Flaw in Hubble Telescope

In response to "Simple Test Would Have Found Flaw in Hubble Telescope," Part A, July 10:

Grinding, polishing and optically figuring a telescope mirror is as much an art as a science. The Hubble mirror apparently suffers from a defect known to amateur telescope builders as a "turned down edge," which can be detected with test equipment not much more elaborate than a flashlight, three razor blades, and some masking tape. It seems astonishing that the superb opticians at Perkin-Elmer could have certified a mirror with this defect. I suspect that in NASA's zeal to use state-of-the-art technology, the trained eye of the optician was not deemed a sufficiently objective tool.

Rather than wait three years for a new camera that may or may not correct the problem, NASA officials should consider the possibility of sending a shuttle crew to mount a mask on the telescope tube to "stop down" the aperture so that the defective edge of the mirror is hidden. This could have the effect of turning a mediocre 94-inch mirror into a superb 80-inch one. It's an unglamorous fix, and would work only if the mirror's edge is indeed turned, but it could salvage most of Hubble's mission. The mask should be taken as a backup option in case the modified camera can't correct the distortion.

DON DIXON

Long Beach

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