ARMS-D-Request@MIT-MC.ARPA (Moderator) (11/12/85)
Arms-Discussion Digest Tuesday, November 12, 1985 8:01AM
Volume 5, Issue 18
Today's Topics:
VMOS instead of krytrons?
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Date: Mon, 11 Nov 85 09:21:18 EST
From: Michael_Joseph_Edelman%Wayne-MTS%UMich-MTS.Mailnet@MIT-MULTICS.ARPA
I recently suggested that a B-52 carrying ALCMs was eqivalent
to the "fourth leg" of the triad proposed by Herbert Spencer. My commments
that I believed the accuracy of ALCMs was inferior to that of Titans
was contested by Fred McCall, who notes that ALCMs have a potential
accuracy of 30 meters. True. However, I have read that ALCMs have yet to
reach this level of accuracy, and that circumstances such as weather
(a heavy snowfall, for example) could strongly interfere with ALCM
guidance. I don't know how serious a problem this is, though, so I really
can't contest McCall's point.
On another point about ALCMs: A number of participants have remarked
that as ALCMs fly in at treetop level they are almost impossible to
detect. I'm not sure of that; the Soviets have an HF (as opposed to
microwave) over-the-horizon radar system, known to radio amateurs as the
"Moscow Woodpecker". I may be mistaken, but I was under the impression
that this system could be used to detect either the launch of ALCMs or
the missiles themselves, although it lacks the resolution to target the
missiles precisely. I was also under the impression that it was targeting
and hitting ALCMs that was difficult, not metecting them, and that this
made them unusable as first-strike weapons. As always, arguments to the
contrary are encouraged.
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Date: Mon, 11 Nov 85 16:52:32 PST
From: Jeffrey S. Gruszynski <jsg@AEROSPACE.ARPA>
Subject: VMOS instead of krytrons?
>Date: 8-Nov-85 15:04:45-PST
>From: jbn@FORD-WDL1.ARPA
>Subject: Re: krytrons
>
> :
> :
>
> What I don't see, though, is that the krytron is a particularly
>essential component. Producing the huge pulses required was really difficult
>when the A-bomb was invented, but since the pulses are so narrow, it should
>be possible to use suitable power semiconductors; National Semiconductor has
>some VMOS power FETs that might be suitable, as does G.E. I suspect that
>the krytron is restricted primarily for historical reasons.
>
> John Nagle
There is a good technical reason, which is in some ways historic.
Unfortunately semiconductors in general are easily blasted by radiation.
Not just from a nuclear "event" (God, I hate that euphemism!) but also from
cosmic rays (like an ICBM would experience in flight), and from that warhead
itself. Single event upset from alphas and cosmic rays are the biggest
problem for VMOS. Also neutrons from spontaneous fission displace atoms in Si
and SiO2 degrading every aspect of performance. VMOS is one of the "softer"
semiconductor devices around. They're generally considered useless for space
applications for this reason. An average off-the-shelf VLSI part won't
last long in radiation environments. At least in space, a 256K DRAM would
last only seconds before burn-out with the data being corrupted beyond
correction within a few refresh cycles (hence their lack of use in such areas).
For example, the shuttle uses core and plated wire memory. The older
technologies are often "harder". Tubes surpass transistors by orders of
magnitude, hence the use of krytrons. It is unlikely that a switching
transistor (VMOS or other) could be made in the immediate future that could
meet Speed, Radiation, full military Temperature range _and_ Reliability
spec's. Krytrons are the best engineering solution at this point in time.
jeff
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End of Arms-Discussion Digest
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