Bruce Rule brought engineers up from Pasadena to study the problem. They timed the period of the vibrations at 1.4 seconds. The oscillation of the telescope was large enough to be visible. Against a fixed mark on the horseshoe bearing, the structure moved as much as one-half millimeter—a tiny wiggle on the huge structure but enough to cripple the telescope.
It didn’t take long to identify the culprit—the great oil bearing. The friction in the bearing was even lower than the optimistic engineers at Westinghouse had predicted. The same almost frictionless movement that let the five-hundred-ton telescope move from the weight of a milk bottle on one horn of the yoke also allowed the yoke to pick up a natural vibration from the torsion tube that connected the drive gear to the yoke. With virtually no friction to dampen the resonance of the system, the entire mount was vibrating like a tuning fork.
The cure was to add friction to the system. The machine shop came up with an assembly of rubber rollers that pressed on the outside of the yoke and drove a series of disks in an oil bath. The device added enough friction to damp the vibrations. The perfect machine had its first Rube Goldberg addition.
When the vibrations settled down, the rest of the mount of the telescope worked better than anyone hoped. Serrurier’s trusses controlled the droop of the ends of the telescope tube so well that the intersection of the optical axis of the mirror and the corrector lens did not vary by more than 0.01 inch, well within the limits Ross had set for the lens.
The real question was the mirror. Ira Bowen started serious testing with star images—the ultimate test of an astronomical mirror. To make certain that atmospheric effects wouldn’t distort the results, Bowen had to wait for nights of optimum seeing and choose stars that could be imaged with relatively short exposures. He reduced the initial data himself to be sure of the results. Later a team of women “computers” were hired to do the measurements of test plates and the calculations.
No one had ever attempted tests as tricky as these. The Foucault tests in the optics shop had demonstrated the detailed smoothness of surface. The disk was beautifully figured, one of the smoothest optical surfaces ever created. But the mirror of the two-hundred-inch telescope needed more than a fine optical surface to function effectively. The ribbed disk, deliberately designed so that no part of its surface was more than four inches thick, was flexible, a “floppy” sheet of glass at optical tolerances. The lab tests had confirmed that the mirror worked when it was vertical, as it would be when the telescope was pointed at the horizon. To function effectively wherever it was turned, the mirror needed the help of the support system, the complex mechanical devices that would compensate for sags in the shape of the mirror with lever-and cam-induced thrusts against the back of the mirror. As part of his lab-testing program, Anderson had introduced artificially large thrusts in some of the individual supports. The disk reacted exactly as the calculations predicted. But until the mirror was in the telescope and duplicating actual observing conditions, there was no way to know whether the supports would produce the exact compensating forces needed to maintain the figure of the mirror.
Despite Hubble’s early pronouncement that the mirror was good as it stood, Bowen’s tests showed the disk was elastic: The mirror was bending and flopping as the telescope moved, with resulting distortions to the focused images. Every adjustment he tried produced some form of distortion or astigmatism. The support systems weren’t doing their job.
It didn’t take Bowen and Rule long to figure out that the problem was their old enemy stiction, the initial friction of a mechanical assembly when it first begins to move. In the optical shop, where the mirror was tested in a fixed vertical position, the support mechanisms had functioned perfectly. In the telescope, where the supports had to respond quickly to the changing position of the mirror, the stiction in those complex systems turned out to be eight to ten times too high. The result was hysteresis: When the telescope moved, the disk would “remember” its previous shape, a few millionths of an inch off what it should be, enough that the mirror could not effectively focus all the light from faint, distant objects.
Rule, Hill, and Bowen tried different lubricants and adjustments to the support systems. In June 1948, after six months of testing, Bowen concluded that no tweaking of the support mechanisms would cure the problem. The supports had been designed with low-friction pivots, but the measured friction of the pivots varied from 0.5 to 1.5 percent. Bowen calculated that to get the mirror to work right the friction in the supports shouldn’t be more than one-tenth of what they measured.
