What's the endurance on sensor buoys like now? I'm having trouble finding documentation. Did they stop having a limit?
Yes they are unlimited now... at least, I've never seen one expire. Shot to pieces by hostile aliens, sure, but never expired.
(Self-propelled commercial pickets were obvious but I want a solution that doesn't strand a size 20+ engine out there supporting ~2 size points worth of sensor systems for a long watch.)
You can roleplay that they conduct local patrols of the JP vicinity and rotate crews with small shuttlecraft not shown in-game if you like... I find them useful for providing a low-cost scout alternative in addition to monitoring duties, but they are the most expensive option so I usually only use these in my Duranium Legion games.