The Lowell Observatory in Flagstaff, Ariz., operates half a dozen telescopes in the U.S. and has shares of one in Australia and one in Chile. Until recently, the newest of its stargazers had been built in the 1960s. For one of the major astronomical research facilities in the nation, the desire for a modern telescope was great. Paying for it, however, was another matter. In 2003, a partnership with Discovery Communications, Silver Spring, Md., which owns The Discovery Channel, revealed a down-to-earth solution to what seemed like an astronomical challenge.
The $44 million Discovery Channel Telescope (DCT), under construction in Happy Jack, Ariz., sits 45 miles southeast of Flagstaff at an altitude 7,760 feet. The collaboration gave The Discovery Channel rights to film the project’s construction, liberty to call on Lowell Observatory astronomical experts whenever needed and ownership rights to any discoveries made with the DCT. Lowell astronomers gain an advanced, high-quality telescope to further their research of the outer solar system.
“The Lowell Observatory is about both astrophysics research and public outreach education, so the objectives of each partner dovetailed nicely,” notes Byron Smith, Lowell’s DCT project manager.
Night Vision
The DCT’s telescope weighs an estimated 300,000 pounds. Its primary mirror alone comes in at a hefty 6,800 pounds. The mirror is 4 inches thick and required nearly three years of meticulous grinding and polishing to perfect. At 4.2 meters in diameter, the primary mirror is more than double the size of the biggest telescope in Lowell’s fleet and offers five times as much light gathering capability.
Research at the DCT includes the evolution of the solar system, the formation and evolution of stellar and planetary systems, and further examination of icy bodies in the Kuiper Belt near Pluto’s orbit and beyond. The DCT mirror’s increased capacity for collecting light will accelerate this research by making fainter celestial objects at the far edge of the solar system more visible.
According to Smith, the main blurring of the telescope’s image comes from heat shimmering in the atmosphere, but some interference can derive from the telescope radiating heat. The goal for improved seeing is to keep everything thermally uniform. The nighttime temperature in Happy Jack is below freezing, and Lowell will take advantage of the climatic conditions by closing the 73-foot-tall dome that houses the telescope during the day and using natural ventilation to cool it at sunset.
“It will be like an icebox inside,” explains Smith. “Because the telescope, dome and building weigh nearly three-quarters of a million pounds, it takes a long time to heat up the building once it’s cold. But we need to insulate it from the Arizona sun, and that’s where the metal panels came in.”
Solar Barrier
Attaching directly to the steel structure, foam-insulated metal panels serve as the DCT dome’s roof and wall siding. The galvanized-zinc coated steel panels protect the sensitive equipment inside from the elements and thermal gain. Each panel consists of an interior 26-gauge sheet and an exterior 24-gauge surface sandwiched around 3 inches of foam. The insulation is foamed-in-place to increase thermal efficiency. In addition, an aluminum foil tape was applied to the face of the panels prior to installation. The reflective tape has low emissivity, which greatly reduces radiation to the sky, and the material stays close to the ambient temperature at night.
On the wall panels, the foam core is chemically bonded to the facings in an effort to help the insulating value of R-25 endure over time. The side joinery offers foam-to-foam contact with a double-sealed tongue-and-groove joint for a full thermal seal. The 42-inch-wide wall panels have a two-piece, thermally broken concealed clip design to reduce heat loss through the side joint and minimize the possibility of condensation.
The mechanically seamed foam roof panels provide tongue-and-groove joints as well and slide together for increased weather resistance. The 25- to 28-foot-long to continuous panels reduce unnecessary flashings and areas of possible water infiltration. Chandler, Ariz.-based installer Kovach Inc. conducted the panel installation. Project manager Luke Brandt says that the long panel lengths coupled with the small site proved challenging.
“Although it’s in a remote location, the dome is a small site perched on a hill. The average clearance to the protective fence was only 15 feet, which made it tricky to maneuver the long panels into place,” explains Brandt.
Perfect Exposure
Two-piece mechanical shutter doors that span the roof and the dome walls open sideways to reveal the telescope to the sky. A steel ring beam on 16 roller assemblies helps the dome rotate to pinpoint the area of observation, and the shutters are computer-controlled and track-guided to follow the telescope’s movements.
The 7,800-square-foot dome has seven 10- by 16-foot roll-up ventilation doors in the walls that can be opened at night to let the southwest winds blow through and cool the space. The openings invite dust and precipitation to accumulate, so the team provided extensive detailing in the form of butyl tape sealant and neoprene sweeps. The shutter doors that cloak and unveil the telescope received triple redundant seals.
Lowell’s oldest telescope is 114 years old, and Brandt points out an added benefit of the metal panels. “With the projected lifespan of a structure like this one, longevity is very important. With its cold temperatures and high winds on the hill, the metal foam wall system makes sense because they will hold up over time better than any other system.”
KJ Fields writes about architecture and sustainability from Portland, Ore.