Somewhat OT: Long term design

Regular aluminums pretty much are self-healing. Tantalums are self-abusive.

We're using a 180 uF 6.3 volt surface-mount alum polymer, 86 cents each. That's a lot more than a regular 'lytic, but a pretty good deal for that low an esr.

John

However, there is a caveat that these rates apply during the design life. That is, a part with a failure rate of one per billion hours cannot be expected to function, on average, for one billion hours before it fails, unless the design life is itself a billion hours. Which it probably isn't.

In the context of this thread, the issue is further complicated by the question of whether a component is using up its design life while doing nothing. It may, or may not, depending.

Sylvia.

Yes....

But now you have to design a mechanism to extract the energy that will work after 1000 years.

Sylvia.

It's not that easy. My only real job was for STC, then part of ITT on undersea telephone systems. The amps had to sit at the bottom of the sea for 25 years without failure.

One of the big concerns was outgassing of corrosive gases from components. All resistors were plain, no coating. By 1977 they were testing PCBs for long term reliablity but stuff was still built on tags rivited to perspex. They were also working on fibre optics for new projects.

I am! Something more obsolete than my TTL clock! :)

A billion hours is a long time, 114K years, but 1000 years is a mere 9 million hours. Unless there's a long-term wearout mechanism (diffusion, corrosion, radiation damage) I'd guess that most parts are still in the flat part of their bathtub curve at 1000 years. If one were designing a 1000 year product, you'd certainly want to look for potential wearouts.

That's an issue in calculating equipment MTBF. The general rule is that if you don't hit your reliability target doing straightforward calculations, then you toss in a use factor.

There are old clocks and watches and scientific instruments around that work after hundreds of years, without benefit of exotic storage. I'd guess that WWII-vintage electronics, stored in military wax-sealed cardboard boxes, usually still works.

What would fail in a conservatively-designed electronic gadget after

1000 years? Barring corrosion, I can't see a wearout or diffusion mechanism for thickfilm resistors or ceramic caps. Given the observable stability of bipolar transistors and ICs, there doesn't seem to be much carrier diffusion or radiation damage going on at room temperature. I'd avoid CMOS type parts where a little charge redistribution could cause problems.

You could cheat and store the gear in Antartica. Most degradation mechanisms follow the Arrhenius relationship.

John

Centuries-old weight-powered clocks still work. Surely we can do better with modern materials.

I don't think 1000 years is a long time for good materials.

A chemical battery with a glass-sealed electrolyte, like used in some proximity fuses, could be designed to last 1000 years.

John

Try this,

ftp://jjlarkin.lmi.net/Prox.zip

about 2 megabytes.

One of the reasons Patton blasted across Europe so fast was that the prox fuze had just been released for land use. It was a devastating and terrifying weapon against ground troops... one howitzer round going off 50 feet above the ground would basically sterilize a few acres, and foxholes weren't much help. It was also hugely effective against German bombers over Britain and against the kamakazies. It's really hard to hit a plane with a bullet.

John

You also have to be fairly cunning to weed out infant mortality in any components that might be vulnerable early on. It would be really annoying to wait 1000 years to find that bad handling had wrecked or weakened a component that failed at switch on.

I am fairly sceptical of anything with wet chemistry inside surviving on these timescales. Electrolytic capacitors have a bad habit of drying out or otherwise developing defective internal behaviour when left alone for a long time. Or for that matter anything using tin, zinc, cadmium or other metals inclined to form whiskers.

Aluminium chassis and heatsinks might not be all that good longer term either. The metal is just too reactive for its own good even if the oxide coat is inert. Copper coated with gold ought to be OK though.

Depends how many bites the rodents have taken out of it. Inductors and galvanometers survive remarkably well - the mirrors may tarnish though and that is over mere couple of hundred years. Clocks that are not well looked after seem to have a half life of about fifty years.

I reckon Zambonni piles might be OK as a maintainence free power source (for tiny currents). The oldest one at the Clarendon lab is still going strong after 170 years running the Oxford Electric bell.

