[amsat-bb] Keep It Simple, MM

MM ka1rrw at yahoo.com
Mon Oct 1 05:06:43 PDT 2007

Keep It Simple Silly KISS
By Miles WF1F

The direction of this tread is caution.  I am not
suggesting that we do not use digital technology for
satellites, just that we need to be careful of the
technology.  The Space environment is not kind to
digital circuits.  Digital circuits are easily
corrupted by solar radiation and thermal stresses.  A
digital circuit designed for use on Earth many not
survive the rigors of outer space.  This is partially
because of the Size of a transistor inside a modern

In 1978 a computer transistor was made up of wires 3
microns in size.  Today’s CPU Itanium, uses wires 0.18
microns in size.  The new DSP chips used on Digital
radio will be some where in-between.  With the wire
sizes in the 0.20-micron range, it’s much easier for
solar radiation to cause temporary shorts, which can
cause system crashes.

In 2004 ago I was visiting NASA Goddard and I was
talking to an engineer building a new communications
satellite.  I asked him “What CPU and OS do you use”.
He responded, “We use Intel 80386 and our own
Operating System”.  He said, the 1.5-micron technology
of the 80386 is more radiation resistant than the new
Pentium CPU’s. 

On the Mir Program, we noticed that simple
Off-the-Shelf TNC modems seemed to only have a life
space of 2-3 years before we began to notice Frequent
Lockups and other strange issues.  
On ISS, a year after we activated the second PacCom
TNC, it began to lock up almost weekly during its last
month of operation.  
The Kenwood TM-D700 on ISS ran ok for three years
until it was discovered there were some anomalies in
the software settings.  The radio was taken off Public
access for a year until the crew was given time to do
a manual partial reprogram of a few channels.  Neither
the cause of the anomalies or the extent has been
One of the ISS crew was allegedly asked once, “What do
you do all day”, he allegedly said, “Reboot computers”
They have 50 laptops on ISS.

In closing
Use caution in your designs.

Keep It simple.  A small satellite that does one or
two features is better than one big satellite that
does 10 big features.

The more transistors, the more points of failure.

Axle lead Resistor and through-hole mounting of
components are much more resilient in space than
surface mount components.

Hardware is not your only problem; you also need to
Extensively Test the software that runs the satellite

You can never do too much Testing.

The Analog satellites AO-7 (launched Nov 1974) and
AO-10 (June 1983) are still there when the sun is

73 Miles WF1F


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