Dennis Overbye is a science correspondent for The Times. His most recent book is ”Einstein in Love: A Scientific Romance.”

In a recent report to Congress (pdf), NASA offered two contradictory statements: a $1.5 billion physics experiment intended for the International Space Station was on track for a 2009 launch, but it had no intention of actually launching the device into space.

Once upon a time the Alpha Magnetic Spectrometer, as it is known, was to be the scientific centerpiece of the space station. By sifting cosmic rays from outer space, the 15,000 pound detector would look for evidence of antimatter or the mysterious dark matter that accounts for 25 percent of creation.

The brainchild of MIT physicist and Nobel laureate Sam Ting, the detector was built by a collaboration of scientists from 16 countries, including China and Taiwan, mostly with their own money. NASA agreed in 1995 to give it a ride to the space station and then reneged 10 years later after the loss of the space shuttle Columbia, saying the remaining flights between now and 2010 when the shuttles are to be retired were all spoken for. This dismayed many physicists who thought the space agency should keep its word and was being a bad international partner.

“It’s a pity that NASA is living up to its commitment to finish the Space Station, but not to its commitment to use it for something scientifically interesting,” said Steven Weinberg, himself a Nobel physicist at the University of Texas, in Austin.

But Dr. Ting has supporters in Congress, including Sen. Bill Nelson, the chairman of the Space, Aeronautics, and Related Sciences Subcommittee who rode the shuttle into space in 1986. In December, he vowed to file legislation adding a shuttle flight for the detector if Michael Griffin, NASA’s administrator did not change his mind.

In a speech on February 8, the day after Atlantis lifted off on the most recent mission to the space station, Sen. Nelson said of Dr. Ting’s experiment, “What it does is it identifies the origin of cosmic rays, and that means it can help us understand the origin of the universe. This is not just an American experiment; this is an international experiment of countries around the world. This is a part of us wanting to understand our beginnings. This is a part of our nature, as a people, to want to explore the heavens and understand the universe.”

As part of the final 2008 budget that was finally approved last fall, NASA was required to report to the Appropriations Committee on the status and prospects of the Alpha Magnetic Spectrometer.

Dr. Griffin has not changed his mind. The report lists tests and safety reviews expected to be completed in the next two years. “The AMS and Shuttle programs are moving forward to develop, by early 2009, all required analytical and operations data to support an AMS launch on the Space Shuttle,” that portion of the report smoothly concludes. There are no “showstoppers,” in NASA terminology, except NASA itself.

In order to fly Dr. Ting’s device before September 2010, the shuttle end date, the agency said, either “critical space station hardware” would have to be bumped from a flight, or an additional flight would have to be booked at a cost of some $300-400 million and additional risk. Extending the shuttle operations into 2011, they said, would cost $3 billion or more and have a “significant negative impact” on NASA’s new exploration program. Moreover, it takes 18 months to get ready for a flight, so the decision to fly the experiment has to be made (and presumably the funds provided) by a year from now.

What about launching the experiment on another unmanned rocket? That could cost as much as $1 billion and couldn’t happen before 2013 or 2014, which raises a final problem: Dr. Ting’s spectrometer is supposed to work for three years, but the money for space station operations, according to the report, is currently scheduled to run out in 2016.

Dr. Ting declined to comment on the NASA report. But he said by e-mail that the detector, being assembled at CERN, the European physics laboratory outside Geneva, was now complete.

“I do hope it will be possible for you to visit CERN in the near future and see the Detector,” he wrote.