I have one somewhere ex WWII image intensifier.

And I am pretty sure there is (or was) something similar at Leiden with a ball of sulphur that is gradually wearing away as it rings. But a quick search failed to find it.

A salt mine is a pretty safe location provided you hermetically seal the kit in dry nitrogen before it is taken down. Steady temperatures also help longevity just as thermal shock accelerate decrepitude. One of the advances neutrino detector experiments is down our local potash mine.

Regards, Martin Brown

George Herold Inscribed thus:

The Ancients created mechanical traps in the pyramids. AFAIA they still worked after how many years 4500 or so.

--
Best Regards:
                Baron.

OK, you're just convincing me I should have said 10,000 years ;)

Or indeed, the 48,000 years in the TV program.

Though in Stargate Atlantis, they do have the advantage of using "naquita" (sp?) for their power source, which seems to be an element oddly overlooked in the periodic table.

Sylvia.

Say 10,000 years? There's a group working on such a project now.

--
Rich Webb     Norfolk, VA

Well, if way take the TV program as an indication, and including my own interpretation of what happened (which wasn't that clear).

It appears we need a radio receiver on some frequency that will be turned on after some number of thousands of years, and then run for perhaps one hundred years. If it detects a radio signal, it has to start up a computer, which is connected to a transmitter on that same frequency. The computer doesn't have to run continuously, but has to be able to run intermittently for a further thousand years. The transmitter is not required to be able to run for more than a few hours once turned on.

There was also a signficant power supply that could be turned on after

48,000 years, and then actually run for a further 1000. I had thought this was a big ask, but perhaps not. U235 has a half life of 700 million years, but is clearly usable to produce power in nuclear reactors.

I suspect that building a computer that would still be functional after even the first 1000 years would be a challenge, even if it were not running during that time.

Sylvia.

Not quite the same problem. They're looking at something that will run for 10,000 years, but with some maintenance, and a constant supply of power (from humans).

I'm thinking of something that could be built now, and be secreted away from human interference, only to perform my biding a thousand years, or perhaps 10 thousand years hence.

Sylvia.

You just put them on the outside of the Space Ship. That way you would never lose the vacuum.

It's all about maintenance. Wonder how often the bellows had to be replaced/rebuilt? Probably even some pipes? ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

I think it's a cheap brand of tequila.

John

Not quite -- interplanetary space is around 10^-6 torr IIRC, which is good enough for crappy triodes, but you won't get a 6L6 working quite well enough out there. There's also a mixture of gas and particles which would be better removed with a getter than the electrodes. A solar powered diffusion pump (wait, do diffusion pumps work without gravity?) would be a low maintenance solution.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

The "equipment" that is suppose to work after 10,000 or 48,000 years is not well defined. Any suggestions on what such "equipment" should do? If it must be a "computing" device of some sorts, what about using glass to construct the following. See:

As far as storing power is concerned, it will depend on the amount of power. What about a CO2 canister. The canister material might be a problem, but could be glass as well.

If it just has to survive the 10,000/48,000 years to be operated by an intelligent being, the users' manual might be a bigger problem. What language should we use or would pictorials on glass be the safest option?

If the "equipment" has to start after 10,000/48,000 years without human intervention, the actual challenge is building the 10 000/48,000 year timer.

One solution is launching it on a 10,000/48,000 year orbit to re-enter and get deployed on re-entering the atmosphere. If it just sits in orbit around the earth for that period someone might fetch it and destroy the 'experiment', so what about launching it in a comet type orbit? Anti-impact defences might just destroy our experiment in the year 12010.

Lots of energy in the re-enter phase (if there is still an atmosphere) Any suggestions on what type of energy the heat should the converted too.

If humans have to operate it after 10,000 years, how can we attract attention to the "arrival" of the "equipment" (or is this a spy device that must operate in the stealth mode ... collecting data for who :-).

Haven't had a good look at

- might be interesting.

Gerhard van den Berg Meraka CSIR