University of Arizona

15 May 2000

Giant mirror transplanted in trend-setting telescope

MT. HOPKINS, Ariz. -- A radical instrument that transformed design and construction of large telescopes is now twice as large. The original 4.5-meter-diameter Multiple Mirror Telescope was the third-largest optical telescope in the world when dedicated on Mt. Hopkins, Arizona, in 1979. Now, converted to the 6.5-meter telescope of the MMT Observatory, it will be the largest single-mirror telescope in North America when rededicated Saturday, May 20.

"The original telescope changed people's expectations of how a telescope should be designed and how a modern telescope should perform," says MMTO Director Craig B. Foltz.

The University of Arizona and the Smithsonian Institution have replaced the MMT's array of six, 1.8-meter mirrors with a single stiff, lightweight 6.5-meter borosilicate "honeycomb" mirror, spin cast and polished to extraordinary precision at the UA Steward Observatory Mirror Lab.

The $20-million conversion project has increased the telescope's light- collecting area by 2.5 times and its field-of-view by about 15 times. A fifteen-fold increase in field-of-view expands the area of sky that astronomers can study by more than 200 times, Foltz says. The combination of the upgraded MMT's much greater light-collecting power, expanded field of view and exquisite image quality will keep this telescope in league with other large telescopes coming on line, he adds.

The MMT used six identical 1.8-meter telescopes in a single altitude-azimuth (naval gun-type) mount. The light gathered by each of the six telescopes was combined at a common focus. This gave the MMT the light-gathering power equivalent to a telescope having a single 4.5-meter primary mirror.

The pointing and tracking of the MMT and the co-alignment of the individual telescopes were all under computer control. The absolute necessity of computers for operation and the use from the start of electronic light detectors made the MMT the first all-electronic telescope. Throughout its career, it remained unrivaled for telescope pointing performance and nearly unrivaled in image quality.

Why change the MMT?

"The MMT has been, throughout its history, at the forefront of modern astronomical research and has contributed significantly to our understanding of phenomena such as young stars, galaxies, quasars, gravitational lenses, and black holes," said then MMT Observatory director Frederic H. Chaffee at the beginning of the conversion process. However, said Chaffee, now director of the Keck Observatories, "The MMT wouldn't be able to compete with the even larger telescopes expected around the year 2000."

Casting mirrors larger than 5 meters in diameter was impractical when the MMT was designed. In fact, the MMT was designed specifically to circumvent the problem of large, heavy, very expensive mirrors. Now, however, thanks to the spin-casting method pioneered by Roger Angel of the University of Arizona, casting mirrors up to 8.4 meters across has become possible and affordable. Mirror lab scientists have polished the 6.5-meter mirror so perfectly that if the glass were the size of the United States, a typical bump on its surface would be only one inch high.

The unprecedented conversion of a working, world-class telescope marks the beginning of what J.T. Williams, project engineer on the MMT conversion, says is sure to be the beginning of a trend, the "recycling" of existing prime astronomical observatory sites. Although the Mount Hopkins site is threatened by ever-increasing light pollution, Williams said, it remains among one of the world's best sites.

In keeping with its groundbreaking predecessor, the new telescope will make use of nascent technologies such as adaptive optics to counteract the "twinkling" of starlight; new large optical-fiber-fed spectrographs able to measure hundreds of galaxies at a time; and thus continue the access of astronomers from the University of Arizona and the Smithsonian Institution to first-class observing instruments.

Images and background information

Images supporting this release


UA News Service

March 25, 1999

THE REBIRTH OF THE MMT: THE TELESCOPE GETS ITS GIANT MIRROR

MOUNT HOPKINS, ARIZ. -- Cheating sleep so they could beat windy weather before an expected storm, astronomical observatory staffs early today lifted a giant mirror into their southern Arizona telescope.

Crews from the MMT Observatory and The University of Arizona Steward Observatory gathered at 6 a.m. on Mount Hopkins, south of Tucson, for the last, major, heart-stopping step in an unprecedented telescope conversion -- the lift of a 21 and 1/2 -foot (6.5-meter) diameter primary mirror into a pioneering telescope known as the MMT.

Temperatures hovered somewhere in the low 40s and wind gusts up to an estimated 20 m.p.h. added to the wind chill.

