> What's the blocker here? To me the likely blocker is reliability/accident. Most places where humans are on Earth, if one piece of equipment fails (say the e

> What's the blocker here? To me the likely blocker is reliability/accident. Most places where humans are on Earth, if one piece of equipment fails (say the engines fall off of your passenger plane while you're over the ocean), you survive and carry on for at least days. In space or on Mars, you're dead in minutes.