Probability of a space expedition failure is too high

The argument

The argument builds from the record of missions that carry no crew. By considering the drone missions, there have been quite a few failures which caused the destruction of the spacecraft. Even successful missions, such as Voyager, experienced some technical failures and issues which luckily still allowed most if not all mission objectives to be accomplished. That is the baseline the argument works from: spaceflight produces faults reliably, and whether a given mission succeeds often turns on whether the particular fault it suffered happened to be survivable. Those faults have been tolerable because of what was at stake in them. Since failure in this case does not imply loss of human lives, the level of acceptable risk is higher — an unmanned mission can be designed to a standard that accepts destruction of the spacecraft as one possible outcome, because the cost of that outcome is counted in hardware and time. A human mission cannot be designed to that standard, and is at the same time harder to make safe. A human mission is more complex since it involves a life-maintaining system that should ensure the safety of the crew. That system is an additional set of components which must work continuously for the whole duration of the flight, and whose failure is not recoverable in the way the loss of an instrument aboard an unmanned probe can be. The risks of a failure are therefore higher precisely where the tolerance for failure is lowest. The definition of success compounds the problem. No human mission can be considered successful unless the astronauts are able to successfully return to Earth; so far all drone missions have been one-way. A crewed mission must complete an entire second phase that unmanned spaceflight has never had to attempt, with the systems that carried the crew out required to work again to bring them home.

Context

There have been already several failures on drone missions. A manned mission is way more complex and consequently the risks

Premises

Counter-arguments

High risks have already been taken in previous mission. It is estmated that Apollo missions had an estimate 50% of failure that might have resulted in fatalities. Even in past centuries explorers take even more risks; in expedition like Magellan's circum-navaigation only a small number of original crew survived the trip. Desire to explore make people accept enormous risks

Rejecting the premises

[Rejecting P1] Uncrewed failure rates do not transfer. Those missions are deliberately flown to a higher accepted risk because no one is aboard, so their record understates what engineering to a crewed standard achieves. [Rejecting P2] Added complexity does not settle the probability. Crewed vehicles carry redundancy, abort systems and a crew able to intervene, none of which a probe has, and the requirement to return is a design constraint rather than a fixed increment of risk. [Rejecting P3] The premise sets the acceptable level of risk without argument. Astronauts are volunteers who accept the danger knowingly, as they did throughout Apollo, and societies routinely permit freely chosen hazardous work — so the question is who decides what risk is acceptable, not whether risk exists.