Sam Ting walked into a meeting with PHYSICS TODAY last
month with an entourage of high-powered scientists from nuclear physics labs across Europe and
Asia. They were there to go to bat for the Alpha Magnetic Spectrometer (AMS), the experiment spearheaded
by Ting, an MIT particle physicist. Despite the AMS being NASA's main science justification for
completing the International Space Station (ISS), the agency announced in February that it has
put the experiment's flight on the chopping block.
By detecting high-energy charged cosmic
rays in space, the AMS might discover unknown pulsars and x-ray sources and observe dark matter
(see PHYSICS TODAY, February 2003, page 30). Above all, it might solve the CP violation
problem: Where is the universe's antimatter? "No one has ever measured primordial antimatter. . . . It
would be another Nobel Prize for Sam Ting," says Giovanni Bignami, the newly nominated president
of the Italian Space Agency (see the story on page 28). "No matter how large an accelerator you make,
you are never going to reach the same high energies as you get with cosmic rays," says Ting, adding
that it's impossible to know what the AMS might discover. "Nearly every major science experiment,
such as the Hubble Space Telescope [HST] or the Tevatron at Fermilab, found major
unexpected discoveries that the machines were not originally designed to study."
A long campaign
Ting first proposed the AMS in the early
1990s, when the US physics community was still reeling from the cancellation of the Superconducting
Super Collider. He persuaded the Department of Energy's Office of Science to support the experiment,
and NASA to ferry the AMS to the ISS and to provide power and communications. CERN agreed to provide
free assembly space and logistics support. Some 16 countries—including both China and Taiwan—signed
on, and 95% of the experiment's $1.5 billion construction costs were paid by space agencies, national
funding agencies, and universities from across Europe and Asia. The DOE provided $30 million.
So far NASA has invested $55 million, mainly toward building a transport cradle for the space shuttle.
In 1998 a 10-day flight
of a prototype proved that one could isolate the powerful magnets in the detector from interference
of Earth's magnetic field, which is vital for detecting charged cosmic rays. The test flight also
discovered helium fluxes in the magnetosphere that behave in ways not predicted by cosmic-ray
models, says Ting. The prototype used permanent ferromagnets; the final version has liquid-helium-cooled
superconducting magnets. Once assembled, the AMS will also have four times as many detectors as
the prototype and incorporate recent advances to shrink the detector—with its more than 300 000 detection channels—to only a 3-meter cube. "The detector is complex even by terrestrial
standards," says Switzerland's AMS team leader, Maurice Bourquin, former rector of the University
of Geneva.
A DOE review last year concluded that
the justification for continuing with the project was undeniable. "Plans should be made to place
[the AMS] onto the space station, in order for it to carry out its promising science," the review
says. "I recognize that NASA has shifted priority to Moon–Mars, but that doesn't justify
walking away from flying this already built, expensive, and beautiful device," says Caltech's
Barry Barish, who chaired the review. "I know of no other missions that are proposed to do this science."
NASA first warned in September 2005
that it might not fly the AMS. Following the Columbia accident in January 2003, the number
of shuttle flights was curtailed. The shuttle is scheduled for retirement in 2010, and NASA has
tagged the remaining flights for completing the ISS and sending a service mission to the HST
(see PHYSICS TODAY, December 2006, page 33).
Late in 2005, NASA started
feasibility studies for alternatives to sending the AMS to the ISS by shuttle. One possibility
would be to use a US or Japanese rocket to launch the AMS in parallel with a shuttle launch. After dropping
supplies off at the ISS, the shuttle would pick up the AMS and deliver it to the station. This proposal,
however, is running against the clock. NASA would have to start work immediately to be able to launch
the AMS at the time of the last two shuttle flights, and it hasn't got the money, says Mark Sistilli,
the NASA AMS project manager. Nonetheless, he insists, "We fully expect to receive AMS in December
2008 and get it ready for flight."
Another option would be
to fly the AMS directly to the Russian module on ISS on a European or
Japanese rocket. Technically, such a mission is possible, says Sistilli; however, "all of the
hypothetical non-US launch options would require major additional funding that does not exist
in the NASA FY 2008 budget . . . and the Russian docking equipment would
not come for free." The alternatives to sending the AMS to the ISS on the shuttle would add an estimated
$380 million to $1 billion to the experiment's price tag.
Failure to fly the AMS would
remove the only US-led major experimental apparatus planned for the ISS, about which congressional
representatives are being privately briefed. And Ting and his entourage are not giving up. "The
US government has an obligation to the international partners to find a way to fly AMS," says Ting.
"In addition to the sheer
waste of effort and money, the damage to international collaboration in science will be the real
legacy of [pulling out of the AMS]," says Barish. "Ting's international collaboration includes
respected strong laboratories from around the world, and I hate to contemplate what they must now
think of the US government and NASA."
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