The sky was a perfect blue over the quadrangle of the Johnson Space Center, as it was on Saturday, when the Columbia disintegrated 40 miles above Texas into a macabre shower of wreckage. Mission Control Center, recipient of Commander Rick D. Husband's garbled last transmission, was quiet today, the flag above the fortress-like building flying at half-staff.

With that backdrop, NASA officials, military chaplains and President Bush assembled today with a promise to honor the memory of the Columbia astronauts -- "seven lives of great purpose and achievement," as the president described them -- by pressing ahead with space travel.

Three days after the Columbia disaster, families of the dead and thousands of space agency workers gathered in grief today at NASA's nerve center. Sitting in the front row with the first lady, newly widowed spouses and children and parents of the dead clutched each other's hands. In the "Astronauts Only" section, those whose fate was not to be on mission STS-107 hugged their husbands and wives.

"Their mission was almost complete, and we lost them so close to home," the president said. Hearing Bush's words, Evelyn Husband, wife of the Columbia commander, leaned on her daughter and quietly wept. When Bush finished, NASA T-38 jets roared overhead in their "Missing Man" formation of mourning.

The president, in his eulogy, remembered mission specialist David M. Brown, who was asked several weeks ago by his brother what would happen if something went wrong with the mission. "This program will go on," Brown told his brother. Today, Doug Brown sat in the first row of the memorial with his mother, father, two cousins and 22 other family members of the crew.

"Captain Brown was correct: America's space program will go on," Bush said. "This cause of exploration and discovery is not an option we choose; it is a desire written in the human heart. We are that part of creation which seeks to understand all creation. We find the best among us, send them forth into unmapped darkness, and pray they will return."

Yarmulkes and military dress caps topped grieving kin who, like the crew, were a mixture of black, white and Indian. A Jewish and Christian chaplain read the Psalm of David in Hebrew and English. From space, said Rabbi Harold Robinson, "we learn the unity of all humanity here on Earth."

This town has become sadly proficient in memorials for fallen space travelers. Three days after the Apollo 1 fire in 1967 killed three astronauts on the launch pad, Houston held their memorial services. Four days after the Challenger explosion in 1986, President Ronald Reagan bid farewell to "our seven star voyagers" in a memorial here at the Johnson Space Center.

And here the mourners of lost astronauts assembled again today, in what for many was a nightmarish rerun of the Challenger memorial, right down to the jet flyover. Bush's nine-minute remarks were strikingly similar to Reagan's 17 years and four days ago. Like Reagan, Bush recalled the astronauts' early desires to travel in space, and their fervent wish that the space program would continue if they were lost.

"Each of these astronauts had the daring and discipline required of their calling," Bush told the crowd of about 10,000. "Each of them knew that great endeavors are inseparable from great risks. And each of them accepted those risks willingly, even joyfully, in the cause of discovery."

In a private meeting with the families after the ceremony, Bush said he "almost broke up" as he gave his eulogy, according to a spokesman's account. Bush rubbed the arm of one father, kidded with the children about school and praised another mourner's strength. "I'm sorry that we have to meet under these circumstances," he told the families.

There were moments of recalled joy today, too, as Kent Rominger, chief of the astronaut corps, remembered the shuttle crew's toy mascot, which sang a "kung fu fighting song," and the temporary tattoos the crew wore at the astronauts' Christmas party. Surviving colleagues chuckled at the retelling of Israeli Ilan Ramon's appearance in a Santa Claus hat and blue underwear, Michael P. Anderson's Porsche, Laurel B. Clark's omnipresent crew insignias, Kalpana Chawla's piloting hobby, David M. Brown's "constant search for food" and William C. McCool's Hawaiian leis.

For Husband, Rominger recalled the commander's favorite biblical passage: "Have I not commanded you: Be strong and courageous? . . . Do not be terrified."

The bright and breezy day, and the mass of flowers, flags and balloons forming a shrine at the space center's entrance, gave an oddly festive appearance to the memorial. To accommodate the crush of media and NASA workers and contractors (14,000 affiliated with the Houston facility), portable toilets, sophisticated electronics and Astroturf were brought in for the event.

But sorrow was evident everywhere. The route from Ellington Air Force Base, where Bush landed, to the Johnson center began on "Challenger 7 Parkway." Listening to the tributes, the astronauts, the nucleus of the "NASA family," stood arm in arm in prayer, some weeping.

Sean O'Keefe, the NASA administrator, recalled "smiles on their faces" as the Columbia crew left Earth three weeks ago. "Today, our grief is overwhelming," he said, offering a "solemn pledge" to fix the shuttle's flaws. "We have a tremendous duty . . . to make sure that this never happens again," O'Keefe said. But he said there would be no relenting in space exploration. "We hope our unceasing efforts will provide a fitting tribute to the Columbia 7," he said.

As thousands of red-eyed former and current NASA employees and defense contractors streamed out of the service, many said that the most important message was that the space program would go on.

Several of the assembled lawmakers vowed unwavering support. "These astronauts have given our national defense every bit as much as if they had died on the battlefield," said Sen. Kay Bailey Hutchison (R-Tex.).

Just as Reagan promised one of the lost Challenger astronauts that "we will build your space station," Bush today spoke of determination to proceed in space. "The people of NASA are being tested once again," the president said, praising them for "responding as your friends would have wished -- with focus, professionalism, and unbroken faith in the mission of this agency."

The astronauts aboard the Columbia wanted very much to be part of that mission. Before Saturday's catastrophe, it was recalled today, Ilan Ramon messaged Earth with a request to "immediately reassign this crew" because of its excellence.

The Columbia 7 were reassigned in a way nobody wished, but in a way they knew possible, despite the public perception that space shuttle trips had become routine. The president recalled today the words of Col. Anderson, who told his minister before leaving, "If this thing doesn't come out right, don't worry about me. I'm just going on higher."

In what has become the traditional close of Houston's space memorials, NASA jets screeched low over the crowd. As three quickly disappeared from view, a fourth, the "Missing Man," soared alone in a steep ascent, then faded slowly from view.

At Johnson Space Center, President Bush prays with families of the Columbia crew, including Sean McCool, left, Lani McCool, the widow of astronaut William C. McCool; Evelyn Husband, the widow of astronaut Rick D. Husband, and Laura Husband and Matthew Husband.At memorial service, Rona Ramon, center, widow of Israeli astronaut Ilan Ramon, with their three children.Former U.S. senator and former astronaut John Glenn, above, attends memorial service at the Johnson Space Center in Houston, with his wife, Annie.Lani McCool, right, widow of astronaut William C. McCool, mourns with son Sean.