Corning, Kodak, and Hubble

This being the 25^th anniversary of the launch of the Hubble Space Telescope, it is an opportune time to take a look at the connections between Upstate New York and the Hubble. I will focus on two companies. Corning, whose technological innovations made the Hubble possible, and Kodak, whose efforts could have spared the NASA the grief of Hubble’s original design flaw.  The story begins in the 1930’s, as the proposed 200-inch Mt. Palomar Observatory mirror required a low expansion material to make the large mirror possible.

During the 1920’s, the largest telescope in the world was the 100-inch reflector at Mt. Wilson Observatory. It was in this decade that Edwin Hubble would make his historic observations at Mt. Wilson, which included the discovery of galaxies outside the Milky Way and the expansion of the universe. At the time, George Ellery Hale was in the planning stages of building the 200-inch telescope at Mt. Palomar. To understand the engineering problem at hand, the surface area of the Mt. Wilson mirror is:

A = πr²

Which is (3.14)(50² inches) = 7850 square inches or 54.5 square feet.

The surface size of the Mt. Palomar mirror would be:

(3.14)(100² inches) = 31,400 square inches or 218 square feet.

Despite the fact the diameter of the mirror at Palomar would be only double that at Mt. Wilson, the surface area would be 4 times larger. The mirror at Mt. Wilson was made at the French Glass Works and weighed 9,000 pounds (the mirror at Mt. Wilson is green just like a wine bottle). The greater surface area of the Mt. Palomar mirror demanded a material that did not expand or contract as much to temperature changes. Unless an alternative material could be found, this expansion and contraction would distort the optics to the point of making the primary mirror useless.

Enter Pyrex

The invention of Pyrex at the Corning Glass Works was the result of an effort to make lantern glass suitable for railroad watchmen. Traditional glass lanterns would shatter when the heat of the flame combined with cold winter weather. By 1915, Pyrex was being produced for its most well known application-kitchenware. The low heat expansion quality of Pyrex made it an excellent material for cooking.

In 1932, George Hale was looking for a material to cast the 200-inch Palomar mirror. His first choice was fused quartz, but the efforts at General Electric to cast the mirror this way proved unsuccessful. After spending $600,000 ($10 million in 2015 dollars) on the failed quartz effort, Hale turned to the Corning Glass Works and its Pyrex product to give it a try for the Palomar mirror.

Besides kitchenware, you may be familiar with Pyrex from your high school chemistry lab. Pyrex is regular glass with borax oxide added to it. The combination produces borosilicate glass, which experiences low expansion when exposed to heat. This is what keeps Pyrex kitchenware and lab equipment from breaking when it is heated up rapidly. So, why is this important for a telescope mirror that does not experience the same type of heating when Pyrex is put in an oven or over a Bunsen burner?

The optical precision required for the Palomar mirror meant that the mirror could not deviate more than two-millionths of an inch from its prescribed shape. Needless to say, the slightest amount of thermal expansion would have grievous effects on the optical quality of the images produced by the mirror. With this in mind, the Corning went to work on producing the Palomar mirror blank with its Pyrex material.

It would take two tries for Corning to build the mirror to be used at Palomar. During the first attempt, pieces of the mold in the mirror broke off due to the heat used in the casting process. This flawed mirror is now on display at the Corning Museum of Glass (see video below). The second mirror was shipped via a highly publicized train ride cross-country to California in 1936. There, over 10,000 pounds of the glass was shaved off in an extensive grinding process to polish the mirror to its required shape to produce the high-quality images for the telescope. World War II delayed this work a few years, but eventually the mirror was installed in the telescope in 1948.

Mt. Palomar would remain the world’s largest telescope until 1993 when the Keck Observatory in Hawaii surpassed it. During its run as the world’s largest telescope, astronomers at Palomar would refine the measurement of the expansion of the universe and discover quasars among its many other discoveries.  At the same time, Corning’s experience with producing observatory mirror blanks would be called upon again to make another groundbreaking instrument of astronomy.

In 1946, Lyman Spitzer proposed an observatory be placed in orbit above the distorting effects of the Earth’s atmosphere. In 1962, at the dawn of the space age, the National Academy of Sciences recommended that Spitzer’s concept be adopted by NASA as a long-term goal of the space agency. In 1977, Congress approved funding for an orbiting space telescope. In 1978, Corning went to work to produce two mirror blanks for the Hubble.