Thirty-six, two-foot diameter suction cups in a spider-like lifting fixture gripped the face of the 21,000-pound mirror by vacuum. The suction had been pumped down last night so staff could monitor for leaks. Final pre-lift checks and preparations this morning took about an hour.

At 7:10 a.m., a 120-ton crane began to hoist the lifting spider holding the $10 million glass reflector higher and higher into the sky.

Watching the fragile, giant mirror dangle almost 70 feet overhead before it was lowered through the telescope mount into its mirror cell produced long, anxious moments, said MMTO Director Craig B. Foltz, who admitted he hadnít slept at all last night. The final six inches before the mirror is completely lowered is potentially as dangerous for the mirror, Foltz added. But it sure doesnít look as scary.

Observatory staff -- including two crew members in climbing rigs roped to the telescope building -- guided the mirror to make sure it cleared the optical support structure as it was lowered into the mirror cell. That was the tensest part of the move, said Steve Warner of the UA Steward Observatory Mirror Lab, because there is only a 5-inch-perimeter clearance between the glass and the surrounding steel.

Until yesterday, the plan was to lift the mirror at dusk. The lift could only be made when the sun was very low on the horizon. Sunlight would unevenly heat and stress the glass -- and unnecessary stress on the glass is always to be avoided. But by noon yesterday the forecast was for a storm to blow in from the west, and wind comes before a storm. Wind could possibly sail the lifting spider into the optical support structure, damaging the mirror. Project engineer J.T. Williams and his team rescheduled the lift for dawn.

By 8:40 a.m., observatory staffs were aligning the mirror very carefully to its cell, to within an accuracy of a couple of millimeters At 10:26 a.m., the mirror cell supported the entire 10-ton weight of the glass, with the crane holding only the 7-ton lifting fixture. Williams announced that the mirror was wholly free of crane support and cradled only by the cell.

A half-hour later, a celebratory bottle of root beer was popped and passed around among staff. They still had a long day ahead, clearing away all of the vehicles and equipment from the small, crowded summit. But they will never face that task again -- the mirror has been installed for the life of the telescope. The MMT contains the biggest single-piece glass reflector on the North American continent.

The UA Steward Observatory and the Smithsonian Astrophysical Observatory dedicated the original MMT 20 years ago. The innovative telescope, which featured an array of six 72-inch diameter mirrors, "changed peopleís expectations of how a telescope should be designed and how a modern telescope should perform," said Foltz.

But in 1987, given success at new giant mirror-making technologies, the UA and Smithsonian agreed to an unconventional undertaking: They agreed to take apart a working, world-class telescope unrivaled for telescope pointing performance and nearly unrivaled in image quality to rebuild it bigger and better.

The UA Steward Observatory Mirror Lab in 1992 spin-cast the borosilicate "honeycomb" mirror in the labís enormous rotating furnace. Lab scientists since have polished it so perfectly that if the glass were the size of the United States, no bump on its surface would be higher than an inch.

On Tuesday, an 18-wheel tractor-trailer hauled the mirror in its steel box, a total load weighing 48,000 pounds, up 4,300 vertical feet along a 13-mile, narrow, winding and mostly unpaved mountain road from Smithsonian base camp to the summit that is 8,550 feet above sea level. The last stretch of road is a spectacular neck of narrow ridge road with a 25 percent grade. A front-end loader pushed the tractor-trailer up the final 500 feet of the trip.

The steel mirror box was hauled in a near vertical position, counterbalanced by a 10,000-pound slab weight mounted underneath the trailer on which it traveled. Bill Omann of the Smithsonian staff rode on the trailer up the mountain, measuring the tilt of the mirror and skillfully positioning the lead slab to counteract the lean of the mirror around steep curves. At a 16-degree tilt, the load would topple. The load tilted as much as 9 degrees around one corner.

Yesterday, Smithsonian and Steward Observatory staff assembled and tested the vacuum system for todayís lift. They also carefully checked the mirror, not surprised but still relieved to discover that it had traveled just fine.

Over the next two months, observatory crews will begin focusing tests and then lift a big, on-site aluminizing chamber over the mirror in the telescope to give it its silver reflective coat.

When the telescope comes on-line later this year, it will give astronomers 2.5-times greater light-collecting power and a 15-fold increase in field of view. A 15-fold increase in field-of-view expands the area of sky that astronomers can study by more than 200 times.


