It's smaller than originally hoped for, but with 42 radio antennas the Allen Telescope Array, or ATA, is the most advanced structure ever built to look for signs of extraterrestrial intelligence. Following technical delays and cost overruns that left it well short of its planned size, the array is expected to begin its mission full-time this month. It began performing radio astronomy last year but wasn't ready to look for artificial radio signals until now.
”We are doing final calibration, testing, and repairs and expect to begin with the first SETI program by about September 1,” Leo Blitz, director of ATA and the Radio Astronomy Laboratory at the University of California, Berkeley, told IEEE Spectrum .
Thanks in part to a gift of US $25 million from Microsoft Corp. cofounder Paul Allen, the SETI Institute (for Search for Extraterrestrial Intelligence) will have its own powerful observatory to search the skies, rather than having to comb through data gathered from other telescopes' observations. The ATA, nestled in a remote volcanic valley about 460 kilometers northeast of San Francisco, will be the first privately funded major radio telescope observatory. However, the original array plan called for 350 dishes. ”The technical challenges wound up significantly adding to costs and producing delays. Building up to a 350-element array depends on getting enough financing to finish it,” says Blitz. ”We need another $45 million, so checks are welcome.”
The original plan called for the purchase of inexpensive 6-meter radio dishes from a commercial product line, but these picked up too much background interference. So the ATA had to go with a more expensive, custom-built design. In addition, the array requires a pointing and tracking system with much greater accuracy than what commercial systems are capable of. So the designers had to invent a new system from scratch, adding to the delays and costs.
The resolution of a radio telescope is proportional to the size of the dish, but if many smaller, cheaper ones are electronically linked, they will have the same resolution as a single large dish. This works because a system called a correlator tracks the differences between the phases of radio waves as they reach the various dishes. This phase information can then be used to construct the same kind of radio image that a single, larger radio dish would provide. From each of the antennas, a broadband feed collects signals over the range of 0.5 to 11.2 gigahertz. The signal from the sky is then amplified over the entire frequency band, encoded onto a laser, and sent over an optical fiber to the control room, where it is digitized and processed.
”The unique aspect is that ATA will be able to conduct radio astronomy and SETI at the same time,” says Blitz. The array's amplification system allows the signals to be split into four independent frequencies, and all four can be analyzed at once—usually two for astronomy and two for SETI.
Seth Shostak, senior astronomer at the SETI Institute, says the first signals they will look for are ”in a large area in the general direction of the center of the Milky Way, to see if there are any ’supertransmitters' sending out signals from advanced civilizations.” Shostak predicts that with the ATA, the first signals from an advanced civilization could be detected within the next 25 years.
”I think that most astronomers believe that there must be intelligent life somewhere out there,” says Arpad Szomoru, head of technical operations and R&D for the Joint Institute for Very Long Baseline Interferometry in Europe, which recently electronically linked radio telescopes around the world [see ”Earth-Size Radio Telescope Opens Its Eye,” IEEE Spectrum, August 2008]. ”Whether SETI has a chance of detecting this is unclear, but as technology advances and instrumentation becomes more sensitive, who knows?”