LIKE THREE guys moving into a new bachelor's pad, a team of astronauts boarded the International Space Station yesterday, turned on the lights and utilities and settled in to make history.

To get them there, the United States and 15 partner nations overcame cost overruns, years of delay, angry debates about the station's usefulness and public ennui about the space program in general.

Although barely noticed on Earth, 250 miles below, the occupation of the station marked humankind's first permanent foothold in space and the beginning of a new era of space exploration.

"It's a great moment for all of us," said mission commander Bill Shepherd, 51, a U.S. Navy captain. He and Russian cosmonauts, Yuri Gidzenko, 38, and Sergei Krikalev, 42, will live and work there for the next 4 1/2 months.

Other teams will follow, keeping the orbiting outpost inhabited continuously for at least 15 years, maybe longer.

Billed as the largest, costliest and most complex engineering structure ever built, the $60 billion machine is an orbiting way station, a scientific lab and a jumping-off point for further exploration of the solar system and perhaps the universe beyond.

Earthbound critics have knocked the space station as being a huge waste of money that could have been spent on other more valuable scientific projects.

The National Aeronautics and Space Administration has long had to fend off challenges that money spent on space exploration could be used more productively on Earth.

While the station is a magnificent feat of engineering, diplomacy and international cooperation, its greatest value is not as a research tool but as a stepping stone to investigating outer space.

Aboard the station there will be experiments on the physical effects of long-term weightlessness and human adaptation to life in space as well as scientific, medical and manufacturing trials in a zero-gravity environment.

But the main purpose of the station is to be a continually inhabited, orbiting platform from which space-farers will carry on humankind's fundamental urge to explore the unknown, learn and accumulate knowledge.

To seek answers to the nature and evolution of the universe may not be the most practical expenditure of tax dollars, but the very process lifts humanity's spirit and inspires the soul. And that's worth every penny.