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For Want Of A Bolt



 
 
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  #11  
Old September 23rd 03, 08:44 PM
Rand Simberg
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Default For Want Of A Bolt

On Tue, 23 Sep 2003 13:13:08 CST, in a place far, far away,
(Henry Spencer) made the phosphor on my monitor
glow in such a way as to indicate that:

I'm told that the component-qualification rules for undersea-cable
repeaters make space-qualification procedures look amateurish.


It would be interesting, then to know how they compare to, say,
satellite transponders in terms of cost per pound.

--
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  #14  
Old September 24th 03, 12:11 AM
Joann Evans
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Default For Want Of A Bolt

Lou Scheffer wrote:

(Lou Scheffer) wrote in message om...
(Derek Lyons) wrote in message ...
h (Rand Simberg) wrote:

"But that doesn't explain why similar systems designed for marine use
[...] can be built for orders of magnitude less."

Please provide a cite of a marine system of the equivalent complexity
and mission of the weather sat with a design lifetime of years or
decades. (Or any marine system with those kinds of lifetime
requirements.)

Transatlantic cables come close. Before fiber optics, these had
repeaters every few km. Since they were in series, ALL of the
repeaters must work. If I remember correctly, they were designed so
the cable as a whole had a 20 year lifetime. Using good old
conservative engineering, the even made this work with vacuum
tubes(!). Needless to say this was one of the first applications of
transistors.


Oops - this was NOT one of the first uses of transistors. Another
article states that they were still built with vacuum tubes in 1964,
10 years after transistors were used for other applications, since
transistors were not yet proven to be more reliable. In retrospect
this makes perfect sense - any reliability conscious field will not
rush to adapt new technology, no matter how promising, if the old
technology is working at least OK.

Lou Scheffer



When a shuttle crew did a satellite upgrade (not sure if it was Solar
Max, or Hubble), it was noted that the replacement units were 386
processor based. Some people didn't understand why...you basically just
answered them. (Espically when you add in uncertainty as to how well a
new processor design will tolerate long term ionizing radiation
exposure)

  #15  
Old September 24th 03, 01:10 AM
Pascal Bourguignon
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Default For Want Of A Bolt

(Lou Scheffer) writes:

h (Rand Simberg) wrote in message . ..
On Tue, 23 Sep 2003 13:13:08 CST, in a place far, far away,
(Henry Spencer) made the phosphor on my monitor
glow in such a way as to indicate that:

I'm told that the component-qualification rules for undersea-cable
repeaters make space-qualification procedures look amateurish.


It would be interesting, then to know how they compare to, say,
satellite transponders in terms of cost per pound.


The undersea repeaters have a big advantage - they really only have
one constraint, reliability. I'd guess they care very little about
weight, very little about thermal control, and they don't need to
endure the stresses of launch. My intuition says that the costs will
go up as something like the square of the number of difficult
constraints. For example, a simple and reliable way to make something
stand up to vibration (or sea water immersion in this case) is to pot
it in epoxy. If you are mass-sensitive, though, you can't do this and
you'll need to do a lot more tricky design and qualification.

So I'll wager (without evidence) that the submarine stuff is still
cheaper, even if the component qualification is even more stringent
and hence the parts more expensive.


What about this for an evidence: the thousands of submarines and the
million or more of people who traveled in them vs. the tens of space
capsule and the hundred of astronauts.

--
__Pascal_Bourguignon__
http://www.informatimago.com/
Do not adjust your mind, there is a fault in reality.

  #16  
Old September 24th 03, 02:22 AM
Derek Lyons
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Default For Want Of A Bolt

(Lou Scheffer) wrote:

(Derek Lyons) wrote in message ...
h (Rand Simberg) wrote:

"But that doesn't explain why similar systems designed for marine use
(the ocean has extremely high positive pressures, and seawater is an
extremely corrosive environment) can be built for orders of magnitude
less."

Please provide a cite of a marine system of the equivalent complexity
and mission of the weather sat with a design lifetime of years or
decades. (Or any marine system with those kinds of lifetime
requirements.)

Transatlantic cables come close. Before fiber optics, these had
repeaters every few km. Since they were in series, ALL of the
repeaters must work. If I remember correctly, they were designed so
the cable as a whole had a 20 year lifetime. Using good old
conservative engineering, the even made this work with vacuum
tubes(!). Needless to say this was one of the first applications of
transistors.


Indeed. And they were *extremely* expensive. Somewhere I have a
telco manual from the early 70's that cites the costs of a repeater as
being in excess of a million dollars a pop. It goes to great lengths
to explain and stress the engineering, qualification, and component
testing required.

Transoceanic cable repeaters and SOSUS arrays are about the only
things marine I can think of that are designed for decades of
unmaintained service, and both are extremely expensive. Most other
things marine seem to be designed for shorter lifetimes and hence
don't meet the similarity requirements Rand specifies, or are far less
complex than a weather sat, and equally fail to meet the similarity
requirement.

FWIW, when pressed Rand declined to supply marine example at all.

D.
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  #17  
Old September 24th 03, 03:48 AM
Sander Vesik
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Default For Want Of A Bolt

In sci.space.policy Joann Evans wrote:


When a shuttle crew did a satellite upgrade (not sure if it was Solar
Max, or Hubble), it was noted that the replacement units were 386
processor based. Some people didn't understand why...you basically just
answered them. (Espically when you add in uncertainty as to how well a
new processor design will tolerate long term ionizing radiation
exposure)


Various x86 with a low number for x are very popular in embedded systems.
No point in paying for more speed than you need (yes, of course you can
cheaper 386 than 486)

--
Sander

+++ Out of cheese error +++

  #18  
Old September 24th 03, 09:47 PM
Lou Scheffer
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Default For Want Of A Bolt

h (Rand Simberg) wrote in message . ..
On Tue, 23 Sep 2003 13:13:08 CST, in a place far, far away,
(Henry Spencer) made the phosphor on my monitor
glow in such a way as to indicate that:

I'm told that the component-qualification rules for undersea-cable
repeaters make space-qualification procedures look amateurish.


It would be interesting, then to know how they compare to, say,
satellite transponders in terms of cost per pound.


From:
http://davidw.home.cern.ch/davidw/public/SubCables.html

"Repeaters are devices which are 100-200 cm long, 30-50 cm in
diameter, weigh about 300-500 kg and cost 500-1000 K$ each. They are
assembled in clean-rooms and typically designed for a lifetime of 25
years at up to 7000 meters depth without maintenance. "

So they are about $2000/kg. Of course, since weight is not a big
concern to them, perhaps the right metric is cost per equivalent
functionality. This would be best obtained from the first generation
of optical repeaters, which did optical-electrical-optical, which is
much more analogous to a satellite transponder.

Lou Scheffer

  #19  
Old October 11th 03, 04:24 PM
G.Beat
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Default For Want Of A Bolt

"Henry Spencer" wrote in message
...
In article ,
Lou Scheffer wrote:
Transatlantic cables...


Oops - this was NOT one of the first uses of transistors. Another
article states that they were still built with vacuum tubes in 1964,
10 years after transistors were used for other applications, since
transistors were not yet proven to be more reliable. In retrospect
this makes perfect sense - any reliability conscious field will not
rush to adapt new technology, no matter how promising, if the old
technology is working at least OK.


I'm told that the component-qualification rules for undersea-cable
repeaters make space-qualification procedures look amateurish.


Correct. Worked with son of the Bell engineer that qualified the capacitors
for the
repeaters on the Transatlantic cable. Quality was unmatched (even by NASA)
..... of
course the price for a one minute Transatlantic call (at that time) was not
cheap either !

GB

 




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