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Re: various OTs

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On Sat, 13 Oct 2018 10:13:10 +0100, Martin Brown
<'''newspam'''@nezumi.demon.co.uk> wrote:

>On 12/10/2018 23:30, John Larkin wrote:
>> On Fri, 12 Oct 2018 14:53:17 -0700, dplatt@coop.radagast.org (Dave
>> Platt) wrote:
>> 
>>>> https://wattsupwiththat.com/2018/10/12/another-space-telescope-shuts-down-one-week-after-hubble/
>>>>
>>>> Gyros, reaction wheels, seem to be a chronic problem in satellites. I
>>>> have a friend who designs cubesats, and he says that the gyros are the
>>>> most expensive and unreliable parts.
>>>
>>> ... which suggests that this is a Hard Problem.  I don't find that
>>> surprising.  Gyro bearings are a "moving part" (unlike a lot of what's
>>> in satellites).  Almost by definition they have to take a big torque
>>> load on the bearing surfaces when they operate, since part of their
>>> job is to twist the satellite around into a new orientation.  They
>>> often have to operate over an extreme temperature range (cold-of-
>>> eclipse to heat-of-full-sun) with the range going back and forth
>>> multiple times per day (for a LEO satellite at least).  And, there's
>>> no opportunity to replace, or relubricate the bearings once the sat is
>>> in service, in most cases.
>>>
>>> I don't know what material they use in the bearings for those gyros,
>>> but suspect that they're probably frightfully expensive.
>> 
>> My naiive concept is that things don't need bearings in zero G and
>> hard vacuum. Just a little magnetic suspension. Of course, a zero-G
>> maglev (spherical?) gyro would be hard to test on the ground; maybe we
>> have finally found a use for the ISS, manufacturing gyros.
>
>They need bearings or magnetic suspension that can handle the forces 
>that occur when the satellite is being rotated by using the gyros. If 
>they could avoid using mechanical bearings they would do so.
>
>Almost all sensor gyros are counter rotating laser beams these days. It 
>is only the devices that have to provide real forces that move.
>
>The moving parts with serious kinetic energy and high torque are always 
>by far the most unreliable components especially in spacecraft.
>
>We had maglev turbopumps for a while on our kit. It was wonderful in 
>earthquake free zones but one day the entire of Tokyo moved an inch to 
>the left and every damn one of the things was written off in an instant. 
>We even had an earthquake in our factory which did in a couple and the 
>UK is not known as a hotbed of earthquake activity. After that they went 
>back to traditional bearings for almost all customer sites.
>
>You have clearly never sat on a swivel chair and played with a spinning 
>lead rimmed bicycle wheel. It is quite fun to try and the forces on the 
>bearings are distinctly non-trivial when you use it to move a mass.

The forces needed to orient a satellite, especially a 1 kg cubesat,
are tiny.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

