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U.S. Department of Energy review panel last week gave a glowing
endorsement for the Stanford Linear Accelerator Center (SLAC)-led project to create the world’s largest
digital camera, which will enable a new telescope being built on a
Chilean mountaintop to investigate key astronomical questions ranging
from dark matter and dark energy to near-Earth asteroids.
After
two and a half days of presentations and meetings at SLAC, the panel of
19 experts recommended that the 3.2 gigapixel (billion pixel) camera
for the Large Synoptic Survey Telescope receive Critical Decision-1 status,
the DOE’s project-management milestone that defines a large project’s
approach and funding for achieving a specific scientific mission.
The
camera, which will be built at SLAC, is expected to cost about one
third of the nearly $500 million price tag for the new telescope, which
is being borne by the DOE and the National Science Foundation, as well
as several public and private organizations in the United States and
abroad.
“The
LSST Camera Project team is experienced and has demonstrated a good
working relationship,” said Kurt Fisher, DOE/SC Review Chairperson from
DOE’s Office of Project Assessment. “The initial, plenary presentations
were impressive, and the team was well-prepared for the review.”
Actual
CD-1 status will not be officially conferred until higher DOE
management reviews the panel’s report, but the experts’ positive
comments had LSST managers very optimistic. “Congratulations! You’ve
reached a very important milestone on the road to becoming real,” said
Fred Borcherding, DOE’s LSST program manager, after the review panel had
presented their findings and recommendations at the review’s final
session.
“This
was an incredibly professional review,” said Steven Kahn, lead
scientist on SLAC’s camera project and deputy director of the overall
LSST effort. “We learned a lot and will take the panel’s recommendations
very seriously as we move forward.” More than 100 people (about 30
full-time equivalents) from four DOE laboratories, nine universities and
one foreign organization are working on the camera project.
The
LSST design is driven by four main science themes: probing dark energy
and dark matter, taking an inventory of the solar system, exploring the
transient optical sky and mapping the Milky Way.
Sporting
an 8.4-m diameter primary mirror, the LSST will be a large, wide-field
ground-based telescope designed to provide time-lapse 3-D maps of the
universe with unprecedented depth and detail. Of particular interest for
cosmology and fundamental physics, these maps can be used to locate the
mysterious dark matter, which many scientists think constitutes more
than 80% of all matter in the universe, and to characterize the
properties of the even more mysterious dark energy, which is driving the
accelerating expansion of the universe.
The
LSST will also create a detailed map of the Milky Way and a
comprehensive census of our solar system and open a movie-like window on
objects that change or move rapidly: exploding supernovae, potentially
hazardous near-Earth asteroids and distant Kuiper Belt Objects. A new
telescope is needed because no existing space- or ground-based
instrument has, or can be economically modified to provide, the
capabilities that LSST’s science mission requires.
“The
speed at which a telescope can survey the sky is proportional to both
the size of its mirror and the field of view of its camera,” said Nadine
Kurita, SLAC Camera Project manager. “While a telescope in space can
take pictures at a finer level of detail because it’s not looking
through a turbulent atmosphere, it would necessarily be much smaller
than LSST, and thus could not possibly provide such an extensive
survey.”
Each
night, the LSST will take more than 800 wide-field 15-second exposures,
each covering 49 times more sky area than the moon. It will photograph
the entire visible sky twice a week. Although it will weigh 650 tons
(including 60 tons of optical components), the LSST will be nimble
enough to move between its image-aiming points in just five seconds.
Since
2001, the LSST has been ranked highly by a dozen national advisory
committees, most recently last year’s National Academy of
Sciences/National Research Council’s “New Worlds, New Horizons” decadal review, which said it was the highest-priority large ground-based telescope for the coming decade.
In
2003, the non-profit LSST Corporation was set up in Tucson, Ariz., to
raise private and agency funding and to manage the collaboration, which
now includes 35 institutions, universities and national labs from around
the world.
DOE
approved the camera’s mission need (CD-0) in June. Future milestones
include CD-2 (baseline design approved), CD-3 (construction start), and
CD-4 (construction finished; full operation begins).
While
SLAC is the lead organization for the LSST camera, the National Optical
Astronomy Observatory will provide the telescope and site team, the
National Center for Supercomputing Applications will construct and test
the archive and data access center, and the Association of Universities
for Research in Astronomy is responsible for overseeing the LSST
construction. Work on the telescope and its site atop Cerro Pachón in
northern Chile is already under way.
At
the heart of the 3.2-gigapixel LSST camera—and its most critical
components—are its 189 sensors, light-sensitive semiconductor chips far
more sophisticated than those used in commercial digital cameras.
“We’re
going to be looking at light that’s 100 million times fainter than the
human eye can see,” said Paul O’Connor, the Brookhaven National
Laboratory scientist in charge of the camera’s sensor subsystem. “The
LSST telescope has enough resolving power to distinguish the images of
two stars separated by the equivalent of a pair of car headlights seen
at a distance of 400 miles. We designed our charge-coupled device (CCD)
chips to record these images with unparalleled clarity while using the
minimum silicon area, cost and power.”
The
LSST sensors are designed to respond to a range of light—ultraviolet,
visible and infrared—that is much broader than commercial CCDs, and must
also be extremely flat so the entire image will be in perfect focus.
Moreover, to move all the image data off the chip in just two
seconds—rather than the several minutes typical of astronomical
images—every sensor is divided into 16 data sectors, each with its own
output channel. Each night the LSST will produce more than 15 TB of raw
astronomical data. Over its 10-year operating lifetime, the LSST will
produce the world’s largest public data set: a 22-petabyte database
catalog and a 100-PB image archive.
LSST
has been designed as a public facility from the beginning, with deep
color imaging and multi-dimensional data products made available quickly
over the Internet. Supercomputers will continuously transform LSST
imaging data into a revolutionary four-dimensional space-time landscape
of color and motion, offering exciting possibilities for exploration and
discovery by curious minds of all ages. Anyone with a computer will be
able to fly through the universe, zooming past objects a hundred million
times fainter than can be observed with the unaided eye.
LSST’s
results may well be much more significant than just learning about the
cosmos, O’Connor said:“I think finding the source of dark energy may
have long term impacts with the potential to transform society—just like
the fundamental discoveries in electromagnetism and atomic physics have
done in producing the technologies we take for granted today.”
Large Synoptic Survey Telescope site
National Optical Astronomy Observatory
