The space shuttle Columbia was on a purely scientific mission when it broke up just minutes before landing on Saturday morning.

Most recent space shuttle missions have been dedicated to building and servicing the International Space Station, a research lab orbiting the Earth. But this mission was different. The Columbia itself, became an orbiting science lab. The shuttle's seven astronauts carried out some 80 research projects from 16 countries, studying everything from soot to cell biology.

NASA science official Howard Ross says the shuttle's experiments worked better than expected.

"Payload operations from this flight were very successful. Unusually successful," he said. "There were very few glitches, as far as actually the crew conducting the experiments. Where there were problems, the crew fixed them, every single one of them." In one project, astronauts examined the formation of soot - a major pollutant created when things burn. Scientists know it's a health hazard, but Mr. Ross says they don't know much about how it's formed. Mr. Ross says the researcher in charge of the experiment got terrific results.

"He [the researcher] saw phenomena in these experiments that he has never seen before on earth," he said. "He had previously flown in space, he never saw anything like what he saw in space. They were the best data that he could ever hope for from this."

Mr. Ross says researchers also got good data from another experiment on how things burn that could be used to help design car engines. The astronauts beamed some of their data from these and other experiments back to Earth while the shuttle was still in orbit, so they were not lost in the crash.

But Mr. Ross says many of the experiments were lost in the crash, especially those the astronauts carried out on plants, animals, cells, and themselves.

"Unfortunately, those experiments rely on specimens and samples and data to be returned post-flight," he said. "And so the loss in that area is quite substantial, probably in some cases, complete."

Mr. Ross says it's too soon to say exactly how much was lost. He says NASA's first priority right now is helping the agency's extended family cope with the loss of the seven astronauts. Then, he says, NASA will assess the impact the shuttle disaster will have on its manned scientific research program. For the time being, science missions on the shuttle are off.

But NASA's Michael Kostelnik, who directs the shuttle projects and the International Space Station, says there are still scientists at work aboard the space station.

"There is still a lot of science and research being done as we speak on orbit today," he said. "And we should not forget that? And that is going to continue unabated."

But critics are questioning whether sending people into space for science is worth it.

"There is no field of science that has been significantly affected by any research on the shuttle or the space station," said Robert Par, spokesman for the American Physical Society.

Mr. Park says the scientific community should take a close look at the cost of data generated by research in space. And he says the results of studies in space do not get published in prestigious journals often enough.

NASA's Howard Ross disagrees.

"We've had publications in the most prestigious journals," he said. "We've had cover stories in the most prestigious journals, based on the human space flight results."

But Mr. Park says technology is moving rapidly toward the point where work in space can be done from the ground by remote control, making manned spaceflight less important and research in space much cheaper.

"I would suggest that we just try to keep a foothold in space, not much more, so enormously scale back the man-in-space program, in case something arises where we simply must have a human being likely," he said. "Now, in fact, every day that goes by makes that less likely."

But NASA and President Bush have said the nation is committed to manned space flight. At a memorial service for the seven astronauts on Tuesday, Mr. Bush said the cause of exploration and discovery is "a desire written in the human heart."