Fabulous Telescope Destined for Modernization in New Mexico

by John W. Briggs of the Springfield Telescope Makers

95-cm Princeton Telescope — Before disassembly began, the 95-cm Princeton telescope
was slewed east for inspection of its two 6-inch f/10 finder telescopes. The observatory's elevating floor was in its near topmost position.

[January 2014] Culminating detailed planning starting in 2012, a major observatory telescope formerly used at Princeton University's FitzRandolph Observatory in New Jersey has been transferred to the Michele and David Mittelman Family Foundation, operator of HUT Observatory in Colorado. Built by the famed Boller & Chivens Company for Princeton in 1965, the reflecting telescope has a clear aperture of 95 cm. Disassembly of the 25,000-pound instrument started in August, 2013, when long-time Stellafaners Kenneth J. Launie and John W. Briggs arrived at Princeton to remove the optics, primary mirror cell, instrument rotator, and other manageable parts. Disassembly of the major components with a crane and riggers came in a follow-up visit at the end of October involving David Mittelman, Alan and Aaron Sliski, and Briggs. The parts are now in storage in Alamogordo, New Mexico, and a survey is underway for a new observatory site, likely to be in New Mexico's Sacramento Mountains near Cloudcroft. Although construction will begin as soon as possible, the scale of the project will require time.

Towering Telescope — The 95-cm Boller & Chivens telescope, with its primary mirror cell removed (in foreground), towers above the elevating observing floor at Princeton's FitzRandolph Observatory.

The telescope is carried on a massive equatorial mounting that was the Boller & Chivens standard for a 40-inch reflector. The mounting is thus twin to instruments made for Yale, Northwestern, and Tel-Aviv Universities, among others. The equatorial's asymmetric design is sometimes referred to as a "torque tube," as explained and illustrated by Clyde L. Tichenor in the May, 1968, issue of Sky & Telescope magazine, page 290-295. Although nominally a 36-inch telescope, the instrument's f/3.82 primary mirror was developed separately by Princeton and has an as-built clear aperture of 37 1/4 inches, or 95 cm. The ultra-precision sidereal worm wheel (the main drive gear) has a diameter of 60 inches and by itself weighs 800 pounds. The instrument payload capacity at Cassegrain focus is nominally 300 pounds using the counterweights provided. But Paul B. Etzel, Director of San Diego State University's Mount Laguna Observatory, wrote, "You're really lucky. Your mount is capable of holding a lot more weight (700 pounds) at Cassegrain focus, if you want. The best thing is that you have really good gearing." A large instrument rotator with a position-angle index facilitates attachment of interchangeable instruments like cameras and spectrographs. The mounting includes pathways for an optional coudé focus, but as originally specified for Princeton, the instrument did not include the necessary extra optical flats and mounting cells.

The optical system is a classical Cassegrain, and the primary mirror is an early lightweight construction of fused quartz that was polished by the J. W. Fecker Company in Pittsburgh. The f/13.14 secondary mirror is mounted in an interchangeable cage assembly that will facilitate a quick change from the Cassegrain focus to an anticipated new prime-focus CCD camera, filter, and coma-correcting lens assembly. There is also the option of a Newtonian focus cage. The Cassegrain focus will remain the most convenient option during general student access, for example, during educational programming already planned in collaboration with the New Mexico Museum of Space History.

As the instrument is little changed from 1965, a new motion control system using DC servo motors and absolute encoders will be specified and installed, exploiting the original worms. The facility will be remote-accessible on the ASCOM standard using ACP software. A variety of modern motion control packages are currently under study, including site visits to telescopes equipped with similar gear hardware, such as the MDM 1.3-meter at Kitt Peak.

Safely moving the Princeton telescope was greatly facilitated by the coincidence that, after storage for some years at Lowell Observatory, the former Northwestern University 40-inch by Boller & Chivens was moved and installed at JPL's Table Mountain Observatory in California during September, 2013. It was thus possible to study the example of that move, as the hardware, rigging, and handling problems were essentially twin. Disassembling the sensitive drive mechanism was in fact non-trivial.