UA News Services

Tuesday, July 28, 1998

UA, SMITHSONIAN STAFF MOVE MMT MIRROR TO BASE CAMP; PLAN MIRROR CELL INSTALLATION ON THURSDAY, AUG. 6

Staff from The University of Arizona Steward Observatory and the Smithsonian Institution Whipple Observatory this morning moved the MMT 6.5-meter primary mirror from the UA Mirror Lab to Whipple Observatory base camp. The move was not publicized in advance for security reasons.

The 21,000-pound borosilicate honeycomb mirror, spin-cast and polished at the Steward Observatory Mirror Lab, was carried flat on a flatbed truck in a special crate that supports the mirror with shock absorbers. The crate and mirror together weigh 50,000 pounds, which is 5,000 pounds less than the MMT mirror cell moved to base camp yesterday.

The crated mirror will remain at a Whipple Observatory base camp warehouse until November, when it will be trucked up the mountain, aluminized and installed in the telescope.

The 50-mile journey from Tucson to Whipple Observatory in the Santa Rita Mountains of southern Arizona today was less eventful than yesterday's move of the mirror cell. Yesterday, the flatbed truck hauling the mirror cell stopped twice en route so staff could secure the huge tarp that covered the cell. The tarp was entirely shredded by wind during that trip.

Also yesterday, when the flatbed truck hauling the mirror cell exited Interstate-19 at Canoa Road toward the observatory base camp, Green Valley area residents with point-and-shoot cameras joined astronomers and media to capture the spectacle.

Observatory staff will truck the mirror cell up the twisting, 12-mile dirt road to the MMT Observatory at the 8,550-foot summit of Mount Hopkins next week, said MMTO director Craig B. Foltz.

Plans are to haul the mirror cell up the first six or seven miles of mountain road on Tuesday, Aug. 4, leaving base camp around noon. Any traffic above on this road will be blocked there overnight. The mirror cell will be driven the rest of the way to the summit on Wednesday, Aug. 5. An enormous crane also will be driven to the summit on Wednesday, and readied to lift the mirror cell into the telescope starting as early as 8:30 a.m. Thursday, Aug. 6. Expect the lift to go snail-pace slow, said J.T. Williams, MMTO project engineer.

These plans, of course, are contingent on good weather. If monsoon storms threaten on Wednesday afternoon, the crane will not be driven up the mountain for mirror cell installation early Thursday morning, Williams said.

Because both the mirror cell and the crane are slow-moving roadblocks, traffic control on the mountain road will be important next week, Foltz said. Reporters planning to cover the move and installation of the mirror cell are advised to meet at the Whipple Observatory Visitor Center at a set departure time. Contact Julieta Gonzalez of UA News Services, 520-621-1877, or Barbara Russ of the MMTO, 520-621-1558, next week for departure times.

The 4.5-meter Multiple Mirror Telescope (MMT), which was a telescope with an array of six 1.8-meter (72-inch) mirrors until last February, is being upgraded to a single 6.5-meter (256-inch) telescope in a $20 million conversion project to be completed by the end of the year. The new 6.5-meter MMT will be the worlds third largest telescope.


July 21, 1998

UA/SMITHSONIAN 6.5-METER MIRROR LIFT NOW SET FOR JULY 22

Staff at The University of Arizona Steward Observatory Mirror Lab are making swift work of readying a giant mirror cell for its big move Monday, July 27, to a southern Arizona mountaintop.

So much so that they will lift the 6.5-meter UA-Smithsonian MMT mirror from the mirror cell on Wednesday morning, July 22. This is one day earlier than previously scheduled. Operations could begin as early as 9 a.m.

The 21,000-pound borosilicate honeycomb mirror will be hoisted from its mirror cell and lowered onto a box, where it will rest on a support frame. The lift of the giant polished mirror is done with vacuum power, which holds 36 two-foot diameter suction cups to the face of the mirror. The suction cups are attached to one of the Lab's "lifting spider" structures that are raised and lowered with a crane.

Technicians will inspect and cover the mirror. It will remain stored at the Lab until arrangements are finalized for installation this fall at the MMT Observatory telescope on Mount Hopkins, Ariz.

