Auxiliary sail on early steamships provides an analogy for a weak but valuable backup propulsion system on a spacecraft. Fuel for a Mars round trip does not solve the problem if a damaged ship cannot repair the machinery that uses it. Workshops and spare parts must be duplicated and distributed so a single debris strike cannot destroy both the casualty and the means of recovery. Age-of-sail ships achieved similar resilience through carpenters, sailmakers, several sets of tools, and crews able to rebuild much of a vessel from the hull upward. The penalty is a larger ship, but the alternative is a single failure that strands everyone aboard.
Notable Point · 8:24-12:03
Sail-and-steam redundancy explains shipboard resilience
Auxiliary sails, duplicated workshops, distributed spares, and shipboard trades show why survivability demands more than one copy of a critical capability.