60-inch Worm Wheel — A sister telescope formerly at Northwestern University was recently installed at JPL's Table Mountain Observatory in California. Its 60-inch-diameter worm wheel is exposed as the worm assembly is positioned underneath. Experience gained during this installation greatly facilitated moving the Princeton telescope, which is similarly mounted, some weeks later.

The Princeton telescope will begin its new life coming from an unusually rich astronomical heritage. The Boller & Chivens firm was second-to-none in the world for research telescopes at the height of the Space Race. The lightweight primary mirror was associated with the famous Project Stratoscope II, a program of high-resolution balloon-borne astronomy using unusually perfect 36-inch mirrors lifted to altitudes of 80,000 feet. A second primary mirror, also recently acquired from Princeton by the Michele and David Mittelman Family Foundation, was the first actual flight mirror from Stratoscope II. The Stratoscope projects were led by Professor Martin Schwarzschild (1912-1997), in close association with his colleague, Lyman Spitzer, for whom NASA's Spitzer Space Telescope is named. Project Stratoscope II, stepping so close to the excellent observing condition of a true space environment, is considered a direct progenitor of Hubble Space Telescope and others in NASA's Great Observatories Program.

Joseph B. Houston, Jr., a past president of SPIE, the international society for optical engineering, was involved, early in his career, testing the Stratoscope II mirrors interferometrically. Recently he was able to clarify regarding the history, both of the primary mirror in the telescope, and of the second primary acquired from Princeton University. The Stratoscope II flights involved two different, solid, fused-silica mirror blanks made by Corning. Both optical surfaces were made at the Perkin-Elmer Corporation and were ultimately tested by Houston. The optical figuring was done by Ben Gay. The first mirror used in flights has a surface figure of 1/20th wave RMS in mercury green light (546 nm); this is the mirror now serving as a spare in New Mexico. Houston wrote, "The first primary mirror to fly, called the "IR" primary, was made and tested by the Foucault method. It was certified later with an interferometer. It was thus a tribute to Perkin-Elmer's master optician, Ben Gay."

The second flight mirror was also a solid disk of fused silica by Corning, but it was figured to 1/37th wave RMS with the help of interferometric testing in a process lasting 2 1/2 years. As reported by Sky & Telescope at the time, "The completed mirror will be the most precise optical element of its size ever fabricated." (See page 345 of the June, 1964, issue.) Houston recorded, "I worked closely with Ben, and we spent many hours together developing a procedure for using interferometry (and the topo maps I created) as a prelude to Computer Assisting Figuring. After I went through the throes of developing the LUPI (laser unequal path interferometer) in 1964 under the sponsorship of General Lew Allen, Program Manager of the CIA's Corona project, it was immediately apparent that the LUPI could serve as a digital link to optical polishing machines for automatically correcting optical surfaces." The later flight mirror from Stratoscope II was mounted by DFM Engineering in 1977 for Monterey Institute for Research in Astronomy. (See the March, 1979, issue of Sky & Telescope, page 223.)*

Dr. Norman Jarosik of Princeton University stands with 37 1/4-inch clear aperture mirror, figured by the J. W. Fecker firm. The blank was a Project Stratoscope II lightweight prototype almost certainly built from Pyroceram by Corning.

The primary mirror in the Boller & Chivens telescope is a construction that matches Houston's description of a prototype lightweight design. As he wrote, "When I worked for Bob Noble at Perkin-Elmer, before I transferred to work directly for Rod Scott on the Stratoscope II optical fabrication and testing project, we talked about using Pyroceram cylinders and fused quartz/fused silica lightweight faceplates as an approach to making some prototype mirrors for Princeton. I understand that Corning made a prototype for Perkin-Elmer as part of Martin Schwarzschild 's plan to find a good lightweight design for the 36-inch primary. Heraeus was also asked by Princeton and Perkin-Elmer to provide two prototypes. All this is contained in Perkin-Elmer's original proposal."

