WASHINGTON — After more than 12 years and at least $100 billion in construction costs, NASA leaders say the International Space Station finally is ready to bloom into the robust orbiting laboratory that the agency envisioned more than two decades ago.

“The ISS has now entered its intensive research phase,” said Bill Gerstenmaier, head of NASA operations and human exploration, in recent testimony to Congress in defense of the roughly $1.5 billion the agency spends annually on the outpost.

But doubts linger.

More than a quarter of the area that NASA has designated for experiments sits empty. Much of the research done aboard the station deals with living and working in space — with marginal application back on Earth. And the nonprofit group that NASA chose to lure more research to the outpost has been plagued by internal strife and recently lost its director.

And more broadly, questions remain about whether NASA can develop U.S. capability to send experiments up and bring them back to Earth — and whether, in fact, the station can live up to the promises that were used to justify its creation.

“Now that NASA has finished ISS construction, I hope the incredible potential of ISS is not squandered,” said Rep. Ralph M. Hall (R-Texas), chairman of the House Science, Space and Technology Committee.

This “incredible potential” is what NASA used to justify the decision to build a space station, which had been in the works since the Reagan administration.

“When we finish, ISS will be a premier, world-class laboratory in low Earth orbit that promises to yield insights, science and information, the likes of which we cannot fully comprehend as we stand here at the beginning,” said then-NASA Administrator Daniel Goldin during a 2001 congressional hearing.

In the decade following, NASA and its international partners used the space shuttle and other vehicles to assemble the station, complete with several onboard laboratories lined with science “racks.” These racks, each about as big as a telephone booth, provide a home for dozens of experiments and can stream data and video to researchers on Earth.

But then — as now — some questioned the station’s future as a center of science. They note that much of the research done aboard the station deals with surviving the space environment.

Privately, some NASA officials worry the outpost could feed into the agency’s reputation as a “self-licking ice cream cone” in that space-based experiments help NASA keep doing space-based experiments.

Others note that station research — there have been about 500 American experiments and 800 international ones — has produced comparatively little scientific literature. Thomson Reuters Web of Science, which tracks such publications, has identified about 3,000 scientific articles that have resulted from station research.

By comparison, a 2001 satellite that cost about $150 million — NASA’s Wilkinson Microwave Anisotropy Probe, known as WMAP — has generated more than three times as many papers. Many scientists used the probe’s analysis of temperature differences in space to theorize about the origin and structure of the universe.

“If you wanted to grade space station science, it would be an incomplete right now,” said Jeff Foust, editor of the Space Review, a popular online magazine.

He said critics could make the argument that money spent on the station might be better invested in other missions.

But, Foust said, “there is a rationale for the ISS that goes beyond simply science” — promoting partnerships and better relations among space-faring nations, including Russia.

NASA officials, however, say research is just beginning and already there have been advances.

Scientists at Johnson Space Center in Houston have taken advantage of the station’s lack of gravity to develop “micro-balloons” the size of red blood cells that can carry drugs to cancer tumors. And the European Space Agency is looking to help doctors better diagnose asthma by using an air-monitoring device developed for astronauts.

“It’s the tip of the iceberg,” said Marybeth Edeen, NASA manager of the station’s national laboratory.

The inability to completely fill NASA’s science racks, she said, is simply one of the priorities. Up until now, NASA has been focused on building the station. Indeed, the station crew, which expanded from three to six members in 2009, now spends about 50 hours a week on science, as opposed to three hours a week in 2008.

mkmatthews@tribune.com