Science on the penultimate space shuttle

KENNEDY SPACE CENTER, Fla. — NASA saved one of its best for nearly its last. Friday’s scheduled launch of the space shuttle Endeavour — its last flight, and the second-to-last planned for any shuttle — will be carrying an ambitious and potentially pioneering particle physics experiment.

The $2-billion, 7.5-ton Alpha Magnetic Spectrometer, or AMS, is destined to nestle along the backbone of the International Space Station, there to study charged particles streaming through space. Designed to hunt for exotic stuff such as dark matter and antimatter, the AMS may also make fundamental discoveries no one can predict.

“AMS will be one of the premier science experiments of the 21st century, we hope,” says Mark Kelly, Endeavour’s commander.

Launch fever was running higher than usual at Cape Canaveral the day before the shuttle’s scheduled April 29 launch. Kelly’s wife, injured Congresswoman Gabrielle Giffords, along with President Barack Obama and his family, are expected to watch the astronauts blast off. The last sitting president to attend a shuttle launch was President Clinton in 1998.

More than 700,000 people are expected to flood Florida’s central coast to watch Endeavour lift off. Hand-lettered signs festoon the roadways into Kennedy Space Center, wishing Giffords a speedy recovery and the astronauts a safe trip to and from space.

Endeavour’s main housekeeping task during its two-week mission is to ferry supplies and spare parts up to the space station. The shuttle also carries a smattering of small science experiments, including tubes with five kinds of microbes being tested for a later trip aboard a Russian spacecraft to the Martian moon Phobos.

But to physicists, the planned AMS launch dwarfs all else. The instrument has been in the works since 1994, when former NASA administrator Dan Goldin was looking for a science rationale for the space station — and Nobel prize–winning physicist Samuel Ting of MIT realized he could help. Ting told Goldin of his dream to study charged particles in space.

On Earth, physicists probe matter by smashing it in particle accelerators such as the Large Hadron Collider on the French-Swiss border. But even that machine can accelerate particles up to an energy of only 7 trillion electron volts. The universe can accelerate particles up to 100 million trillion electron volts — and beyond. “No matter how large an accelerator you build on Earth, you cannot compete with the cosmos,” says Ting.

The AMS will measure the mass, energy, speed and charge of particles flying through space in unprecedented detail. Its heart is a giant doughnut-shaped magnet with a magnetic field 3,000 times that of Earth. As particles zip through the center of the doughnut, the magnetic field causes their path to bend slightly depending on their electric charge. Multiple detectors then record the particles’ vital statistics.

In the end, the AMS took 17 years, 16 countries and 600 physicists to put together, says Ting. To keep costs manageable, international partners split the job of building and testing key components. The Department of Energy managed the project and is flying it under an agreement with NASA.

Key scientific targets include antimatter, the oppositely charged counterpart to normal matter that should have been created in equal parts in the Big Bang but obviously was not (since all the stuff of the universe is here thanks to matter predominating). The AMS will also hunt for dark matter, the as-yet-unseen and mysterious stuff that makes up 90 percent of the universe’s matter.

Another spaceborne instrument, an Italian one called PAMELA, recently spotted intriguing hints of dark matter in the form of excess positrons — the antimatter counterpart of electrons — streaming through space. The AMS aims to confirm that tantalizing finding by seeing if those excess positrons exist at much higher energies that PAMELA can measure, says team member Roberto Battiston of the Italian nuclear research institute INFN.

The PAMELA findings, along with others from experiments flown on balloons as a cheaper alternative to the space shuttle, “are a demonstration of the rich science that is likely to be forthcoming from the AMS,” says AMS team member Eun-Suk Seo, a cosmic ray physicist at the University of Maryland in College Park. “The major strength of AMS is that it can precisely measure all these particles simultaneously with a single instrument,” she says.

Even so, many scientists doubted that AMS would ever fly. After the shuttle Columbia disintegrated on re-entry in 2003, the AMS was taken off the manifest for the remaining shuttle flights. Ting worked the halls of Congress and managed to get it restored.

Then last year, Ting decided to swap out the magnet at the heart of AMS with a smaller, less powerful one that had flown on a prototype mission in 1998. The reason: NASA and its international partners had decided to keep the space station running longer than previously thought, and coolants required to keep the larger magnet humming along would have run out in just a few years.

Now, the instrument 17 years in planning finally looks ready to go. At a news briefing the day before scheduled launch, Ting noted that the real value of the AMS may come not in what scientists think it will find, but in what it will find that they cannot dream of.

“To a scientist,” he said, “the most exciting goal is to probe the unknown — to search for phenomena which exist in nature, but we have not yet the tools or the imagination to find them.”