I will try to find a link, although it's of course quite specialized info that is not often written about.
But for example, I recall that for Spitzer space telescope (I believe) every activation of the transmission hardware consumed it's usable lifetime, or the finite amount of liquid helium coolant that was needed for the operation of the telescope (which only had an expected lifetime of 2.5 years, for the key instruments that relied on coolant).
I know I'm beating a dead horse here, but I thought I'd mention that the idea this isn't written about is incorrect. There are hundreds of papers and publicly available engineering documents about deep space transponder design.
I did a little more research and found that JWST is using the radios on its Raytheon ECLIPSE bus. There's a lot of conference papers and specs available. I haven't found any lifetime estimates yet, presumably because it's just not a concern.
On that, could you explain the term transponder when I would have thought transceiver would be a more apt description. From the SDST and Iris info out there they handle up and downlinks, telemetry and commands etc. which all seem like transceiver functions.
Hm, yeah, I would have called it a "transceiver", but SDST uses "transponder" in the name so I started using that term without thinking. I guess the terms are used interchangeably in this context...
Edit: what's Iris? Also now I'm not sure SDST was sending the data -- was that on a different radio?
Ok https://trs.jpl.nasa.gov/bitstream/handle/2014/38449/04-1359... is pretty clear (telecom section) that SDST was how the data got down. Also interesting that it says the radios were designed to last 5.2 years. I'm guessing it just wasn't worth trying to prove they would last longer.
Sorry, I meant the aspect that for example, Spitzer, only had so much margin to transmit data (or other heat-causing) activities else its lifetime would be shortened. That was not much written about (outside of detailed technical circles).
Helium, for sure. Coolant, propellant, battery charge cycles, flash write cycles are all consumables. Maybe even solar panels -- they wear out. The radio? I doubt it.
But for example, I recall that for Spitzer space telescope (I believe) every activation of the transmission hardware consumed it's usable lifetime, or the finite amount of liquid helium coolant that was needed for the operation of the telescope (which only had an expected lifetime of 2.5 years, for the key instruments that relied on coolant).