The only cure would be new support mechanisms. The estimated cost, even with the machine shop cannibalizing and economizing, was $18,000. There was no contingency fund in the budget. The final Rockefeller funds were already committed, and no new expenditures could be made after April 1948. The Carnegie Institution was responsible only for operating funds. If Caltech wanted to use its new telescope, it had to find some more money.
In 1946 Robert Millikan had turned the reins of Caltech over to the physicist Lee A. DuBridge, who had been a graduate student of Max Mason at the University of Wisconsin. His immediate plans focused on expanding the faculty, increasing the size of the campus, and adding new research fields in chemical biology, planetary science, geochemistry, low-energy nuclear physics, and astrophysics. With so many irons in the fire, DuBridge’s fund-raising efforts were already stretched to the limits. Caltech did not have funds to spare for a twenty-year-old project. The equivalent of the salaries of two or three full professors, $18,000 was a large sum in a contracting postwar economy.
One of DuBridge’s new hires was Jesse Greenstein, the new chair man of the astrophysics faculty. Greenstein had graduated from Harvard, where he had been charmed by Shapley’s brilliance and sociability, and subjected to a heavy dose of Shapley’s prejudice against big telescopes in general and the two-hundred-inch telescope and what Shapley deprecated as “West Coast” or “newspaper” astronomy in particular. After a stint working in a family business, Greenstein decided to go back to astronomy and ended up at Yerkes, which was then working on the optics of an eighty-two-inch telescope for the University of Texas. Greenstein discovered a gross error in the testing of the telescope and later used a nebular spectrograph, which incorporated a small Schmidt camera made by Don Hendrix at the Mount Wilson optical shop, on the big telescope. He became a big-telescope convert. Using data from the new spectrograph like David’s sling and stones, Greenstein wrote an article that challenged Hubble’s measurement of the color temperature of M31.
Greenstein had barely settled in at Caltech when he was told about the need for the new support systems. Greenstein saw his plans for a great astrophysics department stalled. He marched into DuBridge’s office and persuaded a reluctant Caltech administration to come up with the $18,000 for the new supports. Before the telescope was finished, Caltech would have to put between $80,000 and $90,000 into the project.
Once the funds were committed, the astrophysics machine shop went into high gear for the summer to rebuild the supports.*
The newspapers, and George Hall at the Caltech publicity office, couldn’t wait for the slow birth of the telescope. Except for a few astronomers and visiting bigwigs from the Rockefeller Foundation, the world hadn’t seen the big telescope in action, and Caltech was eager to show it off. The gala dedication was scheduled for June 3, 1948. Byron Hill and the staff cleared equipment off the floor of the observatory and set up hundreds of folding chairs in rows under the telescope. The VIPs were scheduled to have a preliminary dinner at Mount Wilson on June 1 and then a private evening at Palomar on June 2—the ecumenical pairing of events was meant to demonstrate the friendly merger of the institutions—before the actual dedication on the afternoon of June 3.
June 3 dawned bright and sunny. The invited crowd filled every chair in the dome. When Vannevar Bush spoke, a meadowlark flew into the dome through the open shutters, and for much of the following remarks by Robert Millikan, Raymond Fosdick of the Rockefeller
Foundation, Max Mason, and James Page, the chairman of the board of Caltech, many in the audience watched the lark as it circled high in the dome.
Evelina Hale, George Hale’s widow, was on the dais, and no one was really surprised when Lee DuBridge, the president of Caltech, announced that the telescope would be named the Hale telescope. The naming had been treated as a “state secret” at Caltech, but as far back as Hale’s death, in 1938, the New York Times had urged that the telescope would be a suitable memorial. Some astronomers close to the project, like Walter Adams, had already begun calling it the Hale telescope.
When the formal speeches concluded, Ira Bowen described how the telescope worked. Bruce Rule stood at the night assistant’s control panel. “Like the usual fond parents,” Bowen said, “We hope that our new child will not follow the precedent of most infants and misbehave badly on this the first occasion that it has been put on display before a large group of distinguished visitors.”
