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various OTs

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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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#519081 — various OTs

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. They should be redundant, or
redesigned, or something.

===========

Another friend, a Fellow of a giant areospace conglomerate, tells me
that they have a new CEO. The old one was big on outsourcing, and they
did stuff like using contract programmers in India, and things went to
hell. They will be hiring 8000 engineers in the next few years, so
they can start learning how to do stuff again.

===========

This is a cool part:

http://www.ti.com/product/lmg1020




-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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#519085

On Friday, October 12, 2018 at 3:51:11 PM UTC-4, John Larkin 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. They should be redundant, or
> redesigned, or something.
> 
> ===========
> 
> Another friend, a Fellow of a giant areospace conglomerate, tells me
> that they have a new CEO. The old one was big on outsourcing, and they
> did stuff like using contract programmers in India, and things went to
> hell. They will be hiring 8000 engineers in the next few years, so
> they can start learning how to do stuff again.
Hmm tell your friend to hold off for a little bit.  My son is still in 
HS, but he wants to be an areospace engineer.  (or nuclear engineer) 

Maybe I'll just hit you up in 5 years for a name so he can get a foot in the door. 

Hey he now has a job, car and girlfriend... life is looking up. :^) 

George H. 
> 
> ===========
> 
> This is a cool part:
> 
> http://www.ti.com/product/lmg1020
> 
> 
> 
> 
> -- 
> 
> John Larkin         Highland Technology, Inc
> picosecond timing   precision measurement 
> 
> jlarkin att highlandtechnology dott com
> http://www.highlandtechnology.com

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#519090

On Fri, 12 Oct 2018 13:04:46 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On Friday, October 12, 2018 at 3:51:11 PM UTC-4, John Larkin 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. They should be redundant, or
>> redesigned, or something.
>> 
>> ===========
>> 
>> Another friend, a Fellow of a giant areospace conglomerate, tells me
>> that they have a new CEO. The old one was big on outsourcing, and they
>> did stuff like using contract programmers in India, and things went to
>> hell. They will be hiring 8000 engineers in the next few years, so
>> they can start learning how to do stuff again.
>Hmm tell your friend to hold off for a little bit.  My son is still in 
>HS, but he wants to be an areospace engineer.  (or nuclear engineer) 
>
>Maybe I'll just hit you up in 5 years for a name so he can get a foot in the door. 
>
>Hey he now has a job, car and girlfriend... life is looking up. :^) 
>
>George H. 

I rember being a college freshman and getting a job (two, actually)
and a car and a girlfriend. It was good.

Aerospace engineering is probably a good career path. Let me know when
he's ready.




-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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#519111

On Friday, October 12, 2018 at 4:48:35 PM UTC-4, John Larkin wrote:
> On Fri, 12 Oct 2018 13:04:46 -0700 (PDT), George Herold
> <gherold@teachspin.com> wrote:
> 
> >On Friday, October 12, 2018 at 3:51:11 PM UTC-4, John Larkin 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. They should be redundant, or
> >> redesigned, or something.
> >> 
> >> ===========
> >> 
> >> Another friend, a Fellow of a giant areospace conglomerate, tells me
> >> that they have a new CEO. The old one was big on outsourcing, and they
> >> did stuff like using contract programmers in India, and things went to
> >> hell. They will be hiring 8000 engineers in the next few years, so
> >> they can start learning how to do stuff again.
> >Hmm tell your friend to hold off for a little bit.  My son is still in 
> >HS, but he wants to be an areospace engineer.  (or nuclear engineer) 
> >
> >Maybe I'll just hit you up in 5 years for a name so he can get a foot in the door. 
> >
> >Hey he now has a job, car and girlfriend... life is looking up. :^) 
> >
> >George H. 
> 
> I rember being a college freshman and getting a job (two, actually)
> and a car and a girlfriend. It was good.
> 
> Aerospace engineering is probably a good career path. Let me know when
> he's ready.
> 
Sure, He's set his sights on Moog, a local (mostly) defense contractor.
He's stuck in NY for his first 4-5 years, after college, (well the 
current plan is some state univ., and NYS picks up the tuition if you
work in the state after college.  That's about $8k/yr. 
If you get a job out of state you have to pay off the ~$32k right 
away... I'm not sure if you owe interest or not?  

I know some guys at Moog, I should see if there are some summer 
internships.  He's more of a motor head than I am, and might 
interview well.  

George H. 



