Henning,

Thank-you very much for taking the time to provide us with your valuable
insight.

While I have you 'on-line' ... Am I under a false understanding that an arc
[plasma] in space is particularly troublesome in that it will not extinguish
until the current ceases?  With no convection currents, there is nothing to
assist with extinguishing the arc [ala Jacob's ladder].

Thanks


Steve Creswick
Sr Associate - Balanced Enterprise Solutions
http://www.linkedin.com/in/stevencreswick
                         616 834 1883



-----Original Message-----
From: Leidecker, Henning W. (GSFC-5600)
[mailto:[log in to unmask]] 
Sent: Friday, March 23, 2012 1:29 PM
To: Bob Landman; 'TechNet E-Mail Forum'; 'Steven Creswick'
Subject: RE: [TN] Out of the world tin whiskers

Dear Bob and others,

The Galaxy IV failed in orbit.  Boeing gave us a presentation that was both
exemplary and convincing that the cause was a tin whisker, but the data and
modeling was stated to be proprietary and (of course) I've always honored
that.

The prototype for the "601" bus series of spacecraft (of which the Galaxy IV
was an instance) suffered a famous double failure during thermal vacuum
testing -- at (about) 80 days into the thermal vacuum testing, the main fuse
on one side interrupted, and the main fuse on the other side interrupted a
few days later.  Inspection showed tin whiskers growing on each of these
relays, of which some were long enough to bridge between conductive
surfaces, one at 50 V bus power (with only a few tens of milliohms back to
the main power) and the other at ground.  Aerospace Corporation gave
essential insight: a whisker shorted and launched a metal vapor arc (50 V is
able to do this in a vacuum, and across a few millimeters or less) that drew
some 150 A to 200 A until the fuse interrupted -- this took between 1.0 and
1.5 milli-seconds.

Jay's web site includes references describing this historic event.  And the
image of the relay on the top left-hand-side of the "spash page" (the home
page) on Jay's web site is a relay from the same stock as these, and the tin
whisker is real.  (Well, Jay took a real image, and then replicated it a
number of times, starting with most of the whisker blacked out, and then
less of it, etc.; then, the sequence plays as a movie suggesting the growth
of the whisker.)

So, this was an example of successfully identifying the cause of a failure
in space, caused by a tin whisker.

We have other examples of successful identification of failures in space,
later confirmed by direct inspection of items.  For example, we are certain
that the interruption of the three fuses protecting the bus of the Solar
Maximum Mission (launched in 1980) was caused by choosing fuses each rated
at 1/8 A (= 125 mA) , each for use in a circuit running at 80 mA -- but
these fuses are "hermetic" in name only and actually slowly leak out the air
in them on the ground -- this removes an important thermal conduction path,
and lowers the actual rating of the fuse to some 34 mA -- so each fuse
interrupted as its air fell below a critical value.  The first interrupted
in 10 months, the second a week later, and the third a month after the
first.  

Perhaps folks would be interested in other examples?

We had no certainty that tin whiskers were the cause of the CAPS instrument
in the CASSINI spacecraft.  We did see tin whiskers on the tin-plated
transformer cans of the very type installed into CAPS:  Jay has images of
these on his web site.  We think it is possible that tin whiskers were the
cause.  We think that other mechanisms are also possible but somewhat less
likely.

Best,
Henning



________________________________________
From: Bob Landman [[log in to unmask]]
Sent: Friday, March 23, 2012 10:36 AM
To: 'TechNet E-Mail Forum'; 'Steven Creswick'
Subject: RE: [TN] Out of the world tin whiskers

Steve,

I asked Henning about a satellite that failed in orbit due to whiskers as to
how they could possibly deduce that when I saw him at the CALCE meeting at
UMd.  He told me it was because they had similar equipment on the ground and
could verify that whiskers had likely erupted.

Bob


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Thursday, March 22, 2012 4:50 AM
To: [log in to unmask]
Subject: Re: [TN] Out of the world tin whiskers

Bob,

Yes, will be very interesting to hear what the group can share.

Could it be possible they still have a back-up/alternate CAPS instrument/s
in storage to physically examine for whiskers, thereby making the problem
definition a bit easier.


Steve C




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