[amsat-bb] Re: Keep It Simple, MM

[David B. Toth]

At 08:06 AM 10/1/2007, MM wrote:
>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.

The SDX is a software-defined radio ... it does not necessarily, and 
probably does not, use a DSP chip.


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

At the cost of launches and satellites, i think this point is easily 
disputable.
I am sure that the engineers are looking at an overall systems approach, AND
they've done this before. The difference is the addition of a 
software-defined approach, which WILL be space-tested in SuitSat2 anyway



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

Miles, do you have any data to support this statement because right 
off-hand, I can't see why this would be true.


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

This is not the first satellite these guys have built - I think they 
had this somewhere on their "To-Do List" ...



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

Well, that is actually a bug, not a feature. We need to have a way 
that we can guarantee that when a satellite dies, it STAYS dead. That 
was a real sticking point with Larry Kayser when he was still alive. 
These things pop up, un-controlled, and if we had enough of them, 
they'd be an interference problem.


Dave