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From: karn@faline.UUCP
Newsgroups: sci.physics,sci.space,comp.lsi
Subject: Re: Radiation effects on semiconductors
Message-ID: <696@faline.bellcore.com>
Date: Thu, 30-Jul-87 21:08:23 EDT
Article-I.D.: faline.696
Posted: Thu Jul 30 21:08:23 1987
Date-Received: Sat, 1-Aug-87 16:32:34 EDT
References: <1356@ssc-vax.UUCP>
Organization: Bell Communications Research, Inc
Lines: 31
Summary: yes, I'm interested
Xref: linus sci.physics:1840 sci.space:2229 comp.lsi:188

Yes, I would find that an interesting discussion, for a very practical
reason.  AMSAT, the volunteer group that builds satellites for amateur
radio communication, is facing this problem. We built and launched a
satellite (Oscar-10) in 1983 aboard Ariane into an elliptical orbit
(inclination 26 degrees, perigee 4000 km, apogee 35000 km).

Oscar-10 carries an onboard computer and quite a bit of random CMOS
logic.  SSI logic is no problem; most RCA CD4000B series ICs are hard to
a megarad. The microprocessor was the rad-hard Sandia version of the
1802. However, the Achilles heel was the 16K bytes of Mostek 4116
dynamic RAM (I know, I know, but it wasn't *my* idea...) At first, the
memory performed fine; the (8,12) Hamming code error correcting hardware
had no problem correcting the one or two soft errors that occurred on
each orbit during passage of the inner Van Allen belt. However, less
than 3 years later the memory hard-failed due to accumulated radiation
damage.  The next spacecraft in the series has been redesigned to use
Harris HS-6564RH static CMOS memories which are claimed to function
after 100 kilorad exposures. It will be aboard Ariane V21 (the first
Ariane 4 launch) late this year or early 1988.

While we hope we have solved our radiation susceptibility problems for
the present spacecraft, it is pretty obvious to everybody that the 1802
is an outdated microprocessor. The 3-axis stabilized spacecraft now
being designed for geostationary service will have much greater onboard
computing requirements, so we are considering the Harris 80C86
microprocessor. (No, we do *not* plan to run MS-DOS on it!) Has this
chip proven itself in radiation environments yet?  How about larger,
cheaper and/or faster rad-hard memory chips?

Phil Karn, KA9Q
Asst VP, AMSAT