Technology for cosmic listening posts has application on Earth

LISTENING for a message from outer space takes faith, hope, and a lot of patience. The ``Great Discovery'' may not be made for many decades, if ever. Nevertheless, the Search for Extraterrestrial Intelligence (SETI), as its practitioners call it, pays current dividends. It provides excellent student training projects, especially in electrical engineering. Also, sophisticated equipment developed to tune in E.T. can have more mundane uses.

The new SETI signal-processing chip produced at Stanford University illustrates this well. It should be cheaper, easier to maintain, and use less power than the circuitry it will replace. It will enhance the ability of a SETI listening post to sort through cosmic radio noise. But it will also be useful in radar system analysis or in high quality processing of medical and satellite imagery. Graduate students who helped design the chip have learned important engineering skills.

``It's support for SETI. But it's also a strong academic program,''explains Stanford's SETI team leader Ivan Linscott.

Stanford's effort is part of a two-fold National Aeronautics and Space Administration (NASA) program. This will search the entire sky for suspicious signals. It will also pay particular attention to Sun-like stars within 75 light years of Earth. If Congress continues to fund it, NASA's All-Sky Survey and Targeted Survey will be the most extensive SETI program yet undertaken.

It's one thing to assume there may be alien civilizations communicating among stars and quite another to know where and how to intercept their signals. Scientists interested in this problem have had to find ways to narrow the search. The traditional strategy is to assume that the aliens use radio waves at frequencies where the natural radio noise is low - 1,000 to 10,000 megahertz (MHz).

Some SETI projects have further narrowed their target range by listening near certain natural frequencies. The favorite is the 1,420 MHz frequency of the radio noise emitted by cosmic hydrogen. This is a universal phenomenon that even a moderately technically advanced society probably would study for scientific purposes. A civilization trying to attract the attention of beings in another star system might broadcast near this frequency.

The most advanced SETI effort currently underway - Project META in Harvard, Mass. - follows this strategy. Supported by the Planetary Society, the Megachannel Extraterrestrial Assay - to use the project's full name - automatically and simultaneously monitors 8.4 million very narrow frequency bands near this so-called ``magic'' 1,420 MHz emission. It's like looking for a message near a prominent landmark. If an alien signal is tuned to any of the 8.4 million channels, META should eventually detect it as it slowly covers the part of the sky available from New England.

NASA's program is not restricted to such ``magic'' frequency regions. It intends to cover the entire range from 1,000 to 10,000 MHz. It would do this using a scanner that monitors 10 million channels, each 1 MHz wide, at a time. This is where the new Stanford chip comes in.

For technical reasons, the current signal processing circuitry being tested has a practical range of only 8 million channels. The new chip would allow engineers to reduce the number of circuit boards needed for the operating SETI system from 2,000 to only 78. At the same time, Linscott says, it should enable the signal processing system to work clearly on all 10 million channels. That's a significant improvement in signal processing at a cost that should be at least 75 percent less than that projected for the old system.

This is the kind of technical advance NASA has hoped to make in this early phase of the program. It's a low-key, low-budget preliminary phase that began in 1983. The plan has been to move into a more active 10-year program to build the working SETI hardware, install it at selected radio observatories, and carry out the search. That phase of the program is projected to cost $77 million spread over the 10 years beginning in 1988.

At this writing, it was unclear whether or not NASA will get the funding for a 1988 start. If funding is delayed, the SETI team will submit proposals again for fiscal 1989, Linscott says. Meanwhile, Stanford's roughly $500,000 a year share of the program has given NASA a useful new signal processor.

As a quest, SETI has a long time horizon. But as a research effort that provides educational opportunities and fosters new technology, it provides more immediate returns.

A Tuesday column. Robert C. Cowen is the Monitor's natural science editor.