The spacecraft was full of life: seven people, many spiders, a nest of carpenter bees, a baker's dozen rodents. Here was moss, yeast, strains of bacteria, cells growing in tissue cultures. In orbit, a silk moth emerged from its cocoon. A fish hatched. Miniature roses and rice flowers bloomed.

The final flight of Columbia was something of an anomaly: a pure science mission. No one asked this crew of astronauts to ferry hardware to the International Space Station. No one asked them to take a wrench to the Hubble Space Telescope. They were expected -- even the fighter jocks among them -- to perform science, in teams, 24 hours a day.

They carried with them a laboratory called Spacehab, crammed with instruments, cameras, computers, test tubes. The astronauts themselves were guinea pigs, swallowing calcium tracers to study the effects of weightlessness.

Columbia had a cargo of human ingenuity, with 80 experiments designed in 16 countries, from Japan to Liechtenstein.

At one point, astronauts used a contraption the size of a trash basket to create tiny, fragile "flame balls" of burning hydrogen and methane. Some winked out quickly, but one lasted 25 minutes and another a heroic 81. Mission specialist Dave Brown decided each had a personality.

"I see one flame ball," he told Mission Control, "and its name is Howard."

As experts try to figure out what went wrong on Columbia, the people who worked with the astronauts talk of much that went right, of hard work and excellent science, and high spirits all the way into space and almost all the way home.

The astronauts were on their backs, helmeted, in orange pressure suits, aimed toward space.

It was Jan. 16, and they were on Launch Pad 39-A, out toward the beach on Cape Canaveral. "The Lord has blessed us with a beautiful day here," Commander Rick Husband said.

At the Cape, and in Mission Control in Houston, NASA officials entertained the public with countdown pronouncements and informative chitchat, but inside Columbia the crew heard nothing. The launch required absolute silence. If something went wrong, the Florida launch team needed to communicate instantly with the crew.

Three of the astronauts had been to space before, but four hadn't. Security had been unusually tight before the launch because of the presence of an Israeli, Ilan Ramon, a military pilot who had brought with him a drawing by a boy killed at Auschwitz.

At 10:38 a.m., with the countdown nearing one minute, the astronauts closed and locked their visors. Six seconds before liftoff, the main engines ignited. The shuttle rocked back and forth a couple of feet, an unnerving feeling for those inside, as if the spacecraft were about to fall over. But there wasn't enough time. The solid fuel booster rockets ignited, and Columbia left the planet.

During liftoff, a piece of insulation broke free from one of Columbia's external fuel tanks and bounced off the left wing, coated with silicon insulation tiles designed to dissipate the heat of reentry. Tile damage could mean nothing. Or it could mean trouble.

Astronauts describe launches as noisy, with a whooshing, roaring sound to accompany the furious shaking -- like a railroad car running too fast for its tracks. But after two minutes the booster rockets dropped off and the ride immediately smoothed out. The spacecraft was traveling faster now, much faster. The G-forces reached about three times the normal sensation of gravity.

And then -- only 81/2 minutes after liftoff -- the main engines shut down, and Columbia was in orbit, floating in splendid silence 178 miles above Earth. Those who have experienced space flight describe it as spectacular, like reaching the top of a mountain after a furious climb. But the calm is illusory. In reality, Columbia had accelerated from a standing start to 17,000 miles per hour, accumulating an incredible amount of energy.

In 16 days it would have to shed that energy in order to land.

Settling In

The crew split into two teams, to work and sleep in shifts (a necessity in any case, since there were only four bunks).

The Red Team would work pre-dawn and daytime -- Houston time, since out the window the sun came up every 90 minutes -- and would include Husband, Ramon, and mission specialists Kalpana Chawla (often called "KC") and Laurel Clark.

The Blue Team would work evening and through the night: Brown, pilot Willie McCool and payload commander Mike Anderson.

They didn't wait long to establish a routine. One of the first orders of business for the Blue team, just four hours into the flight, was to try to go to sleep.

But first they unstowed their gear -- sticking loose objects to the Velcro that lines almost every surface. And they activated Spacehab, the research module in the shuttle's cargo bay that contained 59 of the experiments. They would do most of their work in this laboratory, accessible through tunnels from the mid-area living space.

In space they would be as busy as the carpenter bees, but weightless, forced to operate in a cramped environment without an obvious top or bottom, and dealing with the initial, powerful nausea of zero gravity. Things in space are strange: One must get used to the sensation, for example, of floating inside a sleeping bag.

One thing astronauts don't do in the first couple of days is take a crew picture. In zero gravity, water that gathers naturally in a person's legs on Earth roams freely through the body, and shuttle crews move about with puffy, bloated faces. Gradually, after dehydrating for a couple of days, they look better.

The simple act of changing one's pants can cause a person to tumble head over heels, grabbing for a handhold. Showers don't happen -- astronauts sponge bathe. The toilet is complicated and, as astronauts have periodically pointed out, does not always work immaculately.

