I can tell you that in air with gravity wires cool very quickly especially
small diameter wires. In space they melt with a very low current.
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, March 20, 2012 1:49 PM
To: [log in to unmask]
Subject: Re: [TN] Out of the world tin whiskers
Boy, this raises a whole bunch of questions in my mind:
1. What technology is used that can tell NASA for certain what caused the
"short circuits in the instrument that led to unexpected voltage shifts" on
a satellite still in space? How do they know tin whiskers were the root
cause? Could not small conductive solder slivers, fines, component
malfunctions, etc. have caused the issue? Are there self-test diagnostics
that can be performed electronically that "prove" a tin whisker caused an
electronic malfunction?
2. In the deep vacuum of space, whiskers present a much more serious threat
to electronics than they do here on Earth. Because there is no oxygen in the
vacuum, a whisker half the diameter of a human hair can pass much more
current in space than even a .010" diameter copper wire can here in Earth's
atmosphere. So the statement "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" does not
sound quite right.
Any NASA engineers out there who can shed some light on this?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gervascio, Thomas L
Sent: Tuesday, March 20, 2012 12:08 PM
To: [log in to unmask]
Subject: [TN] Out of the world tin whiskers
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.
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