The Perfect Machine (24 page)

Fast telescopes with traditional paraboloid mirrors also have small
fields of sharp, coma-free focus. The
f-
ratio of the one-hundred-inch Hooker Telescope was
f/5,
which was typical for reflectors used for deep-space research. The uncorrected field of sharpness at the primary focus was less than an inch in diameter, because of an aberration introduced when the light from a parabolic mirror was focused on a plate. If they were to make the new telescope even faster, say
f
/73.3, the field of sharpness at the prime focus would be even smaller. A circle of film half an inch in diameter is a small area in which to concentrate the images of the heavens.

Hale asked Anderson, Adams, Pease, and Frederick Seares, Shapley’s teacher at Missouri and now an astronomer on the staff at Mount Wilson, to explore the diameter of the “good field” at the prime focus of a two-hundred-inch telescope at focal ratios of 1:3.3, 1:4, and 1:5, and to calculate the sharp field that could be used if they tried curved plates instead of a normal flat glass photographic plate. “Considering the great investment in the telescope, and the value of short periods of the best seeing,” he wrote in his memo, “It might easily pay to use such plates for several classes of work.” Graduate students were recruited to do the calculations.

A curved plate, they discovered, would not increase the useful field of a fast telescope. In France, George Ritchey and Henri Chrétien had experimented with a new telescope design that bears their name. By using a hyperboloid shape in the secondary mirror, and a deep, fast primary mirror, the Ritchey-Chrétien design provides an image at the Cassegrain focus free from the coma, or distortions outside the central field of focus, that plague telescopes based on paraboloid mirrors. But the mirrors of the Ritchey-Chrétien design are difficult to figure, it requires curved photographic plates to realize the full promise of the design, and despite the promise on paper, no working telescope had ever been built to the design.

The alternative to increase the useful “good field” of a fast telescope was to use an auxiliary corrective lens to compensate for the aberrations. No one had ever designed a lens that could correct the field of a large
f
/3.3 telescope. Frank E. Ross, at Yerkes, thought he could come up with a corrector lens if the project could support him and his “computer,” a woman named Margaret Johnston, who got fifty dollars for a half month of work. Ross planned to use the sixty-inch and one-hundred-inch telescopes as test beds for the corrector lens design. But his work was another experiment, with no promise of success. Every stage of design of the telescope, it seemed, called for research and engineering that had never been attempted before.

Shortly after the grant was awarded, Hale had written to his friends at Warner & Swasey, who had built the mounts for almost every large telescope since the first big Lick telescope, asking if their chief designer/engineer, E. P. Burrell, could come to Pasadena to assist
in the design. Burrell had recently designed and supervised the construction of the seventy-two-inch Victoria telescope, the newest large telescope, second only to the Hooker.

Pease and Porter had already sketched different designs for a mounting for the telescope. Pease’s was a refinement of the drawings and model he had been working on for almost ten years. It was a conservative approach, a blown-up version of the fork mount of the sixty-inch telescope, relying on massive girders and huge roller bearings for rigidity and smooth motion.

Porter’s telescope design experience was with small amateur telescopes, many of radical and innovative design, like his garden telescope. He had never designed a large telescope. In his early sketches of possible mountings, he tried to combine the rigidity of the English-style mounting of the one-hundred-inch with the versatility of a fork mount. His designs evolved into a split-ring mounting, so different from any other telescope that had been built that the design was relegated to a curiosity.

Hale favored Pease’s design, which drew heavily from features and solutions that had been worked out on the sixty-inch telescope on Mount Wilson and the seventy-two-inch Victoria telescope. The Pease design, which everyone had looked at and talked about, in one form or another, for more than eight years, seemed a safe, simple solution. “It simply remains to adapt the best of these, in the light of recent progress, to the needs of the 200-inch telescope,” Hale wrote. “We now know beyond question that a tube and mirrors having a combined weight of 150 tons, involving a total weight for the moving parts of 500 tons, can be mounted equitorially and without troublesome flexure so as to afford access to the entire available sky.”