Early Monday morning, the UA Steward Observatory and Smithsonian Whipple Observatory team will cover the 55,000-pound mirror cell and secure it on a flatbed truck for the 50-mile drive to the Smithsonian Whipple Observatory base camp in the Santa Rita Mountains. The mirror cell is by far the biggest single piece of equipment to be moved in the telescope conversion project, said Craig B. Foltz, director of the MMTO.

The former 4.5-meter Multiple Mirror Telescope (MMT), which was an array of six 1.8- meter mirrors, is being upgraded to the single 6.5-meter MMT in a $20 million conversion project to be completed by the end of the year.


UA News Services

MMT 6.5-METER MIRROR TO BE LIFTED FROM MIRROR CELL THURSDAY, JULY 23; MIRROR CELL TO BE TOWED TO WHIPPLE BASE CAMP ON MONDAY, JULY 27

It's 25 feet across, weighs 55,000 pounds and features a hundred arms, each of which can support up to 200 pounds of telescope mirror with accuracy tolerances of mere ounces.

And on Monday, July 27, it will travel over Interstate-19 from Tucson to Amado, Ariz., at speeds of more than 50 mph, taking up the entire road. Two Department of Public Safety vehicles, several commercial vehicles and others will escort.

It is the MMT mirror cell. It's the biggest single piece of gear that Smithsonian Whipple Observatory and University of Arizona Steward Observatory staff must move in the $20 million conversion of the Multiple Mirror Telescope (MMT) to a 6.5-meter telescope at Mount Hopkins, Ariz.

After trucking the mirror cell about 50 miles to the Whipple Observatory Base Camp on Monday, and in early August up the twisting 12-mile road to Hopkins' peak, milestones to MMT completion can be counted on one hand, said MMTO Director Craig B. Foltz.

Those remaining milestones to completion include:

SCHEDULE OF EVENTS

  • Thursday, July 23, 9:30 or 10 a.m., Steward Observatory Mirror Lab

    The 21,000-pound 6.5-meter MMT primary cell will be lifted out of the mirror cell at the UA Steward Observatory Mirror Lab. The perfectly polished mirror has been in the mirror cell since October, during which time technicians and engineers integrated critical support and thermal systems. Lifting the mirror from the cell is done with vacuum power, which holds 36 two-foot diameter suction cups to the face of the 10-ton mirror. The suctions cups are attached to one of the "lifting spider" structures the Lab uses to hoist giant mirrors with cranes.

  • Monday, July 27, 9 a.m. to 10 a.m., Steward Observatory Mirror Lab to Whipple Observatory Base Camp at Amado

    The 55,000-pound mirror cell is covered, boxed and secured on a flatbed truck. It will leave the Steward Observatory Mirror Lab between 9 and 10 a.m. From the Mirror Lab it will travel to Campbell Ave., south on Campbell Ave. to Kino Blvd., Kino Blvd. to Irvington Road, west on Irvington Road to Interstate-19 headed south.

    Leave Interstate-19 at Exit 56, the Canoa Road Exit, continue 3 miles south to Elephant Head Road. From this turn, it's 7 miles to the Whipple Observatory Visitor Center and Base Camp. Signs mark the route to the visitor center starting with the turn onto Elephant Head Road, or contact UA News Services, 621-1877, if you need a map.


    University of Arizona News Services

    February 26, 1998

    The 'original' MMT gets its last look at the universe

    The Multiple Mirror Telescope on Mount Hopkins, Ariz., is taking its last views of the universe this weekend. But it will see "first light" again this fall as a bigger and better telescope, one uniquely competitive with other new world-class ground-based telescopes.

    The Multiple Mirror Telescope (MMT), dedicated in 1979, is at present the fifth largest telescope in the world. A joint project of the Smithsonian Institution and The University of Arizona in Tucson, it represented such a radical departure from earlier telescope design that it is considered the first of the new generation of optical telescopes. The MMT's current array of six, 72-inch diameter mirrors have a combined light-gathering power of a 176-inch telescope. The UA and Smithsonian are replacing this array with a single stiff, lightweight 6.5-meter (256-inch) borosilicate "honeycomb" mirror, spin cast and polished to extraordinary precision at the UA Steward Observatory Mirror Lab. It then will be the world's third largest telescope

    The $20 million conversion project will increase the telescope's light-collecting area by 2.5 times and its field-of-view by 15 times. A 15-fold increase in field-of-view expands the area of sky that astronomers can study by more than 200 times, said Craig B. Foltz, director of the MMT Observatory.

