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Apollo LEM computer



 
 
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  #11  
Old July 15th 04, 06:35 PM
Derek Lyons
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rk wrote:
Kevin Willoughby wrote:


Does any of that explain why the S-V guidance computer worked just fine
when the Apollo computer had been knocked sideways by lighting on Apollo
12?


I don't know, have no data, but I always thought about just that issue.


The explanation I heard was that the Apollo computer being in a
smaller volume and nearer the strike was exposed to higher EMF effects
than the S-V computer.

D.
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Touch-twice life. Eat. Drink. Laugh.
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  #12  
Old July 15th 04, 09:51 PM
Bruce Palmer
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Derek Lyons wrote:
rk wrote:

Kevin Willoughby wrote:

Does any of that explain why the S-V guidance computer worked just fine
when the Apollo computer had been knocked sideways by lighting on Apollo
12?


I don't know, have no data, but I always thought about just that issue.


The explanation I heard was that the Apollo computer being in a
smaller volume and nearer the strike was exposed to higher EMF effects
than the S-V computer.


Were the Saturn V guidance computers in the IU with the stable reference
platform?

Apollo 12 was struck twice by lightning ISTR. Were the actual locations
of the lightning strikes on the vehicle documented?

--
bp
Proud Member of the Human O-Ring Society Since 2003
  #13  
Old July 15th 04, 10:28 PM
Derek Lyons
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(Gene Seibel) wrote:

Interesting how they made the computers identical in the LM and
Apollo. Burt Rutan has done the same thing. The White Knight cockpit
is identical to the SpaceShip One cockpit and is used as a simulator.
http://www.scaled.com/projects/tiero..._knight_p2.htm

One wonders how effective it really is given the utter lack of
anything else common between the craft.

D.
--
Touch-twice life. Eat. Drink. Laugh.
  #14  
Old July 16th 04, 12:35 AM
Scott Hedrick
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"Derek Lyons" wrote in message
...
The explanation I heard was that the Apollo computer being in a
smaller volume and nearer the strike was exposed to higher EMF effects
than the S-V computer.


At that point, what would have happened if the escape rocket had been
ignited? Would the system have completed the sequence and cut loose the CM?
Would the rocket have been able to pull off the CM? If not, could the flight
have continued without it?


  #15  
Old July 17th 04, 01:41 AM
James G. Joyce
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"Bruce Palmer" wrote in message
et...
Derek Lyons wrote:
rk wrote:

Kevin Willoughby wrote:

Does any of that explain why the S-V guidance computer worked just fine
when the Apollo computer had been knocked sideways by lighting on

Apollo
12?

I don't know, have no data, but I always thought about just that issue.


The explanation I heard was that the Apollo computer being in a
smaller volume and nearer the strike was exposed to higher EMF effects
than the S-V computer.


Were the Saturn V guidance computers in the IU with the stable reference
platform?

Apollo 12 was struck twice by lightning ISTR. Were the actual locations
of the lightning strikes on the vehicle documented?

--
bp
Proud Member of the Human O-Ring Society Since 2003


digs up trusty copy of Murray and Cox ...

The way it's explained there, Apollo 12 created its own lightning ... (pp.
376-7)

" ... What they had done, they realized later, was to launch a 363-foot
lightning rod, with the equivalent of a copper wire in the form of a trail
of ionized gases running all the way to the ground. Even though there was no
lightning in the vicinity before launch, Apollo 12 could create its own. And
that is exactly what it did, discharging the cloud into which it had entered
....

"Actually, Don Arabian's anomalies team later determined that Yankee Clipper
was hit twice by lightning, once 36.5 seconds after launch at an altitude of
6,000 feet, when it discharged the cloud it was flying through, and again 16
seconds later, when it triggered a cloud-to-cloud bolt."

So it sounds like both bolts hit near the top of the stack (possibly the
LES) first. Apparently, the only physical damage that reuslted from that
60,000-plus-ampere jolt flowing through the skin of the stack was to some
external instrumentation for measuring temperatures and R.C.S. reserves. It
was the induced electromagnetic fields that knocked the fuel cells off line
and tumbled the CM's guidance platform.

And, in a footnote ...

"Part of the reason the spacecraft was so affected by the lightning while
the Saturn was not involved the spacecraft's greater exposure-it was
positioned like the tip of a lightning rod-and part of it was luck, as
Arabian emphatically pointed out ... In the case of the I.U., induced
currents reached the guidance system's circuits but the computer software
kept the platform from tumbling."

I'm guessing that, in addition to being better protected, the differences in
construction and the built-in redundancy of the guidance computers in the
I.U. (thanks, rk, for enlightening me on that with your earlier post) were
why that platform didn't tumble ... thank goodness.

Sorry for the overlong post ... now resuming normal lurking mode ...

James (who still has much to learn)


  #16  
Old July 17th 04, 02:41 AM
Bruce Palmer
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James G. Joyce wrote:
So it sounds like both bolts hit near the top of the stack (possibly the
LES) first. Apparently, the only physical damage that reuslted from that
60,000-plus-ampere jolt flowing through the skin of the stack was to some
external instrumentation for measuring temperatures and R.C.S. reserves. It
was the induced electromagnetic fields that knocked the fuel cells off line
and tumbled the CM's guidance platform.

And, in a footnote ...

"Part of the reason the spacecraft was so affected by the lightning while
the Saturn was not involved the spacecraft's greater exposure-it was
positioned like the tip of a lightning rod-and part of it was luck, as
Arabian emphatically pointed out ... In the case of the I.U., induced
currents reached the guidance system's circuits but the computer software
kept the platform from tumbling."

I'm guessing that, in addition to being better protected, the differences in
construction and the built-in redundancy of the guidance computers in the
I.U. (thanks, rk, for enlightening me on that with your earlier post) were
why that platform didn't tumble ... thank goodness.


Those older gyros/resolvers/sliprings/torquers were very susceptible to
EMI and the platform wasn't redundant - there was only 1. Sounds like
the circuitry was sufficiently robust to protect the guts of the thing.
I wonder if the ST-124 housing had its own electrical shielding.
http://history.nasa.gov/SP-4206/ch8.htm#244

Sorry for the overlong post ... now resuming normal lurking mode ...


Not overly long at all, James, thanks for that.

--
bp
Proud Member of the Human O-Ring Society Since 2003
 




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