> 

> 
> 
> -- 
> 
> John Larkin         Highland Technology, Inc
> picosecond timing   precision measurement 
> 
> jlarkin att highlandtechnology dott com
> http://www.highlandtechnology.com

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#519097

>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.

If you don't use gyros, you need some other way to maintain and change
orientation... and reaction-thruster fuel is an expensive resource!

>                                       They should be redundant, or
>redesigned, or something.

Each time I've heard stories about gyros on a satellite failing, the
information in the story has made it clear that the satellite
in question did contain redundant gyros.  They always seem to have at
least an N+1 set, with N+2 being not unusual.

I imagine that the decision about adding additional gyros (for an
additional level of robustnes) comes with the usual
problems... they're heavy, they take up space, so if you add another
one, either something else has to go or the sat gets bigger/heavier/
more-expensive.

>Another friend, a Fellow of a giant areospace conglomerate, tells me
>that they have a new CEO. The old one was big on outsourcing, and they
>did stuff like using contract programmers in India, and things went to
>hell. They will be hiring 8000 engineers in the next few years, so
>they can start learning how to do stuff again.

That's good news!

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#519099

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.


>
>If you don't use gyros, you need some other way to maintain and change
>orientation... and reaction-thruster fuel is an expensive resource!
>
>>                                       They should be redundant, or
>>redesigned, or something.
>
>Each time I've heard stories about gyros on a satellite failing, the
>information in the story has made it clear that the satellite
>in question did contain redundant gyros.  They always seem to have at
>least an N+1 set, with N+2 being not unusual.
>
>I imagine that the decision about adding additional gyros (for an
>additional level of robustnes) comes with the usual
>problems... they're heavy, they take up space, so if you add another
>one, either something else has to go or the sat gets bigger/heavier/
>more-expensive.
>
>>Another friend, a Fellow of a giant areospace conglomerate, tells me
>>that they have a new CEO. The old one was big on outsourcing, and they
>>did stuff like using contract programmers in India, and things went to
>>hell. They will be hiring 8000 engineers in the next few years, so
>>they can start learning how to do stuff again.
>
>That's good news!

MAGA?


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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#519143

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.

-- 
Regards,
Martin Brown

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#519165

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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#519170

On 10/13/18 12:33 PM, John Larkin wrote:
> 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.
> 
> 
Resetting a reaction wheel is quite another matter.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

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#519344

On 13/10/2018 17:33, John Larkin wrote:
> On Sat, 13 Oct 2018 10:13:10 +0100, Martin Brown
> <'''newspam'''@nezumi.demon.co.uk> wrote:

>> 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.

Hubble is about 11T and 13m by 4m. Time spent slewing between objects is 
wasted so they plan its observing list very carefully. Even so if a 
transient target of opportunity comes up they want to get onto it ASAP.

Most of the serious so called microsatellites* built today are dustbin 
sized and around 30-100kg. You can't do that much interesting science in 
orbit without either a decent sized antenna or a big lens. eg.

https://www.ralspace.stfc.ac.uk/Pages/TopSat.aspx

* an exaggeration if ever there was one - centisatellite is more like it

If you are launching a toy satellite the size and weight of a good 
textbook you might just as well spin stabilise it by bulk rotation. 
Hyperbole means they are called nano satellites (actually sub milli).

Cubesats might be interesting when they get to the stage of being self 
assembling Lego but for the moment they are fun toy research projects 
that are relatively cheap for universities to play around with.

The $25 parts cost credit card sized sprites might sometimes be 
interesting as disposable probes - though the first launch was a failure 
as they didn't get properly deployed by their parent vessel.

https://www.economist.com/technology-quarterly/2014/06/07/nanosats-are-go

-- 
Regards,
Martin Brown

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#519381

On Mon, 15 Oct 2018 10:09:51 +0100, Martin Brown
<'''newspam'''@nezumi.demon.co.uk> wrote:

>On 13/10/2018 17:33, John Larkin wrote:
>> On Sat, 13 Oct 2018 10:13:10 +0100, Martin Brown
>> <'''newspam'''@nezumi.demon.co.uk> wrote:
>
>>> 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.
>
>Hubble is about 11T and 13m by 4m. Time spent slewing between objects is 
>wasted so they plan its observing list very carefully. Even so if a 
>transient target of opportunity comes up they want to get onto it ASAP.
>
>Most of the serious so called microsatellites* built today are dustbin 
>sized and around 30-100kg. You can't do that much interesting science in 
>orbit without either a decent sized antenna or a big lens. eg.
>
>https://www.ralspace.stfc.ac.uk/Pages/TopSat.aspx
>
>* an exaggeration if ever there was one - centisatellite is more like it
>
>If you are launching a toy satellite the size and weight of a good 
>textbook you might just as well spin stabilise it by bulk rotation. 
>Hyperbole means they are called nano satellites (actually sub milli).
>
>Cubesats might be interesting when they get to the stage of being self 
>assembling Lego but for the moment they are fun toy research projects 
>that are relatively cheap for universities to play around with.