The core living space on a shuttle is the "mid-deck area." This is where the crew members eat, sleep, wash, use the toilet, change clothes, read messages from home and practice the things they always wanted to try in space -- dancing on the ceiling like Fred Astaire or doing somersaults in mid-air.

The mid-deck area, points out astronomer Ronald A. Parise, who flew on two shuttles, including Columbia, "is an area about the size of a typical residential bathroom." The difference is that on Earth, everyone has to stand on the same surface, the floor. On the shuttle, all the volume is used. "If I'm looking for a place to eat, I can just float up to the ceiling," he said.

The view is tremendous. At 178 miles altitude Earth is not a blue marble, but something that fills the window with 1,600 miles of territory at a glance: "I can't describe the overwhelming sense of jubilation I feel up here," the boyish pilot, McCool, said later by video link, broadly grinning. "The sun rises, the sun sets, the moon rises, the moon sets, going about the globe, seeing the Himalayan range, the Great Barrier Reef -- it's phenomenal."

Space Music

On Day 3, the astronauts took time out from their experiments to do a series of TV interviews.

"We've really got our space legs up and running," Husband told CNN.

Clark said she was surprised by the sounds inside the shuttle: "The zippers and all the belts that have D-rings that we hold things down with are always floating and hitting each other and jingling. It makes this beautiful tinkling music in the background all the time."

Ramon, the Israeli, didn't merely serve a symbolic function -- he worked hard, like everyone else. Among other things, he wielded a camera to study dust plumes from the desert passing across the Mediterranean. That was tricky at first, because there were too many clouds, not enough dust.

"He was an Israeli jet jock, but he was really interested in learning the science, he went the extra mile," said Paul Ronney, the aerospace and mechanical engineering professor at the University of Southern California who designed the flame balls experiment.

"They had a really deep understanding of all the experiments that they did," said Stein Sture, a civil engineering professor at the University of Colorado.

Ronney, Sture and other scientists talked to the crew throughout the flight, via an intermediary at Mission Control. Spirits were high. "We had excellent results," Sture said.

Grieving since Saturday morning, both scientists said they managed to download data during the flight. Both estimated that their experiments yielded 50 percent of the projected data.

"What I lost," Ronney said, "is trivial and meaningless compared to what others have lost."

Science Marches On

On Day 6, Tuesday the 21st, Ramon used his camera to capture "sprites," electrical charges that pulse from the top of thunderheads. No one had ever studied such a thing.

He also spoke to Israeli Prime Minister Ariel Sharon by video linkup, and held up a small Torah scroll, brought to Israel by a Holocaust survivor. Speaking in Hebrew, he said, "From space, Israel looks like it does on a map: small but charming. I think we have a great people in Israel, and we have to maintain our Jewish heritage."

Sharon told him, "I would like to congratulate you for standing up as a Jew."

As the spaceship went around and around the world, the sleeping astronauts would get wake-up calls in the form of music. The selection for Day 7: "Hakuna Matata" from "The Lion King." (It means no worries, for the rest of your days. . . .) That day, the astronauts beamed down pictures of their smallest passengers. Ants were busily skittering through tunnels in the ant farm contributed by the students of Fowler High School in Syracuse, N.Y. The Glen Waverly Secondary College in Melbourne, Australia, had contributed spiders that were beginning to construct webs. Silkworm larvae were developing in an experiment submitted by the Jingshan School in Beijing. And the Tokyo Institute of Technology had sent medaka fish embryos, which were growing in an aquarium.

The Red Team grew prostate cancer cells, and checked on their plants, including the miniature roses that may yield new fragrances for perfumes.

On Day 8, Anderson and Chawla made flame balls, the weakest forms of fire ever produced, invisible to the naked eye. One had half a watt of power, 100 times weaker than a candle. Scientists think this work could lead to better fuels and less vehicle pollution. That afternoon, Mission Control honored the flame experiments by giving the Blue Team a wake-up call from the Talking Heads: "Burning Down the House."

Science marched on, day after day. More flame balls. More tissue cultures. One experiment examined the way moss responds to light and gravity. Another looked at the "critical viscosity of Xenon-2."

It had been five years since the last shuttle voyage devoted completely to science. If everything had gone as planned this year, the next five shuttle flights would be devoted to supplying crew members and parts to the space station. Columbia was the first shuttle and the heaviest by 7,800 pounds, and although it had made trips to the space station it could not carry the heaviest shuttle payloads. It made a good laboratory, though.

Not everything on this mission worked perfectly. There was a balky air conditioner in Spacehab, and the astronauts had to improvise, funneling air from the crew compartment into the lab.

And in the third round of experiments lighting fires in zero gravity, the combustion module sprang a leak, forcing the crew to spend four hours dismantling the entire apparatus and replacing a critical part.

