A Finer View Of The Heavens (cont'd.)
The dirt road to La Silla blends perfectly with the dun-colored plain and the mountain on which the telescopes sit. A herd of shaggy, brown, free-range goats crossing the road would be almost invisible if their hooves didn't create little explosions of dust. There is so little vegetation, you wonder if the goats have somehow learned to eat rocks. The only contrasting colors are black condors circling on thermals in an almost azure sky.
The other contrast is between the desert's rawness and the sparkling mountaintop technology that lets astronomers probe the mind-numbing mysteries of the cosmos. Silva displays a parental concern about the largest of La Silla's telescopes.
"How could we spend so much on a wonderful building and telescope like this and then 'destroy' the information in the last 15 meters'" Silva asks. "My mission was to design and install a system that would keep the air temperature inside the dome the same temperature as it would be outside the dome at night. Only then could the dome be opened without letting heated air escape."
The Atacama may be known for intense sunlight during the day, but radiational cooling at night quickly lowers the outside even in the summer. That's why anyone walking around inside the actual telescope dome is usually wearing a jacket.
The cooling system is designed for the telescope, not for the astronomers," Silva quips. "Of course, all the astronomers work in control rooms outside the dome, so the low temperature doesn't really matter. The control rooms are air conditioned by Carrier, too, so the astronomers have the best of both worlds."
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Using historical weather data, the dome's daytime interior temperature is based on projections of what the exterior temperature will be that night. When the dome is opened, Silva says, there is rarely more than a degree or two of temperature difference. That wasn't as easy as it would seem since the distance from the dome's floor to the ceiling is an uninterrupted 15 meters. The temperature difference between floor and ceiling used to be seven degrees Celsius. To reduce temperature stratification, Silva's design discharges some cool air directly under the telescope's .6-meter-wide mirror at floor level; the rest of it flows up through snake-like insulated ducts toward the dome's ceiling.
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The system, a 30-series chiller from McMinnville, Tennessee and two chillers from Carrier SA in Montluel, France, is operated by digital Carrier Comfort Network controls. The same Carrier Comfort Network also controls the heat exchanger that keeps the oil in the dome's hydraulic system at the right temperature. The hydraulic system moves the telescope and the 30-ton dome itself.
"There's an important difference between the astronomers and our Carrier system," says Silva. "The astronomers only work at night. The air conditioning works always."
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