How was the second backup primary mirror for the Hubble Space Telescope -- an optic that could have replaced the flawed mirror that famously hobbled the Hubble, had the problem been caught before the spacecraft was launched -- creatively "recycled?"
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?"Get the answer.