In my opinion, any expedition to Mars or outer planets (manned or unmanned) can have its reliability greatly enhanced by using a fleet of two or more identical vehicles, each designed to handle the full complement of crew (for manned systems) in an emergency. These would be large vehicles, probably spun for gravity, with room for stored food, water, fuel and other supplies for the whole mission. Obviously, there is a lot of additional cost in creating much larger and more robust systems than would otherwise be required, never mind the cost of duplicating the entire ship or the tremendous propulsion requirements (almost certainly nuclear). Considerable assembly in Earth orbit would be required, presupposing a robust Earth orbit manned presence.

On the other hand, no advanced technology need be developed for this "brute force" mission, like Mars fuel processing, environmental recycling, or other exotic concepts currently considered essential for such a mission.

It would be interesting to see how the "brute force" concept compares in a detailed study to a "high-tech" mission. It is worth noting that early Mars mission designs almost always fell into this "giant convoy" category.