TECHNET Archives

March 2012

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Inge Hernefjord <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Inge Hernefjord <[log in to unmask]>
Date:
Wed, 21 Mar 2012 22:41:16 +0100
Content-Type:
text/plain
Parts/Attachments:
text/plain (65 lines)
Wow, that's a fraudulent anticipation..

 It is believed that these or additional tin whiskers that may grow on
Cassini cannot carry enough current to cause problems, but will burn out on
their own like a lightweight fuse.

....because

a. singel crystal metals can carry more current

b. some signal paths may measure nanoamps or even picoamps

c. they can start arcing

d. a typical long whisker can carry 10 mA before burning

e. a short one can carry 50 mA

f. dozens of whiskers can be in parallel, thus carrying even more current

g. burnt whiskers can come back if the 'root' is intact

So, to think 'they will just burn away' is not a philosophy when building
radar and other sensors (from where I came).  I have been involved in
Galileo as well. If we found just a few whiskers, it took just a few days
and a whole delegation went to ESA.

I think I will lower my admiration of NASA a little bit. But not Jay....

Inge

On 20 March 2012 18:08, Gervascio, Thomas L <[log in to unmask]>wrote:

> Tin whiskers at Saturn
>
> PASADENA, Calif. -- The Cassini plasma spectrometer instrument (CAPS)
> aboard NASA's Cassini spacecraft at Saturn has resumed operations. Mission
> managers received confirmation on Friday, March 16, that it was turned on.
> They plan to monitor the instrument for any unusual behavior.
> Last June, short circuits in the instrument led to unexpected voltage
> shifts on the spacecraft. As a precaution, mission managers turned off the
> CAPS instrument while engineers investigated the issue. The investigation
> led to the conclusion that tin plating on electronics components had grown
> "whiskers." The whiskers were very small, less than the diameter of a human
> hair, but they were big enough to contact another conducting surface and
> carry electrical current. Researchers are still trying to understand why
> whiskers grow on tin and other metals, but they know now that whiskers can
> grow in space and on Earth. It is believed that these or additional tin
> whiskers that may grow on Cassini cannot carry enough current to cause
> problems, but will burn out on their own like a lightweight fuse.
>
>
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or [log in to unmask]
> ______________________________________________________________________
>


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

ATOM RSS1 RSS2