But on the whole, everything went smoothly -- remarkably so, the NASA officials on the ground thought.

The Blue Team awoke on Day 9, Friday the 24th, to the tune of "Hotel California," by the Eagles, sung by McCool's family. To help with the formation of those fragile flame balls, the astronauts shut down the shuttle thrusters. Columbia drifted serenely in space.

On Day 11, a fish hatched and a silk moth emerged from a cocoon. The astronauts didn't watch the Super Bowl -- there are no couch potatoes in space. But McCool let it be known he was pulling for the Raiders, and Brown rooted for the Buccaneers.

On Day 12, they shut down the flame balls experiment. They also made a long-distance call, speaking to the three astronauts orbiting on the space station.

"I wish I could stay some more time like you guys," Ramon said.

On Day 14, the Blue Team woke to John Lennon singing "Imagine."

The astronauts gave a news conference, and Anderson put the science in context: "The science we're dong here is great and it's fantastic; it's leading edge. But I think once we get a seven-member crew on board the space station you're really going to see some outstanding science in space." The scientists on the station, he said, "will have years to conduct the experiments that we're trying to do here in a relatively short period of time."

McCool spoke of riding an exercise bike:

"There's nothing better than listening to a good album and looking out the windows and watching the world go by while you pedal on a bike."

On Day 16, the 31st, the crew did routine tests of auxiliary power units, getting ready for reentry. They shut down the Spacehab module. No more experiments.

Florida weather is forecast to be excellent on Saturday, NASA said in its daily STS-107 report.

At 8:15 a.m. Eastern time Saturday, on its 255th journey around the planet, Columbia turned tail-first and fired its thrusters, braking its speed and dropping toward Earth. Inside the spacecraft, the crew felt a slight jolt, like a subway train leaving the station.

They took seats and strapped themselves in for reentry. The spacecraft turned nose-first again, all the maneuvers controlled by computers. The crew was dropping ever faster into a thickening atmosphere, so fast that they saw the air outside the windows turn into electrically charged ions -- a bright yellow plasma cloud turning to white as the tiled undersurface of the shuttle neared 2,800 degrees Fahrenheit.

And then they were through the cloud, passing over Arizona and New Mexico, falling toward Earth -- a brilliant light, streaking through a clear blue Texas morning.

Staff researchers Bridget Roeber, Margaret Smith and Margot Williams contributed to this report.

DETAILS OF MISSION STS-107 Launch: Pad 39A, Kennedy Space Center, Cape Canaveral, Fla. Crew: Commander Rick D. Husband, pilot William C. McCool, payload commander Michael P. Anderson, payload specialist Ilan Ramon, mission specialists David M. Brown, Kalpana Chawla and Laurel Blair Salton Clark Purpose: Sixteen-day, round-the-clock science mission mixing competitively selected and commercially sponsored experiments. Payloads: Science module had a capacity of 9,000 pounds, which included 32 payloads with 59 seperate investigations. Eighteen percent of the capacity was dedicated to international and commercial industry users. Eighty-two percent of the capacity was dedicated to NASA research. Experiment highlights: - Physics of combustion, soot production and fire-quenching processes in microgravity. - Compression of granular materials in the absence of gravity to further understanding of contruction techniques. - Formation of zeolite crystals, which can speed the chemical reactions that are the basis for chemical processes used in refining and biomedicine. - Using pressurized liquid xenon to mimic the behaviors of more complex fluids such as blood flowing through capilaries. - Allowing different types of cell cultures to grow together in weightlessness to enhance their development of genetic characteristics - Forming protein crystals more purely and with fewer flaws than is possible on Earth for drub research. - Spaceflight's effects on cardiovascular, muscular and skeletal systems. - Testing new technology to recycle water intended for installation on International Space Station. - Testing navigation systems for future satellites. - Effects of spaceflight on insects and fish. Mission Sequence January 16th 10:39 a.m.: Shuttle launched from Kennedy Space Center. 1:09 P.m.: Spacehab science module activated, beginning research

missions. 27th 12:24 p.m.: Ship-to-ship call with International Space Station. 29th 5:44 a.m.: Crew news conference February 1st 5:35 a.m.: Cargo bay doors closed. 8:15 a.m.: Thrusters fired for de-orbit burn. 9:16 a.m.: Intended landing at Kennedy Space Center. Mission STS-107 Orbits: 255 Distance: 6,649,757 statute miles SOURCE: NASA, Commander Rick D. Husband, front, and Ilan Ramon prepare to give a video tour from Columbia's flight deck.

Mission specialists Kalpana Chawla, left, and Laurel Blair Salton Clark work in the Spacehab on Jan. 17, one day after leaving Earth.

Payload Commander Michael P. Anderson works with the Combustion Module-2 facility in the Spacehab on Jan. 20, Day 5 of the mission.