Editing Hubble Space Telescope (section)

=== Origin of the problem ===
[[File:PIA22913-HubbleSpaceTelescope-ComparisonOfCameraImages-20181204.jpg|thumb|upright=2.5|Optical evolution of Hubble's primary camera system: these images show spiral galaxy [[Messier 100|M100]] as seen with WFPC1 in 1993 before corrective optics (left), with WFPC2 in 1994 after correction (center), and with WFC3 in 2018 (right).]]

A commission headed by [[Lew Allen]], director of the [[Jet Propulsion Laboratory]], was established to determine how the error could have arisen. The Allen Commission found that a reflective [[null corrector]], a testing device used to achieve a properly shaped non-spherical mirror, had been incorrectly assembled—one lens was out of position by {{convert|1.3|mm|in|abbr=on}}.{{sfn|Allen|Angel|Mangus|Rodney|1990|p=7-1|ps=: The spacing of the field lens in the corrector was to have been done by laser measurements off the end of an invar bar. Instead of illuminating the end of the bar, however, the laser in fact was reflected from a worn spot on a black-anodized metal cap placed over the end of the bar to isolate its center (visible through a hole in the cap). The technician who performed the test noted an unexpected gap between the field lens and its supporting structure in the corrector and filled it in with an ordinary metal washer.}} During the initial grinding and polishing of the mirror, [[Perkin-Elmer]] analyzed its surface with two conventional refractive null correctors. However, for the final manufacturing step ([[figuring]]), they switched to the custom-built reflective null corrector, designed explicitly to meet very strict tolerances. The incorrect assembly of this device resulted in the mirror being ground very precisely but to the wrong shape. During fabrication, a few tests using conventional null correctors correctly reported [[spherical aberration]]. But these results were dismissed, thus missing the opportunity to catch the error, because the reflective null corrector was considered more accurate.{{sfn|Dunar|Waring|1999|p=512|ps=: "the firm's optical operations personnel dismissed the evidence as itself flawed. They believed the other two null correctors were less accurate than the reflective null corrector and so could not verify its reliability. Since they assumed the perfection of the mirror and reflective null corrector, they rejected falsifying information from independent tests, believed no problems existed, and reported only good news."}}

The commission blamed the failings primarily on Perkin-Elmer. Relations between NASA and the optics company had been severely strained during the telescope construction, due to frequent schedule slippage and cost overruns. NASA found that Perkin-Elmer did not review or supervise the mirror construction adequately, did not assign its best optical scientists to the project (as it had for the prototype), and in particular did not involve the optical designers in the construction and verification of the mirror. While the commission heavily criticized Perkin-Elmer for these managerial failings, NASA was also criticized for not picking up on the quality control shortcomings, such as relying totally on test results from a single instrument.{{sfn|Allen|Angel|Mangus|Rodney|1990|p=10-1}}