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NSF Grant Accelerates Development for One of World's Most Powerful Telescopes; Test Bed Being Built at UArizona
By Lisa Padilla - Friday Sep 18, 2020
The GMTO Corporation has received a $17.5 million grant from the National Science Foundation to accelerate the prototyping and testing of some of the most powerful optical and infrared technologies ever engineered. The grant will, in part, support the development of a test bed at the University of Arizona.

These crucial advancements for the Giant Magellan Telescope at the Las Campanas Observatory in Chile will allow astronomers to see farther into space with more detail than any other optical telescope before. The NSF grant positions the GMT to be one of the first in a new generation of large telescopes, approximately three times the size of any ground-based optical telescope built to date.

The University of Arizona is heavily involved in making GMT a reality. Not only are the telescope's primary mirrors all manufactured and tested at the Richard F. Caris Mirror Lab, which is part of UArizona Steward Observatory, but various research groups across campus are tackling key challenges in creating a "discovery machine" of unprecedented design and capability.

One of the great challenges of engineering revolutionary technologies is constructing them to operate at optimal performance. The Giant Magellan Telescope is designed to have a resolving power 10 times greater than the Hubble Space Telescope — one of the most productive scientific achievements in the history of astronomy. This advancement in image quality is a prerequisite for the GMT to fully realize its scientific potential and expand our knowledge of the universe.

"Image quality on any telescope starts with the primary mirror," said James Fanson, project manager of GMTO. "The Giant Magellan Telescope's primary mirror comprises seven 8.4-meter mirror segments. To achieve diffraction-limited imaging, we have to be able to phase these primary mirror segments so that they behave as one monolithic 25-meter diameter mirror. Once phased, the team must then correct for Earth's turbulent atmospheric distortion."

Phasing involves precisely aligning a telescope's segmented mirrors and other optical components so that they work in unison to produce crisp images of deep space. Achieving this with seven of the world's largest mirrors ever built is no easy task. The immense size of the GMT's primary mirror requires a powerful adaptive optics system to correct for the blurring effects of the Earth's atmospheric turbulence at kiloHertz speeds. In other words, astronomers need to take the subtle "twinkle" out of the stars in order to capture high-resolution data from celestial objects thousands of light-years from our planet.

The NSF grant will allow the GMT to build two phasing test beds where astro-engineers demonstrate, in a controlled laboratory setting, that its core designs will work to align and phase the telescope's seven mirror segments with the required precision to achieve diffraction-limited imaging at first light in 2029.

This includes a full-scale prototype of the primary mirror support and control system that delivers active optical control. The test beds will be developed at the University of Arizona’s Center for Astronomical Adaptive Optics, or CAAO, and the Smithsonian Astrophysical Observatory, while actuator testing and integration of the primary mirror support will be developed at Texas A&M University.

UArizona researchers have been busy building a test bed that essentially consists of a miniature-sized stand-in for the GMT's seven-piece primary mirror and a special optical sensor that can detect whether or not all mirror segments are perfectly aligned. This test bed specializes in a narrow field of view that will allow the GMT to directly image faint alien planets far outside our own solar system.

"We have to make sure that phasing and adaptive optics will work together seamlessly," said Alex Hedglen, a doctoral student in UArizona's James C. Wyant College of Optical Sciences who is involved in the project.

"To accomplish this, our team has been tasked with building a complex test bed mimicking the seven primary mirror segments, to trick our existing MagAO-X Adaptive Optics system into thinking it is working at the actual GMT telescope," said Laird Close, astronomy professor at Steward Observatory. "We are confident that we can meet this phasing and adaptive optics challenge; there are few different engineering paths to achieve this, and our CAAO test bed will allow us to pick the best one for use at the real GMT."

The UArizona test bed will inform astronomers how to use the GMT's high-fidelity adaptive mirrors and other revolutionary adaptive optics technologies to detect faint biosignatures from distant exoplanets — one of the GMT's primary scientific goals.

"Based on our computer simulations, we are optimistic that our approach will work," said Jared Males, assistant astronomer at Steward Observatory, "but we need to demonstrate phasing control on actual hardware."

The GMT and the Thirty Meter Telescope are a part of the U.S. Extremely Large Telescope Program, a joint initiative with NSF's National Optical-Infrared Astronomy Research Laboratory to provide superior observing access to the entire sky as never before. Upon completion of each telescope, U.S. scientists and international partners will be able to take advantage of the program's two pioneering telescopes to carry out transformational research that answers some of humanity's most pressing questions, such as are we alone in the universe and where did we come from.

"We are honored to receive our first NSF grant," said Robert Shelton, president of GMTO and former president of the University of Arizona. "It is a giant step toward realizing the GMT's scientific goals and the profound impact the GMT will have on the future of human knowledge."

This work is part of a larger $23 million joint award to the Association of Universities for Research in Astronomy and the GMT over the next three years. The GMT project is the work of a distinguished international consortium of leading universities and science institutions.


Contributed by University of Arizona