[codezero]

I imagine this happens more often than most people realize.

I worked on a satellite that was launched in 2003 and had a lifetime of 3 years. It operated until at least 2012 when the Air Force decided it was done paying for the downlink, but the satellite itself was still in pretty good condition.

[okket]

My laymen guess is that unless your satellite electronics get fried by the particle storm of a solar flare not much happen in space. As long as the power source (solar panels) works and you do not need much fuel for repositioning like in low earth orbit, what stops a well built satellite? (sorry if I am too naive/ignorant)

[madaxe_again]

Batteries can only take so many charge cycles, PV cells get pelted by alpha particles and micrometeoroids. Essentially, "wear and tear" is what eventually kills most spacecraft.

[6stringmerc]

Any success by way of a giant Earth-based laser? Asking for a friend.

[mikeash]

I always assumed this happened because the official lifetime is defined in terms of some high probability of surviving that long, maybe 95%. And if you have a 95% chance of lasting 3 years, you probably have something like a 50% chance of lasting a decade or two. Is that assessment vaguely correct?

[mturmon]

That's true ("ability to operate") but another large factor (for scientific space missions) is the demonstrable benefit to continuing -- even if the spacecraft is fully operable. For instance, New Horizons, once it flew by Pluto, had accomplished its primary science mission, and an end could have been declared at that time.

But then the NH science team put together a rationale for an "extended mission" with the new objective of visiting a Kuiper Belt Object, which was accepted by NASA.

But on the other hand, at the same time, the Dawn spacecraft's proposed extended mission to leave Ceres and visit Adeona, was denied, and it is expected to just orbit Ceres for the rest of its lifetime. (More: http://spaceflightnow.com/2016/07/02/pluto-probes-extended-m...)

So the surplus lifetime might not be used if the further science benefit can't be justified -- against engineering effort, downlink, etc. Sometimes portions of a spacecraft are turned off but the low-bandwidth observations are still taken and downlinked.

Or, sometimes a spacecraft is kept operating, with great engineering effort, even though it is not in great shape.

[codezero]

Pretty much. The larger factor is whether you can continue to get funding beyond the end of life.

[comboy]

What is usually the cause to get them in a "bad condition"? Is it just that better technology is available or is it radiation, solar panel issues or other stuff? I'm asking because as far as I understand it's mostly electronics so I always wondered what is causing it to fail while nobody is touching it.

[mturmon]

Besides consumables like fuel, mentioned nearby, there are also mechanical parts like gyroscopes or reaction wheels (https://en.m.wikipedia.org/wiki/Reaction_wheel) which maintain pointing. If the s/c contains an imager, there will probably be a mechanical shutter, protective cover, and/or filter wheel.

There can also be higher power electronics, like signal amplifiers or radios, which tend to fail more often than computer electronics. Finally, there is cumulative radiation damage, and the possibility that a combination of single event upsets can get the s/c into an unrecoverable state.

From time to time, operational changes can force the s/c into new operating modes ("we need to flip the camera to take images to fit a new point spread function"). These new operating modes can cause unforeseen consequences ("when flipped, the antenna has to be pointed differently to target the ground station") that ripple through the system. As the mission wears on, the chance of a new operating condition tickling a latent problem increases, because there are a lot more latent problems.

[david-given]

Another aspect is that many spacecraft use thruster fuel over time, both for pointing and for station-keeping. Once you run out of fuel, the spacecraft may lose the ability to keep its high-gain antenna pointed at Earth, so you may lose touch with it completely, especially for deep space missions; but more seriously, it may also stop being able to keep its solar panels pointed towards the sun.

(Some spacecraft don't use thruster fuel for pointing, so they don't suffer from this so badly.)

In addition, if your vehicle is in Earth orbit, it may be assigned a position. For example, geostationary satellites must keep within their assigned slot or else you'll be very unpopular. (See, for example, the Galaxy 15 zombiesat, which went nuts and started drifting into other satellite's slots, while broadcasting hash.)

So if you run out of fuel, you won't be able to do this any more, and as a result some satellites are required to keep a fuel reserve so that they can be sent into a safe graveyard orbit at end-of-life.