World’s Biggest Binoculars
From a mountain in Arizona, the Large Binocular Telescope peers deep into the heavens as the world’s most powerful optical telescope
A universal trait of engineers is their curiosity with how things work, and nothing arouses more curiosity than the laws that govern the universe itself. Such laws seem to break down at the extremes of size, both on a small scale, in particle accelerators, for example, and on the vast scale, as detected by telescopes. In each case, tools designed by engineers now probe these mysteries, discovering the surprising nature of matter and energy.
A shining example is the new Large Binocular Telescope (LBT) atop Mt. Graham in southeastern Arizona, which enables scientists to study objects like the supermassive black holes at the centers of galaxies. For a personal tour of this revolutionary telescope housed at Mount Graham International Observatory near Safford, I joined Dr. Richard Green, LBT's director, on a clear, sunny day for the 125-mile drive northeast of Tucson to the remote mountain.
At 10,700 feet, Mt. Graham rises from the desert like a sky island of unexpected beauty. In contrast to the cactus below, 200-hundred-year-old Douglas fir trees grace the upper reaches of the mountain. Yet by following a final twisting dirt road to the summit, past several security checkpoints, a more unexpected marvel soon appears--the LBT observatory building itself. This $120 million dollar facility is home to the most powerful optical telescope in the world--a 600 metric ton all-steel mount encapsulating two massive 8.4-meter mirrors, each the largest of their kind yet deployed. Indeed, once the mirrors are phased together, this visionary binocular will function as if it was a Cyclops with a single mirror 11.8 meters wide--impossible to produce with today's technology--and with an angular resolution of 22.8 meters. With a honeycomb design, the mirrors sit on a single mount and are more rigid and lighter weight than conventional solid-glass mirrors. Together they collect more light than any existing single telescope.
While the telescope's size is revolutionary, so is its precision, accuracy, and sensitivity. During my visit, I witnessed the lowering of the twin mirrors for scheduled attachment of a red-sensitive camera to a deployment arm and was told that the moveable mount, despite weighing 600 tons, is steered easily under the power of a one-horsepower electric motor. "The structure actually floats on an oil pressure pad, like a rocking chair, thanks to 12,000 PSI," Dr. Green tells me, "so if you had to move it by hand, you probably could."
Added Dr. John Little, LBT's lead site engineer, "The ride from vertical to horizontal is twelve minutes, or one minute, depending on speed selection of the analog drive." When I asked if there was any smallest degree to which the telescope could be angled, Little replied, "Not really. With digital feeding, the mirrors will be able to be positioned to resolve one thousandth of an arc-second, or roughly a BB at 32 and a half miles." Luckily, testing for degradation of positioning at various elevations has revealed almost no deviation. And though counterbalancing is still a problem, considering the heavy instrumentation that will be swung in and out of position, there is a solution coming in the form of a newly designed dynamic fluid system that will pump a water and antifreeze mixture to various tanks within the structure to compensate. "For now we're using physical weights," says Little, pointing to what looked like stacked barbell rounds at the ends of the matrix.
A Global Effort
Work on the LBT began with construction of the one-of-a-kind telescope building in 1996, led by UA. The structure consists of 16 stories, and the top ten floors rotate.
As to the massive 8.4-meter dual mirrors themselves, they were spun cast in Tucson, at the UA's Steward Observatory Mirror Lab. In the state-of-the-art facility, housed in the campus football stadium, a huge furnace heated the 20 tons of glass, gently spinning it into a parabolic shape at 2130 F before it was cooled and polished to an accuracy of about 3000 times thinner than a human hair.
