Perched on a hill just outside of Victoria, B.C., the Dominion Astrophysical Observatory (DAO) is home to the 1.8-metre Plaskett Telescope—Canada's first major publicly funded science project, which placed the country on the world stage of astrophysics. In the years that followed, the DAO also became home to another remarkable instrument, the 1.2-metre telescope.
The telescopes continue to be used by astronomers every clear night available, and are now operated and managed by the National Research Council of Canada (NRC). The Plaskett and 1.2-metre are optical telescopes that use massive mirrors with ultra-thin metallic coatings to capture the faint light from distant stars and galaxies.
To ensure astronomers can capture the data required to conduct their research, the mirror and coating require regular maintenance.
"As stewards of the telescopes, we take great pride in ensuring we get the best outcome possible for our researchers," says Felipe Miranda, Supervisor of Fabrication at Design and Fabrication Services who has been maintaining the NRC's telescopes since 2008. "It's not lost on us that very few individuals around the world get this opportunity."
Over time, the metallic coating deteriorates, causing small voids on the mirror's surface, reducing their ability to reflect starlight. In addition, light scattering from a dirty mirror creates unwanted light background that reduces the visibility of faint celestial objects, even making them potentially undetectable.
"A telescope often has to stare at an object for hours to collect enough light," says Dmitry Monin, Technical Officer at the NRC's Herzberg Astronomy and Astrophysics Research Centre. "With lower mirror reflectivity, this duration gets even longer, reducing how many objects can be observed on a given night. By maintaining the mirrors, we can maximize the telescope's science output."
Our experts do more than just maintaining telescopes; they also provide support in a variety of ways including custom designing and fabricating mechanical research apparatus and prototypes. "Our mission is to enable our researchers to carry out their research by building new tools and maintaining our specialized facilities," adds Camile Lebrun, Director of Production.
From dust to dazzle: the telescope mirror restoration process
To complete the maintenance, the team first removed the primary mirror from the telescope and lowered it through a hatch in the floor to the coating plant located below the telescope. The deteriorated aluminum coating was then chemically stripped from the mirror and the glass was cleaned using pure soap, distilled water and lint-free cloths.
Next, they loaded the clean glass into a vacuum chamber containing clean tungsten coils wrapped in pure aluminum. Once sealed, the air is removed from the chamber using vacuum pumps.
Finally, the team powered the tungsten coils, which glow like incandescent lightbulbs, until the aluminum wrapped around them melted and wicked into the tungsten coil. A quick increase in voltage vaporized the aluminum, depositing it onto the mirror surface.
The week-long recoating process has been part of the telescope maintenance program for years, with a dedicated coating plant to aluminize the glass located within the observatory. Every time this happens, the team improves and refines their process, adding steps where necessary to ensure the mirror remains as clean as possible while out of the telescope.
"Although the 1.2-metre telescope has been around for 63 years, and the 1.8-metre telescope for 107 years, they are still operating as research instruments every clear night," comments Neal Kelly, Senior Lead of Fabrication. "With this in mind, it is important that the telescopes are maintained on a regular basis, and we take immense pride in doing this work. We keep these telescopes operational and we provide maintenance that is crucial to their ongoing performance today and in the future."