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Three prototype radio dishes
Three prototype radio dishes now in place at Hat Creek Observatory in northern California. Eventually, 350 of these 6.1-meter-diameter dishes will be assembled to form the Allen Telescope Array, the largest radio array in the world. (Radio Astronomy Laboratory)

UC Berkeley, SETI Institute ready to build first phase of Allen Telescope Array

– After more than three years of design, development and testing of a radically new kind of radio telescope, astronomers at the University of California, Berkeley, and the SETI Institute are ready to build the first 32 dishes of the Allen Telescope Array (ATA). This array will eventually consist of 350 radio dishes dedicated to galactic and extragalactic astronomy and the search for intelligent signals from space.

 animation of the ATA 32 array
View a simulated movie of the planned dish array (Notice: 65.6Mb AVI file)

The construction of the 32-dish array, known as the ATA 32, will be funded by investor and philanthropist Paul G. Allen, who on March 18 committed $13.5 million to this initial phase and an expanded, 206-dish array, contingent on the SETI Institute and UC Berkeley raising another $16 million. Allen already contributed $11.5 million over the past three years to research and development, along with a $1 million gift from former Microsoft Chief Technology Officer Nathan P. Myhrvold.

The array will be built at Hat Creek, a UC Berkeley radio observatory site 290 miles northeast of San Francisco.

"I am very excited to be supporting one of the world's most visionary efforts to seek basic answers to some of the fundamental questions about our universe and what other civilizations may exist elsewhere," said Allen, co-founder with Bill Gates of Microsoft Corp. in 1976.

"I am a big proponent of leveraging revolutionary technology and design and applying it to important problems in science. The developments taking place with this new instrument will not only enable us to realize a lot of bang for our research and development buck, but it will also change the landscape of how telescopes will be built in the future."

Allen said that an instrument of this magnitude, which will "result in the expansion of our understanding of how the universe was formed, and how it has evolved, and our place therein," is a powerful enough reason for him to be a primary supporter of its development, design and construction.

According to Leo Blitz, professor of astronomy at UC Berkeley and director of the Radio Astronomy Laboratory, the Allen gift and monies provided by the SETI Institute Board of Trustees and the National Science Foundation should enable the ATA 32 to begin scientific investigations by the end of 2004. Because the telescope design is scalable, the ATA 32 will be able to conduct studies similar to those planned for the final ATA 350, though with less sensitivity and lower resolution.

"We're designing and building a uniquely profound instrument for doing radio astronomy," Blitz said. "The ATA will revolutionize radio astronomy, making it possible to provide answers to the two biggest questions in astronomy: How did we get here? and Are we alone?"

"The ATA's ability to make radio images over large swaths of sky, to make measurements over a uniquely large range of radio wavelengths, its ability to do several kinds of observations at once, provide a power and flexibility that will allow astronomers to address whole areas of astronomy that are currently inaccessible," Blitz. said. "Because of the telescope's unique capabilities, I expect that we'll discover things we don't even know are out there."

The telescope will have unprecedented sensitivity over a large range of wavelengths centered in the centimeter radio band, spanning the equivalent of about four and a half octaves, whereas most radio telescopes span less than half an octave and optical telescopes span perhaps one or two. The wavelength range stretches from 2 to 50 centimeters, including the important 21.1-centimeter radio emissions of cold hydrogen that have allowed astronomers to map the Milky Way galaxy's spiral arms.

"We will be able to survey the entire sky every night to find out what's going on in the transient sky," Blitz added. "We can look for cosmic explosions that go off all the time to learn about the feeding of black holes and the relationship between supernovas and gamma-ray bursts."

As astronomers use the ATA to study galaxies, dust clouds or black holes, others will be analyzing the radio signals for patterns that indicate they came from intelligent civilizations far, far away.

"I am eager to begin observing on the ATA," said astronomer Jill C. Tarter, ATA project leader and director of the Center for SETI Research at the institute. (SETI is short for Search for Extraterrestrial Intelligence.) "Conducting observations 24/7 is a dream come true for any astronomer, and it is particularly exciting for the institute's astronomers, who have been constrained by limited time on other large centimeter-wavelength telescopes. Finally, our tools are becoming commensurate with the size of our task."

The telescope also will be a testbed for technologies that could be used in a more ambitious telescope called the square kilometer array (SKA), a priority this decade of the international radio astronomy community. A hundred times larger than the completed 350-dish ATA, the SKA would have a collecting area 30 times larger than any telescope every built.

