FIRST LIGHT. The sun breaks over the Santa Rita Mountains, 40 miles south of Tucson. Silhouetted on the narrow peak of Mount Hopkins stands the Multiple Mirror Telescope, waiting for a new mirror. The problem is that new mirror weighs more than ten tons and must travel a twisting mountain road often half its width and flanked by rock and precipitous dropoffs.
As I arrive at the MMT Observatory base camp, the crew is preparing an unusual rig—a huge white octagonal box, 5 feet thick and 25 feet across. It rides almost vertically on the back of a flatbed semi-truck. Late this summer, the MMT’s new 6.5 meter (21 foot) mirror will be loaded into the box and transported the 12 miles and 4,000 feet up the mountain. Never before has a piece of glass this large been moved up such primitive road. Today’s run is the final test.
Warren Davison, Mechanical Engineer at U of A’s Steward Observatory, gets much of the credit for designing a transport box that would cushion the mirror effectively. Implying that one can easily get carried away with fancy designs, Warren quips, “It took a lot of creativity to make a simple solution.” He came up with an inner frame that grabs onto the mirror by dozens of cushioned, load-spreading supports glued to the mirror’s back—the same supports that will hold the mirror in the telescope. The inner frame is cradled within a rectangular ring of steel—connected to it only via three large rubber pads, acting as shock absorbers. Most of the “box” is its octagonal cake-pan cover.
The mirror was created in April 1992 at the Steward Observatory Mirror Lab, beneath Arizona Stadium. A technique called “spin-casting,” developed by astronomers Roger Angel and Nick Woolf, uses the centrifugal force of a rotating furnace to create rough castings with the required curved surface—saving the time and cost of grinding away tons of glass. To reduce the mirror’s weight, the glass is melted around blocks of soft-ceramic material, which are blasted out afterward with high-pressure water. This creates a mostly hollow mirror with a stiff honeycomb structure, topped off by an inch-thick plate. After casting, it took more than a year to polish the mirror to fine precision, with the final touches done by hand. The MMT mirror was the first in a series of giant telescope mirrors being produced by the Mirror Lab.
Now it’s time to take this mirror home.
For the final test, a "dummy mirror" made of steel is hooked up to gauges that measure its motion during transit. Bundled wires exit the box and thread to a laptop computer riding shotgun in the cab of the truck. Driver Lynn Harris jokingly expressed the worst-case scenario, “We’ll get all the way up the mountain without falling off, and the computer will tell us we broke the glass!” Eager to get the job done, nobody seemed unnerved by his prediction.
Lynn hasn’t fallen off the mountain yet. He helped build the Mount Hopkins Road in 1967, working with Sierrita Mining and Ranching, and has been maintaining it ever since. Speaking to him, and to others, I get the impression he built the road almost single-handedly. He’s been hauling heavy loads up this road most of his life and probably knows it better than anyone. This job doesn’t faze him at all.
As Lynn pulls the rig past the gates of base camp, J.T. Williams is perched on the cab’s running board, ready to run ahead and guide the truck around hairpin turns or kick stray rocks off the road.
J.T., Project Engineer for the MMT Observatory, is in charge of the telescope’s conversion, including today’s move. Director Craig Foltz describes him as “the kind of guy you’d like have around if you were stranded on a deserted island”—a testimonial to his friendly nature, resourcefulness, and ingenuity. Of his job, J.T. says, “I’ve worked for the Smithsonian essentially all of my life…I don’t think I’ve ever had a real job. It’s great fun.”
Perhaps not having so much fun is MMT Engineer Bill Omann, who quips, “They’re punishing me for building [the trailer]” His punishment? Clouds of dust kicked up by the rig. He is riding on the open flatbed next to the box with his eyes fixed on an inclinometer measuring the tilt of the trailer. To compensate for the shifting weight of the box, Bill drives a 5-ton lead counterweight attached to rails under the trailer. Surprisingly, his precarious perch doesn’t seem to bother him much; while his equipment is well secured, Bill coasts on a rolling office chair. It seemed a rather odd choice for the job, so I asked him why. “I want to be able to get off this thing quickly…at 10 degrees I stand up, at 12 I’m jumping off!” In theory, the trailer is stable to 17 degrees but that’s with no wind, and this box might as well be a sail. With a maximum tilt of 8 degrees during the test run, Bill didn’t even roll closer to the edge.