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various OTs John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-12 12:50 -0700
  Re: various OTs George Herold <gherold@teachspin.com> - 2018-10-12 13:04 -0700
    Re: various OTs John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-12 13:48 -0700
      Re: various OTs George Herold <gherold@teachspin.com> - 2018-10-12 17:46 -0700
  Re: various OTs dplatt@coop.radagast.org (Dave Platt) - 2018-10-12 14:53 -0700
    Re: various OTs John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-12 15:30 -0700
      Re: various OTs Martin Brown <'''newspam'''@nezumi.demon.co.uk> - 2018-10-13 10:13 +0100
        Re: various OTs John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-13 09:33 -0700
          Re: various OTs Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-13 14:15 -0400
          Re: various OTs Martin Brown <'''newspam'''@nezumi.demon.co.uk> - 2018-10-15 10:09 +0100
            Re: various OTs John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-15 06:50 -0700
    Re: various OTs Clive Arthur <cliveta@nowaytoday.co.uk> - 2018-10-13 10:37 +0100
      Re: various OTs DecadentLinuxUserNumeroUno@decadence.org - 2018-10-13 10:01 +0000
        Re: various OTs John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-13 11:08 -0700
      Re: various OTs John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-13 09:55 -0700
      Re: various OTs MikeP <mjp993@googlemail.com> - 2018-10-16 03:22 +0000
    Re: various OTs Robert Baer <robertbaer@localnet.com> - 2018-10-13 22:39 -0700
      Re: various OTs Sjouke Burry <burrynulnulfour@ppllaanneett.nnll> - 2018-10-14 21:43 +0200
        Re: various OTs Robert Baer <robertbaer@localnet.com> - 2018-10-15 19:46 -0700
  Re: various OTs DecadentLinuxUserNumeroUno@decadence.org - 2018-10-12 23:55 +0000
    Re: various OTs Lasse Langwadt Christensen <langwadt@fonz.dk> - 2018-10-12 16:58 -0700
    Re: various OTs bill.sloman@ieee.org - 2018-10-12 17:52 -0700
    Re: various OTs speff <spehro@gmail.com> - 2018-10-18 06:53 -0700
      Re: various OTs John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-18 06:59 -0700
        Re: various OTs tabbypurr@gmail.com - 2018-10-18 14:10 -0700
          Re: various OTs "Tim Williams" <tiwill@seventransistorlabs.com> - 2018-10-18 17:49 -0500
        Re: various OTs Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-18 21:04 -0400
          Re: various OTs Steve Wilson <no@spam.com> - 2018-10-19 01:34 +0000
            Re: various OTs <698839253X6D445TD@nospam.org> - 2018-10-19 07:11 +0000
  Re: various OTs "Tim Williams" <tiwill@seventransistorlabs.com> - 2018-10-12 19:10 -0500
    Re: various OTs Lasse Langwadt Christensen <langwadt@fonz.dk> - 2018-10-13 06:22 -0700
      Re: various OTs Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-13 14:16 -0400
        Re: various OTs John Larkin <jjlarkin@highlandtechnology.com> - 2018-10-13 17:19 -0700
    Re: various OTs whit3rd <whit3rd@gmail.com> - 2018-10-13 12:24 -0700
      Re: various OTs Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-13 17:30 -0400
        Re: various OTs Jasen Betts <jasen@xnet.co.nz> - 2018-10-14 20:13 +0000
          Re: various OTs John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-14 13:59 -0700
            Re: various OTs Steve Wilson <no@spam.com> - 2018-10-14 23:58 +0000
              Re: various OTs Steve Wilson <no@spam.com> - 2018-10-15 01:05 +0000
                Re: various OTs Jasen Betts <jasen@xnet.co.nz> - 2018-10-15 05:57 +0000
                Re: various OTs DecadentLinuxUserNumeroUno@decadence.org - 2018-10-15 11:09 +0000
              Re: various OTs <698839253X6D445TD@nospam.org> - 2018-10-15 07:23 +0000
      Re: various OTs "Tim Williams" <tiwill@seventransistorlabs.com> - 2018-10-13 21:39 -0500
  Re: various OTs bitrex <user@example.net> - 2018-10-13 00:08 -0400
  Re: various OTs <698839253X6D445TD@nospam.org> - 2018-10-13 06:59 +0000
    Re: various OTs John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-13 12:08 -0700
  Re: various OTs <698839253X6D445TD@nospam.org> - 2018-10-13 07:27 +0000
    Re: various OTs speff <spehro@gmail.com> - 2018-10-18 06:55 -0700
  Re: various OTs Winfield Hill <hill@rowland.harvard.edu> - 2018-10-13 07:32 -0700
    Re: various OTs John Larkin <jjlarkin@highland_snip_technology.com> - 2018-10-13 12:17 -0700
  Re: various OTs Joseph Gwinn <joegwinn@comcast.net> - 2018-10-15 08:37 -0400
    Re: various OTs Martin Brown <'''newspam'''@nezumi.demon.co.uk> - 2018-10-15 13:58 +0100
      Re: various OTs Tom Gardner <spamjunk@blueyonder.co.uk> - 2018-10-15 14:34 +0100
      Re: various OTs Clifford Heath <no.spam@please.net> - 2018-10-16 10:26 +1100
    Re: various OTs Clive Arthur <cliveta@nowaytoday.co.uk> - 2018-10-16 10:46 +0100
      Re: various OTs tabbypurr@gmail.com - 2018-10-16 08:46 -0700
        Re: various OTs Clive Arthur <cliveta@nowaytoday.co.uk> - 2018-10-16 19:53 +0100
          Re: various OTs tabbypurr@gmail.com - 2018-10-17 05:56 -0700

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