Burrell drew up a design based on Pease’s sketches and drawings. His drawings were passed on to Professors Paul Epstein and Romeo Martel of the California Institute, for calculations of the flexure in the mounting, and also to Hale’s friend Gano Dunn and his colleague Samuel R. Jones of J. G. White Engineering. The old-boy network was in full swing.

While the engineers calculated, Warner & Swasey built a model of the Pease design for exhibition at the National Academy of Sciences. The model, with a huge fork mount carrying the entire weight of the telescope on oversize roller bearings, and with a filigree box-girder construction for the tube of the telescope, relied on the same Brooklyn Bridge school of over engineering that had produced the one-hundred-inch telescope. Like Pease’s earlier model, which had been brought out for late-night discussions at Mount Wilson, the Smithsonian model was an exhibition piece, to meet public demands and queries. The actual design work on the telescope was in suspension, awaiting progress on the mirror.

While they waited Pease explored options for constructing the telescope. The mounting for the one-hundred-inch telescope had been built on the East Coast, but labor was 15 percent cheaper in California than
on the East Coast, and 15 percent of $2 million—Pease’s estimate of the fabrication cost—was $300,000. Los Angeles had more sunlight, cheaper power, cheaper gas, freedom from extreme temperatures, and freedom from strikes in the nonunion shops. G. W. Sherburne, a local machinist, estimated that they could erect their own local plant for the fabrication, with a salvage value of 50 percent. At Mount Wilson’s own shops, overhead was less than 25 percent. By contrast, when they had paid the Fore River Shipyard to build the one-hundred-inch telescope mounting, the overhead had run from 35 to 110 percent, plus a 10 percent profit.

To explore another option, Pease organized a conference at the Llewellyn Iron Works in Los Angeles, a large foundry that assured him and Anderson that they could fabricate anything that could be built on the East Coast at considerable savings.

With the actual design of the telescope on hold, awaiting progress on the mirrors, Porter turned his efforts to designing an astrophysics laboratory for the California Institute campus. The building would provide laboratory space, offices, a library. Construction was scheduled to start in the spring.

Work was already under way on machine and instrument shops, which Porter had also designed, and Sherburne was persuaded to come in and take charge of the machine shop. Hubble was named chairman of the Astrophysical Observatory and Laboratory Advisory Committee. On the recommendation of the committee, the machine shop was equipped with forty-inch tools, large enough to do much of the fabrication for instruments, auxiliary telescopes, and some of the precision-drive equipment that would be required for the big telescope.

Porter, who had considerable experience with mirror grinding from his days of writing for amateur telescope makers in
Scientific American,
and more experience of cold than anyone else, argued that the original idea of grinding and polishing the mirror at the observatory site was less than ideal. The opticians at the Santa Barbara Street optical labs agreed. The laborious grinding and figuring of a large mirror was too delicate a job for a mountaintop. There wasn’t room in the Santa Barbara Street laboratories for a two-hundred-inch mirror, and after the brouhaha over the application, the relationship between the Mount Wilson Observatory and the new project was still so tentative that an optical laboratory for the Caltech campus, large enough to house the mirror-grinding project, became the next item on Porter’s drafting board. While the architectural details of the buildings were being fleshed out by a New York architectural firm, site work began on California Street in Pasadena—the first tangible evidence of the telescope project.

Visitors to the campus were told the purpose of the buildings, and some were even shown the Porter drawings of various designs that had begun to line the halls and offices of temporary buildings. But buildings and drawings were no substitute for a telescope.

12
Depression

The new year came without good news from the GE labs in West Lynn. Ellis and his staff fiddled for months before they had the furnace and auxiliary equipment ready to surface a twenty-two-inch disk, a substantial leap up from their previous efforts, and the last trial disk on their schedule before they began a five-foot auxiliary mirror that would actually be used in the telescope.

The equipment had to run twenty-four hours a day, spraying layer after layer to build up the clear quartz surface. The operation went well until the blank was half glazed. One of the three heating elements in the furnace burned out. Two elements could maintain the needed 1700° temperature, so work continued. Then another element burned out. Ellis ordered the furnace partially cooled, repaired, and refired. Before it was hot enough to restart the spraying equipment, the repaired elements failed again.

