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From: John Larkin on 22 Oct 2009 10:09 On Thu, 22 Oct 2009 08:53:43 +0100, Martin Brown <|||newspam|||@nezumi.demon.co.uk> wrote: >John Larkin wrote: >> On Tue, 20 Oct 2009 22:28:50 -0700, >> "JosephKK"<quiettechblue(a)yahoo.com> wrote: >> >>> On Mon, 19 Oct 2009 13:02:28 -0700, John Larkin >>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>> On Sat, 17 Oct 2009 21:03:41 -0700, >>>> "JosephKK"<quiettechblue(a)yahoo.com> wrote: >>>> >>>>> On Sat, 17 Oct 2009 09:25:35 -0700, John Larkin >>>>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> >>>> "The Hubble Wars" is especially good. The arrogant mirror grinders >>>> decided their mirror was so good that only one test fixture was good >>>> enough to check it. Basic, routine crosschecks were scorned. A good > >That isn't quite true. Some of the routine cross checks *were* done and >with hindsight showed the fault but were dismissed at the time as >systematic errors in the much cruder procedures. In part it was >management failure under time and cost pressure rather than an >engineering problem. The primary null tester design was the gold >standard and would have worked if it had been assembled and used >correctly. The other two null testers correctly showed the spherical >abberation but were believed at the time to be in error. > >PE manufacturing cocked it up. At the time it was the smoothest manmade >surface ever produced. The backup mirror by Kodak that didn't fly was >perfect in figure but not as nicely polished. I think it is now in a >Washington museum. > >>>> amateur telescope maker could have detected the figure error. It never >>>> made an image before it was launched into orbit. > >That may sound bad to you but the additional support structures to do >that even as a zenith transit instrument in the Earth's gravity would >have needed a lot of extra investment when they were being told to cut >costs so the project could actually go ahead. Chances are if they had >tried to do it right from an engineering perspective the entire thing >would have been cancelled for cost overrun. And no-one wanted that. > >It didn't help that because of the Shuttle explosion the HST spent so >long on the ground after being built that ground based observations and >newer CCD technology moved onto its turf very quickly. It was a real >shock when the HST would not focus properly at first light. >>>> >>>> When the telescope wouldn't focus and a meeting was called to find out >>>> why, and the real problem began to emerge, one of the optics designers >>>> stepped out into the hallway and vomited. > >I am not surprised. They figured the main mirror very precisely to the >wrong curve. Although since it was neither spherical nor parabolic the >average amateur telescope maker would not have been able to test it >reliably without a null corrector. The level of error was huge in >optical terms relative to the complex curve that was needed. But you >cannot judge those sorts of curves with a pinhole and a razor a la ATM. >>>> >>>> John >>> Oh no. That is not the whole story. >> >> Of course it's not the whole story. Read the book for more. > >I suspect there is an element of truth to what JKK says, but I knew >parts of the team that did the HST image deconvolution code and a >holographic determination of the figure error. The methods were borrowed >from big dish radio astronomy. AFAIR the fault was manufactured in by >excessive reliance on the primary test jig and ignoring hints from other >less accurate tests that something might be amiss. > >I have previously posted a link to the NASA engineering report on the >HST optics last time JKK blamed Proxmire for the HST mirror fault. > >Regards, >Martin Brown As I said, for the details read the book. John |