The telescope behaved. No loose parts or oil fell on the guests, and nothing creaked or groaned, as five hundred tons of machine majestically slewed back and forth. There were celebrities and dignitaries in the audience, along with Caltech trustees, distinguished scientists, engineers, and workmen. The actor Charles Laughton was there, wearing a rumpled raincoat. Some men in the audience had worked on the project for as long as fifteen or twenty years. Russell Porter, bitter that he had been slighted for so long, didn’t come, but Marcus Brown was there, and George McCauley had driven across the country to see the complete telescope for the first time.
To give the visitors a peek at the fabled mirror, they were invited to go up to the balcony around the inside of the dome. When Rule rotated the dome, the motion of one thousand tons of steel and aluminum, even with eight hundred people on the balcony, was eerily smooth. A confused radio announcer, ignoring Bowen’s explanations in favor of what he felt, announced that the floor with the telescope on it was rotating inside the dome.
Anne Price, George McCauley’s daughter, had grown up with the telescope as part of her life. She could remember the evenings when her father worked late at the dining table, and the times he had run off to check on the disk after church on Sundays, the crises of the flood and earthquakes, and the high moment when the disk left Corning on its journey across the country. She knew, even as a child, that her father’s part in the building of the telescope had been the centerpiece of his working career, as it had been for so many men. She and her husband were newlyweds. The trip to California was their honeymoon. That bright sunny afternoon she watched her father’s masterpiece become part of America.
When the crowd left, Bowen went back to his test photographs. Every evening with clear weather, he exposed images of stars, using the full-size Hartman screen with four hundred holes. To search for irregularities in the surface between the diameters of the Hartman tests, Bowen set up a knife-edge and photographed the resulting patterns with a Leica camera.
It was the end of the summer before the new support mechanisms were ready. The redesign had included a new compound lever system, a lengthened lever arm, and sixteen new bearings. To make sure the supports were as friction-free as possible, the bearings were preselected from hundreds of samples of each type that Timken and other companies were willing to ship to Pasadena; in return the companies got the right to publicize the use of their bearings in the great telescope. The bearings were run at from 1/50 to 1/100 of their rated load. The initial friction in the supports dropped from 1.30 to 0.12 percent, theoretically low enough for the supports to do their job. A new series of tests showed that the mirror retained its shape, within the design limits, no matter which way it was turned.
With the support system working, the test photographs revealed the work still needed on the mirror: The outside edge was high, and the tests on stars revealed zones in the mirror which needed polishing. Don Hendrix estimated that without interruptions the work would take six months. Bowen thought the estimate reasonable. But the telescope was no longer a private project. Newspaper and magazine reporters had begun asking for results. The repeated answer that more testing was needed, along with some rumors that seem to have originated with Harlow Shapley, prompted gossip that the telescope was a bust.
To silence the rumors another first light was set up for January 1949, again without advance publicity. Edwin Hubble showed up with his favorite eyepiece from Mount Wilson. The eyepiece lacked an illuminating light, so Ben Traxler, then the senior electrician at Palomar, offered to install one. He took the eyepiece down to his workshop, drilled the barrel and carefully mounted a small light. When he was finished, he noticed brass shavings in the brass barrel of the eyepiece and wiped them out, wiping the crosshairs off the lens in the process. There wasn’t time to return to Pasadena for another eyepiece before the observing session. Traxler wasn’t an optician, but he remembered hearing that the opticians used spiderwebs for crosshairs. He ran back to the garage of his cottage, found a black widow spiderweb, and stole some threads to glue them in place. They weren’t perfect—one thread staggered across the eyepiece like the trail of a drunk—but the eyepiece was usable. Improvisation was already a tradition at Palomar.