Ellis and Thomson concluded that the furnace had to be rebuilt. Ellis took advantage of the shutdown to do some planning for the big disks, extrapolating from their experience on the smaller one. The figures he came up with were shocking: A surface layer 2.5 inches thick on a two-hundred-inch-diameter disk would require seven million cubic feet of hydrogen fuel—enough to fill two
Graf Zeppelins.
To surface the disk, GE would need either an enormous hydrogen plant on the premises, or a gasometer one hundred feet in diameter and seven hundred feet tall. In an era long before the creation of the Occupational Safety and Health Administration (OSHA) or the explosion of the dirigible
Hindenburg
at Lakehurst, New Jersey, in 1937, no one gave much thought to the danger of storing that much hydrogen near an industrial plant.

The hydrogen consumption was so daunting that Ellis tried calculations for alternative fuels. A nearby plant produced dissociated (chemically separated) ammonia. A rail spur connected the plants. Ellis calculated that 3,700 tank car-loads, each of 2,500 cubic feet of
ammonia, would be enough for the two-hundred-inch mirror. A shuttle train could carry the tanks, if the trains didn’t break down and if they kept enough men on duty to load and unload the continuous stream of tank cars. With either fuel the lab would need a huge supply of oxygen for the furnace. An on-site plant could be built to produce it. The project was beginning to seem bigger than anyone had anticipated.

Ellis’s mechanics finally got the electric furnace rebuilt. During testing the furnace broke down with nagging regularity, but Ellis persisted and produced two twenty-two-inch fused-quartz disks by mid-August 1929. The disks were suitable for testing, but Ellis warned Anderson in California that the quartz had emerged from the furnace with mysterious black specks embedded in the surface.

With the disks packed and shipped off to Pasadena, Ellis again shut down the furnaces, and had the room sealed off until he could figure out what caused the specks. Chemical analysis was inconclusive. He tried introducing traces of potential contaminants into the flame of the torch to see if he could produce comparable spots. After weeks of testing, iron turned up the likely culprit. When tests of the refractory bricks of the furnace, the piping and burner components, and the oxygen and hydrogen gases that had been fed to the burner could not detect quantities of iron greater than 0.0001 of 1 percent—too small to account for the specks—that left only the quartz itself as the source. The contaminations in the supposedly pure quartz were proving as troublesome and incurable as George Hale’s demons.

One correlation that emerged from the testing was that the specks seemed to be most numerous when the quartz had been deposited onto the disk at relatively low temperatures. That meant an end to Ellis’s idea of using dissociated ammonia as a fuel for the spraying. Ammonia would have been cheaper, safer, and easier to transport and store, but it would fire the burners at a lower temperature than hydrogen. It looked as if they still needed two
Graf Zeppelins
of hydrogen.

Charges for overtime and new equipment piled up. While they waited for the results of the optical tests on the disks that had been shipped to Pasadena, Ellis and Thomson planned for the fabrication of a sixty-inch disk that would actually be used for one of the secondary mirrors in the telescope. The telescope would ultimately require two or three sixty-inch secondary mirrors, on the optical paths for the Cassegrain and Coudé foci. The laboratory at West Lynn was big enough to house the furnace for the mirrors, but Thomson confidently authorized construction of a new building for the next stage of the spraying operation.

No one had ever seen a building quite like what Thomson designed: sheet iron sides and roof over a structural steel frame. And Anderson, in Pasadena, had never seen a bill like the one Thomson forwarded. With the connections for heat, light, water, steam, and gas, the electrical equipment to regulate the furnaces, and the construction
of a furnace large enough for a sixty-inch mirror, the building cost more than $115,000, close to half of the entire original GE budget for producing all the mirror blanks for the telescope. When Anderson questioned the expense, Thomson pointed out the advantages of his design: The structure could easily be expanded to accommodate the spraying of the two-hundred-inch mirror, and the steel walls of the building would have a high salvage value when the operations were finished. Nothing was too good for a perfect machine.