High-Tech Horse Sense

4 June 2002

Optical technicians dressed in clean suits and protective gear incorporate a little old-fashioned "horse sense" into their procedures as they use common horse soap to clean the 8-meter (26-foot) mirror of Gemini North Telescope high atop the nearly 14,000-foot (approximately 4,000 meters) peak of Mauna Kea on the Big Island of Hawai'i. The periodic cleaning is a highly complicated process involving more than 500 steps and a crew of more than 20 engineers, technicians and support personnel. The procedure includes dismounting the 24-ton mirror from the telescope structure, lowering it five stories to the basement, mounting it on a washing frame and then washing the aluminum-coated, 20cm (8-inch) thick glass mirror to remove accumulated contaminants on the mirror surface.

Once the high-tech preparation is completed, however, the Gemini team relies on some very "low-tech" expertise to actually wash the mirror surface. Through experimentation with various detergents, technicians have found that the most efficient way to clean it is to mop the mirror surface using natural sponges soaked in a detergent popularly marketed as horse shampoo, which they purchase at a general store in Hilo, Hawai'i. Optics Technician Clayton Ah Hee, who supervised the actual washing, said the soap is used because it is a strong detergent, yet is not abrasive to the multi-million dollar mirror's delicate surface, and leaves no residue.

"We've found the combination of the natural sponges and horse soap to be the most efficient way to get the mirror surface completely clean," said Ah Hee. "I know this sounds kind of simple, but sometimes the simplest solutions are best, even with something as leading-edge as the Gemini telescopes. And the horse soap really works."

The use of sponges to clean the surface was originally developed by technicians at the Gemini South telescope. Technicians and engineers from Gemini South in Chile also participated in the cleaning of the Gemini North telescope