IT tackles cosmic questions

The National Radio Astronomy Observatory uses telecommunications technology to explore the universe.

The National Radio Astronomy Observatory (NRAO) has tapped the enormous data-handling capabilities of off-the-shelf fiber-optic gear to help it peer through the universe and capture signals from the beginning of time. A $150 million upgrade to the NRAO's Very Large Array (VLA) radio telescope in southern New Mexico will be based on the same technology used by telephone networks.

Once the upgrade is complete, the VLA will be called the Expanded VLA, or EVLA. To process the flood of data that will come from the fiber-optic network, the NRAO is developing what EVLA project scientist Richard Perley calls a "godlike" supercomputer, known as a correlator, which will be built using commercial computer chips.

The VLA, located on the Plains of San Agustin 50 miles west of the NRAO's operations center in Socorro, N.M., consists of 27 radio telescope dishes -- each measuring 82 ft. in diameter and weighing 230 tons -- that scan radio emissions from distant stars and galaxies and can "see" galactic objects undetectable by even the best optical telescopes, according to Perley.

Radio telescopes probe the universe by collecting naturally emitted radio waves from celestial objects, running them through a computer processor and then using the specific radio frequencies emitted by each object to produce an image, according to Dave Finley, a spokesman for the NRAO, which is operated by Washington-based nonprofit Associated Universities Inc. for the National Science Foundation.

When the NRAO built the VLA in the 1970s, it used the best technology available at the time -- hollow metal tubes called waveguides -- to transmit signals from the antennas to a processor.

But analog technology limited the VLA to sampling no more than 512 spectral channels from atoms and molecules in distant galaxies. The EVLA will be able to sample and process 4 million channels, Perley says.

The ability to tune across a broader frequency range is important, Perley explained, "because the further you go back [in time], you go lower in frequency." The EVLA will be able to detect galactic emissions in a frequency range from 200 MHz to 50 GHz, whereas the current VLA covers only about 25% of that range at any one time.

The VLA consists of three arms, each 13 miles long and containing 24 telescope pads, arranged in a Y-shaped pattern. Every four months, the NRAO shifts the 27 telescope dishes among the 72 telescope pads.

By rearranging the antennas -- done with a special rail transporter that moves the massive dishes from pad to pad -- the NRAO can change the focus of the array, much like using a zoom lens in a camera, according to Finley.

Each pad requires a network connection -- analog waveguide today, fiber-optic tomorrow. To serve the 72 pads, the NRAO has started to install a fiber network that will provide a dozen 10Gbit circuits per antenna, adding up to 3.2Tbit of total network capacity, according to Steve Durand, head of the NRAO's electronics division.

Miles of Fiber

The EVLA will require a fiber network that's 2,759 miles long, roughly the distance from Los Angeles to Washington, said Durand.

Durand says the EVLA fiber network is based on existing wave division multiplexing fiber-optic technologies, so he was able to build the system with standard, off-the-shelf optical multiplexers from companies like JDS Uniphase Corp. in San Jose and Applied Micro Circuits Corp. in San Diego.

"We're going to be on the cutting edge of astronomy by capitalizing on advances in the telecommunications industry," Durand says.

Perley says that the NRAO tapped the National Research Council of Canada's Dominion Radio Astrophysical Observatory (DRAO) in Penticton, British Columbia, to design and build the EVLA correlator. The council also funded the $16 million cost of the correlator, which its designer, DRAO engineer Brent Carlson, calls the largest single-purpose supercomputer in the world.

Steve Ellingson, an astronomy engineer at Ohio State University in Columbus, cautions that the EVLA can't be compared with general-purpose supercomputers that can be programmed to perform multiple tasks. The EVLA correlator is a "quite specialized" digital signal processor, he says, "and it's not fair to compare it to a programmable supercomputer."

The correlator system, which the NRAO will build in Canada and then install at the VLA site in 2007, will include 20,000 commercial field-programmable gate-array chips. It will also include 10,000 custom chips designed by the NRAO, each with 3 million gates, Carlson added.

The correlator will send the EVLA's signals to a Beowulf cluster of 64 PCs for further processing, and that cluster's output will be sent to an image-processing system being developed by the NRAO, with all connections via Gigabit Ethernet, Durand says. Storage will be on a constantly expanding RAID system, with access to the data by astronomers through an Internet-based "virtual" observation system, Carlson says.

EVLA project manager Peter Napier says the new array will "provide us with 10 times the resolution and sensitivity" of the current array. This in turn will allow the NRAO "to see through the dust" of space and eventually help the NRAO "resolve the evolution of the universe," he says.

Copyright © 2003 IDG Communications, Inc.

  
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