How could Hubbles mirrors be so wrong?

In 1990 the Hubble Space Telescope could not bring a star into focus. Its main mirror had been polished with extraordinary care into the wrong shape, by about a fiftieth of the width of a human hair, and it had passed its final test. In December 1993 astronauts went up with new optics built to cancel a flaw in a mirror nobody could touch. This is how that happened. At Perkin-Elmer in Danbury, Connecticut, they measured the mirror in the middle of the night, when no trucks were going by, and took the speed bumps out of their own parking lot. Everything rested on one instrument, the ruler they tested it against. In 1990 investigators found that ruler still standing in a locked part of the plant, with a lens about 1.3 millimetres out of place, held there, the reporters found, by three ordinary washers. Then came the question that runs through the rest of the story: who checks the ruler? CHAPTERS 0:00 The first picture 2:33 Fire Insurance 8:26 Textbook 13:47 Three Washers 20:18 Who Checks the Ruler? 26:12 The Train from Baltimore 28:03 Either Way 31:39 Who's Next 33:37 Credits SOURCES - The Hubble Space Telescope Optical Systems Failure Report (the Allen report), NASA TM-103443, November 1990: chapters 4, 6 and 7, appendix D, figures 4-2, 7-1 to 7-5, D-1 and D-2. - Final Report, Hubble Independent Optical Review Panel (the Moore panel), NASA Goddard, 1991. - NASA Facts, NASA's Optical Verification Program, November 1993. - Robert S. Capers and Eric Lipton, The Hartford Courant, 1991 (reprinted as "Hubble Error: Time, Money and Millionths of an Inch", 1993). The Danbury reporting in the film is theirs, paraphrased. - Robert Gainor, Not Yet Imagined, NASA SP-2020-4237 (2020). - Joseph Tatarewicz, "The Hubble Space Telescope Servicing Mission", in From Engineering Science to Big Science, NASA SP-4219 (1998). - NASA oral histories: Edward Weiler (2017), Lennard Fisk (2010). - John Trauger, in Hubble's Legacy (Smithsonian, 2014). - John Krist and Christopher Burrows, Applied Optics 34 (1995) 4951. - NASA's request for information on Hubble servicing, October 2026. Smithsonian National Air and Space Museum collection records, checked November 2026. The white models, the light rays and the star images are our own illustrations. They show how things worked, not how they looked. CREDITS Film: NASA Goddard Space Flight Center (press conferences of 27 June 1990, SVS 13083, and 13 January 1994, SVS 13084; NASA films of 1983 and 1990, SVS 13059); NASA/JPL-Caltech, The Camera That Saved Hubble (2009); NASA STS-31 and STS-61 mission film (STS-31 via A/V Geeks on archive.org); NASA's video release of 13 January 1994. Photos: NASA (8108126, 8109563, 7995584, 9012885, 9015550, 9009633, 9400255, S31-76-026, 8113715, PIA22912); NASA Johnson Space Center (S93-33257, S93-33258, S93-40315, STS061-S-002, STS061-S-088, STS061-73-040, STS061-94-059, STS061-56-027, S125-E-008116, S125-E-010160); NASA/Joel Kowsky; Smithsonian National Air and Space Museum (Hubble's backup primary mirror, A20010288000, CC0); NASA Earth Observatory, Blue Marble by Reto Stöckli; Connecticut DEEP and USGS, 1990 aerial photography via CT ECO; United States Mint. Music: original score. Samples: Salamander Grand Piano by Alexander Holm (CC BY 3.0, https://creativecommons.org/licenses/by/3.0/), VSCO-2 Community Edition (CC0), Versilian Community Sample Library (CC0). Sound effects (Pixabay Content License): Knock on door, Motor Loop, LightClunk1, Dropping Screws #6, Train horn distant lo fi and Champagne cork by freesound_community; Electric Fan Motor (Blades Removed) by edr; Shower in Bathroom by shoryzow; Metallic latch release by Crinkem; shuttlelaunch by klangfabrik. #FarSignal #hubble #nasa