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From: kwan@smeagol.UUCP (Richard Kwan)
Newsgroups: net.space
Subject: Re: Scuttle the Shuttle?
Message-ID: <607@smeagol.UUCP>
Date: Tue, 18-Feb-86 02:35:17 EST
Article-I.D.: smeagol.607
Posted: Tue Feb 18 02:35:17 1986
Date-Received: Thu, 20-Feb-86 00:04:14 EST
References: <8602140147.AA05434@s1-b.arpa>
Organization: Spacecraft Data Systems, JPL, Pasadena, CA
Lines: 29

> >   It's my understanding from my experience in assisting in the design and 
> >fabrication of the ACE electronics package in the Galileo spacecraft that
> >modern microelectronics are MUCH more likely to "die of radiation" than are
> >human beings.
> 
> Microelectronics do suffer from soft errors from radiation, and some kinds
> can be disabled permanently by fairly small doses.  Radiation hardened
> semiconductors, however, can withstand upwards of 1 million rads of
> radiation (LD50 for humans is around 400).  In a teleoperator the real
> smarts will be on the ground anyway.

As far as I can gather, there seems to be several forms of radiation
hardening, i.e., the process depends on what you are trying to harden
against.  Military hardening combats high doses given in short periods.
Space hardening generally combats low doses for long periods of time.   
However, space hardening gets more complex -- depending on what planets
you are flying by, and what fields they possess.  Thus, there is no
such thing as a universal radiation hardening process.

Certain processes (bipolar and perhaps CMOS) which were once considered
naturally radiation-hard are no longer.  TTL was; but with the advent
LS TTL, it is no longer.

I have not raised the issue of hybrid analog/digital chips with anyone
here, but I presume that would be even harder to harden than pure
digital.

		Rick Kwan
		JPL Spacecraft Data Systems