The Hubble Space Telescope is undoubtedly the most famous, and arguably the most effective, astronomic instrument ever built. Findings from the Hubble have led directly to the most accurate estimations of the Hubble constant — the rate of expansion of the universe — ever calculated, which in turn led to the realization that the expansion is accelerating, which in turn led to the theorization of dark energy. Moreover, the Hubble was directly responsible for the observation of the aptly named Hubble Deep Field and Hubble Ultra Deep Field, the most distant portions of the universe ever recorded using visible light.
Thus, today it’s easy to forget that, when it first went into operation, the Hubble was publicly labeled as one of the greatest failures — and most expensive boondoggles — in NASA history.
The Hubble, you may recall, began its mission with blurred vision, because its primary mirror — the most precisely ground optical mirror ever created — was flawed. The mirror was only 2.3 microns out of shape — about a third the width of a human red blood cell, or a little more than one 50th the width of a human hair — but it was still vastly inadequate for observing the deep space objects Hubble was designed to see. The distortion caused the light from stars to warp out into a halo, rather than appear as a bright point of light.
The cause of the flaw was a device known as a null corrector, which precisely measures light reflected from spherical mirrors. The manufacturer of Hubble’s primary mirror, Perkin-Elmer, used a faulty null corrector as the main quality-control instrument for the polishing of the centerpiece Hubble optic. Even though backup null correctors detected the error, Perkin-Elmer assumed the main sensor, and thus the mirror, were correct. As you might imagine, NASA, Perkin-Elmer, and the U.S. Congress exchanged quite a few heated words about no one catching the error until the Hubble was in orbit.
Ironically, NASA had contracted for not one, but two backup primary mirrors to be manufactured for the Hubble — neither of which bore the flaw. Unfortunately, it was impossible to install the backups into the orbiting Hubble, and bringing the spacecraft down for refit was entirely too risky and expensive. Instead, the Hubble got a set of “spectacles,” and the backup mirrors were put to other uses. One Hubble reserve mirror is exhibited in the Smithsonian, and the other was “recycled.”
HOW WAS THE SECOND BACKUP MIRROR FOR THE HUBBLE SPACE TELESCOPE “RECYCLED?”
The second backup to the Hubble’s primary mirror is now the central optic of the 2.4 meter SINGLE Telescope at the Magdalena Ridge Observatory in New Mexico. After all, when you have access to one of the three most precisely ground optical telescope mirrors ever created — and one of only two that were ground correctly — there’s no sense in not making a really nice telescope out of it. The SINGLE went online Sept. 1, 2008 and is currently under contract with NASA to track Low Earth Orbit (LEO) objects and to support the operations and observations of the Fermi Gamma-ray Space Telescope.
And should anything happen to the SINGLE’s main mirror, they can always ask the Smithsonian’s National Air and Space Museum if they’d be willing to lend out the other backup Hubble mirror from their collection to do some actual astronomy.
So why did NASA build three copies of the same mirror? As a guard against a problem in the manufacturing process, ironically. Camera giant Kodak and Itek, a manufacturer of spy satellite optics, originally submitted a tandem bid for the Hubble mirror. Each company would manufacture its own optic, and then each would check the other’s work for accuracy.
Perkin-Elmer won the contract over the Kodak-Itek team because Perkin-Elmer promised to use a then-cutting-edge computer-controlled grinding process to ensure the mirror’s accuracy. NASA desired the promised quality of a computer-created mirror, but as the technology was brand new, it required Perkin-Elmer to subcontract with a traditional manufacturer to create a conventional backup mirror, just in case. The backup manufacturer turned out to be the Kodak-Itek team. Thus, three mirrors were made, but only the flawed computer-“aided” one would end up in space.
While the computer-ground mirror was flawed, it was at least precisely flawed, such that NASA could design the Corrective Optics Space Telescope Axial Replacement (COSTAR), which serves as corrective lenses for the Hubble’s main mirror. COSTAR was installed in December 1993, over two and a half years into Hubble’s mission, and will be removed during the final servicing mission to the Hubble in mid-2009 in favor of the Cosmic Origins Spectrograph. After that, the Hubble will likely never be touched by human hands again and consistently observed only by those who track objects in Low Earth Orbit. Like, for example, the astronomers running the SINGLE Telescope, and its Hubble-donated mirror.
That’s not just some apropos orbital observation; it’s a remarkably retrospective reflection on Geek Trivia.
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