World’s Largest Earthbound Telescope to Outperform Hubble

Having secured more than US$500 million for the project, the aptly named Giant Magellan Telescope (GMT) will utilize seven mirrors spanning 24.5 meters in diameter, weighing 20 tons each. Made from E6 borosilicate glass manufactured by a Japanese company, the glass is made using sand from the Gulf Coast of Florida. Its chemical composition is similar to Pyrex, used in cookware.

Just one of these mirrors can focus more than six times the amount of light than the current largest optical telescopes. Only the first of the seven mirrors have completed construction.

To build the largest telescope in the world, with mirrors able to reveal the first objects to emit light in the universe, one might ask – what kind of challenges will engineers face in this project?

The engineers’ first challenges came in clearing the site of the facility’s construction, back in 2012. Located around 8,200 ft. (2500m) above sea level on Las Campanas Peak in the Chile Andes, construction engineers flattened the peak with explosives and heavy equipment. Four million tons of rock were cleared.

The mirrors themselves created a new mountain of challenges. “We have to make these optics precisely enough so that if the light travels 5, 10 billion lightyears and comes and hits our telescope, we don’t scramble and lose that information,” says Dr. Patrick McCarthy, director of the Giant Magellan Telescope Organization (GMTO). “We have to make this large optics to a 20^th of a wavelength of light even though it’s 25 meters across. It’s a challenge of about one part in ten billion in terms of precision manufacturing, so it’s an extraordinarily challenging process.”

Upon receiving the glass, the mirrors are manufactured at the University of Arizona. The following video explains how they go about this process and what challenges they face.

While waiting for the remaining mirrors to finish production, construction engineers have begun building the steel mount that will hold the mirrors of the telescope. The mirrors will be housed in a 22 story building.

GMT’s mirrors will be controlled using what McCarthy calls a sophisticated autofocus system. “The shape of the mirrors is measured by analyzing the light from stars in the telescope’s field of view. This information is used to determine forces that are applied to the mirror to correct its shape and alignment.”

To account for atmospheric disturbances, the satellite will use an adaptive optics (AO) system, McCarthy adds. “This uses a set of seven adaptive secondary mirrors, which feed light into a wavefront sensor, the measurements of which control the feedback loop to shape the secondary mirrors to correct for the aberrations in the light as it passed through the atmosphere to the telescope. The AO system will use both natural guide stars and laser guide stars.”

The telescope is expected to see first light in 2021 and reach full operation in 2024.

What challenges do you imagine engineers will face in the telescope’s construction? Let us know your thoughts in the comments below.