The Hubble mirrors were not made from Pyrex. By the 1970’s, Corning developed Ultra Low Expansion (ULE) fused titanium glass. Rather than use borax oxide as Pyrex does, ULE is made with a blend of titanium and silica to give it a nearly zero expansion coefficient. Besides being used for telescope mirrors, ULE was also utilized for space shuttle windows, as it could resist expansion when frictional heat built up during re-entry into Earth’s atmosphere.  This ability to maintain its shape made ULE an excellent candidate for the space telescope mirror.

Even though the Hubble mirror is kept at constant 70⁰ F, the mirror shape only deviates 1/800,000 of an inch. If the Hubble mirror were the diameter of the Earth, its highest “mountain” would only be six inches. The nearly expansionless ULE maintains this optical precision.  ULE is also very lightweight.  Despite being the same size as the 100-inch Mt. Wilson mirror, the Hubble mirror is only 20% the weight.

After the production of the two mirror blanks, one was shipped to the Perkin-Elmer Corporation, the other to Kodak-Eastman for polishing. The blank sent to Perkin-Elmer eventually was used for the Hubble.  It was at this stage the fateful flaw would be made in the Hubble mirror.

A Kodak Moment NASA Regrets Passing Up

NASA received two bids to polish the mirror blanks from Corning. The Kodak bid was for $105 million while Perkin-Elmer bid was for $70 million ($300 million and $200 million in 2015 dollars respectively). Naturally, the Perkin-Elmer bid was viewed as the most competitive but it contained some troubling aspects. The Kodak bid was to polish two mirrors with different testing techniques. The testing mechanism on each mirror would then be used on the other to determine which was the better mirror and as a quality control measure. Perkin-Elmer relied on a single method to polish the mirror. It then sub-contracted Kodak to polish the back-up mirror, albeit at NASA’s request.

Further complicating matters (wonderfully described in Robert Capers and Eric Lipton’s report) was the budgetary and time constraints the Perkin-Elmer employees were working under. Perkin-Elmer had deliberately low-balled their bid to win the contract with the expectation Congress would approve more funding as the project progressed. However, the early 1980’s experienced the greatest recession since World War II as unemployment climbed towards 10% and Congress was in no mood to allocate more funding to polish the mirror.

In the proverbial cruel twist of fate, the famous flaw in the Hubble mirror was a result of the use of three washers (yes, the very same kind used in your kitchen faucet) by Perkin-Elmer technicians to shim the optical testing device referred to as a null corrector. A piece of worn paint caused a misalignment of a laser that calibrated the distance from the null corrector to the mirror.  The overworked and rushed Perkin-Elmer technicians failed to report the calibration error to meet the deadline to produce the mirror.  This was combined with overconfidence in the null corrector device as signs of a design flaw in the mirror were ignored by the Perkin-Elmer project management. In the end, the mirror was polished perfectly to the wrong prescription, as the null corrector was 1.3 mm closer to the mirror than it should have been. The flaw in the mirror itself was 2 micrometers or about 1/50^th the width of a piece of paper.

Consequently, the $1.5 billion Hubble was launched into orbit 25 years ago today with spherical aberration in its mirror causing blurry images due to three washers worth about twenty cents.

And what happened to the Kodak mirror? It stayed here on Earth. Kodak was not able to use its cross testing method as it only made one mirror rather than two. However, Kodak had used more traditional, time-tested methods to grind its mirror and finished its work in 1980, well before the Perkin-Elmer mirror. When the Hubble mirror flaw was discovered shortly after launch, the Kodak mirror played a key role in the ensuing investigation. The final determination was that the Kodak mirror was ground to the right specifications and the corrective measures would not have been required had it been placed in the Hubble. Since Kodak was subcontracted by Perkin-Elmer, it was the latter who had the final say which mirror to use and quite naturally, Perkin-Elmer decided to use its own mirror. The flaw was corrected in 1993 by the STS-61 mission.  The shuttle mission replaced the original Wide Field and Planetary Camera (WFPC1) with another^* (WFPC2) that contained optics to counteract the spherical aberration in the Hubble mirror images.  The difference before and after are below:

For the other instruments on the Hubble, the Corrective Optics Space Telescope Axial Replacement (COSTAR) was installed.  This was a set of mirrors used to act as “glasses” to correct the spherical aberration for the Faint Object Camera & Spectrograph, along with the High Resolution Spectrograph.

The Kodak mirror (below) now resides at the Smithsonian Air & Space Museum.

* Both the WFPC2 and COSTAR that corrected the mirror flaw in the Hubble were removed in 2009 by the final Hubble shuttle servicing mission. The WFPC2 and COSTAR were also donated to the Smithsonian Air and Space Museum.

Image on top of post is the Hubble mirror.  Photo:  NASA/ESA