Picture yourself on a future mission to Mars. You’re floating in zero gravity, tools strapped to your suit, when a crewmate slices open their arm while repairing equipment. On Earth, you’d dial 911. In orbit, you’d radio Houston. But on Mars, help is millions of miles away. The signal takes more than 20 minutes to travel one way, and then another 20 minutes for Mission Control to respond. Nearly an hour might pass before you hear back. That’s time you simply don’t have when an astronaut is injur