Change in Experiment Will Delay Shuttle’s End

Change in Experiment Will Delay Shuttle’s End

A $1.5 billion seven-ton cosmic-ray experiment scheduled to be carried aloft July 29 on the space shuttle Endeavour won’t be ready until August, according to the experiment’s leader, Samuel Ting of the Massachusetts Institute of Technology, delaying the end of the 29-year-old shuttle program.

NASA officials acknowledged that there would be a delay but said they had not yet decided when the final launching would be.

The experiment, known as the Alpha Magnetic Spectrometer, was to be installed on the International Space Station as one last scientific errand before the final shuttle launching, of the Discovery, now scheduled for Sept. 16.

Last week, however, Dr. Ting told NASA that he would replace a key component of the spectrometer, a powerful superconducting magnet, with an ordinary magnet. The redesigned instrument would not arrive at the Kennedy Space Center until August. It would be too late for July and is not a part of the final Discovery mission.

“We have an issue,” Dr. Ting said in a telephone interview from CERN, the European Organization for Nuclear Research, in Switzerland, where the instrument was built.

NASA officials said they had not made any decisions on a new shuttle schedule this fall, including whether to switch the last two flights so that Endeavour’s flight would be the finale. “That launch is still where it is,” said Kyle Herring, a spokesman at the Johnson Space Center in Houston.

Asked about a possible delay at a news conference after the recent landing of Discovery, Mike Moses, director of shuttle integration at Kennedy, said that the agency was still looking at the potential impacts to the shuttle schedule, “but we’re still looking to finish this calendar year.”

The cost of extending shuttle flights past September has already been covered by Congress, which allocated $600 million to cover potential shuttle operations in the first quarter of fiscal year 2011, in case the schedule slipped. “So it doesn’t matter if it’s one flight or two flights,” Mr. Herring added.

Dr. Ting said the collaboration had been pondering changing magnets for at least a year and had mentioned it to NASA.

The superconducting magnet, which produces a field 17,000 times that at the Earth’s surface and allows scientists to determine the charge and momentum of particles by how their tracks bend, needs to be cooled to near absolute zero by liquid helium. But tests and calculations showed that the helium would boil away too quickly, within two or three years, leaving the seven-ton spectrometer a dead hulk. Under the Obama administration’s new plan, however, the space station will stay up to 2020 or even 2028.

“I don’t think it’s correct to go there for three years where there is a chance to do physics for 18 years,” Dr. Ting said. “Because there is no way to remove it.”

Dr. Ting plans to replace the magnet with an ordinary one of the exact same size that flew in a test flight aboard the space shuttle in 1998, since it doesn’t need helium cooling and thus will last as long as the station. The new magnet is only one-fifth as strong as the superconducting one, but Dr. Ting said the much longer running time of the experiment along with rearranging some of the layers of silicon that record tracks of particles would more than compensate for the weaker magnet.

Mark Sistilli, an astronomer who is NASA’s program manager for the experiment, said that eliminating the need for handling supercold liquid helium would make things simpler and safer. When it warms up, liquid helium can boil explosively, as scientists at CERN found out a year and a half ago when part of the Large Hadron Collider, whose magnets are also cooled with liquid helium, exploded, delaying its operations for a year. The initial reaction at NASA, he said, was, “Our life just got easier.”

The last-minute switch has caused head-scratching among some physicists, who despite Dr. Ting’s protestations worry that the experiment has been degraded. Gregory Tarle, a physicist at the University of Michigan, said: “It’s highly unusual for an experiment to be redesigned this close to launch. I would question the wisdom of flying something redesigned so close to launch.”

This is only the latest adventure for an experiment that dates to the beginning of the space station era, in 1994, and has been controversial for about as long. It was originally meant to look for antimatter, but in recent years scientists have become more excited about the possibility that it could pick up signals from the mysterious dark matter that pervades the universe. Despite disagreement among scientists about the priority NASA gave to the experiment, a coalition of some 500 physicists from 16 countries, welded together by Dr. Ting’s legendarily iron will, pressed ahead and put it together at an estimated cost of $1.5 billion.

It was tossed off the shuttle manifest in 2004 after the loss of the shuttle Columbia in 2003, and some prominent American physicists accused NASA of not sticking to its international commitments. Dr. Ting began making regular visits to Washington. In the fall of 2008 Congress subsequently ordered NASA to add one more shuttle flight for Dr. Ting’s experiment.