World Trade Center disaster and you know we'd been watching on TV the fires up in the towers and so you sort of had the sickening feeling that here we go again," said Doug Haviland, 76.

The disaster struck deeply for Americans who follow the space program.

"I saw their faces, I saw who they were and to watch this happen is just unbelievable," Traci France, 28, said as she went for a somber walk in Denver. "It really gets you, you feel it, even though you never met these people, you can think about their families and just imagine the pain. It's terrible."

Former astronaut John Glenn and his wife had just turned on their television when communication with the craft was lost as it soared across Texas.

"We were going to be watching the landing and then it got into trouble," Glenn, a former senator from Ohio, said in a telephone interview from his home at Bethesda, Md.

For Grace Corrigan, it was a reminder of the Jan. 28, 1986, Challenger accident that killed her daughter, Concord, N.H., elementary school teacher Christa McAuliffe.

"I'm not doing too well," Corrigan said from her home in Framingham, Mass. "All I know is it's very upsetting. I feel the same way everyone around the country feels."

Douglas Woodward of Concord was in the VIP viewing stands at Cape Canaveral, helping to chaperone members of a third-grade class that included McAuliffe's son, Scott.

"God, it's like deja vu," said Woodward. "Those poor people. Another whole crew."

Ben Provencal, who was one of those third-graders and is now a special education teacher in Concord, said he always thought another accident was inevitable.

"I've always waited for the next thing to happen," the 25-year-old man said. "I conditioned myself — maybe that's how I dealt with Challenger. But it's still horrible."

Memories also flooded back for Paul Resnik, whose cousin, Judith Resnik, was one of the astronauts killed aboard Challenger.

"Today, as soon as I saw the news on the TV, the first thing I thought about was the Challenger," Resnik said from his home at La Plata, Md. "It's certainly an unfortunate situation that the country's going to have to go thorough this all again."

Former shuttle astronaut Winston Scott, whose flights included one aboard Columbia, knew all the crew members except Ilan Ramon, the Israeli crew member aboard. "Willie [McCool]was my basketball buddy," he said.

"You don't dwell a lot on risks," said Scott, an engineering professor at Florida State University in Tallahassee.

At Titusville, Fla., near the Kennedy Space Center, Ted Kretschmer, a retiree from Ventura, Calif., was among the roughly 200 people waiting to watch the landing from Riverfront Park in Titusville.

"What struck me after about 10, 15 minutes past the time it was supposed to land, I saw the people on the pier slumped over, slowly walking back depressed," Kretschmer said.

At the Kennedy Space Center Visitor Complex, former Sky Lab astronaut Bill Pogue spoke to tourists.

"We will go on," Pogue told the crowd. "It's a terrible tragedy, but you don't stop flying airplanes because an airplane crashed. You don't stop driving automobiles because you have an automobile accident. It's the same sort of thing, but it's that this is so dramatic it tears at you emotionally."