The one cubesat company that I know well is making money profiling the
atmosphere and maybe doing some shipboard services. Another is doing
high-res worldwide synthetic apearture radar, which sounds like a
great thing to have. 

Radar doesn't need a transmitter; there's tons of RF around already.
All it needs is a lot of antennas and a lot of DSP.


-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

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#519147

On 12/10/2018 22:53, Dave Platt wrote:
<snipped>
> 
> If you don't use gyros, you need some other way to maintain and change
> orientation... and reaction-thruster fuel is an expensive resource!

AIUI, you still need thrusters to 'reset' the gyros every so often.

Cheers
-- 
Clive

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#519150

Clive Arthur <cliveta@nowaytoday.co.uk> wrote in news:ppsecq$ps1$1@dont-
email.me:

> On 12/10/2018 22:53, Dave Platt wrote:
> <snipped>
>> 
>> If you don't use gyros, you need some other way to maintain and change
>> orientation... and reaction-thruster fuel is an expensive resource!
> 
> AIUI, you still need thrusters to 'reset' the gyros every so often.
> 
> Cheers

Gyros maintain (and adjust) orientation (Atten-Shun!).  Thrusters maintain 
altitude (freefall point)(muster up!).

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#519169

On Sat, 13 Oct 2018 10:01:20 +0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

>Clive Arthur <cliveta@nowaytoday.co.uk> wrote in news:ppsecq$ps1$1@dont-
>email.me:
>
>> On 12/10/2018 22:53, Dave Platt wrote:
>> <snipped>
>>> 
>>> If you don't use gyros, you need some other way to maintain and change
>>> orientation... and reaction-thruster fuel is an expensive resource!
>> 
>> AIUI, you still need thrusters to 'reset' the gyros every so often.
>> 
>> Cheers
>
>Gyros maintain (and adjust) orientation (Atten-Shun!).  Thrusters maintain 
>altitude (freefall point)(muster up!).

Reaction wheels and gyros can integrate up speed without limit, so
rotational thrusters are sometimes used to reset the gyros now and
then. They use up gas or fuel so have to be used sparingly.

Orbital velocity thrusters are a different animal, and need a huge
amount of fuel.


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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#519167

On Sat, 13 Oct 2018 10:37:27 +0100, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

>On 12/10/2018 22:53, Dave Platt wrote:
><snipped>
>> 
>> If you don't use gyros, you need some other way to maintain and change
>> orientation... and reaction-thruster fuel is an expensive resource!
>
>AIUI, you still need thrusters to 'reset' the gyros every so often.
>
>Cheers

Cubesats are light and fly in low orbits, so drag is serious. They
only last a year or two. I'll ask my friend, but I'd expect that the
drag on the surfaces sort of zero-bases the orientation. I don't think
he uses any sort of thrusters to zero out the gyros. He does complain
about the gyro-based orientation package that they buy.

Some satellites apparently use magnets to align with Earth's field.
That sounds complicated. I guess you could use stepper motors to move
magnets around, to get orientation and damping. Some cubesats
apparently use electromagnets or microthrusters. I'll ask M what they
do. 

He owes me; I taught him the value of a rum-and-coke as a skiing
enhancement.

https://www.dropbox.com/s/6v3smot61isam8p/M_at_Squaw.jpg?raw=1

He's from Sweden, skiied all his life, and missed this fundamental
component. Now he has two.

There are two cubesat companies within a 15 minute walk of our place,
and soon to be a third. I wonder if they will survive. The satellites
don't last long, so have to be continuously replaced, so there has to
be an ongoing revenue model.

google   cubesat layoffs



-- 

John Larkin         Highland Technology, Inc

lunatic fringe electronics 

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#519437

On Sat, 13 Oct 2018 10:37:27 +0100, Clive Arthur wrote:

> On 12/10/2018 22:53, Dave Platt wrote:
> <snipped>
>> 
>> If you don't use gyros, you need some other way to maintain and change
>> orientation... and reaction-thruster fuel is an expensive resource!
> 
> AIUI, you still need thrusters to 'reset' the gyros every so often.

