Re: gEDA-user: ESR of 2.2u ceramic capacitor

[John Doty <jpd@xxxxxxxxxxxxx>]

On Feb 26, 2006, at 1:25 AM, Peter Brett wrote:

> On Sunday 26 February 2006 02:52, John Doty wrote:
>
> > When the HETE ground station at Kwajalein was first put into service
> > in 2000, the RF preamps had a very short life span. Apparently the
> > Kwajalein Missile Range occasionally pointed a megawatt radar in our
> > direction :-0. I was thinking 12AT7, but we found a commercial solid
> > state preamp that could take the punishment.
>
> Would it not have been possible to filter the input for high-power  
> spikes
> before the pre-amp? Just curious.

As I recall (this was a few years ago) an external filter wasn't  
enough to fix the trouble with the original preamp, but I believe the  
preamp that works reliably incorporates an internal filter.

> I'm interested to hear that you work on space systems -- it's the  
> field I want
> to get into when I graduate. :)

A technological backwater, more a medieval craft than scientific  
engineering.

The HETE burst alert network (http://space.mit.edu/HETE/sgs.html)  
uses consumer VHF monitor receivers to get the downlink. Nothing  
fancy. I once had a NASA cost expert compute how much such a network  
should cost: his estimate was >100 times more than reality. The crazy  
thing is that a contractor proposing to do this would have to propose  
something approximating the NASA estimated cost, because otherwise  
his bid would be rejected as "risky". Then if he wins he has to use  
an approach backward and crummy enough to justify the cost.

NASA let MIT get away with setting this network up back in the  
"Smaller, Faster, Cheaper" era, but now the propaganda is that this  
was a failure. Failure? HETE-2 science made the AAAS top 10  
breakthroughs list a couple of years ago, and the cover of Nature  
last year. And then there was Mars Pathfinder...

For the Chandra (a mission that squandered money hand over fist)  
electronics, I wound up using big, brittle, poorly spec'd 2N930's for  
video amps because they were on the QPL. For the other missions using  
that design I used BCX70K's: smaller, more rugged, and less noisy.  
Worked fine. But now NASA and JAXA have tightened the rules and I  
couldn't get away with such rationality any more.

We used to be the leaders in miniaturization: now if we tried to make  
a cell phone you'd need an athlete to lift it. We think that a 100  
MHz processor is cutting edge.

Don't get me wrong: space exploration is a lot of fun (I work in high  
energy astronomy), but don't be fooled by our excellence at  
propaganda. Space systems were high tech 30 years ago, but no longer.  
Now I've got nothing against old tech if it's the best, but that  
isn't why we use it in space. It's the blame game: copy something old  
and if it fails it's not your fault, but if you try something new...

So if it's space you're interested in, get involved, but come in with  
your eyes open.

The next human you see on the Moon will be Chinese. You will never  
see a human on Mars (but NASA will squander $100 billion pretending  
to prepare to send one).

John Doty              Noqsi Aerospace, Ltd.
jpd@xxxxxxxxxxxxx