> lead-free solder and just ask yourself why it's banned from aircraft and space applications where reliability is of utmost importance.

Wow, is that really a thing? I would have assumed they'd use leaded solder if it made for more flexible/stable connections, and that technicians would just bear increased safety requirements (masks, ventilation, etc.). Once the craft launched into space the risk of the lead hurting anybody approaches zero. Even burning up due to a failed launch doesn't seem like it would cause any appreciable damage (at least not due to lead).

I figured spacecraft design demanded the best performance and reliability, regardless of possible human impacts (e.g. RTGs and their potential to rain down on people upon failed launch).