[knorby]

A great deal of the value to a manned mission to a planet, in terms of tangibles, exists in coming back. Humans can take samples easily, and a return mission would bring them back. Humans would significant contaminate any site they visit, and drones can be considerably more sterile, not to mention cheaper.

When you are talking about spending many, many billions for a single mission, arguably the success of the spacecraft is worth more than the lives of the humans. If the crew is at a significant risk of death, and it is worth noting that a lot of these risks would affect the crew mostly evenly, then the whole mission is in jeopardy.

[jessriedel]

It's not possible to justify the very high price we pay for human safety within the space program based on value to the mission. If it were only a matter of the mission, we would accept tremendously more risk. Human lives are only valued at a but under $10 million, so even for a 10-person mission to Mars the value of the humans is < 1% of the cost of the mission.

https://en.wikipedia.org/wiki/Value_of_life#Life_Value_in_th...

Because of the diminishing returns to safety spending, it's generally better from an economics perspective to accept an order-unity chance of failure and just send multiple missions. But obviously, this is not how we design human space travel.