One of the first tasks of the ATA 32, Blitz said, will be to search for the spectral signature of atomic deuterium, a heavy form of hydrogen that was most abundant about 10 minutes after the Big Bang that engendered the universe. Mapping atomic deuterium across the sky will tell about the density of the universe shortly after its birth 13 billion years ago.

"This will be an important and independent check on the validity of theories of the Big Bang," he said.

For these observations, the telescope will have to observe at one-meter wavelengths, where it is somewhat less sensitive but still good enough to do new science.

The project was first conceived in 1999 by UC Berkeley and SETI Institute astronomers, and in 2000, the team installed a seven-telescope prototype near the UC Berkeley campus to test the idea and determine how well they could minimize interference. In August 2000, after successful tests, Allen and Myhrvold announced their initial gifts. Since then, engineers and astronomers working on the telescope design have had many obstacles to overcome to make the hardware sensitive enough, sturdy enough and cheap enough to equip 350 identical radio dishes.

The initial idea of using off-the-shelf satellite TV dishes was the first to fall by the wayside, when they were found to pick up too much noise from their surroundings. Instead, special 6.1-meter diameter dishes will be cast by Anderson Manufacturing of Idaho Falls, Idaho. Given their size, only 350 telescopes will be needed instead of the initial estimate of 500-1,000 to achieve a 10,000-square-meter collecting area.

The first three dishes were delivered in June 2002 to Hat Creek, the site of an existing nine-dish radio array called the Berkeley-Illinois-Maryland-Association (BIMA) Array. The BIMA telescopes will be removed in September and trucked to the Inyo Mountains near Big Pine, Calif., to merge with a Caltech array to form a 15-dish Combined Array for Research in Millimeter-wave Astronomy (CARMA).

Because the detector on each ATA telescope must be cooled to liquid nitrogen temperatures (320 degrees below zero Fahrenheit) to minimize thermal noise, telescope engineers had to find a way to make cryogenic coolers much cheaper than the $1 million-per-cooler cost on the open market.

"We had a talented engineer who thought he could make a highly reliable, small, compact and self-contained cooler for a few thousand dollars each," Blitz said. He succeeded in bringing the cost down to between $5,000 and $10,000 each, in the process developing a new patented technology that could soon lead to improved refrigerators.

Other engineers developed an inexpensive but beefy and reliable drive system that points the telescope with a precision that is more than sufficient for their needs, a novel feed system that converts radio waves to electrical signals, and the unique electronic circuits that connect the many telescopes together and allow them to operate as an interferometer. The electronics are built to allow easy upgrades to keep up with the continual improvement in microprocessor speed.

Thanks to these engineering breakthroughs, the team has reduced the cost of a single telescope to about $80,000. The combined cost of 350 dishes - $28 million - is only 20-25 percent the cost of a single large radio telescope with the same collecting area.

With most of the engineering challenges solved, new telescopes will soon be ordered so that the full 32-dish array can be erected and connected during the summer.

"It is especially thrilling to see the Allen Telescope Array approach its first significant milestone," said SETI Institute CEO Tom Pierson. "We are grateful for the additional support from the Allen Foundation that is making this new facility - and further discovery - possible. Mr. Allen and his foundation have set the bar high. Mr. Allen's support of this worthwhile project, when matched by other supporters of radio astronomy and SETI, will quickly bring this project to fruition."

When the 350-dish array is completed in 2007, the ATA will be among the world's largest and fastest observing instruments, Blitz said. Though the 73,000-square-meter Arecibo dish in Puerto Rico - the largest radio telescope in the world - has a collecting area seven times larger than the planned ATA 350, it will not have as large an observing window as the ATA.

"At any one time, we'll be able to look at a patch of sky 2,500 times bigger than the Arecibo dish today, and for a longer period of time than possible at Arecibo," he said.

Blitz notes that the array can be expanded beyond 350 dishes, though the complexity of the electronics and the cost go up geometrically.

"Hat Creek is really the right place to build this telescope, because you could increase the resolution and sensitivity by adding more telescopes," he said.

And many people see the ATA as the prototype for the planned square kilometer array.

"If the SKA is built on the ATA concept," Blitz said, "it might make sense to build an intermediate size telescope at Hat Creek of up to 1,400 dishes to demonstrate that it works, before building a super-telescope."