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RE: Let's build some Linear Transponders



On Thu, 10 Jul 2003, Robert McGwier wrote:

> Building space-rated hardware is not like going
> down to radio shack and getting crummy parts.  Space
> is a harsh environment and building these things with
> some hope of reliability requires specialized
> knowledge and experience.

All that Robert says here is absolutely true... BUT...
Vibration is just vibration, temperature is temperature.
The NASA way spends tremendous amounts of resources and
equipment and plans and reports and paperwork to prove
flight viabilty with calibrated very expensive equipment.
BUT...

VIBRATION:  Attach your device to your lawnmower and run
it for 15 minutes at various speeds and I'll bet you
will be ready for any NASA vibration test.

TEMPERATURE:  Stick it in your oven at 140 degF and
Freezer at 0 degF and back and forth a few times
(taking care to protect it from condensation) and
if it works, then you are good from -18 degC to +60
degC.  Buy some dry ice in a cardboard box if you
want to go to -60.

VACUUM:  Go to your highschool and put your device under
a Bell jar. Run it in vacuum a while.  Understand that
you dont have air cooling anymore and so design for that.
This is not space quality vacuum, but it will sure show
any components that are going to blow up.  (though it
wont show long term effects)...

> All sorts of mechanical and thermodynamic
> factors need to be factored in such as: What range of
> temperatures will the module be subjected to? How much
> impulsive or shock G forces will the module be required
> to survive on the launcher you have chosen?  How many
> G's will the rocket subject the module to? How much
> spacecraft power is available to the transponder.  What
> is the minimum power output to provide adequate link
> margin for the planned activity? (and ON and ON and ON)
> Some people have just gotten away with complete murder
> (can we say it sends lots of APRS?)

We designed PCsat to all those extremes.  We tested cheaply
(as above) to validate our design, and then we submitted it
to all the FORMAL NASA tests and it passed all tests.

> but I wouldn't bank AMSAT's future on repeating that
> roll of the dice nor would I hand this off to some
> college kid with zero experience without a serious level
> of supervision.

Now that is the key.  But be careful of bringing in
off-the-shelf "NASA experts" to help you, because to do
it the NASA way, you can't possibly afford it.  The NASA
way (and the RIGHT way when you have large programs) has
50 managers and tons of specs and QA inspectors for
every single nit-pick and they all go by the written specs,
because the one Engineer who wrote them and knew exactly
why, has long since retired.

So I agree that space is a Harsh environment that has
to be designed in, but today's electronics parts on good
PC boards can survive just about anything if one just
thinks about it...

and thinks, and thinks, and thinks...

de WB4APR, Bob


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