    Foltz and UA Steward Observatory astronomer Christopher D. Impey over the weekend will use the MMT for hunting quasars and studying "gravitational lenses," the kind of science that made the MMT famous. The MMT was used to complete the largest ever survey for quasars, discovering more than 1,000 of these extremely energetic objects that exist near the edges of the universe, back almost to the beginning of time. And the telescope is famous as the instrument used in the discovery of "gravitational lenses," the effect where light from a very distant celestial object is bent by the gravity of a closer, massive object so that astronomers on Earth see multiple images of the distant source.

    "The MMT has contributed significantly to our understanding of phenomena such as young stars, galaxies, quasars, gravitational lenses and black holes," Foltz said. "This telescope has been an outstanding success, both in terms of the high quality of scientific research and in terms of new generation telescope design." The MMT is the prototype for several innovations that have been incorporated into the Earth's greatest telescopes.

    Impey has been at the MMT for the past several nights searching for quasars and studying gravitational lenses. In an interview by e-mail, he said, "The MMT has always been a primary tool in my research, and it will be sorely missed as it goes down for the upgrade.

    "I have probably had well over 100 nights on the MMT since I came to Tucson in 1986, and along with the Hubble Space Telescope, it has fueled most of my research over the years.

    "It is always a pleasure to use a facility of great light-gathering power where the instruments almost always work flawlessly," he added.


    University of Arizona

    January 21, 1998

    MMT telescope conversion begins soon, will be complete in a year

    The University of Arizona in Tucson and the Smithsonian Institution are about to make history by taking apart a working, world-class, ground-based telescope that remains unrivaled for telescope pointing performance and nearly unrivaled in image quality.

    "This is the first time a major, scientifically productive telescope has been disassembled," said Craig B. Foltz, director of the Multiple Mirror Telescope Observatory (MMTO) at Mount Hopkins, Ariz. "This telescope changed people's expectations of how a telescope should be designed and how a modern telescope should perform."

    The UA and the Smithsonian this year will replace the MMT's current array of six, 72-inch diameter mirrors with a single stiff, lightweight 6.5-meter borosilicate "honeycomb" mirror, spin cast and polished to extraordinary precision at the UA Steward Observatory Mirror Lab.

    The $20 million conversion project will increase the telescope's light-collecting area by 2.5 times and its field-of-view by about 15 times. A fifteen-fold increase in field-of-view expands the area of sky that astronomers can study by more than 200 times, Foltz said. The combination of the upgraded MMT's much greater light-collecting power and expanded field of view will keep this telescope in league with other large telescopes soon to come on line, he added.

    The unprecedented conversion of a working, world-class telescope marks the beginning of what J.T. Williams, project engineer on the MMT conversion, and Foltz say is sure to be the beginning of a trend, the "recycling" of existing prime astronomical observatory sites. Although the Mount Hopkins site is threatened by ever- increasing light pollution, Williams and Foltz said, it remains among one of the world's best sites.

    The MMT will close March 1 and be disassembled over a six weeks period. Major new parts of the telescope, including mirror cell, front-end telescope structure, mirror-aluminizing chamber and "dummy" mirror, will be moved to the top of Mount Hopkins beginning in April. The steel dummy mirror will be installed in the reconfigured telescope for telescope tests over the summer, Foltz and Williams said.

    The 6.5-meter glass primary mirror for the MMT is currently at the UA's Mirror Lab, where it is being integrated and tested in the mirror cell. The mirror cell supports the mirror in the telescope. In the new MMT mirror cell, each of 100 "actuators" (pressurized air cylinders) must support up to 200 pounds with accuracy tolerances of only ounces. The mirror cell support forces are critical to maintaining the virtually flawless shape of the polished giant mirror.

    After the primary mirror is installed in the telescope in early fall, UA and Smithsonian staff will put the telescope through another round of tests to learn how to drive the new telescope drive with its updated control system.

    First light for the 6.5-meter MMT will be mid-to-late fall 1998, Foltz said. Astronomers will start using the telescope for science by early 1999.

    Williams and other "early timers" who launched the original MMT 20 years ago plan a kind of farewell party for the telescope at the mountain on February 14.


    Back to ASTRONET's home page
    Terug naar ASTRONET's home page