Giant Magellan Telescope begins primary mirror support system testing

16 Oct 2024

World’s largest optical mirror successfully installed on support system prototype for the first time to validate telescope’s extraordinary performance.

The team behind the Giant Magellan Telescope (GMT) has this week announced the successful installation of one of its completed 8.4-meter-diameter primary mirrors into a support system prototype at the University of Arizona’s Richard F. Caris Mirror Lab.

This sophisticated system — comparable in size to half a basketball court and containing three times the number of parts of a typical car — is vital to the telescope’s optical performance and precision control.

The GMT statement said, “This milestone marks the start of a six-month optical testing phase to demonstrate that the support system can control the mirror as required, validating the revolutionary capabilities of the telescope’s primary light-collecting surface.”

The Giant Magellan’s 368-m²light-collecting surface is composed of seven of the world’s largest optical mirrors arranged in a flower pattern. Together, they will provide the highest image resolution over the widest field of view ever achieved for the exploration of the Universe, delivering up to 200 times the power of today’s best telescopes.

Each primary mirror weighs 17 tons and is supported by a specialized pneumatic support system which is housed in a steel weldment, or “cell.” This system works with nanometer precision, and is designed to adjust the mirror’s position, stabilize its temperature, protect it from seismic activity, and maintain its precise shape by mitigating mirror sagging from gravity as the telescope moves.

The system controls the combined seven primary mirrors to act as a single light-collecting surface, creating the optimal conditions for peak optical performance during scientific observations.

“This work is funded by a National Science Foundation award,” said Barbara Fischer, Primary Mirror Subsystem Manager for the Giant Magellan Telescope. “We began integrating the active support prototype system more than three years ago, and we first used a steel mirror mass simulator to demonstrate that our design was able to safely support and control the completed primary mirror segments.”

While the actual installation of the mirror into the cell took only one day, the process began with four weeks of disassembly to prepare the cell and support system for transport. The system was then moved 20 miles from the University of Arizona’s Tech Park to the Richard F. Caris Mirror Lab for reassembly. This logistically complex operation occurred a few hours after midnight to minimize traffic disruptions, as the wide-load cell required two road lanes for transport.

‘First of its kind’

“The Giant Magellan Telescope’s primary mirror active support system is the first of its kind,” said Trupti Ranka, Principal Opto-Mechanical Control Systems Engineer for the Giant Magellan Telescope.

“The active support system contains an array of approximately 200 actuators and sensors to control the position and shape of the mirror within a fraction of a micron. The control system allows a harmonious operation between the sensor data and actuators to achieve this precision.”

Now that one of the primary mirrors has been successfully integrated with the support system prototype, it will undergo rigorous testing under a metrology tower at the Richard F. Caris Mirror Lab to confirm that the mirror can maintain its shape and performance under various operational conditions. Once testing is complete, the design for the production active support systems will undergo a final design review, and production will commence in 2027.

“This intricate system took years of designing, building, and testing by a team of specialized engineers and technicians,” said Tomas Krasuski, Principal Software and System Test Engineer for the Giant Magellan Telescope. “Now that we’ve installed the mirror segment, we are excited to validate its performance. It has been a challenging yet rewarding process to get here.”

The milestone highlights the next stage of advancement for the Giant Magellan Telescope’s seven primary mirror segments and their support systems. Three of the primary mirror segments are complete, while the remaining four are in various stages of polishing. The Giant Magellan Telescope is now 40% under construction across 36 states and on track to be operational in Chile by the early 2030s.