[time-nuts] Low temperature coefficient capacitors for DMTD

[Lux, Jim (337C)]

> 
> Why would JPL study obscure production details of polycarbonate
> film capacitors in 1990, if they fell of the market six years earlier ?
> 


We study all manner of obscure stuff here.  Comes from using 20 year old parts in spacecraft that will last another 20 years.  Consider Cassini.. launched back in the 90s, with equipment using "heritage" designs from the 80s.  Those designs probably use some peculiarity of the components available, and someone had a box of the parts stashed away which was used.

Every time someone proposes a new widget, they get asked in the design review: "can you use any of the parts we have in bonded flight stores to save money?", and someone says "Well, sure, but they're kind of old, I think we need to study whether they're any good".

(there are octal tube sockets in flight stores, as I recall.  Never know when you might need to refurbish a telemetry transmitter that uses them..<grin>))


> Sounds fishy ?
> 
> Anybody know what this means ?
> 
> 	Electronic Concepts accumulated almost five hundred million
> 	hours of testing military grade Polycarbonate capacitors;
> 	and, currently meet established reliability failure rate
> 	level "R."

It means that they had a raft of life test fixtures with thousands of capacitors running continuously for years (perhaps under accelerated life conditions).  There's a whole lot of research into figuring out failure scaling laws; e.g. does life scale with voltage to the 5.5 or the 7.5 power? Does it scale with temperature according to the Arrhenius equation? With what exponent?

This is the kind of thing that spacecraft components people obsess about, because it allows them to estimate failure probabilities for something 25 years from now.


I, for one, hang onto my 70s and 80s era IC databooks, because those are the parts that are flying.  My grandchildren will thank me if they wind up working here. (Ohh.. I remember, grampa worked to get that radio working because it was a spare on a 1995 mission, before they used iton that outerplanets Oort cloud mission launched in 2011, and here it is at Pluto in 2040, and there's an inflight anomaly, so we better get the breadboard out of storage and see if we can fire it up)