Thirty Meter
Telescope Passes Conceptual Design Review
(1 June 2006) The detailed design for
the Thirty Meter Telescope (TMT) developed by a U.S.-Canadian team is capable
of delivering on the full promise of its enormous light-collecting area,
according to the findings of an independent panel of
experts.
With the TMT, astronomers will be able to analyse the
light from the first stars born after the Big Bang, directly observe the
formation and evolution of galaxies, see planets around nearby stars, and make
observations that test fundamental laws of physics.
"The successful
completion of our Conceptual Design Review means that the TMT has a strong
science vision, good technical requirements, a thoroughly reviewed design and a
powerful team to carry our work forward," says Project Manager Gary
Sanders.
Now in detailed design, the TMT is a concept for the world's
largest telescope. It consists of a primary mirror with 738 individual
1.2-meter segments that span 30 meters in total, three times the effective
diameter of the current largest telescopes. All of the segments will be under
exquisite computer control so that they work together as a single
mirror.
The review panel evaluated all aspects of the project, including
its optical design, the telescope structure, science instrumentation, site
testing, management and cost estimate procedures. The panel was positive on
nearly all fronts and praised in particular the adaptive optics technology
being planned for the giant telescope.
Adaptive optics will allow the
TMT to reach the "diffraction limit," comparable to a telescope's resolution in
space. TMT project engineers are integrating this system with the designs for
the eight science instruments under detailed study, so the power of the
adaptive optics system should be available at the beginning of the telescope's
science operations in 2016, the external panel reported following the May 8-11
conceptual design review.
The baseline adaptive optics (AO) system for
TMT involves nine laser beams that are launched from a small telescope at the
peak of the structure that supports the telescope's secondary mirror. These
laser beams reflect off a layer of sodium gas high in Earth's upper atmosphere
to provide artificial points of light analogous to distant stars. These
point-like laser reflections drift and wobble just like the star light, giving
the AO system reference points to use anywhere in the sky as it compensates for
distortions of the star light by Earth's ever-changing atmosphere. This
technology has been pioneered at the Lick Observatory, the Gemini Observatory
8-meter telescopes and the Keck Observatory 10-meter telescopes.
TMT is
also studying the potential for an adaptive secondary mirror for the telescope.
This would involve covering the bottom of a flexible glass surface as large as
the primary mirror in many current telescopes (a concave hemisphere 3.6 meters
in diameter) with hundreds of tiny pistons to push and pull the surface of the
mirror in minute increments. A computer controls these movements many times per
second, as it works to adjust the mirror so it has the exact opposite shape of
the distortions in the incoming star light.
Much of the TMT's scientific
work will be done in the infrared, where the diffraction limit is easier to
attain, young stars and galaxies are to be found, and the opportunities for new
discoveries are abundant.
The eight scientific instruments in detailed
design for the TMT are huge in comparison to current-generation astronomical
instruments, and equivalently more complex. Each instrument is the size of
school bus or larger, and they rest on two platforms on either side of the
telescope that are each the size of a basketball court. The biggest technical
challenge among the instruments is the Planetary Formation Instrument, which
employs "extreme" adaptive optics in an effort to directly image other planets,
the board found.
The technical requirements for the telescope, its
structure, and its control system are clear and appropriate for this stage of
the project, the review board found.
"The panel's report is glowing in
its praise and confident that TMT is on track," says Richard Ellis of the
California Institute of Technology, one of the partners in the project. "We'll
decide in mid-2008 where to build the telescope and then start construction in
early 2009."
The TMT is a collaboration between the California Institute
of Technology, the University of California, the Association of Universities
for Research in Astronomy, Inc. (AURA) via the U.S. national observatory, and
the Association of Canadian Universities for Research in Astronomy (ACURA),
with significant work being done by industry and by university teams studying
instrument designs.
Canadians welcome the external panel's endorsement
of the depth and quality of the TMT design work. "We look forward to supplying
the enclosure, telescope structure and adaptive optics system in time for first
science," says Ray Carlberg of the University of Toronto, the Canadian project
director for ACURA, an association of 24 Canadian universities in partnership
with the National Research Council of Canada.
The design and development
phase of the TMT project has a budget of US$ 64 million, including US$ 35
million in private sector contributions from the Gordon and Betty Moore
Foundation. The conceptual design review board found that the project is
estimating the cost of the TMT using up-to-date industry standards. A formal
cost review of the project is scheduled for September 2006.
The TMT
project is studying five sites in Chile, Hawaii and Mexico as possible
locations for the telescope. The project office is currently based in Pasadena,
CA, where the conceptual design review was held.
Edward Stone, chair of
the TMT Board of Directors and former director of NASA's Jet Propulsion
Laboratory, is available to answer media questions about the conceptual design
review and the status of this exciting project.
The TMT is designed to
meet the scientific goals of the Giant Segmented Mirror Telescope concept,
which was the highest priority ground-based project in the most recent
astronomy decadal survey conducted by the National Academy of Sciences,
published in 2000.
(source: Thirty Meter Telescope)
