Good times! I wonder if today's satellites will be responding 40 years from now. If consumer technology is any indication, probably not. There's also the small matter of space junk around Earth that will be more and more of a risk to our terrestrial satellites as time goes on - before we invent shields.

Solar batteries do degrade over time, though if Opportunity (still going strong on Mars) is any indication, 40 years is not an impossible age for solar-powered satellites to survive.

With ones powered by RTG the news is worse. That was the Cold War era, and Plutonium-238 was abundant. Voyager-1 has a plenty of it. Nowadays the Cold War stockpile is nearly empty. NASA's budget doesn't let them commission more, ESA has none and no means to produce, and Russians do commercial flights and gave up on space exploration.

The CPUs are very similar to these 40 years ago, and very different from consumer-grade. Harris RTX2010 is about the most universally used model, a 1MHz microprocessor using FORTH as its own machine language and exceptionally hardened against cosmic radiation, so no worries here. Yes, the memories die over time, but the software is often written in a way to account for that and migrate from faulty cells. It can take centuries for these to die.

Ion engines, while not a cure-all for acceleration headaches, can account for orbit decay for long decades.

The one element that is the true death clock for all modern satellites is the flywheel bearing. Back in Voyager days the probes had many tiny jet engines that would turn them around e.g. to let antennas reach Earth. It was expensive, unreliable and if any of these engines ran out of fuel, the probe would just spin around respective axis, losing radio contact, meaning death for all practical purposes.

Nowadays probes have a flywheel, - a gyroscope which accounts for all rotational needs of a probe. It's much more reliable, it's much cheaper, much more precise, it never runs out of fuel (electric), but it's a mechanical part depending on mechanical bearings to rotate. And these do get worn over time. How much? Hard to say. They may fail in five years or ten or fifty, but they *will* fail once the grease runs dry and the axles jam.

Good news is there is a new model of bearings about to reach the market - contactless magnetic bearings. They can only carry a very limited mechanical load (but sufficient here) but they have very low magnetic friction, no mechanical friction, and can run about indefinitely. They must find their way into satellite technology yet though.

Well someone clearly knows their stuff. Thanks for the summary on those technologies... Very interesting!