Ask Slashdot: After We're Gone, the Last Electrical Device Still Working?

Leomania writes: After watching a post-apocalyptic Sci-Fi short on YouTube (there are quite a few) and then having our robot vacuum take off and start working the room, I just wondered what would be the last electric/electronic device still functioning if humans were suddenly gone. I don't mean sitting there with no power but would work if the power came back on; rather, something continuously powered, doing the task it was designed for. Are we talking a few years, decades, or far longer?

Comments

satellites

[Anonymous Coward]

Probably satellites would last the longest, with maybe Pioneer or Voyager probes for however the RT batteries last.

Re:Satellites

[MarkWegman]

The orbit decays and ceases to be geosynced. But it's got a long way to go before it hits the atmosphere and burns up. Remember how much energy was needed to get it up there from low earth orbit. The satellite has to give up all of that because of the tidal effects of the moon before it's close enough to be slowed by the atmosphere. There may also be a very minor effect from the sun's radiation. I think it's safe to assume that the solar cells will deteriorate before the decay of the orbit causes a problem.

Re:satellites

[dj245]

One should be very wary of the distinction between "run without refueling" and "run without regular maintenance". Even assuming that the reactor's fuel would last, the ancillary equipment associated with the reactor's operation (coolant pumps and such) and electricity generation (steam turbines) certainly wouldn't be expected to operate unattended and unmaintained for months, let alone years.

That said, the fifty-year planned lifespan of the Nimitz-class includes, if I'm not mistaken, a mid-life refuelling and complex overhaul (RCOH). To be fair, the reactor's fuel would likely last longer than the planned 20-25 years if the carrier weren't actively steaming--but I wouldn't trust the other parts to last anywhere near so long.

As a steam turbine engineer, I am fairly confident that, given a well maintained system to start with, the first failure would probably be in a stuck steam control valve. Over time, oxides build up on the valve stem, which would cause it to become stuck at some point. This would probably take 3-6 years. When that happened, the instrumentation control loop (need more steam, open valve, need less steam, close valve) would have a hiccup since it would ask for more or less demand and the valve wouldn't move. Valves stuck-open have historically caused many turbine overspeeds and resulting disasters.

Depending on exactly how the system was set up, the stuck steam valve should trigger the control system to automatically close a different valve, shutting down the plant. However, it is possible that it would result in a large kaboom as the turbine entered overspeed and the turbine blades liberated.

As for the last electrical device operating, my money would be on a solar powered yard light. The quality of those devices is generally terrible but the law of averages suggests some of them have to be on the long tail of a MTBF curve.

Satellites

[Gre7g]

Solar-powered, geosynched satellites will keep going for a while.

Re:XKCD answered this

[CheeseyDJ]

IIRC, the conclusion was that it would be status LEDs on space probes or radiation glow from buried nuclear waste.

Why would space probes have status LEDs? Think about it.

Re:XKCD answered this

[someone1234]

Unit testing before launch?