Although it is presently unclear whether Corning or Heraeus made the mirror blank now carried the Boller & Chivens telescope, a contemporary University press release states that the optical finishing was done by the well-known J. W. Fecker firm, a descendent of the John A. Brashear Co. Houston concludes, "The refurbishment effort for this telescope will continue to enhance Martin Schwarzschild's legacy. He was not only my customer but my mentor. Not too many folks realize that he was responsible for sponsoring and encouraging the interferometer revolution! Out of that came all the spinoffs, for example, CAOS (computer assisted optical surfacing), MTF (modulation transfer function), and the recent Time Tool." And regarding the Stratoscope II balloon flights, Houston adds, "They were good and bad! There are tons of anecdotes about Martin searching for the downed balloon in the swamps of Louisiana among the Cajun folks there. And there was one flight where the US Navy was called out to shoot down the balloon over the Atlantic when it was declared a hazard! Dick Perkin said that was his only program that our government shot down." Boller & Chivens became a division of Perkin-Elmer Corporation in 1965, the same year the Princeton telescope was produced.

Regarding earlier history, the FitzRandolph Observatory that housed the Boller & Chivens telescope was built in 1934 using stone recycled from Princeton's older Halsted Observatory. Then known simply as "New Observatory," the building is now likely to be torn down, ending an era. Both FitzRandolph and Halsted were homes to a line of particularly distinguished American astronomers including solar pioneer Charles A. Young, astrophysicist Henry Norris Russell, as well as students Harlow Shapley, Donald H. Menzel, and others who likewise became leaders themselves. A commemorative stone tablet familiar to all these astronomers will be preserved with the reflector. As the telescope was disassembled in late October, it happened to be exactly the 75th anniversary of Orson Welles' notorious 1938 radio broadcast, War of the Worlds. Early in the broadcast, the play mentioned Princeton Observatory in what might be taken now as an amusing, if still sobering, famous cultural reference.

The final use of the 95-cm reflector at Princeton was led by the late Professor David T. Wilkinson in collaboration with Harvard's Paul Horowitz in an Optical Search for Extraterrestrial Intelligence (OSETI). Wilkinson, a famed experimentalist and observational cosmologist, was posthumously honored by the naming of the profoundly productive Wilkinson Microwave Anisotropy Probe spacecraft.

Susan Duncan with the Telescope — Susan Duncan, Manager at
Dept. of Astrophysical Sciences,
Princeton University, with
the 1965 Boller & Chivens telescope.

Dr. Norman Jarosik, a veteran of Princeton's OSETI project, kindly supported the optical disassembly at Princeton in August. Disassembly team members Ken Launie, HUT Observatory associates Alan and Aaron Sliski, and Springfield Telescope Makers member John W. Briggs, also of HUT Observatory, are all active members of the Antique Telescope Society. Peter Abrahams, also of ATS, provided valuable knowledge leading to the discovery of Boller & Chivens mechanical drawings, specific to the Princeton Telescope, in storage at University of Wyoming's Department of Physics and Astronomy. University of Wyoming, in turn, kindly shared them. Of particularly generous and key assistance was Ralph Nye, Head of Technical Services at Lowell Observatory, who was responsible for the original disassembly and recent installation of the Northwestern University 40-inch telescope at JPL's Table Mountain Observatory in California. Heath A. Rhoades, Astronomy Team Lead at Table Mountain, greatly facilitated a transfer of information from Table Mountain's experience to the team's knowledge base. Department Manager Susan Duncan at Princeton worked to facilitate the material transfer to the Foundation, with the cooperation and understanding of Professors David Spergel, Chairman, and Jim Gunn. Early in the process, discussions with Wayne Green, of Colorado's Longmont Astronomical Society, were extremely helpful. For some time the Michele and David Mittelman Family Foundation has helped sponsor Stellafane's annual Hartness House Workshop, 2014 being its sixth year.

Mr. Houston, who has been so helpful in our understanding of the Princeton mirrors, was a frequent participant at Stellafane in the 1960s, visiting the Convention with friends from Perkin-Elmer and ITEK. He has recently visited the Hartness-Porter Museum of Amateur Telescope Making, also operated by the Springfield Telescope Makers. Houston writes, "Stellafane has always represented "Mecca" to me and has been at the core of my love of astronomy and amateur telescope making."

--John W. Briggs, HUT Observatory, Eagle, Colorado.

*Note that accounts differ regarding the flight history of the mirror now at Monterey Institute for Research in Astronomy. Until otherwise corrected, this report follows the account of Joseph B. Houston, Jr., who says the MIRA mirror was indeed a Stratoscope II flight mirror and not merely a backup.

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