Carrying the hastily repaired eyepiece, Hubble ascended the elevator to the prime-focus cage and over the intercom gave the night assistant the coordinates for Coma Berenices. At 10:06 P.M. PST, on January 26, 1949, Hubble pulled the slide of the plate holder to expose photographic plate P.H.-1-H. (the P for Palomar, the first H for Hale [telescope], and the second H for the observer). The first image was of NGC 2261, a variable galactic nebula—a comet-shaped mass with a variable star, R Monocerotis, at the apex—that Hubble had discovered at Yerkes.*
The control mechanism did the guiding without intervention. When the plates were developed later that night, Hubble announced that the threshold images, the faintest specks that could be resolved, appeared to be nebulae rather than stars, and that some of the faint nebulae were “presumably at about twice the distance reached with the 100-inch.” Exposures of only five or ten minutes, he later told audiences and reporters, recorded stars the one-hundred-inch telescope could not reach in a full night’s exposure. “The 200-inch opens to exploration a volume of space about eight times greater than that previously accessible for study…. The region of space that we can now observe is so substantial that it may be a fair sample of the universe as a whole.” While Hubble gave speeches to quell the rumors, Bowen and the opticians went back to work on the mirror.
Working in a cleared area of the floor of the dome, Don Hendrix and Mel Johnson stripped the aluminum coating off the disk and set up a portable polishing machine, with its hub in the center of the mirror and the outer edge resting on the rim of the disk. After each polishing session, Byron Hill and his crew would mount the mirror into the telescope, and Bowen would wait for a good night to take more test photographs. The disk was uncoated—the aluminizing procedure was far too complex to be used for each test—so he used only the reflectivity of the glass surface for his test photographs of stars. When he had another good set of test photographs, Hill’s crew would remove the mirror from the telescope and Hendrix and Johnson would go to work again.
Hendrix started with a twelve-inch polishing tool on his machine and gradually worked his way down to tools the size of a half-dollar. As the edge was brought down, Bowen and Hendrix began to identify small zones of the mirror that needed correction. The zones were too small to use the polishing machine, so Hendrix and Johnson would use handheld cork tools to remove five-or six-millionths of an inch of material. The observatory wasn’t a “clean room” like the optics lab, but for the sake of the opticians’ concentration and cleanliness, no one else was allowed on the observatory floor while Hendrix and Johnson worked.
Sometimes the weather or the seeing wasn’t good enough for testing the mirror, and everyone would have to wait for days for another round of tests. When the remaining defects were too small for the cork tools, Hendrix and Johnson would polish the mirror w
ith their thumbs. They would dip a watercolor brush in a slurry of water and polishing compound—a mixture called Barnesite—paint the zone with the brush, then polish with a few strokes of a naked thumb. The thumb was a good instrument; it didn’t slip. Each stroke would remove one-or two-millionths of an inch of glass. After a few strokes, sometimes only one or two, they had to stop, because the heat of their thumbs and the pressure of the polishing would have heated and expanded the mirror. The whole polishing that day might have taken two or three minutes. The disk then had to be remounted on the telescope, an operation that took most of a day. The crews got practiced at removing and re-attaching fourteen and a half tons of mirror and mirror cell.
The final figuring of a telescope mirror is a battle between perfection and reality. The opticians begin talking fractions of a wavelength of light, distances that have little meaning when they are translated into inches or even millimeters. The opticians’ eyes glisten as they dream of achieving what no other optical surface has achieved, a surface so smooth that if the two-hundred-inch mirror were the size of the continental United States, it would have no bumps on its surface higher than a few inches.
Several times a week Bowen would give the lunch group at his favorite sandwich shop his latest report on the status of the mirror. The astronomers were champing at the bit: There are never enough big telescopes, never enough hours of observation time. While the opticians polished, the research projects—especially projects that could only be completed on the two-hundred-inch telescope—piled up. The astronomers wanted, needed, the telescope. Atmospheric effects and defects in the photographic emulsions, they argued, would mask any further improvements in the mirror.
The Perfect Machine Page 56