First North American antenna enables next phase in ALMA Observatory

February 9, 2009
The formal acceptance of the first North American antenna by the Joint Atacama Large Millimeter/submillimeter Array (ALMA) Observatory was celebrated February 6 by astronomers. ALMA is a gathering armada of short-wavelength radio telescopes whose combined power will enable astronomers to probe with unprecedented sharpness phenomena and regions that are beyond the reach of visible-light telescopes. The observatory is being assembled high in the Chilean Andes by a global partnership.

The 39-foot-diamater (12-meter) antenna delivered February 6 is the first of 25 being provided by North America's ALMA partners, whose efforts are led by the National Radio Astronomy Observatory (NRAO) and supported by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada and the National Science Council of Taiwan. The antenna was manufactured by General Dynamics SATCOM Technologies.

The acceptance comes just weeks after the first ALMA antenna, produced under the direction of the National Astronomical Observatory of Japan on behalf of ALMA's East Asian partners, was handed over to the observatory.

"These ALMA antennas are technological marvels," said Thijs de Graauw, ALMA director. "They are more precise and more capable than any ever made. Their performance in the harsh winds and temperatures of our high-altitude site bodes well for the observatory's future."

A single 39-foot (12-meter) antenna's dish is bigger than the largest optical telescope's reflective mirror, but to match the sharpness achieved by an optical telescope, a millimeter-wavelength dish would have to be impossibly large, miles across. ALMA will combine signals from dozens of antennas spread across miles of desert to synthesize the effective sharpness of such a single, gigantic antenna. The process involves analysis of the ways in which the signals coming from each antenna interfere with one another - called interferometry.

"This is a major milestone for the ALMA project. With two antennas now on site, we begin the real work of combining signals from them. We are advancing toward ALMA's ultimate goal of surpassing by tenfold existing technology in this area," said Philip Puxley, the NSF's ALMA program manager.

ALMA officials expect the pace of antenna acceptance to accelerate. "We have nine (North American) antennas on site already," said Adrian Russell, NRAO's ALMA project director, "and following handover of number three, we plan to get one through the test procedure each month. Additional North American antennas will be arriving in Chile at a rate of one every two months, and General Dynamics is on track to complete delivery of these systems within days of the original schedule."

When completed early next decade, ALMA will have a total of 66 antennas (with the option of further expansion) provided by partners in North America, Europe, and East Asia. The first European antennas, produced under the auspices of the European Organization for Astronomical Research in the Southern Hemisphere (ESO) are scheduled to begin arriving early this year.

The ALMA Project is a partnership between the scientific communities of East Asia, Europe, and North America with Chile.