Have any space vehicles with rechargeable batteries prioritized a factor other than battery longevity when controlling their charging cycle?
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2$\begingroup$ Guidance for battery charge is specific to certain battery types. My car's longest-life charge is 80%, but not everything is like that (not every battery is even rechargeable) $\endgroup$– Erin AnneCommented Sep 4 at 16:32
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$\begingroup$ Also satellite lifespans tend to be limited primarily by how much fuel they have for stationkeeping rather than by battery degradation. It doesn't matter how good your power system is if you're about to run out of thruster gas and need to deorbit or graveyard the thing before it becomes uncontrollable. $\endgroup$– Darth PseudonymCommented Sep 4 at 18:46
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$\begingroup$ Some situations like rovers trying to make it through the Martian night almost certainly charge up to full. But it's an interesting question whether any Earth orbiting satellites have their batteries sized so that they only charge to 80%, and deplete to 20%, or some other determined levels, in order to extend the battery's lifetime. The tradeoff however would be additional battery weight, so in the end they will likely install only the amount of battery needed to last for the expected lifetime of the satellite, which already has some margin for expected degradation. $\endgroup$– Steve PembertonCommented Sep 4 at 19:04
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$\begingroup$ IIRC the ISS charges their "new" batteries to ~4 volts out of a max of ~4.5 volts $\endgroup$– Organic MarbleCommented Sep 4 at 20:23
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1$\begingroup$ OP, would something like "have any space vehicles with rechargeable batteries prioritized a factor other than battery longevity when controlling their charging cycle" be pretty much what you're asking? I think that question could be answered (the most likely candidates would be vehicles charging for long eclipses like nights on the lunar surface) $\endgroup$– Erin AnneCommented Sep 4 at 20:58
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Yes. For a satellite in low Earth orbit that serves customers that are mostly located on landmasses, the amount of power that the satellite needs while it's in the Earth's shadow and running off its batteries will depend on several factors. These factors include the amount of time the satellite is over landmasses, the customer population density distribution on those landmasses, and the time of day for each of the customers. This means that the amount of power that the satellite will consume will vary with each pass. It will also be somewhat - but not entirely - predictable.
In the design phase, the satellite's battery capacity will be sized to accommodate the worst-case nighttime ground track at the end of the satellite's life. When in orbit, and when a worst-case night-side pass is anticipated, the target charge level will be set to a maximum value to ensure uninterrupted service. For the more typical night-side passes, the charge level can be set to various values that are somewhere below the maximum.
The satellite designers will run some simulations to determine how to size the battery and where to set the maximum charge level to achieve the goal of having the satellite remain operational up to the end of its service life.
Because for typical-case passes, the batteries do not need to be charged up to anywhere near the maximum value, the maximum value will be set above the average charging value, and could very well be set at a value close to what we would normally associate with 100% - if we were talking about an EV or a phone.
A full simulation would account for many more factors than what I've mentioned above (such as battery temperature management, using the satellite as an inter-satellite relay while it's over the ocean, etc.) but hopefully, this simplified explanation will shed some light on why it makes sense to occasionally charge a battery past the "70%" mark.
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$\begingroup$ "In the design phase, the satellite's battery capacity will be sized to accommodate the worst-case nighttime ground track at the end of the satellite's life." "The satellite designers will run some simulations to determine how to size the battery and where to set the maximum charge level to achieve the goal of having the satellite remain operational up to the end of its service life." You've sized your batteries in two different ways there. $\endgroup$ Commented Sep 5 at 3:24
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1$\begingroup$ One sentence is what, and the other is how. $\endgroup$– phil1008Commented Sep 5 at 3:26
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$\begingroup$ +1 for detail. It's also important to note that some satellites that survive their design life multiple times over sometimes experience battery problems later on and become unable to operate on the "dark side" of the Earth. Oddly, the main vehicles I've heard about this happening to have mostly been NASA LEO research vessels. $\endgroup$ Commented Sep 5 at 4:48
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2$\begingroup$ Do you have a reference for any of this? $\endgroup$ Commented Sep 5 at 11:58