Staying ahead of the pack, I wait on exposed turns, the road below disappearing into a sweeping vistas of the Santa Cruz Valley and southern Arizona. And always, Lynn and his parade of support vehicles come snaking up the mountainside. They’re making excellent progress—you’d have to run to keep up on the straight-aways. The longest delay—a flat tire—was far from the worst thing that could have happened. And while most tire changes don’t take three people an hour of hard work, it was still a routine process.
Underway again, we near the rocky peak of Mount Hopkins and the steepest sections of roadway. The final approach skirts a dizzying precipice at a grade of 26 percent—6 percent merits a highway warning sign! But then, highways don’t have heaters under them to melt the ice. Not unexpectedly, Lynn’s heavy-duty rig spins its tires about a mile short of the summit. Standing by to help is a front-loading tractor, also from SMR. With an 8-foot section of telephone pole lashed to its shovel, the tractor comes up from behind to give the rig a shove. “I sure felt it when he took it to 2,200 rpm!” says Lynn of the feeling as the tractor helped propel him to the top. J.T. is right, it does look like fun—big boys and their Tonka toys.
After the move, I asked J.T. about what went right. “It didn’t fall over! It didn’t fall off the mountain, the wind didn’t blow it around…none of those horror stories happened. It was a great testimonial to our modeling and engineering. The idea of carrying a large expensive piece up a mountain road like that, when you look at the whole problem, it overwhelms you. But…you start with the basic laws, principles, and physics and you start breaking the problem down piece by piece…then it starts to feel more plausible.” More than plausible, they made it look easy. And the computer says they did not break the glass.
Reflections on Multiple Mirrors
Built in 1979 and jointly operated by the Smithsonian Institution and the U of A, the Multiple Mirror Telescope has always been a leader in telescope technology. It was the first optical telescope to combine the light from multiple mirrors, in this case, six 1.8 meter mirrors with an equivalent diameter of 4.5 meters. Doing that successfully was itself a major breakthrough. Its altitude-azimuth drive, which both tilts the telescope and rotates the entire building, is the world’s most accurate pointing system. It could line up on a basketball in Tucson if you simply entered the ball’s location into the computer. Other innovations allowed astronomers to combine starlight in ways never done before, including being able to “tune in” specific colors of light, a key in the search for extra-solar planets.
The new MMT Observatory is scheduled to see “first light” by the end of 1998. Research will resume early next year. The 6.5 meter mirror will more than double the telescope’s light gathering surface area—and at $20 million, the cost is a fraction of building a new observatory. In a sentimental gesture, the telescope’s name will not change with the shedding of its multiple mirrors. “It’s an acronym in search of a name,” declared Craig. But it does have a cool new logo.
The reincarnated MMT won’t be the largest telescope in the world. That honor goes to the twin 10-meter Keck Telescopes in Hawaii. Several 8 meter telescopes are also under construction, as well as two telescopes that will use multiple 8-meter mirrors, one in Chile, the other on Mount Graham.
What Mount Hopkins has is nearly the best “seeing” (quality of observation) in the continental United States, rivaled only by Mount Graham. Our clear, dry weather and unique geology make Arizona prime for astronomy. And the proximity of the U of A to observatories like the MMT and Kitt Peak allows students and researchers easy access to world-class instruments, encouraging innovative projects.
The lights of Green Valley, Sahuarita and Tucson.Eric J. Anderson has been working for Steward Observatory since 1987, after a failing classmate tipped him off that “the eggheads over there need some kind of drafting done…you’d get along well with them.”