I was reading this question and wondered why there were so many that were inactive. Considering the cost to build/launch/ship them, and that they are mostly powered by solar energy, why would they go inactive after a relatively short time?

List of Mars Orbiters on WikiPedia

  • $\begingroup$ I think about 60% are inactive (based on that question and en.wikipedia.org/wiki/List_of_Mars_ ) Some were only active < 300 days! $\endgroup$
    – nycynik
    Feb 19, 2021 at 17:03
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    $\begingroup$ Some early ones failed relatively quickly just due to limited technology (especially the Soviet probes), but the oldest active probe was launched about 20 years ago. That's not a particularly short time by any standard...it's been in orbit for nearly half the time we've been exploring the planet with probes. Why do you find the numbers surprising or unusual? $\endgroup$ Feb 19, 2021 at 17:12
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    $\begingroup$ Let's turn it around - every orbiter that entered Mars orbit in the last 24 years is still active. $\endgroup$
    – asdfex
    Feb 19, 2021 at 17:49
  • $\begingroup$ @asdfex indeed, I'm far more surprised that Mars Odyssey is still going than I am that the older probes are no longer functioning. $\endgroup$ Feb 19, 2021 at 18:16
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    $\begingroup$ The unusual thing would be to see something still functioning after 15-20 years, as that is the upper end of the operational lifespans for sats in general. Much better to launch something new and take advantage of massive gains in tech than it is to try and extend something for decades. And of course the early ones will have very short planned lifetimes as the main goal is to learn what you don't know (the unknown unknowns) so you can better plan future, more lengthy, missions. $\endgroup$
    – eps
    Feb 20, 2021 at 16:34

1 Answer 1


Vehicles in space need propellant for attitude maintenance. The vehicle is essentially dead when the propellant runs out. Propellant depletion is the end goal of a good spacecraft designer. All of the other reasons that follow represent situations that preferably should not happen. But they do happen, at least to some space vehicles.

Vehicles in space need functional avionics systems to gather data and to communicate with the Earth. The vehicle is essentially dead when its avionics have been fried by one too many cosmic rays.

Vehicles in space need electrical power. The vehicle is essentially dead when its solar arrays have degraded to such an extent that the vehicle can no longer serve its secondary (let alone primary) mission.

Nothing in space lives forever. Designing a space vehicle to live forever would be extreme overkill. Space vehicles are instead designed to live for a minimum period of time, but also are designed to not live after some extended period of time.

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    $\begingroup$ Also, it takes continuing budget to fund the people on the ground supporting the mission. $\endgroup$ Feb 20, 2021 at 9:48

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