IEEE Spectrum September, 2008 - 11

wE'rE LIsTEnIng: Forty-two radio dishes in
Hat creek, calif., will start listening for signs of
extraterrestrials this month.
photo: seth shostAK

Allen Telescope
Array Starts
Search for E.T.
radio telescope array will
seek out new life and new
civilizations

I

t'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
16

NA * Ieee Spectrum * September 2008

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?"
-Barry E. DiGregorio
www.SPEcTrUm.iEEE.orG
http://www.SPEcTrUm.iEEE.orG
Table of Contents for the Digital Edition of IEEE Spectrum September, 2008