UA engineer Warren Davison developed the telescope’s innovative compact, stiff design in collaboration with other engineers in the United States and Italy. The major mechanical parts for the LBT were fabricated, pre-assembled, and tested at the Ansaldo-Camozzi steel works in Milan, one of Italy’s oldest steel manufacturers. Then the telescope was disassembled and shipped by freighter to Houston, Texas, and overland to Safford. The mirror cell continued to the Mirror Lab, where a team integrated the mirror support system and mirrors into the cell before a heavy equipment moving company hauled the assembly up the mountain. The LBT saw first light in 2005, and the LBT Observatory currently has a staff of approximately 50 scientists, engineers and technicians.
Other career paths to LBT played out differently. Dr. John Little, who worked in medical electronics, industrial controls, and military electronics before coming to the project, wasn't very familiar with astronomy at all, except as an amateur. "I went to Cal State at Sacramento for a degree in electrical engineering and remote sensing, then to the University of New Mexico for a masters in electromagnetics before some work at Utah State in optics," he told me, his steady blue eyes focused on days past. "So what's great about working here is that all these disciplines are involved. On top of that, it's exciting to see the data come in. When we get our adaptive optics running--taking the 'twinkle' out of the stars, so to speak--the clarity will be ten times that of Hubble. And so when we're pulling in images for the first time here, we'll be seeing them come right off the camera, and that'll be a thrill."
Also working in controlling the axis to position the telescope accurately, but in software rather than hardware, is Chief Software Engineer Norm Cushing, who told me, "At one point in my career I was working on HDTV set boxes, digital recorders and the like, and I realized right away that just wasn't as intellectually fulfilling. There was something missing. Call it awe. That's the missing ingredient which LBT supplies." Immediately prior to his arrival at LBT, Cushing developed software related to satellite tracking. "That background in image processing married well to what happens here, but it's been a phenomenal learning experience, too. When I arrived, I learned how little I really knew, especially about astronomy. Some know a lot, like Joar Brynnel, chief hardware engineer, who told me he needs his people to understand the concepts to fix problems in a reasonable time."
Members of Cushing's group write low-level embedded software in assembly language and higher level software modules running in Linux that talk to each other through reflective memory. "Algorithms for right ascension and declination are created to actually steer the telescope and make it move to position and track objects," Cushing explains. "Lower level commands control the motion of the building to follow the telescope." And is this software new and as exciting as being an astronomer? "All of it is new, written from scratch for this system," he replies, then adds, "When I was a boy, running around in my PJs, my sister would call me whenever Carl Sagan was on TV. I'd run out, and it was all fascinating. So it's been a dream come true for me, too."
Astronomers as Engineers
"Two interferometers are being made for this telescope," Roberto tells me over a plate of spaghetti in the observatory's kitchen. "One at the U of A, and the other in Germany and Italy.” An interferometer combines the signals of two separate telescopes (or mirrors) almost as if they were coming from separate portions of a telescope (or mirror) as big as the distance between the two telescopes. It works on the principle that two waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out, assuming both have the same amplitude. The instrument provides unprecedented imaging capability at infrared wavelengths and in its "nulling" mode reduces the glare from stars, thereby permitting the detection of orbiting planets or dust disks, which would otherwise be overwhelmed by the star light. “What's new is the scale to which this technology is being applied, and also, instead of using a laser for alignment, we use a wider field of view, with the light from several faint stars, which are then combined."
With such technology, astronomers can use the LBT to find and image the first Earth-sized extra-solar planets, employing the telescope’s astonishing light gathering power accompanied by an array of cameras, spectrometers, and interferometers--some the size of compact cars and weighing a ton. Or it can map the neighborhood of the inner Milky Way, where a monster black hole flings stray stars off on wild eccentric orbits as if they were mere marbles in a child's game.
After Roberto ate his plate of spaghetti with garlic and olive oil, I asked him if astronomers like him were not actually providing a microscope for laymen to see themselves as smaller and smaller as the universe they saw got bigger and bigger in their giant lenses. He laughed. Perhaps I reminded him of the children he once talked to about his work in adaptive optics, when one asked how he "made a star, which was so big, look so small."
For more information on the Large Binocular Telescope, visit www.lbto.org