Most of these are do to SEI [Single event interrupt's] caused by Iron particles

Dave N6CO

----- Original Message ----- From: "MM" ka1rrw@yahoo.com To: amsat-bb@amsat.org Sent: Monday, October 01, 2007 5:06 AM Subject: [amsat-bb] Keep It Simple, MM

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 CPU.

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 determined. 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 project.

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 shining.

73 Miles WF1F

www.marexmg.org

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