What sort of major overhaul do you have in mind? A spacecraft on a multi-century flight would presumably have continuous ongoing maintenance and repair, but wou

What sort of major overhaul do you have in mind? A spacecraft on a multi-century flight would presumably have continuous ongoing maintenance and repair, but would need to function without a spell in space-dry-dock halfway through its journey. So to answer your question, what about the London Underground? It's a pretty complex machine that has been running for 120 years, with various overhauls, but of the frequent short shutdown type rather than total closure and redevelopment. The challenge for a spacecraft is being a closed system, but it's just an engineering problem.