[0] http://www.nasa.gov/feature/goddard/saving-nasas-stereo-b-th...
Kind of had a funny mental image of the team wrapping up the shut-down process. Then, recently, all of them still at NASA get a calendar notification from the past: "SETERO-B about to return from behind the sun - go try and jump start it!" and they get back on the case.
The total cost of building, launching, landing and operating the rovers on the surface for the initial 90-sol primary mission was US$820 million.[4] Since the rovers have continued to function beyond their initial 90 sol primary mission, they have each received five mission extensions. The fifth mission extension was granted in October 2007, and ran to the end of 2009.[4][5] The total cost of the first four mission extensions was $104 million, and the fifth mission extension is expected to cost at least $20 million.[4]
Jet Propulsion Laboratory (JPL) lost contact with Spirit after last hearing from the rover on March 22, 2010 and continued attempts to regain communications lasted until May 25, 2011, bringing the elapsed mission time to 6 years 2 months 19 days, or over 25 times the original planned mission duration.[9]
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.
> "In 2019, the spacecraft will be far enough from the sun
> that we could image it directly with Hubble and figure
> out the rate of spin," said Ossing.
https://www.youtube.com/user/Suspicious0bservers
(Today's news, mentioning the return of stereo https://www.youtube.com/watch?v=MhSCMR0YP8Q )
> The STEREO Missions Operations team plans further recovery processes to assess observatory health, re-establish attitude control
Did they mean altitude? What does attitude mean?
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.
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.
(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.