You're thinking of "magnetorquers".

https://en.wikipedia.org/wiki/Magnetorquer

Mike

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#519232

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.
> 
> If you don't use gyros, you need some other way to maintain and change
> orientation... and reaction-thruster fuel is an expensive resource!
> 
>>                                        They should be redundant, or
>> redesigned, or something.
> 
> Each time I've heard stories about gyros on a satellite failing, the
> information in the story has made it clear that the satellite
> in question did contain redundant gyros.  They always seem to have at
> least an N+1 set, with N+2 being not unusual.
> 
> I imagine that the decision about adding additional gyros (for an
> additional level of robustnes) comes with the usual
> problems... they're heavy, they take up space, so if you add another
> one, either something else has to go or the sat gets bigger/heavier/
> more-expensive.
> 
>> Another friend, a Fellow of a giant areospace conglomerate, tells me
>> that they have a new CEO. The old one was big on outsourcing, and they
>> did stuff like using contract programmers in India, and things went to
>> hell. They will be hiring 8000 engineers in the next few years, so
>> they can start learning how to do stuff again.
> 
> That's good news!
> 
   How about a magnetic design - -no surface-to-surface friction?

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#519265

On 14-10-2018 7:39, Robert Baer wrote:
> 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.
>>
>> If you don't use gyros, you need some other way to maintain and change
>> orientation... and reaction-thruster fuel is an expensive resource!
>>
>>>                                         They should be redundant, or
>>> redesigned, or something.
>>
>> Each time I've heard stories about gyros on a satellite failing, the
>> information in the story has made it clear that the satellite
>> in question did contain redundant gyros.  They always seem to have at
>> least an N+1 set, with N+2 being not unusual.
>>
>> I imagine that the decision about adding additional gyros (for an
>> additional level of robustnes) comes with the usual
>> problems... they're heavy, they take up space, so if you add another
>> one, either something else has to go or the sat gets bigger/heavier/
>> more-expensive.
>>
>>> Another friend, a Fellow of a giant areospace conglomerate, tells me
>>> that they have a new CEO. The old one was big on outsourcing, and they
>>> did stuff like using contract programmers in India, and things went to
>>> hell. They will be hiring 8000 engineers in the next few years, so
>>> they can start learning how to do stuff again.
>>
>> That's good news!
>>
>     How about a magnetic design - -no surface-to-surface friction?
>
They did that already 10-20 years ago.

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#519436

Sjouke Burry wrote:
> On 14-10-2018 7:39, Robert Baer wrote:
>> 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.
>>>
>>> If you don't use gyros, you need some other way to maintain and change
>>> orientation... and reaction-thruster fuel is an expensive resource!
>>>
>>>>                                         They should be redundant, or
>>>> redesigned, or something.
>>>
>>> Each time I've heard stories about gyros on a satellite failing, the
>>> information in the story has made it clear that the satellite
>>> in question did contain redundant gyros.  They always seem to have at
>>> least an N+1 set, with N+2 being not unusual.
>>>
>>> I imagine that the decision about adding additional gyros (for an
>>> additional level of robustnes) comes with the usual
>>> problems... they're heavy, they take up space, so if you add another
>>> one, either something else has to go or the sat gets bigger/heavier/
>>> more-expensive.
>>>
>>>> Another friend, a Fellow of a giant areospace conglomerate, tells me
>>>> that they have a new CEO. The old one was big on outsourcing, and they
>>>> did stuff like using contract programmers in India, and things went to
>>>> hell. They will be hiring 8000 engineers in the next few years, so
>>>> they can start learning how to do stuff again.
>>>
>>> That's good news!
>>>
>>     How about a magnetic design - -no surface-to-surface friction?
>>
> They did that already 10-20 years ago.
   Yea...magnetic bearings were old-hat back then (~40+ yrs old).
   Maybe it is so old,,,'twaz fergotten?

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#519103

John Larkin <jjlarkin@highland_snip_technology.com> wrote in 
news:r2u1sddojvr815ukjlm0qhsr5bpa2fbe6s@4ax.com:

> 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. They should be redundant, or
> redesigned, or something.
> 

  You do know that they number among the only moving parts in such a 
device.

  They are like hard drives.  But AFAIK they are called gyros.
What is a "reaction wheel"?  Is that a Larkin term?

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