The extreme requirements for autonomy, reliability, and automation I’ve outlined are old news to designers of deep-space probes. The solar system is full of hardware beeping serenely away decades after launch, most spectacularly the forty-six-year-old Voyager spacecraft.

But no one has ever tried attaching a box of large primates to a deep space probe with the goal of keeping them alive, happy, and not tweeting about how NASA sent them into the vast empty spaces to die. A Mars-bound spacecraft will be the most complicated human artifact ever built, about a hundred times bigger than any previous space probe, and inside it will be a tightly-coupled system of software, hardware, bacteria, fungi, astronauts, and (for half the mission) whatever stuff the crew tracks with them back onto the spacecraft.

Designing such a machine means taking something at the ragged edge of human ability (building interplanetary probes) and combining it with something that we can’t even do yet on Earth (keep a group of six or eight humans alive for years with regenerative life support).

– Maciej Cegłowski, The Shape of a Mars Mission