Sam Ting is on a mission: find the other half of the universe.
- By Andrew Lawler
- Air & Space magazine, May 2001
(Page 4 of 5)
Ting and his small team closeted themselves for two months, putting together an extensive proposal for the AMS. To expand its scientific goals beyond just the search for primordial anti-matter, the team made room for experiments to look for evidence of dark matter, which likely makes up some 90 percent of all ordinary matter, and to investigate the origin of cosmic rays. For Ting, these bread-and-butter experiments had the benefit of winning over more conventional scientists. “I’m personally not very interested in this,” he admits.
After a series of formal reviews, the proposal won approval from independent panels of scientists. Many critics still grumble about the fast-track decision, saying it was politically motivated. AMS collaborators bristle at the claim, saying the program went through traditional peer review and is taking no money from other U.S. projects, as its funding comes mostly from European countries. The decision was, however, sobering news for the small cadre of astrophysicists conducting balloon-borne anti-matter searches. Ting’s project spelled the beginning of the end for those efforts, says Jonathan Ormes, who heads the high-energy astrophysics lab at NASA’s Goddard Space Flight Center in Maryland. It would be nearly impossible to compete with the AMS, with its more powerful magnet and far longer life.
NASA and Ting’s group also agreed to first conduct a test flight on the space shuttle. They wanted to be sure that the technology would work, that it would be safe, and that it was well tested. “I didn’t understand then how hostile the space environment is,” Ting admits. Most high-energy physics experiments work perfectly well in normal temperatures and atmospheric conditions, and can be easily modified if operators need to tweak the hardware. The AMS would be strapped to trusswork 250 miles in space, would be subjected to brutal sunlight and freezing shadow, and, once launched, would offer scientists only limited access to its systems.
So with no previous spaceflight experience, Ting set out to raise a team and the money to design, build, test, and fly the first experiment. The challenge sent the physicist on a frenetic round-the-world mission to lobby colleagues and their government ministers. The speed with which he worked astonished NASA managers, who can spend 15 years or more getting their projects from concept to orbit.
The instrument Ting’s team designed for the shuttle flight is a two-ton cylindrical magnet that is about three feet high and three feet in diameter at the core. The magnet creates a uniform field; a piece of matter entering the bore of the cylinder will bend one way, while oppositely charged anti-matter will bend another. Arranged like parallel shelves inside the bore hole are a series of highly sensitive detector plates that measure a particle’s speed, momentum, charge, and path. A system of counters sorts electrons from anti-protons, and another counter rejects those particles that leave or enter through the inner shell of the magnet, to rule out particles bouncing off the AMS itself. Colliding particles of dark matter—the invisible stuff whose presence physicists infer from its gravitational effect on the visible universe—also should produce telltale anti-protons, positrons, and gamma rays, and the AMS includes instruments to measure the spectrum of such particles. The same instruments can help characterize incoming cosmic ray particles. All data is transmitted directly to NASA’s Johnson Space Center, with no assistance from the astronauts.
Pulling all of these pieces together required help from more than a dozen countries. To produce the strong magnetic field he had in mind, Ting had to go to China, the primary source of a high-grade neodymium-iron-boron alloy favored for making powerful magnets. His fluent Chinese helped him win a quick endorsement from the Chinese Academy of Sciences, which agreed to build the magnet. He assembled a team of Germans, Italians, Finns, and Swiss to provide the silicon tracker plates, while German and Italian teams coordinated the design and construction of the counters. Engineers and scientists from more than half a dozen countries pitched in to provide electronics, software, and ground support systems.
The 1998 shuttle mission STS-91 proved a success, save for an annoying problem with downlinking data from orbit. Although the week-long test run did not find any evidence of primordial anti-matter, it did spot anti-protons, and all the instrument’s systems worked as planned. So Ting had a green light to build the second-generation instrument, which will be attached to the outside of the space station in 2003 for a three-year experi-
ment — long enough, he hopes, for a wayward anti-particle from an anti-star to find its way to his magnet.